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In mammals, the chemical profiles of individuals are complex and variable mixtures, and animals perceive information based on variation in the overall quality of these mixtures. A variety of compounds potentially involved in chemical communication have been characterized in the urine of different felid species, but little is known about the information content of felid scent marks. In this study, we investigated whether chemical composition of Eurasian lynx Lynx lynx urine was related to sex, reproductive state, and individual identity. We further analysed if elemental sulphur in lynx urine could serve as a dietary cue or as an indicator for the freshness of a scent mark. We collected urine from captive and wild Eurasian lynx, and analysed volatile constituents of urine by means of solid phase microextraction and gas chromatography-mass spectrometry. Our results show that lynx scent profiles contain sex-specific information on reproductive state, as well as individual identity cues. Urine marks are, therefore, well-suited to fulfil a role in reproductive behaviour and social organisation of wild lynx populations. Relative sulphur content was unrelated to time since last feeding, but decreased with age of the urine sample. The influence of diet and body condition on scent profiles should be further investigated by means of experimental studies, and may shed more light on the messages encoded in carnivore scent-marks.

The costs of signalling are often expressed in terms of increased predation risk to the signaller; however, whether signalling predators also incur costs due to eavesdropping by prey and may attempt to reduce these costs is less well studied. In this study, we investigated whether there is a trade-off between intraspecific communication through scent marking and the risk of alerting prey in a wild population of a stalking predator, the Eurasian lynx. We followed lynx tracks in the snow and recorded scent marks and evidence of hunting behaviour along these tracks. Lynx preferred conspicuous objects for marking and increased scent marking rate when walking along linear structures, such as forest roads. This association was strongest when lynx were hunting, while there was only a weak correlation when no evidence of hunting could be detected. On tracks with evidence of hunting behaviour, lynx engaged less in scent marking. The relationship was most evident during the mating season, when lynx increased scent marking rates while they were not hunting. We further expected lynx to mark most in areas where they had recently hunted successfully, but time and distance to the last kill were not associated with scent marking rate. Our study supports the hypothesis that lynx face a trade-off between enhancing the detection probability of scent marks by conspecifics and avoiding eavesdropping by prey, and indicates that scent marking rate is influenced by several factors.

NWB was funded by fellowships from the UK Natural Environment Research Council [NE/G014906/1 and NE/L011255/1]. Our understanding of the evolutionary stability of socially‐selected traits is dominated by sexual selection models originating with R. A. Fisher, in which genetic covariance arising through assortative mating can trigger exponential, runaway trait evolution. To examine whether non‐reproductive, socially‐selected traits experience similar dynamics—social runaway—when assortative mating does not automatically generate a covariance, we modelled the evolution of socially‐selected badge and donation phenotypes incorporating indirect genetic effects (IGEs) arising from the social environment. We establish a social runaway criterion based on the interaction coefficient, ψ, which describes social effects on badge and donation traits. Our models make several predictions. (1) IGEs can drive the original evolution of altruistic interactions that depend on receiver badges. (2) Donation traits are more likely to be susceptible to IGEs than badge traits. (3) Runaway dynamics in non‐sexual, social contexts can occur in the absence of a genetic covariance. (4) Traits elaborated by social runaway are more likely to involve reciprocal, but non‐symmetrical, social plasticity. Models incorporating plasticity to the social environment via IGEs illustrate conditions favouring social runaway, describe a mechanism underlying the origins of costly traits such as altruism, and support a fundamental role for phenotypic plasticity in rapid social evolution. Postprint

The patterns of multiple paternity among the progeny of females are key properties of genetic mating systems. Female multiple mating should evolve due to direct or indirect benefits, but it may also partly be driven by the encounter rate with different potential mates. 2. In this study this hypothesis was experimentally tested in the European earwig (Forficula auricularia L.) by establishing experimental mating groups that differed in the number of males and females (i.e. density). The number of sires and mean sibling relatedness in each clutch were estimated using microsatellite-based paternity analysis. 3. As predicted, the mean number of sires per clutch was significantly increased, and sibling relatedness decreased, in the higher density treatment where more potential male mates were available. This change was less than proportional to the number of males in the mating groups, indicating that mechanisms limiting multiple paternity in large mating groups were involved. There were no significant relationships between female reproductive success or male siring success with morphology (body size, weight, and forceps size). 4. The present results show that multiple paternity in F. auricularia clutches is partly determined by the availability of male mates and suggest that this effect is modulated by mechanisms in males and/or females that limit multiple paternity.

Benefits and costs of group living may be differentially influenced by kinship or familiarity and depend on context. For example, aggregation with kin may be costly in a mating context due to the risk of inbreeding, but beneficial in social interactions because it may reduce within-group competition. Research investigating aggregation behaviour in different contexts is scarce, especially in gregarious invertebrates. In the present study, we investigated the aggregation among adult European earwigs (Forficula auricularia) by comparing the aggregation behaviour of groups composed of individuals from two different families with the aggregation dynamics of groups composed of individuals from the same family (siblings). Aggregation behaviour was measured both during the night (active phase) and during the day (inactive phase). Our results showed enhanced aggregation among individuals from the same family at night, but lack of such preferences during the day. These findings demonstrate that earwigs are able to recognize familiar relatives and that this information is used for aggregation decisions at night, while they are most active, but not during the day when they rest.

Many insects raise their offspring on organic substrates or in the soil where microorganisms are abundant. Microbes may pose a serious threat to offspring development and survival by either decomposing food resources or directly infecting the offspring. Selection to cope with these effects may favor social defenses, for example, through forms of parental care that can limit or eliminate these threats to offspring fitness. In this study, we experimentally tested if maternal egg attendance in the European earwig Forficula auricularia has a function as a social defense against mold infection of eggs by manipulating exposure of eggs to mold spores and the presence of the mother in a fully factorial design. Furthermore, we investigated the potential roles of egg grooming behavior and maternal transfer of chemicals as underlying mechanisms. As predicted, the beneficial effect of egg attendance on hatching success was significantly enhanced when eggs were exposed to the mold. Females significantly increased their egg grooming duration in response to mold exposure of her eggs, and the quantity of chemicals (identified as hydrocarbons) was maintained among attended eggs but decreased substantially among unattended eggs. Maternal transfer of chemicals was confirmed in extractions of glass beads that were mingled into attended or unattended clutches. This study shows that maternal egg attendance in the European earwig has a social defense function protecting offspring against mold infection. The maternal egg grooming behavior seems to be key for this effect, probably through both the mechanical removal of spores and the continued application of chemical substances on the egg surface.

Families with parental care show a parent-offspring conflict over the amount of parental investment. To date, the resolution of this conflict was modeled as being driven by either purely within-brood or between-brood competition. In reality the partitioning of parental resources within- versus between-broods is an evolving life history trait, which can be affected by parent-offspring interactions. This coevolutionary feedback between life history and family interactions may influence the evolutionary process and outcome of parent-offspring coadaptation. We used a genetic framework for a simulation model where we allowed parental parity to coevolve with traits that determine parental investment. The model included unlinked loci for clutch size, parental sensitivity, baseline provisioning, and offspring begging. The simulation showed that tight coadaptation of parent and offspring traits only occurred in iteroparous outcomes whereas semelparous outcomes were characterized by weak coadaptation. When genetic variation in clutch size was unrestricted in the ancestral population, semelparity and maximal begging with poor coadaptation evolved throughout. Conversely, when genetic variation was limited to iteroparous conditions, and/or when parental sensitivity was treated as an evolutionarily fixed sensory bias, coadapted outcomes were more likely. Our findings show the influence of a feedback between parity, coadaptation, and conflict on the evolution of parent-offspring interactions.

Parental care increases the fitness of offspring at a cost to the parents in terms of residual reproductive success. This trade-off may be affected by ecology, life history and the social environment, which raises the question as to how these factors contribute to the evolution of parental care. Here, previous hypotheses concerning the evolution of parental care in insects are summarized and discussed and the underlying empirical evidence is reviewed. Ecological factors such as harsh environments, ephemeral food sources or predation pressure are broadly accepted as evolutionary drivers of parental care. The most consistent evidence supports a role for natural enemies such as predators, microbes and cannibalistic conspecifics. Also, the importance of ecological factors may interact with the life history (parity) of a species, either as a pre-adaptation facilitating the evolution of parental care or as a consequence of enhanced parental investment under parental care. Yet, only limited experimental research has been carried out to test the combined influence of ecology and life history in the evolution of parental care. Several forms of care can mediate the transition from solitary to family living, which entails the emergence of a novel – social – environment that generates new selection pressures from interactions within and between families. In this context, we review examples of studies on communal breeding, brood parasitism, parent–offspring conflict and co-adaptation, and discuss how these social interactions may in turn be influenced by ecological factors such as food availability or population density. Insects are uniquely suitable for experimental and comparative research on the complex interplay between ecology, life history, and the social environment.

Parental care is beneficial for offspring, but costly for parents. Thus, it seems maladaptive to care for unrelated offspring unless the additional offspring provide direct benefits to the carer's own offspring or discrimination costs are high. Females of the European earwig, Forficula auricularia, provide maternal care for their own offspring (nymphs), but also for foreign nymphs that join their brood. Nymphs preferentially kill and cannibalize nonsiblings and individuals that are smaller or in poor condition. Here, we tested the effects of nymph condition and food availability on brood mixing in F. auricularia. We experimentally manipulated nymph condition by feeding or food depriving groups of unrelated nymphs. The resident groups remained with their mothers whereas the mothers were removed from the foreign groups. Since nymph condition determines the direction of cannibalism, we hypothesized that brood mixing is dependent on nymph condition and food availability in the environment. Our results show that brood mixing was initially driven by condition-dependent effects on nymph activity, and later by the fed foreigners invading resident broods, suggesting that foreigners control brood mixing, independent of food availability. These results are consistent with our hypothesis that the dynamics of brood mixing are condition dependent, possibly mediated by corresponding cannibalism threats.

Families with parental care show a parent-offspring conflict over the amount of parental investment. To date, the resolution of this conflict was modeled as being driven by either purely within-brood or between-brood competition. In reality the partitioning of parental resources within- versus between-broods is an evolving life history trait, which can be affected by parent-offspring interactions. This coevolutionary feedback between life history and family interactions may influence the evolutionary process and outcome of parent-offspring coadaptation. We used a genetic framework for a simulation model where we allowed parental parity to coevolve with traits that determine parental investment. The model included unlinked loci for clutch size, parental sensitivity, baseline provisioning, and offspring begging. The simulation showed that tight coadaptation of parent and offspring traits only occurred in iteroparous outcomes whereas semelparous outcomes were characterized by weak coadaptation. When genetic variation in clutch size was unrestricted in the ancestral population, semelparity and maximal begging with poor coadaptation evolved throughout. Conversely, when genetic variation was limited to iteroparous conditions, and/or when parental sensitivity was treated as an evolutionarily fixed sensory bias, coadapted outcomes were more likely. Our findings show the influence of a feedback between parity, coadaptation, and conflict on the evolution of parent-offspring interactions.

In agricultural landscapes, the lack of floral nectar can be a major difficulty for nectar feeding parasitoids. This problem can be reduced by the addition of suitable wildflowers. To date, flowers have mainly been studied in terms of effects on parasitoid fitness, not taking into account the essential role of flower attractiveness for foraging parasitoids. This study experimentally tested the olfactory attractiveness of five wildflowers (bishop’s weed, cornflower, buckwheat, candytuft, and oregano) to the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae). We conducted choice experiments in a Y-tube olfactometer to test the attractiveness of flowers against air, and relative attractiveness in paired choice tests. Our results showed that all the flowers were highly attractive and that in paired choice tests cornflower and candytuft were equally attractive and more attractive than buckwheat. These results indicate that M. mediator has evolved innate preferences that could be effectively exploited in biological control.

The aggregation of parents with offspring is generally associated with different forms of care that improve offspring survival at potential costs to parents. Under poor environments, the limited amount of resources available can increase the level of competition among family members and consequently lead to adaptive changes in parental investment. However, it remains unclear as to what extent such changes modify offspring fitness, particularly when offspring can survive without parents such as in the European earwig,Forficula auricularia. Here, we show that under food restriction, earwig maternal presence decreased offspring survival until adulthood by 43 per cent. This effect was independent of sibling competition and was expressed after separation from the female, indicating lasting detrimental effects. The reduced benefits of maternal presence on offspring survival were not associated with higher investment in future reproduction, suggesting a condition-dependent effect of food restriction on mothers and local mother–offspring competition for food. Overall, these findings demonstrate for the first time a long-term negative effect of maternal presence on offspring survival in a species with maternal care, and highlight the importance of food availability in the early evolution of family life.

Parental care typically enhances offspring fitness at costs for tending parents. Asymmetries in genetic relatedness entail potential conflicts between parents and offspring over the duration and the amount of care. To understand how these conflicts are resolved evolutionarily, it is important to understand how individual condition affects offspring and parental behaviour and whether parents or offspring make active choices in their interactions. Condition effects on offspring have been broadly studied, but the effect of parental condition on parentoffspring interactions is less well understood, in particular in species where care is facultative and offspring have the option to beg for food from the parents or to self-forage. In this study, we carried out two experiments in the European earwig Forficula auricularia, a system where females provide facultative care, in which we manipulated female condition (through a high-food and low-food treatment) and the degree by which mothers and offspring could make active choices. In a first experiment, where female mobility was limited, female condition had no significant effect on the rate of offspring self-foraging, which increased with nymph age. In a second experiment, nymph access to food was limited and females in poor nutritional condition provided food to significantly fewer nymphs than high condition females. In both experiments, offspring attendance remained at a constantly high level and was independent of female condition even after experimental separation of females and offspring. Our results show that earwig nymphs do not use cues of female condition to adjust rates of self-foraging, that females control food provisioning depending on their own condition, and that females and nymphs share control over offspring attendance, a form of care not influenced by female condition.

Whether to reproduce once or multiple times (semelparity vs. iteroparity) is a major life-history decision that organisms have to take. Mode of parity is usually considered a species characteristic. However, recent models suggested that population properties or condition-dependent fitness payoffs could help to maintain both life-history tactics within populations. In arthropods, semelparity was also hypothesised to be a critical pre-adaptation for the evolution of maternal care, semelparous females being predicted to provide more care due to the absence of costs on future reproduction. The aim of this study was to characterize potential fitness payoffs and levels of maternal care in semel- and itero-parous females of the European earwig Forficula auricularia. Based on 15 traits measured in 494 females and their nymphs, our results revealed that iteroparous females laid their first clutch earlier, had more eggs in their first clutch, gained more weight during the 2 weeks following hatching of the first clutch, but produced eggs that developed more slowly than semelparous females. Among iteroparous females, the sizes of first and second clutches were significantly and positively correlated, indicating no investment trade-off between reproductive events. Iteroparous females also provided more food than semelparous ones, a result contrasting with predictions that iteroparity is incompatible with the evolution of maternal care. Finally, a controlled breeding experiment reported full mating compatibility among offspring from females of the two modes of parity, confirming that both types of females belong to one single species. Overall, these results indicate that alternative modes of parity represent coexisting life-history tactics that are likely to be condition-dependent and associated with offspring development and specific levels of maternal care in earwigs.

Social structures such as families emerge as outcomes of behavioural interactions among individuals, and can evolve over time if families with particular types of social structures tend to leave more individuals in subsequent generations. The social behaviour of interacting individuals is typically analysed as a series of multiple dyadic (pair-wise) interactions, rather than a network of interactions among multiple individuals. However, in species where parents feed dependant young, interactions within families nearly always involve more than two individuals simultaneously. Such social networks of interactions at least partly reflect conflicts of interest over the provision of costly parental investment. Consequently, variation in family network structure reflects variation in how conflicts of interest are resolved among family members. Despite its importance in understanding the evolution of emergent properties of social organization such as family life and cooperation, nothing is currently known about how selection acts on the structure of social networks. Here, we show that the social network structure of broods of begging nestling great tits Parus major predicts fitness in families. Although selection at the level of the individual favours large nestlings, selection at the level of the kin-group primarily favours families that resolve conflicts most effectively.

In group-living or social species intraspecific predation and cannibalism can lead to substantial decreases in inclusive fitness because related individuals may encounter one another. Therefore, selection on the ability and accuracy of kin recognition to avoid losses in inclusive fitness is expected. Competition and relatedness are two key factors for the evolution of siblicide and cannibalism. However, our knowledge of the temporal dynamics and the accuracy of kin-mediated siblicide and cannibalism is scarce and experiments have usually focused on either relatedness (kin recognition) or weight asymmetry (dominance and competition) as independent components. In an experiment we set up mixed-kinship groups of three nymphs of the European earwig, Forficula auricularia Linnaeus, a gregarious and (sub-)social species, to investigate the combined effects of relatedness and weight asymmetry on the temporal dynamics of siblicide and cannibalism. We found that the temporal dynamics were jointly influenced by relatedness and weight asymmetry among nymphs. Weight asymmetry effects on siblicide and cannibalism were stronger between unrelated individuals than between related individuals as shown by a significant relatedness∗weight asymmetry interaction on survival patterns. The opportunity to choose between related and unrelated individuals did not enhance the accuracy of kin recognition but induced the above interaction between relatedness and weight asymmetry on cannibalistic outcomes. These results show that relatedness and weight affect siblicidal and cannibalistic behaviour, and that their combined effect depends on the social context.

Parent–offspring conflict theory predicts the evolution of offspring solicitation signals that can influence the amount and/or the duration of parental investment. Short-term effects of offspring solicitation signals on parental food provisioning have been widely demonstrated, but persistent effects of offspring signals on the maintenance of parental care have been rarely studied. Also, the relation between the amount of care provided to the brood and how it is distributed among individual offspring within a brood is not well enough understood. Here, we investigated in the European earwig (Forficula auricularia) the effects of offspring condition-dependent chemical signals on the maintenance of maternal care among broods and the distribution of maternal food within broods. Mothers were isolated from their brood for 3 days and continuously exposed to chemical signals extracted from broods of experimentally manipulated nutritional state. After re-introducing mothers to their brood, a range of maternal behaviours were quantified. We found that earwig mothers groomed their offspring significantly more after exposure to chemical extract from high-food brood in comparison with mothers exposed to extract from low-food brood, which in turn displayed significantly more aggressive behaviour. Furthermore, we manipulated offspring individual nutritional condition within the brood to evaluate the effect of offspring state on the within-brood food distribution. Within broods, poorly fed individuals received significantly more food than well-fed individuals, probably due to scramble competition. These results show that earwig nymphs express multi-component condition-dependent signals and behaviours differentially affecting maternal care provisioned to the brood and the distribution of care within broods.

Aggression levels among individuals can severely increase under high density or shortage of crucial resources, sometimes resulting in individuals killing conspecifics. This is not uncommon in family groups of diverse taxa, where the dependent offspring compete for the limited resources provided by their parents. Killing a nest mate can relax the level of competition, and cannibalism provides a direct nutritional benefit. However, nest-mate killing bears the risk of reducing indirect fitness if the victim is related (i.e., siblicide), imposing selection on kin-recognition abilities. Based on this hypothesis, we predicted that first instar juveniles (nymphs) of the European earwig (Forficula auricularia) kill and cannibalize unrelated nest mates earlier and more often than related nest mates and that cannibalism has a direct nutritional benefit in terms of survival. We tested these predictions experimentally by establishing related and unrelated pairs of nymphs and recorded survival, aggregation behavior, and cannibalistic outcomes in the absence of alternative food sources. In order to obtain expected survival probabilities of victims and survivors in the absence of any interaction, we simulated virtual nymph pairs based on survival data of singly held control individuals. As predicted, victims lived for less time and survivor for longer than expected from the simulated survival distributions, demonstrating nest-mate killing and cannibalism. Furthermore, unrelated individuals were killed significantly earlier and were more often cannibalized than related individuals. The survival patterns of victims and survivors were quantitatively consistent with the expectations of Hamilton's rule. Our study shows that earwig nymphs recognize kin and adjust their nest-mate killing and cannibalistic behavior as predicted under the hypothesis of kin-selected siblicide and cannibalism. Copyright 2010, Oxford University Press.

Posthatching maternal care such as food provisioning and protection has evolved several times in insects, allowing offspring (larvae, nymphs) to interact with their mothers and potentially influence their investment. The evolutionary conflict over the duration and amount of parental care is thought to promote the evolution of offspring begging behaviours either as honest signals of need or as competitive signals with the potential to manipulate parents into investing more. In most social insects, parental care is not obligatory and may represent a less derived state than in vertebrate systems making them more appropriate to test ancestral conditions for the evolution of begging signals. Here, we review forms of maternal care in insects ranging from protection to food provisioning and evidence of offspring begging behaviours influencing maternal care, including condition-dependent chemical cues produced by offspring that may turn out to be solicitation pheromones. Since behavioural parent–offspring interactions are embedded in the reproductive and developmental physiology of mother and offspring, we stress the need for behavioural studies to be complemented by physiological measurements which will allow us to understand better the nature of conflict resolution. We propose a hypothetical mechanism of maternal care regulation by direct internal chemical signals (i.e. hormones) and indirect external chemical signals (i.e. solicitation pheromones) influencing maternal reproductive physiology and future reproduction. Social insect species and the integrated study of behavioural interactions and physiological/reproductive consequences may represent promising new experimental systems for direct tests of the evolution of begging signals, complementing current research on parent–offspring conflict.

The evolution of the complex and dynamic behavioural interactions between caring parents and their dependent offspring is a major area of research in behavioural ecology and quantitative genetics. While behavioural ecologists examine the evolution of interactions between parents and offspring in the light of parent–offspring conflict and its resolution, quantitative geneticists explore the evolution of such interactions in the light of parent–offspring co-adaptation due to combined effects of parental and offspring behaviours on fitness. To date, there is little interaction or integration between these two fields. Here, we first review the merits and limitations of each of these two approaches and show that they provide important complementary insights into the evolution of strategies for offspring begging and parental resource provisioning. We then outline how central ideas from behavioural ecology and quantitative genetics can be combined within a framework based on the concept of behavioural reaction norms, which provides a common basis for behavioural ecologists and quantitative geneticists to study the evolution of parent–offspring interactions. Finally, we discuss how the behavioural reaction norm approach can be used to advance our understanding of parent–offspring conflict by combining information about the genetic basis of traits from quantitative genetics with key insights regarding the adaptive function and dynamic nature of parental and offspring behaviours from behavioural ecology.

Sibling and parent–offspring conflicts arise mainly over the amount and distribution of parental care, especially food. In altricial bird species where the young depend on parents for obtaining food, parents may control sibling competition by the choice of their respective provisioning locations. In great tits, the parents use fixed provisioning positions on the nest rim that are determined early in the breeding cycle and maintained until fledging. The two parents may choose positions that are close to each other, or far apart, and thereby increase or relax the pressure for optimal feeding positioning among nestlings. As an inspiration to this study we previously found that the two parents provide food from closer positions if the nest is infested by ectoparasites. Here, we tested the hypothesis that the parental choice of relative provisioning locations could be strategically used to control nestling competition. We forced parents to feed from either one or two provisioning locations and assessed the induced change in nestling movement, weight gain, and food distribution among siblings. We show that the angular distance between male and female locations influences the level of behavioural competition and affects nestling weight gain and food distribution. It is the first evidence for hole-nesting birds, where it was assumed that the nestling closest to the entrance hole was fed first, that the apparent choice of feeding positions by parents could be a way of controlling sibling competition and thereby also taking partial control over the outcome of parent–offspring conflict.

The evolution of parent-offspring interactions for the provisioning of care is usually explained as the phenotypic outcome of resolved conflicting selection pressures. However, parental care and offspring solicitation are expected to have complex patterns of inheritance. Here we present a quantitative genetic model of parent-offspring interactions that allows us to investigate the evolutionary maintenance of a state of resolved conflict. We show that offspring solicitation and parental provisioning are expected to become genetically correlated through coadaptation and that their genetic architecture is dictated by an interaction between patterns of selection and the proximate mechanisms regulating supply and demand. When selection is predominately on offspring solicitation, our model suggests that the genetic correlations between provisioning and solicitation are usually positive if provisioning reduces solicitation. Conversely, when selection is predominately on parental provisioning, the correlations are mostly negative as long as parents show a positive response to offspring demand. Empirical estimates of the genetic architecture of traits involved in family interactions fit these predictions. Our model demonstrates how the evolutionary maintenance of parent-offspring interactions can result in variable patterns of coadaptation, and it provides an explanation for the diversity of family interactions within and among species.

Female burrower bugs (Sehirus cinctus, Hemiptera: Cydnidae) show extended care for their offspring. They guard their clutch and feed the hatched nymphs up to the third larval instar. Previous research indicated that nymphs partly regulate maternal food provisioning, but how nymphs accomplish this is unknown. We tested the hypothesis that nymphs solicit maternal provisioning by condition-dependent chemical signalling and we postulated the existence of a solicitation pheromone. Clutches of 30 nymphs were handreared in either low- or high-food conditions. After moult to second instar, cuticular compounds were extracted in hexane. An independent set of test mothers caring for offspring were subsequently exposed to extracts of nymphs from either the low- or the high-food treatment. Two control groups were also involved, one exposed to the solvent hexane and one with no treatment. As predicted for a solicitation pheromone, test mothers exposed to extracts from nymphs reared under low food provisioned more than those exposed to extracts from nymphs reared under high-food treatment. Contrary to our expectation, however, nymph extracts had an overall inhibiting effect on maternal provisioning. The effects of extract exposure on maternal provisioning were short-lasting, suggesting that the critical cues may be volatile. Our results suggest complex chemical communication in burrower bug families for the short-term regulation of maternal provisioning, potentially involving both provisioning-releasing solicitation pheromones and inhibiting chemical cues.

The most commonly used modelling methods for targeting customers in direct marketing are artificial neural networks (ANNs), classification trees (CTs) and logistic regression (LR). These methods differ in how rules for the association between purchase behaviour and customer information are derived from the data. The authors investigated the predictive performances of the three methods in a competitive test in a simulated direct marketing scenario. The experimental design consisted of a number of situations comprising varying sample sizes and data complexities. The results show that the performance of all methods increased with the size of the customer base. This relation was less strong for ANNs than for CTs and LR, especially when data complexity was high. As a consequence ANNs outperformed the other methods when sample size was small, but CTs and LR yielded better results when sample size was large — with LR being generally superior to CTs. The combination of the prediction scores of ANNs, CTs and LR into a single model revealed synergistic effects among the three modelling approaches. The combination mostly resulted in better results than any single model. This study shows that ANNs may be especially valuable for small customer bases, but might not be used in isolation for analysing larger customer bases. Irrespective of the size of the customer base and the underlying data complexity, the combination of ANNs, CTs and LR into a single model mostly resulted in the best prediction, suggesting that model combination might be a safe way of maximising predictive performance when the degree of data complexity is unknown (as is the case for most real customer bases).

The evolutionary transition from solitary to social life is driven by direct and indirect fitness benefits of social interactions. Understanding the conditions promoting the early evolution of social life therefore requires identification of these benefits in nonderived social systems, such as animal families where offspring are mobile and able to disperse and will survive independently. Family life is well known to provide benefits to offspring through parental care, but research on sibling interactions generally focused on fitness costs to offspring due to competitive behaviors. Here we show experimentally that sibling interactions also reflect cooperative behaviors in the form of food sharing in nonderived families of the European earwig, Forficula auricularia. Food ingested by individual offspring was transferred to their siblings through mouth-to-anus contacts and active allo-coprophagy. These transfers occurred in both the presence and the absence of the tending mothers, even though the direct contact with the mothers limited sibling food sharing. Neither food deprivation or relatedness influenced the total amount of transferred food, but relatedness affected frass release and the behavioral mechanisms mediating food sharing. Related offspring obtained food predominately through allo-coprophagy, whereas unrelated offspring obtained food through mouth-to-anus contacts. Overall, this study emphasizes that sibling cooperation may be a key process promoting the early evolution of social life.

Scent-marking is widespread among mammals and has been observed in many felid species. Although the behaviour is well-described, little is known about its function in wild felid populations. We investigated patterns of scent-marking and its role in intra- and intersexual communication among resident and non-resident Eurasian lynx Lynx lynx by observing interactions among wild lynx at natural marking sites by means of infrared camera traps. Marking activity of resident animals showed a peak during the mating season and was lowest during the time when females gave birth and lactated. Both sexes scent-marked, but male lynx visited marking sites much more often than females and marked relatively more often when visiting a site. Most visits to marking sites were by residents but we also observed scent-marking by non-residents. Juveniles were never observed marking. We found no evidence of lynx regularly renewing scent-marks after a certain 'expiry date' but the presence of a strange scent-mark triggered over-marking. Males responded similarly to the presence of another individual's scent-mark, irrespective of whether it was the top- or the underlying scent-mark in a mixture of scent-marks they encountered. Our results suggest that marking sites could serve as 'chemical bulletin boards', where male lynx advertise their presence and gain information on ownership relationships in a given area. Females placed their urine marks on top of the ones left by resident males, but further studies are needed to explain the functions of over-marking in females.

Solicitation displays by offspring and responses by parents are commonly regarded as phenotypic expressions of the conflict over parental investment between genes expressed in offspring and their parents. Models for the resolution of the parent–offspring conflict have assumed genetic variation for levels of both offspring solicitation and parental response in order to allow offspring and parental strategies to coevolve and the conflict to be evolutionarily resolved. Empirical research has focused on the phenotypic predictions of these models, and little is known about the genetics of parent–offspring interactions. We review the existing evidence for genetic variation in offspring solicitation behaviours and parental responses from a variety of animal species. This evidence confirms the fundamental assumption of genetic variation in offspring solicitation and parental response, indicating that offspring and parental strategies can (co-) evolve. We discuss potential reasons for the maintenance of genetic variation in offspring solicitation and parental response, and the implications genetic variation and covariation and/or parental effects may have for the resolution of the parent–offspring conflict. Further research on the genetic bases of parent–offspring interactions may be crucial for understanding the resolution of parent–offspring conflict and the coevolution of the behaviours involved.

Host nests are the key habitat for ectoparasite species that live and reproduce within the nest material. Nest properties can influence host and parasite reproductive success, and therefore the outcome of host–parasite interactions, as well as the composition of parasite communities. Previous correlational results suggested that nest humidity may increase the negative effect of fleas on Great Tit (Parus major) reproductive success. Since the causality of the relationship was unknown, we simultaneously manipulated both hen flea (Ceratophyllus gallinae) infestation and nest humidity in order to investigate: (1) the effect of flea infestation on nest humidity, (2) the effect of nest humidity on the prevalence of flea infestations, (3) the effect of nest humidity on adult flea survival and reproduction, (4) the interaction between flea infestations and nest humidity on Great Tit reproductive performance, and (5) the effect of both factors on secondary infestations by ectoparasitic Protocalliphora flies. The p...

Although inbreeding is commonly known to depress individual fitness, the severity of inbreeding depression varies considerably across species. Among the factors contributing to this variation, family interactions, life stage and sex of offspring have been proposed, but their joint influence on inbreeding depression remains poorly understood. Here, we demonstrate that these three factors jointly shape inbreeding depression in the European earwig, Forficula auricularia. Using a series of cross-breeding, split-clutch and brood size manipulation experiments conducted over two generations, we first showed that sib mating (leading to inbred offspring) did not influence the reproductive success of earwig parents. Second, the presence of tending mothers and the strength of sibling competition (i.e. brood size) did not influence the expression of inbreeding depression in the inbred offspring. By contrast, our results revealed that inbreeding dramatically depressed the reproductive success of inbred adult male offspring, but only had little effect on the reproductive success of inbred adult female offspring. Overall, this study demonstrates limited effects of family interactions on inbreeding depression in this species and emphasizes the importance of disentangling effects of sib mating early and late during development to better understand the evolution of mating systems and population dynamics.

Benefits and costs of parental care are expected to change with offspring development and lead to age-dependent coadaptation expressed as phenotypic (behavioural) matches between offspring age and parental reproductive stage. Parents and offspring interact repeatedly over time for the provision of parental care. Their behaviours should be accordingly adjusted to each other dynamically and adaptively, and the phenotypic match between offspring age and parental stage should stabilize the repeated behavioural interactions. In the European earwig (Forficula auricularia), maternal care is beneficial for offspring survival, but not vital, allowing us to investigate the extent to which the stability of mother–offspring aggregation is shaped by age-dependent coadaptation. In this study, we experimentally cross-fostered nymphs of different age classes (younger or older) between females in early or late reproductive stage to disrupt age-dependent coadaptation, thereby generating female–nymph dyads that were phenotypically matched or mismatched. The results revealed a higher stability in aggregation during the first larval instar when care is most intense, a steeper decline in aggregation tendency over developmental time and a reduced developmental rate in matched compared with mismatched families. Furthermore, nymph survival was positively correlated with female–nymph aggregation stability during the early stages when maternal care is most prevalent. These results support the hypothesis that age-related phenotypically plastic coadaptation affects family dynamics and offspring developmental rate.

Maternal effects can induce adjustments in offspring phenotype to the environment experienced by the mother. Of particular interest is if mothers can programme their offspring to cope best under matching environmental conditions, but the evidence for such anticipatory maternal effects (AME) is limited. In this study, we manipulated experimentally the food availability experienced by mothers and their offspring in the European earwig ( Forficula auricularia ). Offspring produced by females that had access to high or low food quantities were cross-fostered to foster mothers experiencing matched or mismatched environments. Offspring experiencing food availability matching the one of their mothers had an increased survival to adulthood compared with offspring experiencing mismatched conditions. Females experiencing high food laid larger clutches. This clutch-size adjustment statistically explained the matching effect when offspring experienced high food, but not when experiencing low food conditions. There were no effects of matching on offspring growth and developmental rate. Overall, our study demonstrates that AME occurs in relation to food availability enhancing offspring survival to adulthood under matching food conditions.

Parental care is a trait that shows tremendous diversity both within and across different animal taxa, and is an important topic in evolutionary biology and behavioural ecology. Parental care forms an integral part of an organism’s reproduction, development, and life-history, and because caring for offspring means that parents have less time, resources, or energy available to search for or attract mates, the evolution of parental care is closely linked with sexual selection. In addition, the evolution of parental care represents an important step in the evolution of sociality as it leads to the formation of family groups, which provides a bridge to more complex forms of social structures. But because parents and offspring share only some of their genes, conflicts emerge in sexually reproducing organisms that shape the evolution of parental care and offspring strategies to demand care. As a consequence, the family also constitutes a model to understand the evolutionary tension between cooperation and conflict. This edited book is: The first comprehensive review of the evolution of parental care for over 20 years Integrates contributions from leading international authors to provide an interdisciplinary synthesis of the field Establishes key concepts and draws on general principles whilst emphasizing a broad taxonomic approach Emphasizes behavioural interactions and the co-evolution of parents and offspring Includes the latest research findings, suggesting avenues for future study Parental care includes a wide variety of traits that enhance offspring development and survival. It is taxonomically widespread and is central to the maintenance of biodiversity through its close association with other phenomena such as sexual selection, life-history evolution, sex allocation, sociality, cooperation and conflict, growth and development, genetic architecture, and phenotypic plasticity. This novel book provides a fresh perspective on the study of the evolution of parental care based on contributions from some of the top researchers in the field. It provides evidence that the dynamic nature of family interactions, and particularly the potential for co-evolution among family members, has contributed to the great diversity of forms of parental care and life-histories across as well as within taxa. The Evolution of Parental Care aims to stimulate students and researchers alike to pursue exciting new directions in this fascinating and important area of behavioural and evolutionary biology. It will be of relevance and use to those working in the fields of animal behaviour, ecology, evolution, and genetics, as well as related disciplines such as psychology and sociology. Readership: Suitable for researchers and students working in the fields of animal behaviour, ecology, evolution, and genetics, as well as related disciplines such as psychology and sociology.

Solicitation signals by offspring are well known to influence parental behaviour, and it is commonly assumed that this behavioural effect translates into an effect on residual reproduction of parents. However, this equivalence assumption concerning behavioural and reproductive effects caused by offspring signals remains largely untested. Here, we tested the effect of a chemical offspring signal of quality on the relative timing and amount of future reproduction in the European earwig ( Forficula auricularia ). We manipulated the nutritional condition of earwig nymphs and exposed females to their extract, or to solvent as a control. There were no significant main effects of exposure treatment on 2nd clutch production, but exposure to extracts of well-fed nymphs induced predictable timing of the 2nd relative to the 1st clutch. This result demonstrates for the first time that an offspring signal per se , in the absence of any maternal behaviour, affects maternal reproductive timing, possibly through an effect on maternal reproductive physiology.

Consistent inter-individual variation in behaviour over time and across contexts has been reported for a wide variety of animals, a phenomenon commonly referred to as personality. As behavioural patterns develop inside families, rearing conditions could have lasting effects on the expression of adult personality. In species with parental care, conflicts among family members impose selection on parental and offspring behaviour through coadaptation. Here, we argue that the interplay between the evolution of personality traits (i.e. boldness, exploration, activity, aggressiveness and sociability) expressed outside the family context and the specialized behaviours expressed inside families (i.e. offspring begging behaviour and parental response to offspring solicitations) can have important evolutionary consequences. Personality differences between parents may relate to the typically observed variation in the way they respond to offspring demand, and dependent offspring may already express personality differences, which may relate to the way they communicate with their parents and siblings. However, there has been little research on how personality relates to parental and offspring behaviours. Future research should thus focus on how and why personality may be related to the specialized parent and offspring behaviour that evolved as adaptations to family life.

Background In species across taxa, offspring have means to influence parental investment (PI). PI thus evolves as an interacting phenotype and indirect genetic effects may strongly affect the co-evolutionary dynamics of offspring and parental behaviors. Evolutionary theory focused on explaining how exaggerated offspring solicitation can be understood as resolution of parent-offspring conflict, but the evolutionary origin and diversification of different forms of family interactions remains unclear. Methodology/Principal Findings In contrast to previous theory that largely uses a static approach to predict how “offspring individuals” and “parental individuals” should interact given conflict over PI, we present a dynamic theoretical framework of antagonistic selection on the PI individuals obtain/take as offspring and the PI they provide as parents to maximize individual lifetime reproductive success; we analyze a deterministic and a stochastic version of this dynamic framework. We show that a zone for equivalent co-adaptation outcomes exists in which stable levels of PI can evolve and be maintained despite fast strategy transitions and ongoing co-evolutionary dynamics. Under antagonistic co-adaptation, cost-free solicitation can evolve as an adaptation to emerging preferences in parents. Conclusions/Significance We show that antagonistic selection across the offspring and parental life-stage of individuals favors co-adapted offspring and parental behavior within a zone of equivalent outcomes. This antagonistic parent-offspring co-adaptation does not require solicitation to be costly, allows for rapid divergence and evolutionary novelty and potentially explains the origin and diversification of the observed provisioning forms in family life.

Begging signals of offspring are condition-dependent cues that are usually predicted to display information about the short-term need (i.e. hunger) to which parents respond by allocating more food. However, recent models and experiments have revealed that parents, depending on the species and context, may respond to signals of quality (i.e. offspring reproductive value) rather than need. Despite the critical importance of this distinction for life history and conflict resolution theory, there is still limited knowledge of alternative functions of offspring signals. In this study, we investigated the communication between offspring and caring females of the common earwig, Forficula auricularia , hypothesizing that offspring chemical cues display information about nutritional condition to which females respond in terms of maternal food provisioning. Consistent with the prediction for a signal of quality we found that mothers exposed to chemical cues from well-fed nymphs foraged significantly more and allocated food to more nymphs compared with females exposed to solvent (control) or chemical cues from poorly fed nymphs. Chemical analysis revealed significant differences in the relative quantities of specific cuticular hydrocarbon compounds between treatments. To our knowledge, this study demonstrates for the first time that an offspring chemical signal reflects nutritional quality and influences maternal care.

Theory for the evolution of social interactions based on continuous strategies often assumes for simplicity that expressed behaviours are independent of previous encounters. In reality, however, such dependencies are likely to be widespread and often strong, generating complex behavioural dynamics. To model this process and illustrate potential consequences for the evolution of behavioural interactions, we consider the behavioural dynamics of the interaction between caring parents and their demanding offspring, a prime example of long series of interdependent and highly dynamic interactions. These dynamics can be modelled using functions describing mechanisms for how parents and their offspring respond to each other in the interaction. We establish the general conditions under which the behavioural dynamics converge towards a proximate equilibrium and refer to such converging interactions as behaviourally stable strategies (BSSs). We further demonstrate that there is scope for behavioural instability under realistic conditions; that is, whenever parents and/or offspring ‘overreact’ beyond some threshold. By applying the derived condition for behavioural stability to evolutionary models of parent–offspring conflict resolution, we show by numerical simulations that evolutionarily stable strategies (ESSs) of current models are not necessarily behaviourally stable. Because behavioural instability implies that expressed levels of behaviours deviate from the ESS, behavioural stability is required for strict evolutionary stability in repeated behavioural interactions.

The occurrence of parental food regurgitation as a form of parental care in (sub-) social insects has been little studied and is largely based on anectodal and indirect evidence. However, understanding the behavioural mechanisms mediating the benefit of parental care is critical to advance research on the evolution of family interactions. Here, we report results from a study where we experimentally tested the hypothesis that European earwig (Forficula auricularia) females regurgitate food to their nymphs. We used a simple experimental method based on food dyes as colour markers to separate maternal food regurgitation and nymphal self-feeding as the two components of food intake by nymphs. Two different food dyes were used to label the food offered to the earwig mother and the nymphs respectively. By analysing the colour of the gut content of the nymphs, we demonstrate significant food transfer from the mother to the nymphs. This study demonstrates unambiguously that maternal food regurgitation exists in earwigs and presents a simple and easily applicable technique to trace maternal food regurgitation in the study of insect parental care and family interactions.

The distribution of food among altricial bird nestlings is the result of an interaction between parental feeding decisions and scramble competition between nestmates. Both young and parents can potentially be in control of the outcome of this interaction. In great tits, each parent feeds from a fixed location on the nest rim, thereby forcing nestlings to choose between the father's and the mother's location. It was previously found that hungry nestlings approached the female preferentially and were more likely to be fed, appearing as if females showed a stronger preference to feed hungry young than males. However, nestlings were free to move in that study, and the effects of nestling positioning could not be disentangled from those of parental food allocation decisions. Here, we experimentally divided broods into two halves and randomly assigned each half of the brood to one side of the nest cup where only one parent could feed them. One nestling in each half-brood was food deprived to manipulate short-term hunger state. Both parents showed a similar preference to feed the more hungry nestlings, suggesting that the previously observed difference was due to offspring positioning rather than active parental choice. Our study shows that food allocation is partially under nestling control and suggests that nestlings adjust positioning and begging behaviour to the profitability of a given position in the nest cup.

The sensory modalities used for communication among family members have at least partly evolved within an organism's pre-existing sensory context. Given the well-known general importance of chemical communication in insects, we hypothesized in sub-social insects with parental care that chemical signals emitted by larvae to influence parental care (i.e. solicitation pheromones) would have evolved. To test this hypothesis, we performed an experiment in the burrower bug Sehirus cinctus (Hemiptera: Cydnidae) where nymphs were hand-reared under high- or low-food conditions. These hand-reared clutches were used as a source of volatiles. The volatiles were collected for chemical analysis and delivered to caring mothers to quantify their behavioural response. As predicted, mothers exposed to volatiles from nymphs in poor condition provisioned significantly more food than those exposed to air (controls) or volatiles from high-condition nymphs. Chemical analysis revealed that nymphs emitted a blend of eight compounds of which α-pinene and camphene showed the strongest relationship with food treatment. Exposure to pure synthetic α-pinene and camphene did not affect maternal provisioning, however, suggesting that the functional significance of α-pinene and/or camphene may occur in a blend with other compounds. This study shows a clear effect of condition-dependent offspring odours on maternal food provisioning and identifies, for the first time, candidate compounds for a potential chemical offspring begging signal.

When ontogeny takes place in a family, and parents provide essential resources for development, the parents become an environmental component to the development of a wide range of offspring traits. Because differences among parents may partly reflect genetic variation, this environmental component contains genes and may itself evolve. Also, when offspring play an active role in family interactions, offspring become a social environmental component to parents, affecting their behavior in turn, which potentially results in reciprocal social selection. Thus, an evolutionary process of coadaptation to family life, additionally driven by conflicts of interests, may have shaped the expression and development patterns underlying infant behaviors. The complex genetics arising from family interactions can be formalized by extending standard quantitative genetic models. These models demonstrate how the explicit consideration of the family environment can profoundly alter both the expression and evolutionary response to selection of behaviors involved in family interactions. Behavioral genetic studies have begun to unravel the complex genetics underlying infant solicitation behaviors and parental provisioning, although many focus on one side of the interaction. A genetic analysis incorporating interactions among family members explicitly may be critical because the genes underlying the expression of parental provisioning indirectly affect offspring behaviors, and vice versa.

Evolutionary models for the resolution of family conflicts are sensitive to assumptions regarding the behavioural mechanisms regulating parental resource provisioning and offspring begging. Thus, quantitative empirical estimates of the mechanisms are critical to validate current evolutionary models, but a standardized method is lacking. I present a formalization of Hussell's (1988 Am. Nat. 131, 175-202) original graphical model of mechanisms regulating the effect of begging on provisioning, and of provisioning on begging, based on linear regression equations. The model makes it possible to estimate quantitatively the behavioural mechanisms and the resulting proximate equilibria for begging and provisioning by the use of appropriate experiments and standard linear regression analysis.

Kin recognition is a key mechanism to direct social behaviours towards related individuals or avoid inbreeding depression. In insects, recognition is generally mediated by cuticular hydrocarbon (CHC) compounds, which are partly inherited from parents. However, in social insects, potential nepotistic conflicts between group members from different patrilines are predicted to select against the expression of patriline-specific signatures in CHC profiles. Whereas this key prediction in the evolution of insect signalling received empirical support in eusocial insects, it remains unclear whether it can be generalized beyond eusociality to less-derived forms of social life. Here, we addressed this issue by manipulating the number of fathers siring clutches tended by females of the European earwig,Forficula auricularia, analysing the CHC profiles of the resulting juvenile and adult offspring, and using discriminant analysis to estimate the information content of CHC with respect to the maternal and paternal origin of individuals. As predicted, if paternally inherited cues are concealed during family life, increases in mating number had no effect on information content of CHC profiles among earwig juveniles, but significantly decreased the one among adult offspring. We suggest that age-dependent expression of patriline-specific cues evolved to limit the risks of nepotism as family-living juveniles and favour sibling-mating avoidance as group-living adults. These results highlight the role of parental care and social life in the evolution of chemical communication and recognition cues.

International audience; The evolution of parent-offspring communication was mostly studied from the perspective of parents responding to begging signals conveying information about offspring condition. Parents should respond to begging because of the differential fitness returns obtained from their investment in offspring that differ in condition. For analogous reasons, offspring should adjust their behavior to cues/signals of parental condition: parents that differ in condition pay differential costs of care and, hence, should provide different amounts of food. In this study, we experimentally tested in the European earwig (Forficula auricularia) if cues of maternal condition affect offspring behavior in terms of sibling cannibalism. We experimentally manipulated female condition by providing them with different amounts of food, kept nymph condition constant, allowed for nymph exposure to chemical maternal cues over extended time, quantified nymph survival (deaths being due to cannibalism) and extracted and analyzed the females' cuticular hydrocarbons (CHC). Nymph survival was significantly affected by chemical cues of maternal condition, and this effect depended on the timing of breeding. Cues of poor maternal condition enhanced nymph survival in early broods, but reduced nymph survival in late broods, and vice versa for cues of good condition. Furthermore, female condition affected the quantitative composition of their CHC profile which in turn predicted nymph survival patterns. Thus, earwig offspring are sensitive to chemical cues of maternal condition and nymphs from early and late broods show opposite reactions to the same chemical cues. Together with former evidence on maternal sensitivities to condition-dependent nymph chemical cues, our study shows context-dependent reciprocal information exchange about condition between earwig mothers and their offspring, potentially mediated by cuticular hydrocarbons.

Current theory proposes that nestlings beg to signal hunger level to parents honestly, or that siblings compete by escalating begging to attract the attention of parents. Although begging is assumed to be directed at parents, barn owl (Tyto alba) nestlings vocalize in the presence but also in the absence of the parents. Applying the theory of asymmetrical contests we experimentally tested three predictions of the novel hypothesis that in the absence of the parents siblings vocally settle contests over prey items to be delivered next by a parent. This 'sibling negotiation hypothesis' proposes that offspring use each others' begging vocalization as a source of information about their relative willingness to contest the next prey item delivered. In line with the hypothesis we found that (i) a nestling barn owl refrains from vocalization when a rival is more hungry, but (ii) escalates once the rival has been fed by a parent, and (iii) nestlings refrain from and escalate vocalization in experimentally enlarged and reduced broods, respectively. Thus, when parents are not at the nest a nestling vocally refrains when the value of the next delivered prey item will be higher for its nest-mates. These findings are the exact opposite of what current models predict for begging calls produced in the presence of the parents.

As a consequence of the deleterious effects of parasites on host fitness, hosts have evolved responses to minimize the negative impact of parasite infection. Facultative parasite-induced responses are favoured when the risk of infection is unpredictable and host responses are costly. In vertebrates, induced responses are generally viewed as being adaptive, although evidence for fitness benefits arising from these responses in natural host populations is lacking. Here we provide experimental evidence for direct reproductive benefits in flea-infested great tit nests arising from exposure during egg production to fleas. In the experiment we exposed a group of birds to fleas during egg laying (the exposed group), thereby allowing for induced responses, and kept another group free of parasites (the unexposed group) over the same time period. At the start of incubation, we killed the parasites in both groups and all nests were reinfested with fleas. If induced responses occur and are adaptive, we expect that birds of the exposed group mount earlier responses and achieve higher current reproductive success than birds in the unexposed group. In agreement with this prediction, our results show that birds with nests infested during egg laying have (i) fewer breeding failures and raise a higher proportion of hatchlings to fledging age; (ii) offspring that reach greater body mass, grow longer feathers, and fledge earlier, and (iii) a higher number of recruits and first-year grandchildren than unexposed birds. Flea reproduction and survival did not differ significantly between the two treatments. These results provide the first evidence for the occurrence and the adaptiveness of induced responses against a common ectoparasite in a wild population of vertebrates.

The evolutionary conflict over the amount of resources transferred between a parent and its offspring may be resolved by honest signalling of 'need' by offspring and parental investment in relation to signalling level. In birds, biparental care is the norm and evidence that male and female parents differ in their investment pattern in individual offspring is growing. In an experiment on great tits, Parus major, we investigated how and why parents differ in food allocation when responding to similar chick signals, which supposedly uniquely reflect the chick's nutritional condition. Nestling hunger level was manipulated by food deprivation and hand-feeding. Subsequent filming revealed that parents fed from significantly different locations on the nest and thereby forced chicks to choose between them when competing for favourable positions. Deprived nestlings approached, and fed ones retreated (or were displaced by siblings) from, positions near the female. No such behaviour was observed towards the male. Females allocated more feeds than males to the food-deprived nestlings. The results are discussed in terms of nestling competition for access to 'begging patches'. By varying their 'begging patch' value, parents may exploit competitive inter-sibling dynamics to influence the outcome of competition among chick phenotypes (e.g. 'need', size, sex). Parent birds may thereby exert considerable control over the information content of chick begging behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.