Search

Obtaining nesting material presents an optimal foraging problem, collection of materials incurs a cost in terms of risk of predation and energy spent and individuals must balance these costs with the benefits of using that material in the nest. The hazel dormouse, Muscardinus avellanarius is an endangered British mammal in which both sexes build nests. However, whether material used in their construction follows the predictions of optimal foraging theory is unknown. Here, we analyze the use of nesting materials in forty two breeding nests from six locations in Southwest England. Nests were characterized in terms of which plants were used, the relative amount of each plant, and how far away the nearest source was. We found that dormice exhibit a preference for plants closer to the nest, but that the distance they are prepared to travel depends on the plant species. Dormice traveled further to collect honeysuckle Lonicera periclymenum, oak Quercus robur, and beech Fagus sylvatica than any other plants. Distance did not affect the relative amount used, although the proportion of honeysuckle in nests was highest, and more effort was expended collecting honeysuckle, beech, bramble Rubus fruticosus and oak compared to other plants. Our results suggest that not all aspects of optimal foraging theory apply to nest material collection. However, optimal foraging theory is a useful model to examine nest material collection, providing testable predictions. As found previously honeysuckle is important as a nesting material and its presence should be taken account when assessing suitability of sites for dormice.

Understanding the determinants of fighting ability (or resource-holding potential, RHP) is key to elucidating the evolution of aggressive behaviour, as current tests of contest theory rely on realistic proxies for overall RHP. Traditionally, RHP is considered equivalent to body size but it is increasingly clear that a wider range of morphological and physiological traits contribute to fighting ability. In situations analogous to contests, such as courtship displays in animals and competitive sport in humans, the role of skill has long been appreciated but this component has been neglected in analyses of animal fights. Here, we investigated two spatial components of skill, accuracy and precision, during shell fights in hermit crabs, where an attacker repeatedly strikes (raps) its shell against that of a defender. By analysing the points of impact of these strikes, we found that attackers that rapped with coarse-scale accuracy were more likely to win the fight, indicating that the ability to target a ‘sweet spot’ on the defender's shell is an important determinant of contest success. Furthermore, we found that this element of skill correlated with temporal performance (vigour). Taken together these results show that spatial skill is an RHP component. Moreover, in contrast to the traditional assumption that fighting ability is equivalent to body size, RHP is actually underpinned by a suite of interlinked traits including performance capacities, morphology and skill., Highlights • Fighting often involves the repeated performance of agonistic behaviours. • Individuals may vary in how skilfully they perform such behaviours. • We investigate the link between spatial skill and fighting success in hermit crabs. • We find that winners perform rapping behaviour more skilfully than losers. • Our results indicate that skill is tightly correlated with other fighting traits.

Theoretical models of animal contests such as the Hawk-Dove game predict that variation in fighting behavior will persist due to mixed evolutionarily stable strategies (ESS) under certain conditions. However, the genetic basis for this variation is poorly understood and a mixed ESS for fighting can be interpreted in more than one way. Specifically, we do not know whether variation in aggression within a population arises from among-individual differences in fixed strategy (determined by an individual’s genotype—direct genetic effects [DGEs]), or from within-individual variation in strategy across contests. Furthermore, as suggested by developments of the original Hawk-Dove model, within-individual variation in strategy may be dependent on the phenotype and thus genotype of the opponent (indirect genetic effects—IGEs). Here we test for the effect of DGEs and IGEs during fights in the beadlet sea anemone Actinia equina. By exploiting the unusual reproductive system of sea anemones, combined with new molecular data, we investigate the role of both additive (DGE + IGE) and non-additive (DGE × IGE) genetic effects on fighting parameters, the latter of which have been hypothesized but never tested for explicitly. We find evidence for heritable variation in fighting ability and that fight duration increases with relatedness. Fighting success is influenced additively by DGEs and IGEs but we found no evidence for non-additive IGEs. These results indicate that variation in fighting behavior is driven by additive indirect genetic effects (DGE + IGE), and support a core assumption of contest theory that strategies are fixed by DGEs., We show that for beadlet sea anemones, the likelihood of winning a fight depends on both the genotype of the individual and the genotype of its opponent. We find heritable variation in fighting success and evidence that fights last longer between more related opponents. Our results indicate that an individual’s ability to win will vary from fight to fight depending on the genetic identity of its opponent.

Fighting experience (specifically winning or losing a fight) can significantly alter boldness, a component of resource-holding potential (RHP). Previous studies have shown that both the repeatability of boldness and mean-level boldness can be affected by fighting experience and that these effects are strongest in the recipients of agonistic behaviour. However, whether these postfight changes in boldness impact future contest success and whether subsequent contests further affect boldness remain unknown. Furthermore, little is known about the effects of the specific tactics used within a fight (within-fight experience) and how these might influence future fight performance and boldness. Here, we investigated the relationship between fighting success and boldness (measured as recovery time when startled) across repeated contests in the beadlet sea anemone, Actinia equina , measuring boldness on five occasions before, between and after two contests. We found that boldness (both repeatability and mean-level) was generally robust to the effects of fighting experience, apart from a decrease in the immediate boldness of losers after their second fight. Furthermore, we found that while prefight boldness significantly predicted fighting success and the level of aggression used in an individual's first fight, it did not predict victory or aggression in the second fight. Our findings thus indicate that different traits may be important in determining fighting success in consecutive fights and, moreover, that fighting experience may alter which traits contribute to an individual's RHP.

Theoretical models of injurious animal contests, such as the cumulative assessment model (CAM), predict that an individual's decision to give up and retreat from a fight is determined by reaching a maximum cost threshold (Cmax). Under this model, an individual gives up when the accumulated costs of persisting exceed this threshold. CAM predicts that the velocity with which Cmax is reached depends on both the energetic (physiological) costs of remaining in the fight and the damage costs of injuries received. Here we propose that damage costs are accumulated not only by receiving injuries, but in some cases also by inflicting injury (attacking). We argue that these self-inflicted damage costs need to be incorporated into theoretical frameworks to fully understand what drives an individual to make the decision to give up, and we call for further research into this area.

The contamination of natural systems with plastic debris has become one of the most pressing global environmental issues. Microplastics (MPs) are of particular concern because their ubiquity and small size make them available for ingestion by a range of aquatic biota. MP exposure studies are hence proliferating rapidly but are typically limited to the analyses of population-level responses in toxicity endpoints across treatments. Potential contaminant-induced alterations in behavioural patterns, however, could manifest on numerous levels of variation: at the population-level, between individuals and within individuals. Here, we used repeated measures on startle response durations – a risk-avoidance mechanism – in European hermit crabs, Pagurus bernhardus, to measure behavioural responses to MP exposure across multiple levels of variation. We found that MP exposure led to a significant decrease of startle duration at the population-level as well as a reduction of intra-individual variation. In other words, crabs became less risk averse on average and their behaviour became more predictable with increasing MP concentrations. Collectively, our findings indicate that MP pollution might increase susceptibility to predation in hermit crabs.

Animals utilize an incredible array of traits for offence and defence during conflict. These traits range from exaggerated morphological structures such as the antlers of stags and the horns of beetles, to an arsenal of noxious chemicals emitted, secreted, and injected. However, the breadth of these traits appears to be underappreciated in our current thinking about aggression in animals. Use of the term "weapon" in the current literature is largely restricted to studies of conspicuous morphological structures used by males during contests over access to females, and as a result, our understanding of other types of weapons is limited. In this article, I explore the diversity of traits utilized by animals to manipulate and control the behavior of other individuals in a number of agonistic contexts, with the aim to encourage a reappraisal of the way in which behavioral and evolutionary biologists view animal weapons. I discuss the advantages of including this broader range of traits in studies of animal weaponry and explore the unifying features that distinguish animal weapons from other traits.

Sexual conflict results in a diversity of sex-specific adaptations, including chemical additions to ejaculates. Male decorated crickets (Gryllodes sigillatus) produce a gelatinous nuptial gift (the spermatophylax) that varies in size and free amino acid composition, which influences a female's willingness to fully consume this gift. Complete consumption of this gift maximizes sperm transfer through increased retention of the sperm-containing ampulla, but hinders post-copulatory mate choice. Here, we examine the effects of protein (P) and carbohydrate (C) intake on the weight and amino acid composition of the spermatophylax that describes its gustatory appeal to the female, as well as the ability of this gift to regulate sexual conflict via ampulla attachment time. Nutrient intake had similar effects on the expression of these traits with each maximized at a high intake of nutrients with a P : C ratio of 1 : 1.3. Under dietary choice, males actively regulated their nutrient intake but this regulation did not coincide with the peak of the nutritional landscape for any trait. Our results therefore demonstrate that a balanced intake of nutrients is central to regulating sexual conflict in G. sigillatus, but males are constrained from reaching the optima needed to bias the outcome of this conflict in their favour.

Summary Condition is defined as the pool of resources available to an individual that can be allocated to fitness-enhancing traits. Consequently, condition could influence developmental trade-offs if any occur. Although many studies have manipulated diet to demonstrate condition-dependent trait expression, few studies have determined the contribution of specific nutrients to condition or trade-offs. We used nutritional geometry to quantify the effects of dietary protein and carbohydrate content on larval performance and the development of adult morphology including body size as well as a primary and secondary sexually selected trait in male broad-horned beetles, Gnatocerus cornutus. We found that offspring survival, development rate and morphological traits were highly affected by dietary carbohydrate content and to a lesser extent by protein content and that all traits were maximized at a protein-to-carbohydrate ratio around 1:2. The absolute size of a secondary sexual character, the mandibles, had a heightened response to the increased availability and ratio of both macronutrients. Male genitalia, in contrast, were relatively insensitive to the increased availability of macronutrients. Overall, while nutrition influenced trait expression, the nutritional requirements of development rate and morphological traits were largely the same and resource acquisition seems to implement only weak trade-offs in this species. This finding contrasts with some resource constraint predictions, as beetles seem able to simultaneously meet the nutritional requirements of most traits.

Lay Summary Males adjust both courtship effort and ejaculate expenditure when mating with females that are coated in the chemical cues of other males. Using a manipulative approach, we show that male flour beetles use the chemical cues of rival males left behind on virgin female cuticles to assess sperm competition risk. These cues do not make virgin females more chemically similar to mated females but appear to allow males to indirectly assess competition within the population., Males can gather information on the risk and intensity of sperm competition from their social environment. Recent studies have implicated chemosensory cues, for instance cuticular hydrocarbons (CHCs) in insects, as a key source of this information. Here, using the broad-horned flour beetle (Gnatocerus cornutus), we investigated the importance of contact-derived rival male CHCs in informing male perception of sperm competition risk and intensity. We experimentally perfumed virgin females with male CHCs via direct intersexual contact and measured male pre- and post-copulatory investment in response to this manipulation. Using chemical analysis, we verified that this treatment engendered changes to perfumed female CHC profiles, but did not make perfumed females “smell” mated. Despite this, males responded to these chemical changes. Males increased courtship effort under low levels of perceived competition (from 1–3 rivals), but significantly decreased courtship effort as perceived competition rose (from 3–5 rivals). Furthermore, our measurement of ejaculate investment showed that males allocated significantly more sperm to perfumed females than to control females. Together, these results suggest that changes in female chemical profile elicited by contact with rival males do not provide males with information on female mating status, but rather inform males of the presence of rivals within the population and thus provide a means for males to indirectly assess the risk of sperm competition.

An individual's performance during a fight is influenced by a combination of their capacity and willingness to compete. While willingness to fight is known to be determined by both intrinsic and extrinsic drivers, an individual's capacity to fight is generally thought of as solely intrinsic, being driven by a host of physiological factors. However, evidence indicates that variation in fighting ability can also be generated through exposure to different environmental conditions. Environmental contributions to fighting ability may be particularly important for animals living in spatially and temporally heterogeneous habitats, in which fights can occur between rivals recently exposed to different environmental conditions. The rapidly changing environment experienced within intertidal zones, for example, means that seawater parameters, including dissolved oxygen content and temperature, can vary across small spatial and temporal scales. Here we investigate the relative importance of these extrinsic contributions to fighting ability and resource value on contest dynamics in the beadlet sea anemone Actinia equina. We manipulate the extrinsic fighting ability of both opponents (through dissolved oxygen concentration prior to fights) and resource value (through seawater flow rate during the fight). Our results indicate that the extrinsic fighting ability of both opponents can interact with resource value to drive escalation patterns and that extrinsic drivers can be more important in determining contest dynamics than the intrinsic traits commonly studied. Our study highlights the need to combine data on intrinsic state and extrinsic conditions in order to gain a more holistic view of the factors driving contest behaviour.

The ability to mitigate the costs of engaging in a fight will depend on an individual's physiological state. However, the experience of fighting itself may, in turn, affect an individual's state, especially if the fight results in injury. Previous studies have found a correlation between immune state and fighting success, but the causal direction of this relationship remains unclear. Does immune state determine fighting success? Or does fighting itself influence subsequent immune state? Using the beadlet anemone

The ability to mitigate the costs of engaging in a fight will depend on an individual9s physiological state. However, the experience of fighting itself may, in turn, affect an individual9s state, especially if the fight results in injury. Previous studies have found a correlation between immune state and fighting success, but the causal direction of this relationship remains unclear. Does immune state determine fighting success? Or does fighting itself influence subsequent immune state? Using the beadlet anemone, Actinia equina , we disentangled the cause and effect of this relationship, measuring immune response once pre-fight and twice post-fight. Contrary to previous findings, pre-fight immune response did not predict fighting success, but rather predicted whether an individual used its weapons during the fight. Furthermore, weapon use and contest outcome significantly affected post-fight immune response. Individuals that used their weapons maintained a stable immune response following the fight, whereas those that fought non-injuriously did not. Furthermore, although winners suffered a reduction in immune response similar to that of losers immediately post-fight, winners began to recover pre-fight levels within 24 h. Our findings indicate that immune state can influence strategic fighting decisions and, moreover, that fight outcome and the agonistic behaviours expressed can significantly affect subsequent immunity.

Genotype-by-environment interactions (G × Es) describe genetic variation for phenotypic plasticity. Recent interest in the role of these interactions in sexual selection has identified G × Es across a diverse range of species and sexual traits. Additionally, theoretical work predicts that G × Es in sexual traits could help to maintain genetic variation, but could also disrupt the reliability of these traits as signals of mate quality. However, empirical tests of these theoretical predictions are scarce. We reared iso-female lines of Drosophila simulans across two axes of environmental variation (diet and temperature) in a fully factorial design and tested for G × Es in the expression of cuticular hydrocarbons (CHCs), a multivariate sexual trait in this species. We find sex-specific environmental, genetic and G × E effects on CHC expression, with G × Es for diet in both male and female CHC profile and a G × E for temperature in females. We also find some evidence for ecological crossover in these G × Es, and by quantifying variance components, genetic correlations and heritabilities, we show the potential for these G × Es to help maintain genetic variation and cause sexual signal unreliability in D. simulans CHC profiles.

Sexual selection is responsible for the evolution of many elaborate traits, but sexual trait evolution could be influenced by opposing natural selection as well as genetic constraints. As such, the evolution of sexual traits could depend heavily on the environment if trait expression and attractiveness vary between environments. Here, male Drosophila simulans were reared across a range of diets and temperatures, and we examined differences between these environments in terms of (i) the expression of male cuticular hydrocarbons (CHCs) and (ii) which male CHC profiles were most attractive to females. Temperature had a strong effect on male CHC expression, whereas the effect of diet was weaker. Male CHCs were subject to complex patterns of directional, quadratic and correlational sexual selection, and we found differences between environments in the combination of male CHCs that were most attractive to females, with clearer differences between diets than between temperatures. We also show that genetic covariance between environments is likely to cause a constraint on independent CHC evolution between environments. Our results demonstrate that even across the narrow range of environmental variation studied here, predicting the outcome of sexual selection can be extremely complicated, suggesting that studies ignoring multiple traits or environments may provide an over-simplified view of the evolution of sexual traits.

A magneto-optically active thin film of Rb$_{j}$Co$_{k}$[Fe(CN)$_{6}$]$_{l}$ $\cdot$$n$H$_{2}$O has been prepared using a sequential assembly method. Upon irradiation with light and at 5 K, the net magnetization of the film increased when the surface of the film was oriented parallel to the external magnetic field of 0.1 T. However, when the surface of the film was perpendicular to the field, the net magnetization \emph{decreased} upon irradiation. The presence of dipolar fields and the low-dimensional nature of the system are used to describe the orientation dependence of the photo-induced magnetization. The ability to increase or decrease the photo-induced magnetization by changing the orientation of the system with respect to the field is a new phenomenon that may be useful in future device applications.

The surface coverage of phosphorylated oligonucleotides immobilized on a zirconium-phosphonate surface was analyzed using X-ray photoelectron spectroscopy (XPS). By quantifying the intensity of the N 1s signal originating from the oligonucleotide and the Zr 3d peak from the metal-phosphonate surface, the surface coverage of the oligonucleotide could be calculated with a modified substrate-overlayer model. We found relatively low surface coverages indicating that once covalently bound via the terminal phosphate the polymer chain further physisorbs to the surface limiting the adsorption of additional molecules.

International audience; A new process for preparing oligonucleotide arrays is described that uses surface grafting chemistry which is fundamentally different from the electrostatic adsorption and organic covalent binding methods normally employed. Solid supports are modified with a mixed organic/inorganic zirconium phosphonate monolayer film providing a stable, well-defined interface. Oligonucleotide probes terminated with phosphate are spotted directly to the zirconated surface forming a covalent linkage. Specific binding of terminal phosphate groups with minimal binding of the internal phosphate diesters has been demonstrated. On the other hand, the reaction of a bisphosphonate bone resorption inhibitor (Zoledronate) with calcium deficient apatites (CDAs) was studied as a potential route to local drug delivery systems active against bone resorption disorders. A simple mathematical model of the Zoledronate/CDA interaction was designed that correctly described the adsorption of Zoledronate onto CDAs. The resulting Zoledronate-loaded materials were found to release the drug in different phosphate-containing media, with a satisfactory agreement between experimental data and the values predicted from the model.