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The article discusses the research challenge of the biological impacts of artificial light at night. Daily, lunar and seasonal cycles of natural light have been major types of environmental difference the Earth's surface since the first coming into being of life. They have propelled the development of biological reality from the molecule to the ecosystem.

Within-individual variation in virtually every conceivable morphological and functional feature of reiterated structures is a pervasive feature of plant phenotypes. In particular, architectural effects, regular, repeatable patterns of intra-individual variation in form and function that are associated with position are nearly ubiquitous. Yet, flowers also are predicted to be highly integrated. For animal-pollinated plants, the coordination of multiple organs within each flower is required to achieve the complex functions of pollinator attraction and orientation, pollen donation and pollen receipt. To the extent that pollinators may select for multiple independent functions, phenotypic integration within flowers may also be modular. That is, subsets of floral structures may be integrated but vary independently of other subsets of structures that are themselves integrated. How can phenotypic integration and modularity be understood within the context of architectural effects? This essay reviews recent research on patterns of floral integration and modularity and explores the potential for spatial and temporal changes in the selective environment of individual flowers to result in positional variation in patterns of morphological integration. [ABSTRACT FROM AUTHOR]

How will people respond to the discovery of extra-terrestrial life? Potentially useful resources for addressing this question include historical prototypes, disaster studies and survey research. Reactions will depend on the interplay of the characteristics of the newly found life, the unfolding of the discovery, the context and content of the message and human information processing as shaped by biology, culture and psychology. Pre-existing images of extra-terrestrials as god-like, demonic, or artificial will influence first impressions that may prove highly resistant to change. Most probably people will develop comprehensive images based on minimal information and assess extra-terrestrials in the same ways that they assess one another. Although it is easy to develop frightening scenarios, finding microbial life in our Solar System or intercepting a microwave transmission from many light years away are less likely to be met with adverse reactions such as fear and pandemonium than with positive reactions such as equanimity and delight. [ABSTRACT FROM AUTHOR]

The search for another type of life in the Solar System addresses the fundamental question of life in the Universe. To determine if life forms we discover represent a second genesis, we must find biological material that would allow us to compare that life to the Earth’s phylogenetic tree of life. An organism would be alien if, and only if, it did not link to our tree of life. In our Solar System, the worlds of interest for a search for life are Mars, Europa, Enceladus and, for biochemistry based on a liquid other than water, Titan. If we find evidence for a second genesis of life, we will certainly learn from the comparative study of the biochemistry, organismal biology and ecology of the alien life. The discovery of alien life, if alive or revivable, will pose fundamentally new questions in environmental ethics. We should plan our exploration strategy such that we conduct biologically reversible exploration. In the long term we would do well, ethically and scientifically, to strive to support any alien life discovered as part of an overall commitment to enhancing the richness and diversity of life in the Universe. [ABSTRACT FROM AUTHOR]

This paper describes the chemical concepts used for the purpose of detecting life in extra-terrestrial situations. These methods, developed initially within the oil industry, have been used to determine when life began on Earth and for investigating the Moon and Mars via space missions. In the case of Mars, the Viking missions led to the realization that we had meteorites from Mars on Earth. The study of Martian meteorites in the laboratory provides tantalizing clues for life on Mars in both the ancient and recent past. Meteorite analyses led to the launch of the Beagle 2 spacecraft, which was designed to prove that life-detection results obtained on Earth were authentic and not confused by terrestrial contamination. Some suggestions are made for future work. [ABSTRACT FROM AUTHOR]

The global contiguity of life on the Earth today is a result of the high flux of carbon and oxygen from oxygenic photosynthesis over the planetary surface and its use in aerobic respiration. Life’s ability to directly use redox couples from components of the planetary lithosphere in a pre-oxygenic photosynthetic world can be investigated by studying the distribution of organisms that use energy sources normally bound within rocks, such as iron. Microbiological data from Iceland and the deep oceans show the kinetic limitations of living directly off igneous rocks in the lithosphere. Using energy directly extracted from rocks the lithosphere will support about six orders of magnitude less productivity than the present-day Earth, and it would be highly localized. Paradoxically, the biologically extreme conditions of the interior of a planet and the inimical conditions of outer space, between which life is trapped, are the locations from which volcanism and impact events, respectively, originate. These processes facilitate the release of redox couples from the planetary lithosphere and might enable it to achieve planetary-scale productivity approximately one to two orders of magnitude lower than that produced by oxygenic photosynthesis. The significance of the detection of extra-terrestrial life is that it will allow us to test these observations elsewhere and establish an understanding of universal relationships between lithospheres and life. These data also show that the search for extra-terrestrial life must be accomplished by ‘following the kinetics’, which is different from following the water or energy. [ABSTRACT FROM AUTHOR]

Astrobiology is the study of the origins, evolution, distribution and future of life in the Universe, and specifically seeks to understand the origin of life and to test the hypothesis that life exists elsewhere than on Earth. There is a general mathematics, physics and chemistry; that is, scientific laws that obtain on Earth also do so elsewhere. Is there a general biology? Is the Universe life-rich or is Earth an isolated island of biology? Exploration in the Age of Enlightenment required the collection of data in unexplored regions and the use of induction and empiricism to derive models and natural laws. The current search for extra-terrestrial life has a similar goal, but with a much greater amount of data and with computers to help with management, correlations, pattern recognition and analysis. There are 60 active space missions, many of them aiding in the search for life. There is not a universally accepted definition of life, but there are a series of characteristics that can aid in the identification of life elsewhere. The study of locations on Earth with similarities to early Mars and other space objects could provide a model that can be used in the search for extra-terrestrial life. [ABSTRACT FROM AUTHOR]

Life-history theory predicts that traits involved in maturity, reproduction and survival correlate along a fast-slow continuum of life histories. Evolutionary theories and empirical results indicate that senescence- related traits vary along this continuum, with slow species senescing later and at a slower pace than fast species. Because senescence patterns are typically difficult to estimate from studies in the wild, here we propose to predict the associated trait values in the frame of life-history theory. From a comparative analysis based on 81 free-ranging populations of 72 species of birds and mammals, we find that a nonlinear combination of fecundity, age at first reproduction and survival over the immature stage can account for ca two-thirds of the variance in the age at the onset of actuarial senescence. Our life-history model performs better than a model predicting the onset based on generation time, and it only includes life-history traits during early life as explanatory variables, i.e. parameters that are both theoretically expected to shape senescence and are measurable within relatively short studies. We discuss the goodfit of our life-history model to the available data in the light of current evolutionary theories of senescence. We further use it to evaluate whether studies that provided no evidence for senescence lasted long enough to include the onset of senescence. [ABSTRACT FROM AUTHOR]

Considerable research has focused on understanding variation in reproductive skew in cooperative animal societies, but the pace of theoretical development has far outstripped empirical testing of the models. One major class of model suggests that dominant individuals can use the threat of eviction to deter subordinate reproduction (the ‘restraint’ model), but this idea remains untested. Here, we use long-term behavioural and genetic data to test the assumptions of the restraint model in banded mongooses (Mungos mungo), a species in which subordinates breed regularly and evictions are common. We found that dominant females suffer reproductive costs when subordinates breed, and respond to these costs by evicting breeding subordinates from the group en masse, in agreement with the assumptions of the model. We found no evidence, however, that subordinate females exercise reproductive restraint to avoid being evicted in the first place. This means that the pattern of reproduction is not the result of a reproductive ‘transaction’ to avert the threat of eviction. We present a simple game theoretical analysis that suggests that eviction threats may often be ineffective to induce pre-emptive restraint among multiple subordinates and predicts that threats of eviction (or departure) will be much more effective in dyadic relationships and linear hierarchies. Transactional models may be more applicable to these systems. Greater focus on testing the assumptions rather than predictions of skew models can lead to a better understanding of how animals control each other's reproduction, and the extent to which behaviour is shaped by overt acts versus hidden threats. [ABSTRACT FROM AUTHOR]

Explaining why organisms schedule reproduction over their lifetimes in the various ways that they do is an enduring challenge in biology. An influential theoretical prediction states that organisms should increasingly invest in reproduction as they approach the end of their life. An apparent mismatch of empirical data with this prediction has been attributed to age-related constraints on the ability to reproduce. Here we present a general framework for the evolution of age-related reproductive trajectories. Instead of characterizing an organism by its age, we characterize it by its physiological condition. We develop a common currency that if maximized at each time guarantees the whole life history is optimal. This currency integrates reproduction, mortality and changes in condition. We predict that under broad conditions it will be optimal for organisms to invest less in reproduction as they age, thus challenging traditional interpretations of age-related traits and renewing debate about the extent to which observed life histories are shaped by constraint versus adaptation. Our analysis gives a striking illustration of the differences between an age-based and a condition-based approach to life-history theory. It also provides a unified account of not only standard life-history models but of related models involving the allocation of limited resources. [ABSTRACT FROM AUTHOR]

The article provides information on a study that investigated female life-history trade-offs in a population of rhesus macaques (Macaca mulatta) by using quantitative genetic techniques. It discusses the material and methods used in the study. It examines the phenotypic correlations between age of first reproduction (AFR) and survival rate. An important genetically mediated constraint on the reproductive decision making of female primates have been identified by the strong positive genetic correlation between female AFR and adult survival.

This paper addresses the question of environmental change in Amazônia, by looking at the experiences of the large-scale biosphere–atmosphere (LBA) experiment in the Amazon, and three other enterprises—the extractive reserves, the Pilot Programme to Conserve the Brazilian Rain Forest (PPG7) and ecological-economic zoning—that address questions of sustainable development in the region. The LBA experience shows how the integration with the social sciences can be critical for science to explore its own outcomes for society, while the other programmes expose environmental change as a problem with too many intersections within society, so the outcomes of any initiative depends on placing it before a complex, tense and wide arena. [ABSTRACT FROM AUTHOR]

Hormonal control systems are complex in design and well integrated. Concern has been raised that these systems might act as evolutionary constraints when animals are subject to anthropogenic environmental change. Three systems are examined in vertebrates, especially birds, that are important for assessing this possibility: (i) the hypothalamic–pituitary–gonadal (HPG) axis, (ii) the activational effects of sex steroids on mating effort behaviour, and (iii) sexual differentiation. Consideration of how these systems actually work that takes adequate account of the brain's role and mechanisms suggests that the first two are unlikely to be impediments to evolution. The neural and molecular networks that regulate the HPG provide both phenotypic and evolutionary flexibility, and rapid evolutionary responses to selection have been documented in several species. The neuroendocrine and molecular cascades for behaviour provide many avenues for evolutionary change without requiring a change in peripheral hormone levels. Sexual differentiation has some potential to be a source of evolutionary inertia in birds and could contribute to the lack of diversity in certain reproductive (including life history) traits. It is unclear, however, whether that lack of diversity would impede adaptation to rapid environmental change given the role of behavioural flexibility in avian reproduction. [ABSTRACT FROM AUTHOR]

In highly social species, dominant individuals often monopolize reproduction, resulting in reproductive investment that is status dependent. Yet, for subordinates, who typically invest less in reproduction, social status can change and opportunities to ascend to dominant social positions are presented suddenly, requiring abrupt changes in behaviour and physiology. In this study, we examined male reproductive anatomy, physiology and behaviour following experimental manipulations of social status in the cooperatively breeding cichlid fish, Neolamprologus pulcher. This unusual fish species lives in permanent social groups composed of a dominant breeding pair and 1–20 subordinates that form a linear social dominance hierarchy. By removing male breeders, we created 18 breeding vacancies and thus provided an opportunity for subordinate males to ascend in status. Dominant females play an important role in regulating status change, as males successfully ascended to breeder status only when they were slightly larger than the female breeder in their social group. Ascending males rapidly assumed behavioural dominance, demonstrated elevated gonadal investment and androgen concentrations compared with males remaining socially subordinate. Interestingly, to increase gonadal investment ascending males appeared to temporarily restrain somatic growth. These results highlight the complex interactions between social status, reproductive physiology and group dynamics, and underscore a convergent pattern of reproductive investment among highly social, cooperative species. [ABSTRACT FROM AUTHOR]

Reproduction is thought to entail costs, but assessing survival costs associated with maturation as organisms express reproductive genes for the first time is problematic because many will die prior to expressing a phenotype. We quantified selection acting on this invisible fraction by measuring selection on predicted breeding values for clutch size estimated from a multigenerational pedigree of side-blotched lizards in which clutch size was heritable (h2=0.25±0.04). The survival effects of predicted breeding values for clutch size during maturation, however, differed between males and females indicating ontogenetic conflict. Increased mortality during maturation was associated with lower predicted breeding values for clutch size for females, but higher predicted breeding values for males who do not produce a clutch. Genetic correlations between clutch size and male and female survival were consistent with calculated selection differentials. Experimental yolk removal did not affect progeny survival during maturation, indicating that selection on maturing progeny was not due to confounding yolk-volume maternal effects, and hormone manipulations confirmed clutch size as the target of viability selection during maturation. Such episodes of selection prior to phenotypic expression of the trait will have important consequences for the evolution of reproductive investment. [ABSTRACT FROM AUTHOR]

The antagonistic pleiotropy (AP) theory of ageing predicts genetically based trade-offs between investment in reproduction in early life and survival and performance in later life. Laboratory-based research has shown that such genetic trade-offs exist, but little is currently known about their prevalence in natural populations. We used random regression ‘animal model’ techniques to test the genetic basis of trade-offs between early-life fecundity (ELF) and maternal performance in late life in a wild population of red deer (Cervus elaphus) on the Isle of Rum, Scotland. Significant genetic variation for both ageing rates in a key maternal performance measure (offspring birth weight) and ELF was present in this population. We found some evidence for a negative genetic covariance between the rate of ageing in offspring birth weight and ELF, and also for a negative environmental covariance. Our results suggest rare support for the AP theory of ageing from a wild population. [ABSTRACT FROM AUTHOR]

Maternal fitness should be maximized by the optimal division of reproductive investment between offspring number and offspring quality. While evidence for this is abundant in many taxa, there have been fewer tests in mammals, and in particular, humans. We used a dataset of humans spanning three generations from pre-industrial Finland to test how increases in maternal fecundity affect offspring quality and maternal fitness in contrasting socio-economic conditions. For ‘resource-poor’ landless families, but not ‘resource-rich’ landowning families, maternal fitness returns diminished with increased maternal fecundity. This was because the average offspring contribution to maternal fitness declined with increased maternal fecundity for landless but not landowning families. This decline was due to reduced offspring recruitment with increased maternal fecundity. However, in landowning families, recruited offspring fecundity increased with increased maternal fecundity. This suggests that despite decreased offspring recruitment, maternal fitness is not reduced in favourable socio-economic conditions due to an increase in subsequent offspring fecundity. These results provide evidence consistent with an offspring quantity–quality trade-off in the lifetime reproduction of humans from poor socio-economic conditions. The results also highlight the importance of measuring offspring quality across their whole lifespan to estimate reliably the fitness consequences of increased maternal fecundity. [ABSTRACT FROM AUTHOR]

Pathogens do not normally drive their hosts to extinction; however, Batrachochytrium dendrobatidis, which causes amphibian chytridiomycosis, has been able to do so. Theory predicts that extinction can be caused by long-lived or saprobic free-living stages. The hypothesis that such a stage occurs in B. dendrobatidis is supported by the recent discovery of an apparently encysted form of the pathogen. To investigate the effect of a free-living stage of B. dendrobatidis on host population dynamics, a mathematical model was developed to describe the introduction of chytridiomycosis into a breeding population of Bufo bufo, parametrized from laboratory infection and transmission experiments. The model predicted that the longer that B. dendrobatidis was able to persist in water, either due to an increased zoospore lifespan or saprobic reproduction, the more likely it was that it could cause local B. bufo extinction (defined as decrease below a threshold level). Establishment of endemic B. dendrobatidis infection in B. bufo, with severe host population depression, was also possible, in agreement with field observations. Although this model is able to predict clear trends, more precise predictions will only be possible when the life history of B. dendrobatidis, including free-living stages of the life cycle, is better understood. [ABSTRACT FROM AUTHOR]

Appropriately timed integration of breeding into avian annual cycles is critical to both reproductive success and survival. The mechanisms by which birds regulate timing of breeding depend on environmental cue response systems that regulate both when birds do and do not breed. Despite there being multiple possible explanations for birds'' abilities to time breeding appropriately in different environments, and for the distribution of different cue response system characteristics among taxa, many studies infer that adaptive specialization of cue response systems has occurred without explicitly considering the alternatives. In this paper, we make explicit three hypotheses concerning the timing of reproduction and distribution of cue response characteristics among taxa: adaptive specialization; conditional plasticity; and phylogenetic history. We emphasize in particular that although conditional plasticity built into avian cue response systems (e.g. differing rates of gonadal development and differing latencies until onset of photorefractoriness) may lead to maladaptive annual cycles in some novel circumstances, this plasticity also can lead to what appear to be adaptively specialized cue response systems if not viewed in a comparative context. We use a comparative approach to account for the distribution of one important feature of avian reproductive cue response systems, photorefractoriness. Analysis of the distribution within songbirds of one criterion for absolute photorefractoriness, the spontaneous regression of the gonads without any decline in photoperiod, reveals that a failure to display this trait probably represents an adaptive specialization to facilitate a flexible reproductive schedule. More finely resolved analysis of both criteria for absolute photorefractoriness (the second being total lack of a reproductive response even to constant light after gonadal regression has occurred) within the cardueline finches not only provides further confirmation of this interpretation, but also indicates that these two criteria for photorefractoriness can be, and have been, uncoupled in some taxa. We suggest that careful comparative studies at different phylogenetic scales will be extremely valuable for distinguishing between adaptive specialization and non-adaptive explanations, such as phylogenetic history as explanations of cue response traits in particular taxa. We also suggest that particular focus on taxa in which individuals may breed on very different photoperiods (latitudes or times of year) in different years should be particularly valuable in identifying the range of environmental conditions across which conditionally plastic cue responses can be adaptive. [ABSTRACT FROM AUTHOR]

Life-history trade-offs between components of fitness arise because reproduction entails both gains and costs. Costs of reproduction can be divided into ecological and physiological costs. The latter have been rarely studied yet are probably a dominant component of the effect. A deeper understanding of life-history evolution will only come about once these physiological costs are better understood. Physiological costs may be direct or indirect. Direct costs include the energy and nutrient demands of the reproductive event, and the morphological changes that are necessary to facilitate achieving these demands. Indirect costs may be optional ‘compensatory costs’ whereby the animal chooses to reduce investment in some other aspect of its physiology to maximize the input of resource to reproduction. Such costs may be distinguished from consequential costs that are an inescapable consequence of the reproductive event. In small mammals, the direct costs of reproduction involve increased energy, protein and calcium demands during pregnancy, but most particularly during lactation. Organ remodelling is necessary to achieve the high demands of lactation and involves growth of the alimentary tract and associated organs such as the liver and pancreas. Compensatory indirect costs include reductions in thermogenesis, immune function and physical activity. Obligatory consequential costs include hyperthermia, bone loss, disruption of sleep patterns and oxidative stress. This is unlikely to be a complete list. Our knowledge of these physiological costs is currently at best described as rudimentary. For some, we do not even know whether they are compensatory or obligatory. For almost all of them, we have no idea of exact mechanisms or how these costs translate into fitness trade-offs. [ABSTRACT FROM AUTHOR]

The majority of vertebrates have a life span of greater than one year. Therefore individuals must be able to adapt to the annual cycle of changing conditions by adjusting morphology, physiology and behaviour. Phenotypic flexibility, in which an individual switches from one life history stage to another, is one way to maximize fitness in a changing environment. When environmental variation is low, few life history stages are needed. If environmental variation is large, there are more life history stages. Each life history stage has a characteristic set of sub-stages that can be expressed in various combinations and patterns to determine state at any point in the life of the individual. Thus individuals have a finite number of states that can be expressed over the spectrum of environmental conditions in their life spans. Life history stages have three phases–development, mature capability (when characteristic sub-stages can be expressed) and termination. Expression of a stage is time dependent (probably a minimum of one month), and termination of one stage overlaps development of the next stage. It follows that the more life history stages an individual expresses, the less flexibility it will have in timing those stages. Having fewer life history stages increases flexibility in timing, but less tolerance of variation in environmental conditions. To varying degrees it is possible to overlap mature capability of some life history stages to effectively reduce ‘finite stage diversity’ and maximize flexibility in timing. Theoretical ways by which this can be done, and the implications for neuroendocrine and endocrine control mechanisms are discussed. Twelve testable hypotheses are posed that relate directly to control mechanisms. [ABSTRACT FROM AUTHOR]

Endogenous circannual clocks are found in many long-lived organisms, but are best studied in mammal and bird species. Circannual clocks are synchronized with the environment by changes in photoperiod, light intensity and possibly temperature and seasonal rainfall patterns. Annual timing mechanisms are presumed to have important ultimate functions in seasonally regulating reproduction, moult, hibernation, migration, body weight and fat deposition/stores. Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons (e.g. equatorial residents, migrants to equatorial/tropical latitudes) rely more on their endogenous clocks than birds living in environments that show a tight correlation between photoperiod and seasonal events. Such population-specific/interspecific variation in reliance on endogenous clocks may indicate that annual timing mechanisms are adaptive. However, despite the apparent adaptive importance of circannual clocks, (i) what specific adaptive value they have in the wild and (ii) how they function are still largely untested. Whereas circadian clocks are hypothesized to be generated by molecular feedback loops, it has been suggested that circannual clocks are either based upon (i) a de-multiplication (‘counting’) of circadian days, (ii) a sequence of interdependent physiological states, or (iii) one or more endogenous oscillators, similar to circadian rhythms. We tested the de-multiplication of days (i) versus endogenous regulation hypotheses (ii) and (iii) in captive male and female house sparrows (Passer domesticus). We assessed the period of reproductive (testicular and follicular) cycles in four groups of birds kept either under photoperiods of LD 12L:12D (period length: 24h), 13.5L:13.5D (27h), 10.5L:10.5D (23h) or 12D:8L:3D:1L (24-h skeleton photoperiod), respectively, for 15 months. Contrary to predictions from the de-multiplication hypothesis, individuals experiencing 27-h days did not differ (i.e. did not have longer) annual reproductive rhythms than individuals from the 21- or 24-h day groups. However, in line with predictions from endogenous regulation, birds in the skeleton group had significantly longer circannual period lengths than all other groups. Birds exposed to skeleton photoperiods experienced fewer light hours per year than all other groups (3285 versus 4380) and had a lower daily energy expenditure, as tested during one point of the annual cycle using respirometry. Although our results are tantalizing, they are still preliminary as birds were only studied over a period of 15 months. Nevertheless, the present data fail to support a ‘counting of circadian days’ and instead support hypotheses proposing whole-organism processes as the mechanistic basis for circannual rhythms. We propose a novel energy turnover hypothesis which predicts a dependence of the speed of the circannual clock on the overall energy expenditure of an organism. [ABSTRACT FROM AUTHOR]

Long-distance migration, and the study of the migrants who undertake these journeys, has fascinated generations of biologists. However, many aspects of the annual cycles of these migrants remain a mystery as do many of the driving forces behind the evolution and maintenance of the migrations themselves. In this article we discuss nutritional, energetic, temporal and disease-risk bottlenecks in the annual cycle of long-distance migrants, taking a sandpiper, the red knot Calidris canutus, as a focal species. Red knots have six recognized subspecies each with different migratory routes, well-known patterns of connectivity and contrasting annual cycles. The diversity of red knot annual cycles allows us to discuss the existence and the effects of bottlenecks in a comparative framework. We examine the evidence for bottlenecks focusing on the quality of breeding plumage and the timing of moult as indicators in the six subspecies. In terms of breeding plumage coloration, quality and timing of prealternate body moult (from non-breeding into breeding plumage), the longest migrating knot subspecies, Calidris canutus rogersi and Calidris canutus rufa, show the greatest impact of bottlenecking. The same is true in terms of prebasic body moult (from breeding into non-breeding plumage) which in case of both C. c. rogersi and C. c. rufa overlaps with southward migration and may even commence in the breeding grounds. To close our discussion of bottlenecks in long-distance migrants, we make predictions about how migrants might be impacted via physiological ‘trade-offs’ throughout the annual cycle, using investment in immune function as an example. We also predict how bottlenecks may affect the distribution of mortality throughout the annual cycle. We hope that this framework will be applicable to other species and types of migrants, thus expanding the comparative database for the future evaluation of seasonal selection pressures and the evolution of annual cycles in long-distance migrants. Furthermore, we hope that this synthesis of recent advancements in the knowledge of red knot annual cycles will prove useful in the ongoing attempts to model annual cycles in migratory birds. [ABSTRACT FROM AUTHOR]

Some organisms can manipulate the nervous systems of others or alter their physiology in order to obtain benefit. Ants are known to limit alate aphid dispersal by physically removing wings and also through chemical manipulation of the alate developmental pathway. This results in reduced dispersal and higher local densities of aphids, which benefit ants in terms of increased honeydew and prey availability. Here, we show that the walking movement of mutualistic apterous aphids is also reduced by ant semiochemicals. Aphids walk slower and their dispersal from an unsuitable patch is hampered by ants. If aphid walking dispersal has evolved as a means of natural enemy escape, then ant chemicals may act as a signal indicating protection; hence, reduced dispersal could be adaptive for aphids. If, however, dispersal is primarily a means to reduce competition or to maintain persistent metapopulations, then manipulation by ants could be detrimental. Such manipulation strategies, common in host–parasite and predator–prey interactions, may be more common in mutualism than expected. [ABSTRACT FROM AUTHOR]

Life-history theory states that reproductive events confer costs upon mothers. Many studies have shown that reproduction causes a decline in maternal condition, survival or success in subsequent reproductive events. However, little attention has been given to the prospect of reproductive costs being passed onto subsequent offspring, despite the fact that parental fitness is a function of the reproductive success of progeny. Here we use pedigree data from a pre-industrial human population to compare offspring life-history traits and lifetime reproductive success (LRS) according to the cost incurred by each individual's mother in the previous reproductive event. Because producing a son versus a daughter has been associated with greater maternal reproductive cost, we hypothesize that individuals born to mothers who previously produced sons will display compromised survival and/or LRS, when compared with those produced following daughters. Controlling for confounding factors such as socio-economic status and ecological conditions, we show that those offspring born after elder brothers have similar survival but lower LRS compared with those born after elder sisters. Our results demonstrate a maternal cost of reproduction manifested in reduced LRS of subsequent offspring. To our knowledge, this is the first time such a long-term intergenerational cost has been shown in a mammal species. [ABSTRACT FROM AUTHOR]

The reproduction of a living cell requires a repeatable set of chemical events to be properly coordinated. Such events define a replication cycle, coupling the growth and shape change of the cell membrane with internal metabolic reactions. Although the logic of such process is determined by potentially simple physico-chemical laws, modelling of a full, self-maintained cell cycle is not trivial. Here we present a novel approach to the problem that makes use of so-called symmetry breaking instabilities as the engine of cell growth and division. It is shown that the process occurs as a consequence of the breaking of spatial symmetry and provides a reliable mechanism of vesicle growth and reproduction. Our model opens the possibility of a synthetic protocell lacking information but displaying self-reproduction under a very simple set of chemical reactions. [ABSTRACT FROM AUTHOR]

Cells are the building blocks of biological complexity. They are complex systems sustained by the coordinated cooperative dynamics of several biochemical networks. Their replication, adaptation and computational features emerge as a consequence of appropriate molecular feedbacks that somehow define what life is. As the last decades have brought the transition from the description-driven biology to the synthesis-driven biology, one great challenge shared by both the fields of bioengineering and the origin of life is to find the appropriate conditions under which living cellular structures can effectively emerge and persist. Here, we review current knowledge (both theoretical and experimental) on possible scenarios of artificial cell design and their future challenges. [ABSTRACT FROM AUTHOR]

Endocrine-disrupting compounds (EDCs) have the capacity of altering the normal function of the endocrine system. EDCs have shown dramatic effects on the reproductive biology of aquatic wildlife and may affect human reproduction as well. Studies on EDCs in mammalian species have often investigated the effects of short-term, high doses on male and female reproductive physiology. However, it is difficult to predict from such studies the effects of EDC on populations that are exposed to very low doses throughout their life via contaminated food and water. We studied the effects of EDC on mammalian reproduction with an environmental-like protocol where the endpoint is the reproductive success of exposed pairs. We focused on a subclass of EDC, the xenoestrogens, which mimic the action of natural oestrogen hormones. Male and female rats were exposed to low doses of the pure oestrogen, ethynyloestradiol, during development, by oral administration to their mothers during pregnancy and lactation, and to them until puberty. We evaluated the effects of the exposure on development and reproductive physiology of individuals, and on fertility and fecundity of pairs in which both members had been exposed to the same treatment. We found that low doses caused major reproductive deficits in the experimental animals. Very low, environmentally relevant doses did not have evident effects on exposed animals; however, the fecundity of exposed pairs was substantially altered. Environmentally relevant doses of xenoestrogens which have no evident physiological effects can alter the reproductive success of exposed pairs in natural populations. [ABSTRACT FROM AUTHOR]

Male–male competition over territorial ownership suggests that winning is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over sunspot territories on the forest floor; winners gain sole residency of a sunspot, whereas losers patrol the forest in search of females. It is currently not known whether residents experience greater mating success than non-residents, or whether mating success is contingent on environmental conditions. Here we performed an experiment in which virgin females of P. aegeria were allowed to choose between a resident and a non-resident male in a large enclosure containing one territorial sunspot. Resident males achieved approximately twice as many matings as non-residents, primarily because matings were most often preceded by a female being discovered when flying through a sunspot. There was no evidence that territorial residents were more attractive per se, with females seen to reject them as often as non-residents. Furthermore, in the cases where females were discovered outside of the sunspot, they were just as likely to mate with non-residents as residents. We hypothesize that the proximate advantage of territory ownership is that light conditions in a large sunspot greatly increase the male's ability to detect and intercept passing receptive females. [ABSTRACT FROM AUTHOR]

The reason why some bird species live in family groups is an important question of evolutionary biology that remains unanswered. Families arise when young delay the onset of independent reproduction and remain with their parents beyond independence. Explanations for why individuals forgo independent reproduction have hitherto focused on dispersal constraints, such as the absence of high-quality breeding openings. However, while constraints successfully explain within-population dispersal decisions, they fail as an ultimate explanation for variation in family formation across species. Most family-living species are long-lived and recent life-history studies demonstrated that a delayed onset of reproduction can be adaptive in long-lived species. Hence, delayed dispersal and reproduction might be an adaptive life-history decision rather than ‘the best of a bad job’. Here, we attempt to provide a predictive framework for the evolution of families by integrating life-history theory into family formation theory. We suggest that longevity favours a delayed onset of reproduction and gives parents the opportunity of a prolonged investment in offspring, an option which is not available for short-lived species. Yet, parents should only prolong their investment in offspring if this increases offspring survival and outweighs the fitness cost that parents incur, which is only possible under ecological conditions, such as a predictable access to resources. We therefore propose that both life-history and ecological factors play a role in determining the evolution of family living across species, yet we suggest different mechanisms than those proposed by previous models. [ABSTRACT FROM AUTHOR]

The ubiquity of sexual reproduction despite its cost has lead to an extensive body of research on the evolution and maintenance of sexual reproduction. Previous work has suggested that sexual reproduction can substantially speed up the rate of adaptation in diploid populations, because sexual populations are able to produce the fittest homozygous genotype by segregation and mating of heterozygous individuals. In contrast, asexual populations must wait for two rare mutational events, one producing a heterozygous carrier and the second converting a heterozygous to a homozygous carrier, before a beneficial mutation can become fixed. By avoiding this additional waiting time, it was shown that the benefits of segregation could overcome a twofold cost of sex. This previous result ignores mitotic recombination (MR), however. Here, we show that MR significantly hastens the spread of beneficial mutations in asexual populations. Indeed, given empirical data on MR, we find that adaptation in asexual populations proceeds as fast as that in sexual populations, especially when beneficial alleles are partially recessive. We conclude that asexual populations can gain most of the benefit of segregation through MR while avoiding the costs associated with sexual reproduction. [ABSTRACT FROM AUTHOR]

Zyginidia pullula is a grass-dwelling leafhopper characterized by a bisexual reproduction mode. In this species, some females collected in Northern Italy, when mated with males, gave origin to an exclusively female brood. Here, we demonstrated that in these lineages an infection by a new strain of Wolbachia pipientis—designated as wZygpul—was detected by amplifying and sequencing the wsp and 16S rRNA genes. About half of the female progeny were characterized by intersexual phenotypes, i.e. showing upper pygofer appendages, a typical male secondary sexual feature. The karyological analysis proved that while phenotypically normal females had a female genotype, those with upper pygofer appendages had a male genotype and were thus feminized males.The complete removal of W. pipientis after tetracycline treatment of morphologically normal females, and the consequent re-appearance of males in the brood, permitted us to connect the feminizing effect with the presence of the bacterium. This is the first case of feminization by W. pipientis in an XX/X0 sex-determination system, and is the second case reported in insects. [ABSTRACT FROM AUTHOR]

In this paper we propose a novel form of social control of mate choice. Through mother guarding, offspring can help in protecting the paternity of their father by preventing their mother from engaging in extra-pair matings. We present a model that predicts the circumstances under which mothers should be selected to seek or avoid extra-pair matings, and existing offspring should be selected to prevent or promote such matings. In its simplest form, our model shows that offspring are selected to mother guard as long as the viability of extra-pair young is less than twice that of within-pair young; when the relative viability is greater, offspring are selected to promote extra-pair mating by their mother. If the existing offspring are not necessarily sired by their mother's social mate, then the potential for conflict is further reduced. We also consider whether offspring have an interest in the extra-pair reproduction of their fathers. We show that when the costs of the father's infidelity to the mother's brood are high, existing offspring are selected to prevent extra-pair mating by their father; when such costs are low, offspring are selected to promote extra-pair mating by their father. In principle, our model applies to all species where offspring show delayed dispersal and where breeding pairs raise multiple broods or litters. This situation exists in, but is not limited to, the majority of cooperatively breeding species. The significance of this model with regard to our current understanding of the evolution of extra-pair behaviour in such species is discussed. [ABSTRACT FROM AUTHOR]

In many taxa, reproductive performance increases throughout the lifespan and this may occur in part because older adults invest more in reproduction. The mechanisms that facilitate an increase in reproductive performance with age, however, are poorly understood. In response to stressors, vertebrates release glucocorticoids, which enhance survival but concurrently shift investment away from reproduction. Consequently, when the value of current reproduction is high relative to the value of future reproduction and survival, as it is in older adults, life history theory predicts that the stress response should be suppressed. In this study, we tested the hypothesis that older parents would respond less strongly to a stressor in a natural, breeding population of common terns (Sterna hirundo). Common terns are long-lived seabirds and reproductive performance is known to increase throughout the lifespan of this species. As predicted, the maximum level of glucocorticoids released in response to handling stress decreased significantly with age. We suggest that suppression of the stress response may be an important physiological mechanism that facilitates an increase in reproductive performance with age. [ABSTRACT FROM AUTHOR]

This study reports an experimental confirmation of the terminal investment hypothesis, a longstanding theoretical idea that animals should increase their reproductive effort as they age and their prospects for survival and reproduction decline. Previous correlational and experimental attempts to test this hypothesis have yielded contradictory results. In the blue-footed booby, Sula nebouxii, a long-lived bird, after initial increase, male reproductive success declines progressively with age. Before laying, males of two age classes were challenged with lipopolysaccharide to elicit an immune response, which induced symptoms of declining survival prospects. Reproductive success of immune-challenged mature males fell, while that of immune-challenged old males showed a 98% increase. These results demonstrate that senescent males with poor reproductive prospects increase their effort when those prospects are threatened, whereas younger males with good reproductive prospects do not. [ABSTRACT FROM AUTHOR]

Life-history theory has suggested that individual body size can strongly affect the allocation of resources to reproduction and away from other traits such as survival. In many insects, adults eclose with a proportion of their potential lifetime egg production that is already mature (the ovigeny index). We establish for the solitary parasitoid wasp Aphaereta genevensis that the ovigeny index decreases with adult body size, despite both initial egg load and potential lifetime fecundity increasing with body size. This outcome is predicted by adaptive models and is the first unequivocal intraspecific demonstration. Evidence suggests that a high ovigeny index carries a cost of reduced longevity in insects. Our results therefore contribute to the emerging evidence that small body size can favour a developmental shift in juveniles that favours early reproduction, but which has adverse late-life consequences. These findings are likely to have important implications for developmental biologists and population biologists. [ABSTRACT FROM AUTHOR]

There is increasing evidence that the environment experienced early in life can strongly influence adult life histories. It is largely unknown, however, how past and present conditions influence suites of life-history traits regarding major life-history trade-offs. Especially in animals with indeterminate growth, we may expect that environmental conditions of juveniles and adults independently or interactively influence the life-history trade-off between growth and reproduction after maturation. Juvenile growth conditions may initiate a feedback loop determining adult allocation patterns, triggered by size-dependent mortality risk. I tested this possibility in a long-term growth experiment with mouthbrooding cichlids. Females were raised either on a high-food or low-food diet. After maturation half of them were switched to the opposite treatment, while the other half remained unchanged. Adult growth was determined by current resource availability, but key reproductive traits like reproductive rate and offspring size were only influenced by juvenile growth conditions, irrespective of the ration received as adults. Moreover, the allocation of resources to growth versus reproduction and to offspring number versus size were shaped by juvenile rather than adult ecology. These results indicate that early individual history must be considered when analysing causes of life-history variation in natural populations. [ABSTRACT FROM AUTHOR]

We present a general analytical result for the probability that a newly introduced pathogen will evolve adaptations that allow it to maintain itself within any novel host population, as a function of disease life-history parameters. We demonstrate that this probability of ‘evolutionary emergence’ depends on two key properties of the disease life history: (i) the basic reproduction number and (ii) the expected duration of an infection. These parameters encapsulate all of the relevant information and can be combined in a very simple expression, with estimates for the rates of adaptive mutation, to predict the probability of emergence for any novel pathogen. In general, diseases that initially have a large reproductive number and/or that cause relatively long infections are the most prone to evolutionary adaptation. [ABSTRACT FROM AUTHOR]

Many cultural attributes such as adornment, language slang, mannerisms and rituals are thought to have little or no influence on individual survival and reproduction, functioning rather as markers of cultural identity that promote group cohesion. Here, I show that if cultural markers are under weak selection and subject to loss or substitution, then the breakdown of cultural cohesiveness may proceed without stabilizing reactions until many or most of a culture's identifiers are forever lost. This may culminate in a 'cultural meltdown', whereby the culture is caught in a vortex of ever-decreasing membership and insufficient selection against the accumulation of unfamiliar markers. In progressively altering the topology of communication from diffusion to broadcasting, globalization may be both accelerating the erosion of cultural identities and amplifying dominance behaviours above their normal adaptive levels. [ABSTRACT FROM AUTHOR]

In most organisms, transitions between different life-history stages occur later and at smaller sizes as growth conditions deteriorate. Day and Rowe recently proposed that this pattern could be explained by the existence of developmental thresholds (minimum sizes or levels of condition below which transitions are unable to proceed). The developmental-threshold model predicts that the reaction norm of age and size at maturity will rotate in an anticlockwise manner from positive to a shallow negative slope if: (i) initial body size or condition is reduced; and/or (ii) some individuals encounter poor growth conditions at increasingly early developmental stages. We tested these predictions by rearing replicated populations of soil mites Sancassania berlesei (Michael) under different growth conditions. High-food environments produced a vertical relationship between age and size at maturity. The slope became increasingly shallow as food was reduced. By contrast, high food in the maternal environment reduced the slope of the reaction norm of age and size at maturity, whereas low food increased it. Overall, the reaction norm of age and size at maturity in S. berlesei was significantly nonlinear and differed for males and females. We describe how growth conditions, mother's environment and sex determine age and size at maturity in S. berlesei. [ABSTRACT FROM AUTHOR]

A widely held ecological tenet is that, at the local scale, populations of K-selected species (i.e. low fecundity, long lifespan and large body size) will be less variable than populations of r-selected species (i.e. high fecundity, short lifespan and small body size). We examined the relationship between long-term population trends and life-history attributes for 185 bird species in the Czech Republic and found that, at regional spatial scales and over moderate temporal scales (100-120 years), K-selected bird species were more likely to show both large increases and decreases in population size than r-selected species. We conclude that life-history attributes commonly associated with variable populations at the local scale, confer stability at the regional scale. [ABSTRACT FROM AUTHOR]

Oxalis pes-caprae, a native of South Africa is a very successful, globally widely distributed, aggressive colonizer weed. It spreads vegetatively (through bulbils and underground shoots) in most of its colonized areas. In Israel, it is characterized by the total lack of seed set. Using 121 amplified fragment length polymorphism (AFLP) putative loci we have analysed the genetic structure of five representative populations in Israel. Despite the complete lack of sexual reproduction and the total dependency on vegetative dispersal, populations were found to be genetically variable. Surprisingly, considerable genetic diversity was found within and between all of the populations tested. We speculate that this diversity could be the result of an accumulation of mutations or genome rearrangement. [ABSTRACT FROM AUTHOR]

'Most habitable worlds in the cosmos will have no remotely detectable signs of life' is proposed as a biological hypothesis to be tested in the study of exoplanets. Habitable planets could be discovered elsewhere in the Universe, yet there are many hypothetical scenarios whereby the search for life on them could yield negative results. Scenarios for habitable worlds with no remotely detectable signatures of life include: planets that are habitable, but have no biosphere (Uninhabited Habitable Worlds); planets with life, but lacking any detectable surface signatures of that life (laboratory examples are provided); and planets with life, where the concentrations of atmospheric gases produced or removed by biota are impossible to disentangle from abiotic processes because of the lack of detailed knowledge of planetary conditions (the 'problem of exoplanet thermodynamic uncertainty'). A rejection of the hypothesis would require that the origin of life usually occurs on habitable planets, that spectrally detectable pigments and/or metabolisms that produce unequivocal biosignature gases (e.g. oxygenic photosynthesis) usually evolve and that the organisms that harbour them usually achieve a sufficient biomass to produce biosignatures detectable to alien astronomers. [ABSTRACT FROM AUTHOR]