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The role of female choice in sexual selection is well established, including the recognition that females choose their mates based on multiple cues. These cues may include intrinsic aspects of a male's phenotype as well as aspects of the environment associated with the male. The role of the spatial location of a potential mate has been well studied in territorial vertebrates. However, despite their role as laboratory models for studies of sexual selection, the potential for insects to choose their mates on the basis of location has scarcely been studied. We studied a natural population of individually tagged crickets (Gryllus campestris) in a meadow in Northern Spain. Adults typically move between burrows every few days, allowing us to examine how pairing success of males can be predicted by the burrow they occupy, independent of their own characteristics. We observed the entirety of ten independent breeding seasons to provide replication and to determine whether the relative importance of these factors is stable across years. We find that both male ID and the ID his burrow affect the likelihood that he is paired with a female, but the burrow has a consistently greater influence. Furthermore, the two factors interact: the relative attractiveness of an individual male depends on which burrow he occupies. Our finding demonstrates a close interaction between naturally and sexually selected traits. It also demonstrates that mate choice studies may benefit from considering not only obvious secondary sexual traits, but also more cryptic traits such as microhabitat choice. We show that female insects choosing to cohabit with a male place more importance on where he lives than on who he is, but the combination of the two is more important still. We know that female birds often choose a male based on the quality of his territory; our 10 years of observing crickets moving around a Spanish meadow to share burrows with members of the opposite sex, reveals insects can do the same.

Understanding how species can thrive in a range of environments is a central challenge for evolutionary ecology. There is strong evidence for local adaptation along large-scale ecological clines in insects. However, potential adaptation among neighbouring populations differing in their environment has been studied much less. We used RAD sequencing to quantify genetic divergence and clustering of ten populations of the field cricket Gryllus campestris in the Cantabrian Mountains of northern Spain, and an outgroup on the inland plain. Our populations were chosen to represent replicate high and low altitude habitats. We identified genetic clusters that include both high and low altitude populations indicating that the two habitat types do not hold ancestrally distinct lineages. Using common-garden rearing experiments to remove environmental effects, we found evidence for differences between high and low altitude populations in physiological and life-history traits. As predicted by the local adaptation hypothesis, crickets with parents from cooler (high altitude) populations recovered from periods of extreme cooling more rapidly than those with parents from warmer (low altitude) populations. Growth rates also differed between offspring from high and low altitude populations. However, contrary to our prediction that crickets from high altitudes would grow faster, the most striking difference was that at high temperatures, growth was fastest in individuals from low altitudes. Our findings reveal that populations a few tens of kilometres apart have independently evolved adaptations to their environment. This suggests that local adaptation in a range of traits may be commonplace even in mobile invertebrates at scales of a small fraction of species' distributions.

Many organisms are capable of growing faster than they do. Restrained growth rate has functionally been explained by negative effects on lifespan of accelerated growth. However, the underlying mechanisms remain elusive. Telomere attrition has been proposed as a causal agent and has been studied in endothermic vertebrates. We established that telomeres exist as chromosomal-ends in a model insect, the field cricket, using terminal restriction fragment andBal 31methods. Telomeres comprised TTAGGn repeats of 38kb on average, more than four times longer than the telomeres of human infants.Bal 31assays confirmed that telomeric repeats were located at the chromosome-ends. We tested whether rapid growth is achieved at the expense of telomere length by comparing crickets reared at 23°C with their siblings reared at 28°C, which grew three times faster. Surprisingly, neither temperature treatment nor age affected average telomere length. Concomitantly, the broad sense heritability of telomere length was remarkably high at ~100%. Despite high heritability, the evolvability (a mean standardized measure of genetic variance) was low relative to that of body mass. We discuss the different interpretations of these scaling methods in the context of telomere evolution. It is clear that some important features of vertebrate telomere biology are evident in an insect species dating back to the Triassic, but also that there are some striking differences. The apparent lack of an effect of growth rate and the total number of cell divisions on telomere length is puzzling, suggesting that telomere length could be actively maintained during the growth phase. Whether such maintenance of telomere length is adaptive remains elusive and requires further study investigating the links with fitness in the wild.

The age of potential mates has been proposed to be an important target for mate choice by females. Alternative hypotheses predict preferences in either direction. Females might be expected to prefer older males because such males have demonstrated their capacity to survive. Alternatively, they might prefer younger males that have not accumulated deleterious mutations. Preferences in both directions have been observed in laboratory experiments, suggesting that this is an issue that needs to be understood within its ecological context. We measured individual behaviour and reproductive success in a natural population of the field cricket Gryllus campestris over 10 years. We found that in this annual insect, a male's age relative to his peers was poorly correlated with his life span. This suggests that there is limited potential for selection to favour female choice for older males because a strategy of choosing older males would not significantly increase a female's likelihood of mating with a long-lived male. Older males were more successful at pairing up with females at a burrow, but once paired they were less likely to mate with them. By genotyping the next generation of adults we confirmed that observations of both pairing up with a female and matings were associated with successful offspring production. However, there was no relationship between how old a male was at mating and how many adult offspring he had. This lack of evidence for any fitness benefits to females from mate choice in relation to male age was consistent with the observation that the age of males had opposite effects on their success in pairing up with females compared to their success in mating with them.

Male parents face a choice: should they invest more in caring for offspring or in attempting to mate with other females? The most profitable course depends on the intensity of competition for mates, which is likely to vary with the population sex ratio. However, the balance of pay‐offs may vary among individual males depending on their competitive prowess or attractiveness. We tested the prediction that sex ratio and size of the resource holding male provide cues regarding the level of mating competition prior to breeding and therefore influence the duration of a male's biparental caring in association with a female. Male burying beetles, Nicrophorus vespilloides were reared, post‐eclosion, in groups that differed in sex ratio. Experimental males were subsequently translocated to the wild, provided with a breeding resource (carcass) and filmed. We found no evidence that sex ratio cues prior to breeding affected future parental care behaviour but males that experienced male‐biased sex ratios took longer to attract wild mating partners. Smaller males attracted a higher proportion of females than did larger males, securing significantly more monogamous breeding associations as a result. Smaller males thus avoided competitive male–male encounters more often than larger males. This has potential benefits for their female partners who avoid both intrasexual competition and direct costs of higher mating frequency associated with competing males.

1. In burying beetles (Nicrophorinae), body size is known to provide both a fecundity advantage (in females) and successful resource defence (in males and females). Despite this, considerable variation in body sizes is observed in natural populations. 2. A possible explanation for the maintenance of this variation, even with intra- and inter-specific resource competition, is that individuals might assort according to body size on different-sized breeding resources. 3. We tested prediction that ‘bigger is always better’, in the wild and in the laboratory, by experimentally manipulating combinations of available breeding-resource size (mouse carcasses) and competitor's body size in Nicrophorus vespilloides (Herbst 1783). 4. In the field, large female beetles deserted small carcasses, without breeding, more often than they did larger carcasses, but small females used carcasses indiscriminately with respect to size. In the laboratory, large beetles reared larger broods (with more offspring) on larger carcasses than small beetles, but on small carcasses small beetles had a reproductive advantage over large ones. Offspring size covaried with carcass size independently of parental body size. 5. The present combined results suggest breeding resource value depends on an individual's body size, and variation in body size is environmentally induced: maintained by differences in available carcass sizes. This produces a mechanism by which individual specialisation leads to an increase in niche variation via body size in these beetles.

Summary Food availability can be unpredictable. When food becomes more abundant following a period of low food availability, developing larvae or juveniles often allocate resources preferentially towards increasing growth. This has important long-term effects on adult phenotypes and longevity. Despite the importance of strategic resource allocation during early development, few studies have examined how changes in resource availability during other windows of development affect reproductive strategies and fitness independent of growth. We manipulated food availability in a burying beetle, Nicrophorus vespilloides, during a subadult period of sexual maturation when individuals cannot increase structural size but are still undergoing reproductive maturation. In contrast to the trade-offs during larval or juvenile growth, beetles that experienced delayed feeding during reproductive maturation allocated resources preferentially towards maintaining both reproductive function and longevity. In both sexes, delayed feeding beetles were much less successful in competition for carcasses. However, delayed feeding males and females provided similar amounts of parental care and did not differ in reproductive success or longevity. These results indicate that the nutritional environment experienced during a key developmental window may be an important determinant of the expression of alternative reproductive strategies in adulthood, independent of body size.

Among-individual variation in behavioral plasticity—the modification of behavior in response to changes in environment experienced by individuals—is increasingly recognized as an important, but relatively poorly understood, feature of organisms that facilitates adaptation to environmental change. It is expected to evolve when there is rapidly fluctuating or directional environmental change during the lifetime of individuals. This is particularly likely to occur in the context of reproductive behaviors, when the outcomes of unpredictable social interactions with other individuals during mating and parental care determine how selection acts on males and females and mating systems evolve. To better understand patterns of mating and parental care and organismal adaptation to environmental change, we need to know why there is so much variation in behavioral plasticity between and within species. Here we address this question using burying beetles as a model. Burying beetles have unusually variable, facultatively expressed, modes of parental care and variation between the sexes and among individuals in the plasticity of reproductive behaviors. We present evidence to show that variation in male plasticity of mating behavior is a key driver of the evolution of patterns of parental care in Nicrophorus vespilloides burying beetles. More generally, we conclude that behavioral plasticity in burying beetles, and likely other taxa, has evolved as a consequence of a resource requirement bottle-neck (niche specialization) in combination with highly unpredictable availability of such suitable resources and the social unpredictability that arises as a result: constraint is the mother of plastic invention.

Male parents spend less time caring than females in many species with biparental care. The traditional explanation for this pattern is that males have lower confidence of parentage, so they desert earlier in favour of pursuing other mating opportunities. However, one recent alternative hypothesis is that prolonged male parental care might also evolve if staying to care actively improves paternity. If this is the case, an increase in reproductive competition should be associated with increased paternal care. To test this prediction, we manipulated the level of reproductive competition experienced by burying beetles, Nicrophorus vespilloides (Herbst, 1783). We found that caregiving males stayed for longer and mated more frequently with their partner when reproductive competition was greater. Reproductive productivity did not increase when males extended care. Our findings provide support for the increased paternity hypothesis. Extended duration of parental care may be a male tactic both protecting investment (in the current brood) and maximizing paternity (in subsequent brood(s) via female stored sperm) even if this fails to maximize current reproductive productivity and creates conflict of interest with their mate via costs associated with increased mating frequency.

Good early nutritional conditions may confer a lasting fitness advantage over individuals suffering poor early conditions (a ‘silver spoon’ effect). Alternatively, if early conditions predict the likely adult environment, adaptive plastic responses might maximize individual performance when developmental and adult conditions match (environmental-matching effect). Here, we test for silver spoon and environmental-matching effects by manipulating the early nutritional environment of Nicrophorus vespilloides burying beetles. We manipulated nutrition during two specific early developmental windows: the larval environment and the post-eclosion environment. We then tested contest success in relation to variation in adult social environmental quality experienced (defined according to whether contest opponents were smaller (good environment) or larger (poor environment) than the focal individual). Variation in the larval environment influenced adult body size but not contest success per se for a given adult social environment experienced (an ‘indirect’ silver spoon effect). Variation in post-eclosion environment affected contest success dependent on the quality of the adult environment experienced (a context-dependent ‘direct’ silver spoon effect). By contrast, there was no evidence for environmental-matching. The results demonstrate the importance of social environmental context in determining how variation in nutrition in early life affects success as an adult.