Sex‐specific telomere length and dynamics in relation to age and reproductive success in Cory’s shearwaters

Individuals in free‐living animal populations generally differ substantially in reproductive success, lifespan and other fitness‐related traits, but the molecular mechanisms underlying this variation are poorly understood. Telomere length and dynamics are candidate traits explaining this variation, as long telomeres predict a higher survival probability and telomere loss has been shown to reflect experienced “life stress.” However, telomere dynamics among very long‐lived species are unresolved. Additionally, it is generally not well understood how telomeres relate to reproductive success or sex. We measured telomere length and dynamics in erythrocytes to assess their relationship to age, sex and reproduction in Cory's shearwaters (Calonectris borealis), a long‐lived seabird, in the context of a long‐term study. Adult males had on average 231 bp longer telomeres than females, independent of age. In females, telomere length changed relatively little with age, whereas male telomere length declined significantly. Telomere shortening within males from one year to the next was three times higher than the interannual shortening rate based on cross‐sectional data of males. Past long‐term reproductive success was sex‐specifically reflected in age‐corrected telomere length: males with on average high fledgling production were characterized by shorter telomeres, whereas successful females had longer telomeres, and we discuss hypotheses that may explain this contrast. In conclusion, telomere length and dynamics in relation to age and reproduction are sex‐dependent in Cory's shearwaters and these findings contribute to our understanding of what characterises individual variation in fitness.     

Sex‐specific effects of protein and carbohydrate intake on reproduction but not lifespan in Drosophila melanogaster

Modest dietary restriction extends lifespan (LS) in a diverse range of taxa and typically has a larger effect in females than males. Traditionally, this has been attributed to a stronger trade‐off between LS and reproduction in females than in males that is mediated by the intake of calories. Recent studies, however, suggest that it is the intake of specific nutrients that extends LS and mediates this trade‐off. Here, we used the geometric framework (GF) to examine the sex‐specific effects of protein (P) and carbohydrate (C) intake on LS and reproduction in Drosophila melanogaster. We found that LS was maximized at a high intake of C and a low intake of P in both sexes, whereas nutrient intake had divergent effects on reproduction. Male offspring production rate and LS were maximized at the same intake of nutrients, whereas female egg production rate was maximized at a high intake of diets with a P:C ratio of 1:2. This resulted in larger differences in nutrient‐dependent optima for LS and reproduction in females than in males, as well as an optimal intake of nutrients for lifetime reproduction that differed between the sexes. Under dietary choice, the sexes followed similar feeding trajectories regulated around a P:C ratio of 1:4. Consequently, neither sex reached their nutritional optimum for lifetime reproduction, suggesting intralocus sexual conflict over nutrient optimization. Our study shows clear sex differences in the nutritional requirements of reproduction in D. melanogaster and joins the growing list of studies challenging the role of caloric restriction in extending LS.     

Genetic correlations and sex‐specific adaptation in changing environments

Females and males have conflicting evolutionary interests. Selection favors the evolution of different phenotypes within each sex, yet divergence between the sexes is constrained by the shared genetic basis of female and male traits. Current theory predicts that such “sexual antagonism” should be common: manifesting rapidly during the process of adaptation, and slow in its resolution. However, these predictions apply in temporally stable environments. Environmental change has been shown empirically to realign the direction of selection acting on shared traits and thereby alleviate signals of sexually antagonistic selection. Yet there remains no theory for how common sexual antagonism should be in changing environments. Here, we analyze models of sex‐specific evolutionary divergence under directional and cyclic environmental change, and consider the impact of genetic correlations on long‐run patterns of sex‐specific adaptation. We find that environmental change often aligns directional selection between the sexes, even when they have divergent phenotypic optima. Nevertheless, some forms of environmental change generate persistent sexually antagonistic selection that is difficult to resolve. Our results reinforce recent empirical observations that changing environmental conditions alleviate conflict between males and females. They also generate new predictions regarding the scope for sexually antagonistic selection and its resolution in changing environments.     

Diet and a developmental time constraint alter life‐history trade‐offs in a caddis fly (Trichoptera: Limnephilidae)

Environmental factors influence variation in life histories by affecting growth, development, and reproduction. We conducted an experiment in outdoor mesocosms to examine how diet and a time constraint on juvenile development (pond‐drying) influence life‐history trade‐offs (growth, development, adult body mass) in the caddis fly Limnephilus externus (Trichoptera: Limnephilidae). We predicted that: (1) diet supplementation would accelerate larval growth and development, and enhance survival to adulthood; (2) pond‐drying would accelerate development and increase larval mortality; and (3) the relationship between adult mass and age at maturity would be negative. Diet supplementation did lead to larger adult mass under nondrying conditions, but did not significantly alter growth or development rates. Contrary to predictions, pond‐drying reduced growth rates and delayed development. The slope (positive or negative) of the female mass–age at maturity relationship depended on interactions with diet or pond‐drying, but the male mass–age relationship was negative and independent of treatment. Our results suggest that pond‐drying can have negative effects on the future fitness of individuals by increasing the risk of desiccation‐induced, pre‐reproductive mortality and decreasing adult body size at maturity. These negative effects on life history cannot be overcome with additional nutritional resources in this species. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 495–504.     

Lifetime fitness consequences of early‐life ecological hardship in a wild mammal population

Early‐life ecological conditions have major effects on survival and reproduction. Numerous studies in wild systems show fitness benefits of good quality early‐life ecological conditions (“silver‐spoon” effects). Recently, however, some studies have reported that poor‐quality early‐life ecological conditions are associated with later‐life fitness advantages and that the effect of early‐life conditions can be sex‐specific. Furthermore, few studies have investigated the effect of the variability of early‐life ecological conditions on later‐life fitness. Here, we test how the mean and variability of early‐life ecological conditions affect the longevity and reproduction of males and females using 14 years of data on wild banded mongooses (Mungos mungo). Males that experienced highly variable ecological conditions during development lived longer and had greater lifetime fitness, while those that experienced poor early‐life conditions lived longer but at a cost of reduced fertility. In females, there were no such effects. Our study suggests that exposure to more variable environments in early life can result in lifetime fitness benefits, whereas differences in the mean early‐life conditions experienced mediate a life‐history trade‐off between survival and reproduction. It also demonstrates how early‐life ecological conditions can produce different selection pressures on males and females.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

Two sides of a coin: host‐plant synchrony fitness trade‐offs in the population dynamics of the western spruce budworm

Conifer‐feeding budworms emerge from overwintering sites as small larvae in early spring, several days before budburst, and mine old needles. These early‐emerging larvae suffer considerable mortality during this foraging period as they disperse in search of available, current‐year buds. Once buds flush, surviving budworms construct feeding shelters and must complete maturation before fresh host foliage senesces and lignifies later in the summer. Late‐developing larvae suffer greater mortality and survivors have lower fecundity when feeding on older foliage. Thus, there is a seasonal trade‐off in fitness associated with host synchrony: early‐emerging budworms have a greater risk of mortality during spring dispersal but gain better access to the most nutritious foliage, while, on the other hand, late‐emerging larvae incur a lower risk during the initial foraging period but must contend with rapidly diminishing resource quality at the end of the feeding period. We investigate the balance that results from these early‐season and late‐season synchrony fitness trade‐offs using the concept of the phenological window. Parameters associated with the variation in the phenological window are used to estimate generational fitness as a function of host‐plant synchrony. Because defoliation modifies these relationships, it is also included in the analysis. We show that fitness trade‐offs characterizing the phenological window result in a robust synchrony relationship between budworm and host plant over a wide geographic range in southern British Columbia, Canada.     

Trade‐offs to flight capability in Gryllus firmus: the influence of whole‐organism respiration rate on fitness

Wing dimorphism, where some macropterous long‐winged (LW) individuals can fly whereas micropterous short‐winged (SW) individuals cannot, is common in insects and believed to be maintained in part by trade‐offs between flight capability and reproductive traits. In this paper we examine differences in whole‐organism respiration rate between wing morphs of the sand cricket Gryllus firmus. We hypothesized that maintenance of the flight apparatus would result in elevated CO₂ respired because of the high metabolic cost of these tissues, which, in turn, constrain resources available for egg production in females. As the trade‐off involves calling behaviour in males, we predicted no equivalent constraint on organ development in this sex. We found female macropters (particularly older crickets) had significantly higher residual respiration rates than micropters. In males, we found only marginal differences between wing morphs. In both sexes there was a highly significant effect of flight muscles status on residual respiration rate, individuals with functional muscles having higher respiration rates. Both female and male macropters had significantly smaller gonads than micropters. Whole‐organism residual respiration rate was negatively correlated with fecundity: macropterous females with high respiration rates had smaller gonads compared with macropterous females with lower respiration rates.     

Sex‐ratio in natural and experimental populations of Drosophila subobscura from North America

The sex‐ratio (SR), defined as the proportion of males, has been studied in three North American colonizing populations of Drosophila subobscura (Eureka, Davis and Gilroy). The proportion of sexes under laboratory conditions was studied using the one‐generation serial transfer technique in one‐ and two‐species populations, to infer whether biased SR affects the outcome when competing with Drosophila pseudoobscura, another member of the same group now in sympatry with D. subobscura in North America. The wild samples of D. subobscura yielded a significantly higher number of males than females during those months where the species is more abundant. However, there was no significant deviation in the 1 : 1 proportion of sexes in the descendants of D. subobscura at any of the experimental conditions. On the contrary, D. pseudoobscura produced a higher proportion of females which could be responsible for the exclusion of D. subobscura in laboratory competition experiments with overlapping generations. Thus, if sexes are equal at birth and survival is similar, the preponderance of males of D. subobscura in our wild collections could indicate greater activity and probably greater chance of dispersal of males versus females especially under favourable conditions.     

The evolution of sex‐determining mechanisms: lessons from temperature‐sensitive mutations in sex determination genes in Caenorhabditis elegans

Sexual reproduction is one of the most taxonomically conserved traits, yet sex‐determining mechanisms (SDMs) are quite diverse. For instance, there are numerous forms of environmental sex determination (ESD), in which an organism’s sex is determined not by genotype, but by environmental factors during development. Important questions remain regarding transitions between SDMs, in part because the organisms exhibiting unique mechanisms often make difficult study organisms. One potential solution is to utilize mutant strains in model organisms better suited to answering these questions. We have characterized two such strains of the model nematode Caenorhabditis elegans. These strains harbour temperature‐sensitive mutations in key sex‐determining genes. We show that they display a sex ratio reaction norm in response to rearing temperature similar to other organisms with ESD. Next, we show that these mutations also cause deleterious pleiotropic effects on overall fitness. Finally, we show that these mutations are fundamentally different at the genetic sequence level. These strains will be a useful complement to naturally occurring taxa with ESD in future research examining the molecular basis of and the selective forces driving evolutionary transitions between sex determination mechanisms.     

Sex ratio,sex‐specific pattern in vegetative growth and gemma production in an aquatic liverwort,Scapania undulata (Marchantiophyta: Scapaniaceae)

Scapania undulata is an aquatic dioicous liverwort growing in shallow streams in boreal to subtropical zones. We studied the expressed sex ratio, sex‐specific differences in shoot architecture and possible trade‐off between sexual and asexual reproduction in ten populations of S. undulata by surveying 100 plots in ten streams in southern Finland. The expressed sex ratio was male biased, in contrast with the sex ratio in most dioicous bryophytes. It was also highly variable between the streams, but individual plots frequently comprised shoots from only one sex. The overproduction of males might be a strategy to overcome sperm dilution and ensure fertilization over longer distances in water. No size differences between females and males were detected, but they differed in branching patterns. Evidence for a higher cost of sexual reproduction in females than males can be seen from the following: the male‐biased sex ratio; low number of sex‐expressing female shoots in female‐only plots; no co‐occurrence of gemmae and female sex organs on a single branch, and no more than one sexual branch per female shoot. In contrast, high gemma production of male and female sex‐expressing shoots indicates a minimal trade‐off between sexual and asexual reproduction. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 229–241.     

Risk‐sensitive reproductive allocation: fitness consequences of body mass losses in two contrasting environments

For long‐lived organisms, the fitness value of survival is greater than that of current reproduction. Asymmetric fitness rewards suggest that organisms inhabiting unpredictable environments should adopt a risk‐sensitive life history, predicting that it is adaptive to allocate resources to increase their own body reserves at the expense of reproduction. We tested this using data from reindeer populations inhabiting contrasting environments and using winter body mass development as a proxy for the combined effect of winter severity and density dependence. Individuals in good and harsh environments responded similarly: Females who lost large amounts of winter body mass gained more body mass the coming summer compared with females losing less mass during winter. Additionally, females experienced a cost of reproduction: On average, barren females gained more body mass than lactating females. Winter body mass development positively affected both the females' reproductive success and offspring body mass. Finally, we discuss the relevance of our findings with respect to scenarios for future climate change.     

Sex‐specific distribution and diet of Platichthys flesus at the end of spawning in the northern Baltic Sea

This study examined the relationship of seascape structure, prey availability and sex on the post‐spawning distribution and diet of European flounder Platichthys flesus in the northern Baltic Sea. The objectives were to determine whether: (1) wave exposure and substratum affect abundance and distribution of P. flesus, (2) diet reflects the benthic prey composition and (3) sex affects the distribution or diet of P. flesus. The results showed that P. flesus was evenly spread in the archipelago with no correlation to wave exposure. The distribution was, however, sex specific; reproductive males dominated the exposed zone and mainly post‐reproductive females dominated the intermediate and sheltered zones. Platichthys flesus fed mainly on two bivalve prey species: blue mussels Mytilus edulis and Baltic tellins Macoma balthica. Hard substratum invertebrates dominated the diet in all habitats and apart from some typical soft substratum species, there was no clear link between fish feeding and the dominance structure of benthic prey. Diet was further sex specific, with females showing a broader range of diet than males. Results suggest that P. flesus is a specialist molluscivore found commonly and equally in soft‐ and hard‐substratum habitats throughout the archipelago area. Previous studies on P. flesus in the Baltic Sea have yielded inconsistent results regarding diet and it has commonly been believed that the distribution of Baltic Sea P. flesus is linked to sand and soft substrata. The present findings emphasize the importance of including the entire range of habitats when diet and regional species distributions are assessed.     

The short‐ and long‐term fitness consequences of natal dispersal in a wild bird population

Dispersal is a key process in population and evolutionary ecology. Individual decisions are affected by fitness consequences of dispersal, but these are difficult to measure in wild populations. A long‐term dataset on a geographically closed bird population, the Mauritius kestrel, offers a rare opportunity to explore fitness consequences. Females dispersed further when the availability of local breeding sites was limited, whereas male dispersal correlated with phenotypic traits. Female but not male fitness was lower when they dispersed longer distances compared to settling close to home. These results suggest a cost of dispersal in females. We found evidence of both short‐ and long‐term fitness consequences of natal dispersal in females, including reduced fecundity in early life and more rapid aging in later life. Taken together, our results indicate that dispersal in early life might shape life history strategies in wild populations.     

Pathways to fitness: carry‐over effects of late hatching and urbanisation on lifetime mating success

Life history theory and most empirical studies assume carry‐over effects of larval ­conditions to shape adult fitness through their impact on metamorphic traits (age and mass at metamorphosis). Yet, very few formal tests of this connection across metamorphosis exist, because this entails longitudinal studies from the egg stage and requires measuring fitness in (semi)natural conditions. In a longitudinal one‐year common‐garden rearing experiment consisting of an outdoor microcosm part for the larval stage and a large outdoor insectary part for the adult stage, we studied the effects of two factors related to time constraints in the larval stage (egg hatching period and urbanisation) on life history traits and lifetime mating success in the males of the damselfly Coenagrion puella. We reared early‐ and late‐hatched larvae from each of three rural and three urban populations from the egg stage throughout their adult life. Key findings were that both the hatching period and urbanisation shaped adult fitness, yet through different pathways. As expected, the more time‐constrained late‐hatched individuals accelerated their larval life history and this was associated with a lower lifetime mating success. A path analysis revealed this carry‐over effect was mediated by the changes in the two metamorphic traits (reduced age and lower mass at emergence). Notably, urban males had a 50% lower lifetime mating success, which was not mediated by age and mass at emergence, and possibly driven by their shorter lifespan. Our results point to long‐term carry‐over effects of the usually ignored natural variation in egg hatching dates, and further contribute to the limited evidence showing fitness costs of adjusting to an urban lifestyle.     

The “unguarded‐X” and the genetic architecture of lifespan: Inbreeding results in a potentially maladaptive sex‐specific reduction of female lifespan in Drosophila melanogaster

Sex differences in ageing and lifespan are ubiquitous in nature. The "unguarded‐X” hypothesis (UXh) suggests they may be partly due to the expression of recessive mutations in the hemizygous sex chromosomes of the heterogametic sex, which could help explain sex‐specific ageing in a broad array of taxa. A prediction central to the UX hypothesis is that inbreeding will decrease the lifespan of the homogametic sex more than the heterogametic sex, because only in the former does inbreeding increase the expression of recessive deleterious mutations. In this study, we test this prediction by examining the effects of inbreeding on the lifespan and fitness of male and female Drosophila melanogaster across different social environments. We found that, across social environments, inbreeding resulted in a greater reduction of female than male lifespan, and that inbreeding effects on fitness did not seem to counterbalance sex‐specific effects on lifespan, suggesting the former are maladaptative. Inter‐ and intra‐sexual correlation analyses also allowed us to identify evidence of an underlying joint genetic architecture for inbreeding effects on lifespan. We discuss these results in light of the UXh and other alternative explanations, and suggest that more attention should be paid to the possibility that the “unguarded‐X” may play an important role in the evolution of sex‐specific lifespan.     

樟叶蜂两性生殖与孤雌生殖方式下雌虫生殖适合度及子代生活史特征的比较

【目的】樟叶蜂Mesoneura rufonota是危害樟树Cinnamonum campora的重要食叶性害虫,该虫的繁殖策略包括两性生殖和孤雌生殖两种模式。本研究旨在明确孤雌生殖在樟叶蜂生活史中的生物学意义。【方法】在室内25℃恒温条件下,测定并分析了樟叶蜂孤雌生殖和两性生殖两种生殖方式在亲代生殖适合度(雌虫寿命、产卵量和卵孵化率)和子代生活史(各虫态发育历期、死亡率、子代性比和产卵量等)特征上的差异。【结果】孤雌生殖的樟叶蜂雌虫寿命显著长于两性生殖的雌虫寿命,而雌虫产卵量和卵孵化率在两种生殖方式间均无差异。子代各虫态的发育历期和死亡率以及子代单雌产卵量在两种生殖方式间均无差异,但子代成虫性比在两种生殖方式间存在显著差异,表现为孤雌生殖大多产雄性子代,而两性生殖大多产雌性子代。【结论】樟叶蜂的孤雌生殖延长了亲代雌虫的寿命,且为产雄孤雌生殖。这些研究结果表明,樟叶蜂的孤雌生殖不但具有自身建群的能力,同时在种群繁衍中可以提供大量的雄虫以弥补两性生殖后代雄性个体的不足。     

Population consequences of maternal effects: sex‐bias in egg‐laying order facilitates divergence in sexual dimorphism between bird populations

Abstract When costs and benefits of raising sons and daughters differ between environments, parents may be selected to modify their investment into male and female offspring. In two recently colonized environments, breeding female house finches (Carpodacus mexicanus) modified the sex and growth of their offspring in relation to the order in which eggs were laid in a clutch. Here we show that, in both populations, these maternal effects strongly biased frequency distribution of tarsus size of fully grown males and females and ultimately produced population divergence in this trait. Although in each population, male and female offspring show a wide range of growth patterns, maternal modifications of sex‐ratio in relation to egg‐laying order resulted in under‐representation of the morphologies that were selected against and over‐representation of morphologies that were favoured by the local selection on juveniles. The result of these maternal adjustments was fast phenotypic change in sexual size dimorphism within and between populations. Maternal manipulations of offspring morphologies may be especially important at the initial stages of population establishment in the novel environments and may have facilitated recent colonization of much of North America by the house finch.     

Cold‐induced expression of diapause in Praon volucre: fitness cost and morpho‐physiological characterization

Cold exposure (2°C for 7 days) in constant darkness at mummy stage induces diapause expression in 9% of the Praon volucre Haliday population. Diapausing parasitoids show a significant delay in emergence time compared with nondiapausing counterparts. A diapause‐mediated polyphenism is observed in mummy colour, with diapausing mummies being clearly darker than nondiapausing ones. The diapause status of dark mummies is confirmed by a significant reduction in metabolic rate. Diapausing parasitoids also display specific morphological characteristics: they are heavier (fresh and dry mass) and accumulate larger fat reserves than nondiapausing counterparts. The diapause status is associated with a fitness cost in terms of adult longevity. There is no evidence of diapause‐related change in supercooling ability.