No evidence of sex‐biased dispersal in an island population of Common Blackbirds Turdus merula

Natal dispersal has major consequences for the dynamics and genetic structure of populations. Female‐biased natal dispersal, otherwise the norm in birds, is overridden when the place to move is limited, as on isolated islands. This effect was confirmed for the fist time in a European study system, the Common Blackbird breeding on Heligoland Island. Spatially restricted and sexually uniform natal dispersal may be a prerequisite for successful establishment of populations on remote islands or isolated habitat fragments, and this could play a major role in speciation processes.     

Reproductive and post‐reproductive life history of wild‐caught Drosophila melanogaster under laboratory conditions

The life history of the fruit fly (Drosophila melanogaster) is well understood, but fitness components are rarely measured by following single individuals over their lifetime, thereby limiting insights into lifetime reproductive success, reproductive senescence and post‐reproductive lifespan. Moreover, most studies have examined long‐established laboratory strains rather than freshly caught individuals and may thus be confounded by adaptation to laboratory culture, inbreeding or mutation accumulation. Here, we have followed the life histories of individual females from three recently caught, non‐laboratory‐adapted wild populations of D. melanogaster. Populations varied in a number of life‐history traits, including ovariole number, fecundity, hatchability and lifespan. To describe individual patterns of age‐specific fecundity, we developed a new model that allowed us to distinguish four phases during a female's life: a phase of reproductive maturation, followed by a period of linear and then exponential decline in fecundity and, finally, a post‐ovipository period. Individual females exhibited clear‐cut fecundity peaks, which contrasts with previous analyses, and post‐peak levels of fecundity declined independently of how long females lived. Notably, females had a pronounced post‐reproductive lifespan, which on average made up 40% of total lifespan. Post‐reproductive lifespan did not differ among populations and was not correlated with reproductive fitness components, supporting the hypothesis that this period is a highly variable, random ‘add‐on’ at the end of reproductive life rather than a correlate of selection on reproductive fitness. Most life‐history traits were positively correlated, a pattern that might be due to genotype by environment interactions when wild flies are brought into a novel laboratory environment but that is unlikely explained by inbreeding or positive mutational covariance caused by mutation accumulation.     

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.     

The impact of reproductive investment and early‐life environmental conditions on senescence: support for the disposable soma hypothesis

Several hypotheses have been put forward to explain the evolution of senescence. One of the leading hypotheses, the disposable soma hypothesis, predicts a trade‐off, whereby early‐life investment in reproduction leads to late‐life declines in survival (survival senescence). Testing this hypothesis in natural populations is challenging, but important for understanding the evolution of senescence. We used the long‐term data set from a contained, predator‐free population of individually marked Seychelles warblers (Acrocephalus sechellensis) to investigate how age‐related declines in survival are affected by early‐life investment in reproduction and early‐life environmental conditions. The disposable soma hypothesis predicts that higher investment in reproduction, or experiencing harsh conditions during early life, will lead to an earlier onset, and an increased rate, of senescence. We found that both sexes showed similar age‐related declines in late‐life survival consistent with senescence. Individuals that started breeding at a later age showed a delay in survival senescence, but this later onset of breeding did not result in a less rapid decline in late‐life survival. Although survival senescence was not directly related to early‐life environmental conditions, age of first breeding increased with natal food availability. Therefore, early‐life food availability may affect senescence by influencing age of first breeding. The disposable soma hypothesis of senescence is supported by delayed senescence in individuals that started breeding at a later age and therefore invested less in reproduction.     

Diet and social conditions during sexual maturation have unpredictable influences on female life history trade‐offs

The trade‐off between gametes and soma is central to life history evolution. Oosorption has been proposed as a mechanism by which females can redirect nutrients invested in oocytes into survival when conditions for reproduction are poor. Although positive correlations between oocyte degradation and lifespan have been documented in oviparous insects, the adaptive significance of this process in species with more complex reproductive biology has not been explored. Further, environmental condition is a multivariate state, and combinations of environmental stresses may interact in unpredictable ways. Previous work on the ovoviviparous cockroach, Nauphoeta cinerea, revealed that females manipulated to mate late relative to sexual maturation experience age‐related loss in fecundity because of loss of viable oocytes via apoptosis. This loss in fecundity is correlated with a reduction in female mate choice. Food deprivation while mating is delayed further increases levels of oocyte apoptosis, but the relationship between starvation‐induced apoptosis and life history are unknown. To investigate this, virgin females were either fed or starved from eclosion until provided with a mate at a time known to be suboptimal for fertility. Following mating, females were fed for the duration of their lifespan. We measured lifetime reproductive performance. Contrary to predictions, under conditions of delayed mating opportunity, starved females had greater fecundity, gave birth to more high‐quality offspring and had increased longevity compared with that of fed females. We suggest that understanding proximal mechanisms underlying life history trade‐offs, including the function of oocyte apoptosis, and how these mechanisms respond to varied environmental conditions is critical.     

Geographical variation in reproductive ageing patterns and life‐history strategy of a short‐lived passerine bird

We investigated differences in ageing patterns in three measures of breeding performance in populations of barn swallows Hirundo rustica L. from Spain and Denmark differing in breeding latitude and hence migration distance and duration of the breeding season. We found differences in ageing patterns between populations. Generally, young (i.e. yearling) and old females (i.e. ≥ 5 years of age) laid their first eggs later and produced smaller clutches than middle‐aged females (i.e. 2–4 years of age) in both populations. The southernmost population (i.e. Spanish) showing the shorter migratory distance experienced a greater within‐individual increase in timing of breeding and clutch size in early life and a greater within‐individual decrease in laying date but not in clutch size during senescence compared with the northernmost population (i.e. Danish). We also found that the number of fledglings produced annually was related to the age of the two members of the breeding pairs with pairs composed of young and old females performing less well than breeding pairs composed of middle‐aged females. We did not find reproductive senescence for the age of the male while controlling for the age of the female on the number of fledglings produced annually by the breeding pair. Differential survival between individuals did not explain age effects on laying date or annual clutch size in neither population. However, the increase in the number of fledglings produced annually with age was partly explained by the disappearance of poor‐quality members of the pairs, mainly poor‐quality males. Age‐related breeding success (i.e. number of fledglings) was similar for barn swallows from Spain and Denmark. Therefore, the study of ageing patterns and life‐history strategies in free‐ranging animals from more than a single population can throw new light on life‐history theory, population dynamics and evolutionary studies of senescence.     

Investment in survival and reproduction along a semelparity–iteroparity gradient in the Beta species complex

The Beta species complex shows a gradient of life histories from pronounced semelparity (big‐bang reproduction) to pronounced iteroparity (repeated reproduction). Models assume a trade‐off between investment in reproduction and survival. Reproductive effort is thought to increase with decreasing life span, and to be invariable in semelparous plants and susceptible to environmental conditions in iteroparous plants. These assumptions and hypotheses were verified by a greenhouse experiment testing six different life cycles at three contrasting nutrient levels. This study suggests that reproductive effort is negatively correlated with mean life span along the life‐cycle gradient. Unlike semelparous beets, reproductive effort in iteroparous beets is extremely sensitive to nutrient level. Phenotypic correlation between allocation to reproduction and allocation to survival generally appeared significantly negative in the longest‐lived iteroparous beets, nonsignificant in intermediate life histories and obviously positive in semelparous beets (no trade‐off control).     

Age‐specific oxidative status and the expression of pre‐ and postcopulatory sexually selected traits in male red junglefowl, Gallus gallus

Oxidative stress is emerging as a key factor underpinning life history and the expression of sexually selected traits. Resolving the role of oxidative stress in life history and sexual selection requires a pluralistic approach, which investigates how age affects the relationship between oxidative status (i.e., antioxidants and oxidative damage) and the multiple traits contributing to variation in reproductive success. Here, we investigate the relationship between oxidative status and the expression of multiple sexually selected traits in two‐age classes of male red junglefowl, Gallus gallus, a species which displays marked male reproductive senescence. We found that, irrespective of male age, both male social status and comb size were strongly associated with plasma oxidative status, and there was a nonsignificant tendency for sperm motility to be associated with seminal oxidative status. Importantly, however, patterns of plasma and seminal antioxidant levels differed markedly in young and old males. While seminal antioxidants increased with plasma antioxidants in young males, the level of seminal antioxidants remained low and was independent of plasma levels in old males. In addition, old males also accumulated more oxidative damage in their sperm DNA. These results suggest that antioxidant allocation across different reproductive traits and somatic maintenance might change drastically as males age, leading to age‐specific patterns of antioxidant investment.     

The effects of age at mating on female life-history traits in a seed beetle

Age at first reproduction is an important component of lifehistory across taxa and can ultimately affect fitness. Becausegenetic interests of males and females over reproductive decisionscommonly differ, theory predicts that conflict may arise overthe temporal distribution of matings. To determine the potentialfor such sexual conflict, we studied the direct costs and benefitsassociated with mating at different times for females, usingseed beetles (Acanthoscelides obtectus) as a model system. Virginfemales were resistant to male mating attempts at a very earlyage but subsequently reduced their resistance. Although we foundno difference in life span or mortality rates between femalesmated early in life and those mated later, females that matedearly in life suffered a 12% reduction in lifetime fecundity.Thus, there are direct costs associated with mating early inlife for females. Yet, males mate even with newly hatched females.We suggest that these data indicate a potential for sexual conflictover the timing of first mating and that female resistance tomating, at least in part, may represent a female strategy aimedat delaying mating to a later time in life.     

Human longevity and early reproduction in pre‐industrial Sami populations

Senescence is predicted to be associated with the intensity and timing of reproduction at an earlier age. Here, we examine the phenotypic association between reproduction and post‐reproductive survival in three pre‐industrial human populations that lived in Northern Scandinavia during 1640–1870. In both sexes longevity was independent of the total number of born or adult children, whereas early reproduction was negatively associated with the longevity of females and males. Our results thus do not support the view that reproductive investment as such has a negative impact on longevity, but suggest that survival costs are associated with the scheduling of reproduction. We discuss, however, an alternative point of view suggesting that less intense selection for early reproduction, extended parental care, and social structure allowing kin selection through the effects of close relatives are factors that have selected for the long post‐reproductive life span in humans.     

Age‐specific recruitment and natality of California sea lions at San Miguel Island,California

We conducted a 15 yr mark‐resight study of branded California sea lions (Zalophus californianus) at San Miguel Island, California, to estimate age‐specific recruitment and natality of the population. We used the Schwarz and Stobo model to estimate sighting, survival, recruitment, timing of births, abundance, and age‐specific natality from sighting histories of 1,276 parous females. The advantage of this approach was that the reproductive status of females did not have to be known for all females of reproductive age. Probability of recruitment into the reproductive population began at age 3 or 4, peaked between ages 5 and 7, and slowly declined. Age‐specific natality was similar for ages 4–16 but declined after age 17, suggesting that reproductive senescence occurs in older females. The average annual natality for parous females 4–16 yr of age was 0.77 (SE = 0.03); natality declined to 0.56 (SE = 0.10) for parous females 17–21 yr of age. Natality for both age classes was reduced during El Niño conditions by 24% and 34%, respectively. In addition to reducing natality, El Niño events may result in a delay of recruitment if females experience El Niño conditions before they turn 4 yr of age.     

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.     

Cost of reproduction and the evolution of deferred breeding in the western gull

Survival patterns in a population of western gulls (Larus occidentalis)of known age of first breeding, a, indicate a cost of reproductionrelated to the age of initial breeding. Among both sexes, birdsthat commenced breeding at the earliest ages (3 years in malesand 4 years in females) had higher annual mortality than thosethat deferred breeding one or more years. In addition, females(but not males) evidenced a cumulative cost of reproduction:holding age constant, females with more annual breeding attemptsdemonstrated poorer survival. These patterns of -specific survivalwere statistically significant after controlling for interannualvariation in food availability and are not explained simplyby variation in the intrinsic quality of individuals. To assessthe effects of these sex-specific costs on fitness, we combinedthe observed survival patterns with data on prebreeding survivorshipand -specific reproductive success to estimate rates of populationgrowth and lifetime reproductive success for different agesat first reproduction. Males showed a clearly defined fitnessoptimum at = 4 years, which coincided with the modal for malesin the population. Females showed no clear optimum, except thatbreeding at age 4 was suboptimal, hence females benefited fromdeferring breeding to ages 5-7 years. Observed age of firstbreeding also showed no clear mode for females, with slightpeaks at ages 5 and 7. As a result, in both sexes, the fitnesssurface for corresponded well with observed frequencies of. We suggest that stabilizing selection has acted to shape thephenotypic distribution of in males but, due to trade-offsbetween survival and early reproduction, stabilizing selectionis weak or absent in females     

Landscape heterogeneity drives intra‐population niche variation and reproduction in an arctic top predator

While intra‐population variability in resource use is ubiquitous, little is known of how this measure of niche diversity varies in space and its role in population dynamics. Here we examined how heterogeneous breeding environments can structure intra‐population niche variation in both resource use and reproductive output. We investigated intra‐population niche variation in the Arctic tundra ecosystem, studying peregrine falcon (Falco peregrinus tundrius, White) breeding within a terrestrial‐marine gradient near Rankin Inlet, Nunavut, Canada. Using stable isotope analysis, we found that intra‐population niches varied at the individual level; we examined within‐nest and among‐nest variation, though only the latter varied along the terrestrial‐marine gradient (i.e., increased among‐nest variability among birds nesting within the marine environment, indicating higher degree of specialization). Terrestrial prey species (small herbivores and insectivores) were consumed by virtually all falcons. Falcons nesting within the marine environment made use of marine prey (sea birds), but depended heavily on terrestrial prey (up to 90% of the diet). Using 28‐years of peregrine falcon nesting data, we found a positive relationship between the proportion of terrestrial habitat surrounding nest sites and annual nestling production, but no relationship with the likelihood of successfully rearing at least one nestling reaching 25 days old. Annually, successful inland breeders raised 0.47 more young on average compared to offshore breeders, which yields potential fitness consequences for this long‐living species. The analyses of niche and reproductive success suggest a potential breeding cost for accessing distant terrestrial prey, perhaps due to additional traveling costs, for those individuals with marine nest site locations. Our study indicates how landscape heterogeneity can generate proximate (niche variation) and ultimate (reproduction) consequences on a population of generalist predator. We also show that within‐individual and among‐individual variation are not mutually exclusive, but can simultaneously arise and structure intra‐population niche variation.     

Determinants and long‐term costs of early reproduction in males of a long‐lived polygynous mammal

In long‐lived polygynous species, male reproductive success is often monopolized by a few mature dominant individuals. Young males are generally too small to be dominant and may employ alternative tactics; however, little is known about the determinants of reproductive success for young males. Understanding the causes and consequences of variability in early reproductive success may be crucial to assess the strength of sexual selection and possible long‐term trade‐offs among life‐history traits. Selective pressures driven by fluctuating environmental conditions may depend on age class. We evaluated the determinants of reproduction in male bighorn sheep (Ovis canadensis) aged 2–4 years using 30 years of individual‐level data. These young males cannot defend estrous ewes and use alternative mating tactics. We also investigated how the age of first detected reproduction was correlated to lifetime reproductive success and longevity. We found that reproductive success of males aged 3 years was positively correlated to body mass, to the proportion of males aged 2–4 years in the competitor pool, and to the number of females available per adult male. These results suggest that reproductive success depends on both competitive ability and population age–sex structure. None of these variables, however, had significant effects on the reproductive success of males aged 2 or 4 years. Known reproduction before the age of five increased lifetime reproductive success but decreased longevity, suggesting a long‐term survival cost of early reproduction. Our analyses reveal that both individual‐level phenotypic and population‐level demographic variables influence reproductive success by young males and provide a rare assessment of fitness trade‐offs in wild polygynous males.     

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.     

Ontogenetic timing as a condition‐dependent life history trait: High‐condition males develop quickly,peak early,and age fast

Within‐population variation in ageing remains poorly understood. In males, condition‐dependent investment in secondary sexual traits may incur costs that limit ability to invest in somatic maintenance. Moreover, males often express morphological and behavioral secondary sexual traits simultaneously, but the relative effects on ageing of investment in these traits remain unclear. We investigated the condition dependence of male life history in the neriid fly Telostylinus angusticollis. Using a fully factorial design, we manipulated male early‐life condition by varying nutrient content of the larval diet and, subsequently, manipulated opportunity for adult males to interact with rival males. We found that high‐condition males developed more quickly and reached their reproductive peak earlier in life, but also experienced faster reproductive ageing and died sooner than low‐condition males. By contrast, interactions with rival males reduced male lifespan but did not affect male reproductive ageing. High‐condition in early life is therefore associated with rapid ageing in T. angusticollis males, even in the absence of damaging male–male interactions. Our results show that abundant resources during the juvenile phase are used to expedite growth and development and enhance early‐life reproductive performance at the expense of late‐life performance and survival, demonstrating a clear link between male condition and ageing.     

Intra‐population trends in the maturation and reproduction of a temperate marine herbivore Girella elevata across latitudinal clines

Latitudinal variation in the reproductive characteristics of a temperate marine herbivore, rock blackfish Girella elevata, was examined from three regions of the south‐eastern Australian coast. Biological sampling covered 780 km of coastline, including the majority of the species distribution. The sampling range incorporated three distinct oceanographic regions of the East Australian Current, a poleward‐flowing western boundary current of the Southern Pacific Gyre and climate‐change hotspot. Girella elevata are a highly fecund, group synchronous (multiple batch)‐spawner. Mean fork length (L_F) and age at maturity were greater for females than males within all regions, with both male and female G. elevata of the southern region maturing at a greater size and age than those from the central region. Estimates of batch fecundity (F_B) were greatest in the northern and southern regions, relative to the central region where growth rates were greatest. Significant positive relationships were observed between F_B and L_F, and F_B and total fish mass. Gonado‐somatic indices indicated latitudinal synchrony in spawning seasonality between G. elevata at higher latitudes, spawning in the late austral spring and summer. A late or prolonged spawning period is evident for G. elevata from the northern region. Juvenile recruitment to intertidal rock pools within the central and southern regions was synchronous with the spawning season, however, no juveniles were found within the northern region. The implications of latitudinal variation in reproductive characteristics are discussed in the context of climate and oceanographic conditions of south‐east Australia.     

Heat shock proteins mediate trade‐offs between early‐life reproduction and late survival in Drosophila melanogaster

Ageing and the resulting increased likelihood mortality are the inescapable fate of organisms because selection pressures on genes that exert their function late in life is weak, promoting the evolution of genes that enhance early‐life reproductive performance at the same time as sacrificing late survival. Heat shock proteins (HSP) are known to buffer various environmental stresses and are also involved in protein homeostasis and longevity. The characteristics of genes for HSPs (hsp) imply that they affect various life‐history traits, which in turn affect longevity; however, little is known about the effects of hsp genes on life‐history traits and their interaction with longevity. In the present study, the effects of hsp genes on multiple fitness traits, such as locomotor activity, total fecundity, early fecundity and survival time, are investigated in Drosophila melanogaster Meigen using RNA interference (RNAi). In egg‐laying females, RNAi knockdown of six hsp genes (hsp22, hsp23, hsp67Ba, hsp67Bb, hsp67Bc and hsp27‐like) does not shorten survival but rather increases it. Knockdown of five of those genes on an individual basis reduces early‐life reproduction, suggesting that several hsp genes mediate the trade‐off between early reproduction and late survival. The data indicate a positive effect of hsp genes on early reproduction and also negative effects on survival time, supporting the antagonistic pleiotropic effects predicted by the optimality theory of ageing.