Capital Breeders Research Articles

Intermittent reproduction, mortality patterns and lifetime breeding frequency of females in a population of the adder (Vipera berus).

Female adders (Vipera berus) are “capital breeders” that exhibit delayed maturity and intermittent reproductive frequency. We studied the attainment of sexual maturity, the initiation of annual breeding in mature females, the energy and mortality costs associated with breeding, the length of the reproductive cycle and female lifetime reproductive frequency. We use longitudinal data obtained during an 18-year (2000–2017) mark–recapture study in a large population of adders in northern Belgium. A minority (15%) of the females gave birth to their first litter when they attained the actual age of 3 years, upon surpassing a minimum snout-vent-length of 38 cm. However, most females reproduced for the first time when they were 4 years or older. In mature females, breeding in a given year depends to a large extent on their body condition at the onset of the active season, indicating that a threshold level of energy reserves is necessary to start a reproductive cycle. During breeding years females stop growing, lose about one-third of their initial body mass and are very emaciated after parturition. The decrease in relative body mass was most notable initially in the largest and fattiest females. During the non-breeding years, females forage intensely to rebuild their fat reserves; their abilities to do so will strongly affect whether and when they engage in subsequent reproductive bouts. We used a multistate mark–recapture analytical method to simultaneously estimate the capture and survival rates of breeding and non-breeding females, a necessary procedure to obtain accurate estimates of survival probabilities. The analysis indicated much higher capture rates during the breeding years, but did not reveal a substantial effect of reproductive state on annual survival rates. Although some females were observed to breed in successive years, the reproductive cycle was most often biennial or triennial. However, most females (ca. 70%) that attained sexual maturity reproduced only once during their lifetime, while a minority of the females (ca. 5%) were observed to breed on 3–5 annual occasions. On average, females produced only ca. 1.3 litters during their reproductive lifetime. The short reproductive lifetime is a consequence not only of mortality directly related to the reproductive activities, but also of mortality associated with recovering from the weakened post-parturient body condition during the long intervals (1–2 years) between reproductive bouts.

Size‐related life‐history traits in geometrid moths: a comparison of a temperate and a tropical community

1. Comparative studies on insect life histories are facilitated by the increasing availability of reliable phylogenies but are hampered by the scarcity of comparable data. Fortunately, morphological proxies of some life‐history traits can be measured on preserved specimens.2. This study compared values of size‐related life‐history traits among a tropical (Ugandan) and a temperate (Estonian) assemblage of geometrid moths.3. A comparative analysis based on an originally derived phylogeny revealed that tropical moths were, on average, larger than temperate ones. Tropical moths also had somewhat lower relative abdomen masses than temperate ones. This indicates that the tropical rather than the temperate moths tend to use an income (rather than capital) breeding strategy. Nevertheless, no difference was found in a related index of pro‐ovigeny. When body size was accounted for, tropical moths were found to lay smaller eggs than temperate ones.4. The differences between the two compared areas are consistent with selection on higher mobility of the moths imposed by the more diverse tropical vegetation. Relatively larger eggs of temperate moths may constitute an adaptation to overcome the presumably stronger quantitative defences of their host plants.5. Overall, however, we conclude that the differences in ecologically relevant size‐related traits are relatively low among moth assemblages of a tropical and a temperate forest region, indicating that these environments may not impose radically different selective pressures on insect life histories.

Maternal age influences offspring behaviour and growth efficiency during provisioning in northern elephant seals

Offspring growth rates impact fitness and can be influenced by maternal effects. Despite efforts to understand the influence of maternal traits (e.g. age, size, body condition) on reproductive effort, much less is known about how maternal traits and environment influence the behaviour of offspring and ultimately, how offspring behaviour may influence the efficiency of the translation of maternal investment into offspring growth. Offspring of capital breeders, such as the northern elephant seal, Mirounga angustirostris, are nursed exclusively from maternal body reserves and investment is limited by the resources acquired prior to parturition. Combined new and previously published milk energy intake and offspring storage data (N = 38) suggest impacts of maternal age on growth efficiency that are independent of rates of energy delivery. To determine the mechanisms underlying this effect of maternal age, behavioural data were collected from pups of 46 known-age females, from parturition to weaning, across 6 years and three different sites along the central California coast, representing 3954 seal-hours of observation. Pup behaviours were divided into five mutually exclusive categories that potentially impacted pup energetics. The offspring of older females spent more time resting, while offspring of younger females spent more time locomoting and distant from their mother. As pups developed, they spent more time suckling and locomoting and less time resting. Pup behaviour showed strong diel patterns, with activity decreasing over the day. The magnitude of these relationships varied between rookeries, suggesting influences of harem size, topography or environmental features on pup behaviour. Together these findings suggest direct impacts of maternal age and breeding experience on pup behaviour and growth efficiency.

Intersexual Resource Competition and the Evolution of Sex-Biased Dispersal

Resource competition is a major driver of dispersal: an emigrating individual leaves more resources to its kin. Existing models of sex-biased dispersal rarely consider intersexual competition for resources. Instead, male reproductive success is often solely assumed to depend on female availability, implying a tacit assumption that male presence never depletes resources, such as food, that are of interest to female kin. In reality, both male and female offspring typically consume resources on their natal site before departing to consume resources elsewhere, and sexually dimorphic body sizes imply that the resource needs can differ. The goal of our study is to investigate how intersexual competition for resources can affect the evolution of sex-specific dispersal, via competition between kin of the same sex or different sexes and the subsequent success elsewhere. Our individual-based simulation model allows not only the dispersal probability but also its timing to evolve. We consider dispersal timing because later dispersal yields a longer period of kin competition than dispersal that occurs soon after independence. We also highlight the role of sex-specific income/capital breeding strategies, which is understudied in both empirical and theoretical literature of sex-specific dispersal. We show that sex biases in dispersal probability and timing are sensitive to the presence of intersexual competition, sexual differences in capital vs. income breeding strategies, and sexual dimorphism in the quantity of resources consumed. Males may evolve to disperse earlier if they also consume more food, as a result of selection to reduce intersexual kin competition. Alternatively, males may evolve to disperse less as well as later than females, if male fitness depends more on resource accumulation (e.g., building a large body to succeed in mating competition under polygyny) whereas female fitness depends more on reliable income (e.g., in species that require extended periods of maternal foraging), even if both sexes are equally competitive in consuming resources. Although the more dispersive sex is often the earlier departing sex, we also find cases where the only clear dimorphism is found in dispersal timing. We thus encourage more studies on the timing aspect of sex-biased dispersal.

Quantification of the full lifecycle bioenergetics of a large mammal in the high Arctic

Energy is a critical driver of animal life-history traits and Darwinian fitness, with direct implications for population dynamics. In the Arctic, extreme seasonal climatic conditions dictate energy flow and physiology of resident species. Consequently, vital rates of animal populations in the Arctic are tightly linked to climatic factors influencing food availability and quality. The muskox (Ovibos moschatus) is a capital breeder and the largest herbivore in the Arctic. Seasonal changes in energy intake influence body reserve dynamics of this species, impacting inter-annual and spatial variations in survival and recruitment. Yet, little is known about the full lifecycle bioenergetics of this and other Arctic species, and the impact of extreme seasonal conditions on life-history traits have never been quantified. By integrating energetic and physiological processes throughout the full lifecycle of individuals, we developed an individual-based model using dynamic energy budget theory (DEB-IBM) of the muskox that covers all aspects of mammalian life-history. We parameterized a baseline muskox model using data from a well-studied captive research herd, and then explored its application to a wild population in the high Arctic to assess the life-history implications of seasonal food availability. Our baseline DEB-IBM, which for the first time explicitly characterized fetal development using DEB theory, successfully predicted life-history traits as well as patterns of growth, body condition, feeding, metabolic rates, and reproduction of captive muskoxen. Adaptation of the model to the wild population required re-parameterization of only three variables that controlled seasonal food availability and upregulated assimilation. The wild model successfully captured inter-annual costs of reproduction, such that lactating females were in poorer body condition than females without calves. Arctic seasonal food limitations reduced fecundity in wild muskoxen by 42% compared to annual reproduction in well-fed captive individuals. We have developed a mechanistic energy-based framework to study life-history processes of muskoxen but the model is broadly applicable also for other mammals in the Arctic. Our study quantifies and highlights the strong interplay between energetics and individual fitness components, opening the door to future applications of the model in assessments of population dynamics and climate change impacts.

Testosterone trends within and across seasons in male humpback whales (Megaptera novaeangliae) from Hawaii and Alaska

Understanding reproductive profiles and timing of reproductive events is essential in the management and conservation of humpback whales (Megaptera novaeangliae).Yet compared to other parameters and life history traits, such as abundance, migratory trends, reproductive rates, behavior and communication, relatively little is known about variations in reproductive physiology, especially in males. Here, an enzyme immunoassay (EIA) for testosterone was validated for use in biopsy samples from male humpback whales. Analyses were conducted on 277 North Pacific male humpback whale blubber samples, including 268 non-calves and 9 calves that were collected in the Hawaiian breeding grounds and the Southeast Alaskan feeding grounds from 2004 to 2006. Testosterone concentrations (ng/g) were significantly different between non-calves sampled in Hawaii (n = 182) and Alaska (n = 86, p < 0.05) with peak testosterone concentrations occurring in the winter (January–March) and the lowest concentrations occurring in the summer (June–September). Fall and spring showed increasing and decreasing trends in testosterone concentrations, respectively. Blubber testosterone concentrations in non-calves and calves sampled in Alaska were not significantly different. Blubber and skin from the same individual biopsies (n = 37) were also compared, with blubber having significantly higher testosterone concentrations (p < 0.05) than skin samples. We found variability in testosterone concentration with age, suggesting that male humpbacks reach peak lifetime testosterone concentrations in the breeding grounds around age 8–25 years. The testosterone profile of male humpback whales follows a predictable pattern for capital breeders, where testosterone begins to increase prior to the breeding season, stimulating the onset of spermatogenesis. Incorporation of reproductive hormonal profiles into our overall understanding of humpback whale physiology will shed additional light on the timing of reproduction and overall health of the recently delisted Hawaii distinct population segment (DPS).

Live fast, don't die young: Survival-reproduction trade-offs in long-lived income breeders.

Trade‐offs between survival and reproduction are at the core of life‐history theory, and essential to understanding the evolution of reproductive tactics as well as population dynamics and stability. Factors influencing these trade‐offs are multiple and often addressed in isolation. Further problems arise as reproductive states and survival in wild populations are estimated based on imperfect and potentially biased observation processes, which might lead to flawed conclusions.In this study, we aimed at elucidating trade‐offs between current reproduction (both pregnancy and lactation), survival and future reproduction, including the specific costs of first reproduction, in long‐lived, income breeding small mammals, an under‐studied group.We developed a novel statistical framework that encapsulates the breeding life cycle of females, and accounts for incomplete information on female pregnancy and lactation and imperfect and biased recapture rates. We applied this framework to longitudinal data on two sympatric, closely related bat species (Myotis daubentonii and M. nattereri).We revealed the existence of several, to our knowledge previously unknown, trends in survival and breeding of these closely related, sympatric species and detected remarkable differences in their age and costs of first reproduction, as well as their survival–reproduction trade‐offs.Our results indicate that species with this type of life history exhibit a mixture of patterns expected for long‐lived and short‐lived animals, and between income and capital breeders. Thus, we call for more studies to be conducted in similar study systems, increasing our ability to fully understand the evolutionary origin and fitness effects of trade‐offs and senescence.

Food availability before aestivation governs growth and winter reproductive potential in the capital breeding fish, Ammodytes japonicus.

Capital breeders develop gametes by using energy that was stored before the spawning season. Energy is allocated to growth and reproduction, and limited food availability affects the balance of energy allocation, especially in fish that mature within a year, such as western sand lance (Ammodytes japonicus). This species aestivates without feeding until winter spawning and utilize energy stores that were accumulated prior to aestivation for maturation and spawning. This study aimed to evaluate the growth, energy storage, maturation rate, and reproduction of A. japonicus in response to food availability before aestivation. We conducted laboratory experiments in which young-of-the-year A. japonicus were fed at rates of 4% and 1% of their body weight per day; assigned as high and low ration groups, respectively. In June, body length was found to be significantly larger in the high ration group than in the low ration group, but the somatic condition did not differ significantly between the groups. Maturation rates and average fecundities were 1.0 and 6297 in the high ration group and 0.8 and 2251 in the low ration group, respectively. These results indicate that food availability before aestivation strongly governs the reproductive potential of A. japonicus, and suggest the involvement of mechanisms in the inter-annual recruitment variation in sand lance species.

Blubber transcriptome responses to repeated ACTH administration in a marine mammal

Chronic physiological stress impacts animal fitness by catabolizing metabolic stores and suppressing reproduction. This can be especially deleterious for capital breeding carnivores such as marine mammals, with potential for ecosystem-wide effects. However, the impacts and indicators of chronic stress in animals are currently poorly understood. To identify downstream mediators of repeated stress responses in marine mammals, we administered adrenocorticotropic hormone (ACTH) once daily for four days to free-ranging juvenile northern elephant seals (Mirounga angustirostris) to stimulate endogenous corticosteroid release, and compared blubber tissue transcriptome responses to the first and fourth ACTH administrations. Gene expression profiles were distinct between blubber responses to single and repeated ACTH administration, despite similarities in circulating cortisol profiles. We identified 61 and 12 genes that were differentially expressed (DEGs) in response to the first ACTH and fourth administrations, respectively, 24 DEGs between the first and fourth pre-ACTH samples, and 12 DEGs between ACTH response samples from the first and fourth days. Annotated DEGs were associated with functions in redox and lipid homeostasis, suggesting potential negative impacts of repeated stress on capital breeding, diving mammals. DEGs identified in this study are potential markers of repeated stress in marine mammals, which may not be detectable by endocrine profiles alone.

A comparative morphometric study of sensory capacity in geometrid moths

Diet breadth and the degree of capital breeding have been established as major determinants of species-specific ecology of herbivorous insects. Both of these variables are related to resource foraging and therefore can be expected to have effects on sensory capacity. However, such effects have remained poorly studied, let alone in phylogenetically explicit multi-species comparisons. We contribute to filling this gap in a study of 60 species of geometrid moths (Lepidoptera: Geometridae), using adult head measures (eye size, antennal length and shape, forehead width) as indices of sensory capacity. When controlled for body size, eyes of the more capital breeding species (i.e. those with low contribution of adult feeding to reproduction) were found to be smaller, and female antennae shorter, than in income breeders. Feathery (vs simple filiform) male antennae were more frequently present in the capital breeders and in larger species. Regarding diet breadth, generalist species were found to have relatively wider male foreheads than specialists. The results suggest that (a) breeding strategy rather than diet breadth predicts sensory capacity in geometrids, (b) capital breeding (vs income breeding) is related to low sensory capacity in females, and (c) in contrast, males of the capital breeding species have evolved towards elevated olfactory capacity.

Should I store, or should I sync? The breeding strategy of two small Neotropical primates under predictable resource availability.

Primates employ many strategies to deal with the costs of reproduction. While income breeders exploit the food available in their environment during lactation, the most costly phase of reproduction, capital breeders tend to store energy for use in the period. We analyzed the relationship between resource availability and lactation in Callicebus coimbrai (n = 2 groups) and Callicebus nigrifrons (n = 2 groups) in four Brazilian Atlantic forest remnants, to assess their breeding strategy. We recorded the occurrence of births and breastfeeding events to assess birth seasonality and lactation period and length while monitoring monthly fruit availability. We recorded 11 births (five for C. coimbrai, and six for C. nigrifrons), all restricted to the end of the lean season and the beginning of the rich season. Lactation coincided with periods of increased fruit availability. We suggest that the breeding pattern of Callicebus coimbrai and C. nigrifrons is compatible with an income-based breeding strategy.

Spermatogenesis, reproductive maturation, and spawning seasonality of male winter flounder, Pseudopleuronectes americanus: Comparisons among fishery stocks

Winter flounder, Pseudopleuronectes americanus, were collected from three fishery stocks in the United States (U.S.) during 2009–2013 to describe spermatogenesis. Spermatogenesis included rapid, synchronous transitions during autumn from mitotic spermatogonia to meiotic spermatocytes, then to haploid spermatids, and the release of spermatozoa into lobule lumen. As these transitions occurred several months prior to the spring spawning season, maturity of the testes are a poor indicator of spawning season, however, individuals can be readily evaluated prior to the spawning season for evidence of skipped spawning. Throughout this process, the gonad weight increased dramatically, with spawning-season maxima from 11 to 17% relative to individual somatic weight, suggesting considerable reproductive investment relative to other flatfishes. Fish condition also cycled seasonally, which indicated that males follow a capital breeding pattern that has been reported for female winter flounder. The timing of spermiogenesis was very similar in the fish among each U.S. stock (Southern New England [SNE], Georges Bank [GB], and the Gulf of Maine [GOM]) and published data from coastal Newfoundland, even though U.S. winter flounder spawned earlier in spring than fish in the Canadian stock. Male maturity varied in relation to both size and age, and over time, in patterns similar to those reported for female winter flounder, but at smaller and younger sizes than females. These intra-specific variations in reproductive seasonality, maturation, and skipped spawning suggest that winter flounder have the potential to adaptively respond to a dynamic environment in a region where ocean warming is occurring rapidly.

Increased Body Mass Supports Energy Compensation Hypothesis in the Breeding Female Natal Long-Fingered Bat Miniopterus Natalensis

Lactation is one of the most energetically demanding periods in the life cycle of a small mammal. Classified as income breeders, hibernating small colonial insectivorous bats are hypothesised to compensate for the energetic demand of lactation by increasing daily food intake, which increases body mass. The Natal long-fingered bat Miniopterus natalensis is a colonial hibernating species in southern Africa for which energy compensation was hitherto unknown. We tested predictions of the energy compensation hypothesis using a wild population of M. natalensis during the parturition and maternity period of November–December in 2015–2017. The study was conducted at the Meletse Bat Research and Conservation Training Centre near Gatkop Cave, in Limpopo Province, South Africa. We weighed and categorised 2,707 M. natalensis females captured during evenings and mornings into one of four groups including not pregnant with a sclerotized nipple (NP-SC), not pregnant with a non-sclerotized nipple (NP-NSC), lactating with a sclerotized nipple (L-SC), and pregnant with a sclerotized nipple (P-SC). NP-NSC and NP-SC females were classified as non-reproductive, whilst L-SC and P-SC females were classified as active breeders. Results showed that females in the L-SC category were 6% heavier than females in non-reproductive categories (NP-NSC and NP-SC). Pregnant females were 25% heavier than non-reproductive females due, at least in part, to foetus mass, whilst the mean body mass did not differ between females in non-reproductive categories. Whilst the body mass of females in the NP-NSC, NP-SC and L-SC categories did not differ during evening captures, L-SC females showed the biggest mass increase between evening and morning captures. Proportions of females captured from reproductive categories differed among years, with a higher overall proportion of active breeders (70%) in 2017 than either 2016 (33%) or 2015 (31%). This may be related to inter-annual variation in climate and warrants further investigation. Our results suggest female M. natalensis were heavier, on average, during lactation and support the energy compensation hypothesis.

Energy acquisition and allocation to the gonadal development of Cynoscion leiachus (Perciformes, Sciaenidae) in a tropical Brazilian bay

ABSTRACTThe process of energy acquisition and allocation to the gonadal development involves the use of reserves obtained from the food intake and/or stored in different parts of the body. Some fish species acquire and store energy prior the spawning season (capital breeders). For others species, the energy acquisition through by feeding activity continues actively throughout the spawning season (income breeders). This process of acquisition/allocation of energy to gonadal development was investigated for Cynoscion leiarchus an important fishery resource in southeastern Brazil. Monthly measurements of the gonadosomatic, hepatosomatic, condition factor and stomach repletion indices were carried out. Size at the first maturation was also assessed. Fish, mainly teleosts, were the main source of energy in the diet suggesting a carnivorous behaviour. We found evidences of use of stored body energy reserves during the spawning period, associated concomitantly with a decrease of feeding activity, suggesting a capital breeder. However, the wide spawning season, together with asynchronic oocyte development and indeterminate fecundity (typical of income breeders) suggest that the mixed-breeder strategy should be more suitable for this species. The high plasticity regarding the capital-income breeder strategy during the reproductive cycle of the genus Cynoscion is discussed.

Liver Antioxidants in Relation to Beak Morphology, Gizzard Size and Diet in the Common Eider Somateria mollissima.

Antioxidants in the liver are particularly abundant in capital breeders that rely on stored resources for egg production. Capital breeders like eider (hereafter common eider) Somateria mollissima have disproportionately large livers with low levels of coenzyme Q10 when compared to other bird species. Concentrations of total carotenoids and vitamin E in the livers of eiders were smaller than predicted for similarly sized bird species. Eiders with high body condition estimated as body mass relative to skeletal body size had high levels of total carotenoids and low levels of coenzyme Q10. The concentration of total carotenoids per gram of liver increased with age, and vitamin E and total carotenoids accumulated during the winter onwards from February to peak at the start of incubation in April. Total vitamin E, total carotenoids, and coenzyme Q10 per gram of liver decreased with increasing beak volume. The size of the empty gizzard increased with increasing liver mass but decreased with total carotenoids and coenzyme Q10. The main components of the diet were blue mussels Mytilus edulis (40%), draft whelk Nassarius reticulatus (27%), and periwinkle Littorina littorea (10%). The concentration of vitamin E increased with the number of razor clams Ensis sp. and draft whelks in the gizzard and the concentration of total carotenoids increased with the number of beach crabs Carcinus maenas. These observations are consistent with the hypothesis that eiders are limited in their levels of antioxidants through food limitation. Furthermore, they imply that diet and morphological characters involved in food acquisition and processing are important determinants of the level of antioxidants in the liver.

Income and capital breeding in males: energetic and physiological limitations on male mating strategies.

Income and capital breeding describe two dichotomous breeding strategies that characterise the allocation of resources to reproduction. Capital breeders utilise stored endogenous resources (typically lipids) to finance reproduction, whereas income breeders use exogenous resources (typically carbohydrates). The basis for such characterisation has mainly come from studying females, yet for many species, male and female reproductive success may be determined by substantially different factors. Females allocate resources to offspring production, whereas males typically allocate resources to accessing mating opportunities, e.g. from contests or displays. The primary metabolic fuel (lipids or carbohydrates) in males appears to be dependent on the type of activity being performed (i.e. high versus low intensity or long versus short duration), rather than capital or income breeding strategy per se. Males performing sustained, long-duration effort typically utilise lipids, whereas those undergoing intense activity more often utilise carbohydrates. As a result, either fuel type can be used in either strategy. Breeding season duration can constrain strategy choice; lipids and carbohydrates can be used in short breeding season species, but only lipids provide a viable fuel source for long breeding season capital breeders. Both capital- and income-breeding males must manage their resource use during the breeding season, but capital breeders must also cope with physiological stressors associated with extended fasting. Overall, the capital-income breeding concept applies equally to male reproduction, but compared with females, there are different physical and physiological constraints that shape choice of strategy. This Commentary also highlights some key future areas that need to be investigated to further understand how capital-income breeding strategies shape male mating strategies.

As clear as day: nocturnal activity differs from diurnal activity in a temporally constrained capital breeder

Abstract Time-activity budgets are fundamental to behavioural studies, allowing examination of how individuals allocate their time, and potentially energy, and how these patterns vary spatially and temporally and in relation to habitat, individual identity, sex, social status and levels of anthropogenic disturbance. Direct observations of animal behaviour, especially in the wild, are often limited to daylight hours; therefore, many activity budgets relate to diurnal activity only, or assumptions are made about nocturnal activity. Activity budgets have been a key component of many behavioural and energetics studies of breeding grey seals (Halichoerus grypus, Fabricius, 1791), and yet very little is known about nocturnal activity of grey seals, and a general, implicit assumption of no significant change from day to night seems to pervade the literature. Here we use a combination of high resolution digital video and thermal imaging video camera to follow known individual grey seal mothers from day into night to examine activity patterns during lactation. We show distinct differences in nocturnal activity budgets relative to diurnal activity budgets. Mothers spent significantly more time resting with a reduction of time spent in the alert and comfort move behavioural categories during nocturnal periods. It is clear that diurnal time-activity patterns of breeding female grey seals cannot be extrapolated to represent activity across a 24-hour cycle. These considerations are particularly critical in studies that aim to use time-activity budgets as proxies for energy budgets.

Making use of multiple surveys: Estimating breeding probability using a multievent-robust design capture-recapture model.

Increased environmental stochasticity due to climate change will intensify temporal variance in the life‐history traits, and especially breeding probabilities, of long‐lived iteroparous species. These changes may decrease individual fitness and population viability and is therefore important to monitor. In wild animal populations with imperfect individual detection, breeding probabilities are best estimated using capture–recapture methods. However, in many vertebrate species (e.g., amphibians, turtles, seabirds), nonbreeders are unobservable because they are not tied to a territory or breeding location. Although unobservable states can be used to model temporary emigration of nonbreeders, there are disadvantages to having unobservable states in capture–recapture models. The best solution to deal with unobservable life‐history states is therefore to eliminate them altogether. Here, we achieve this objective by fitting novel multievent‐robust design models which utilize information obtained from multiple surveys conducted throughout the year. We use this approach to estimate annual breeding probabilities of capital breeding female elephant seals (Mirounga leonina). Conceptually, our approach parallels a multistate version of the Barker/robust design in that it combines robust design capture data collected during discrete breeding seasons with observations made at other times of the year. A substantial advantage of our approach is that the nonbreeder state became “observable” when multiple data sources were analyzed together. This allowed us to test for the existence of state‐dependent survival (with some support found for lower survival in breeders compared to nonbreeders), and to estimate annual breeding transitions to and from the nonbreeder state with greater precision (where current breeders tended to have higher future breeding probabilities than nonbreeders). We used program E‐SURGE (2.1.2) to fit the multievent‐robust design models, with uncertainty in breeding state assignment (breeder, nonbreeder) being incorporated via a hidden Markov process. This flexible modeling approach can easily be adapted to suit sampling designs from numerous species which may be encountered during and outside of discrete breeding seasons.

Reproductive Ecology and Life History of Female Sonoran Desert Tortoises (Gopherus morafkai)

Abstract We studied female Gopherus morafkai reproduction for 10 yr to evaluate reproductive variation and environmental factors that influenced reproduction. In contrast to vitellogenesis in other Gopherus, substantial follicle growth occurred during the spring after emergence from hibernation. Vitellogenesis and egg production varied considerably among individuals. The smallest egg-producing female had a carapace length of 220 mm, and no female produced more than one clutch per year. Compared to small females, large females were more likely to reproduce in a given year and produced larger eggs, but body size did not affect clutch size. Good maternal body condition contributed to follicle growth in winter, larger clutches, and larger eggs in a clutch. Females that emerged from hibernation earlier were more likely to produce eggs. Early-emerging females also produced larger eggs than did females that emerged later. These reproductive traits contribute to a life history that resembles an income breeder com...

Trade-offs between storage and survival affect diapause timing in capital breeders

Many organisms spend the unfavourable part of the year, such as the winter season, in diapause or dormancy and reproduce in spring shortly after emergence. Reserves are acquired prior to diapause to cover metabolic costs and in some species also reproduction (capital breeding) directly after diapause. Storage is then a component of future reproduction, and capital breeders consequently pay a pre-breeding cost of reproduction as they risk dying while obtaining and carrying the reserves. How large should the reserves be, and to what extent should optimal storage, and thereby timing of diapause, depend on predation risk and reproductive strategy? We present a general and simplistic life history model of an arthropod (e.g. crustaceans or insects) that is exposed to background mortality risk when it accumulates reserves before diapause. The model optimizes diapause timing and resultant reserves for income, mixed and capital breeders, and predicts how mortality risk affects the degree of capital breeding. For income breeders, timing of diapause is insensitive to the risk while obtaining reserves as they, regardless of risk, acquire the minimum amount needed to survive the winter. For capital breeders, the higher the risk the earlier the diapause and less is consequently stored. Mixed breeders diapause late and store as much as pure capital breeders when exposed to low risk, but behave as income breeders and diapause early when mortality is high. Our model shows that the degree of capital breeding impacts phenology of diapause in a risk-dependent manner. This prediction should impact how diapause timing is thought of across a wide range of taxa, including the much studied marine copepods. Timing of diapause, including triggers and cues, can only be understood when the diversity of reproductive strategies and the adaptive value of storage is taken into account.