Variation In Reproductive Output Research Articles

Feather growth rate and hormone deposition vary with elevation but not reproductive costs in resident Mountain Chickadees

Abstract Many organisms engage in metabolic trade-offs to manage costs associated with reproductive output which often leads to these costs carrying over into the future. Compensatory mechanisms vary across life-history strategies and are expected to result in near optimal fitness gains for the investor. Here we investigated whether environmental differences associated with increasing montane elevation and variation in reproductive output of a resident passerine songbird, the Mountain Chickadee (Poecile gambeli), were related to physiological condition during annual molt. Higher elevations are associated with harsher environmental conditions during the winter, which results in later and shorter breeding seasons than at lower elevations. We sampled the outermost tail feathers from adult birds in the fall after their prebasic molt, which initiates closely after reproduction (e.g., after parental care has ceased, ~1–3 weeks). We measured the hormone corticosterone deposited in feathers (fCORT) and feather growth rates for evidence of physiological effort predicted to be driven by several units of reproductive output (e.g., breeding timing, clutch and brood size, offspring mass). There were no relationships between any measure of reproductive output and feather characteristics between elevations or across years, despite substantial variation in reproductive output in the wider population across this same time. However, birds at the high elevation site grew their tail feathers significantly faster and had higher fCORT deposition compared to low elevation birds. These results suggest that although differences in reproductive output and any related signals of associated physiological effort (e.g., fCORT and feather growth rate) may not extend into individual condition during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter.

Can population models be a useful tool for evaluating the status of data-deficient species?

Population and life history data remains sparse for many species, with low prospects for improvement due to the costs of research and difficulties associated with gathering field data. However, data-deficient species may nevertheless face substantial threats. Effective approaches are required to quantitatively assess threats and the effects of data uncertainty in the assessments. We explore the use of population models to assess the impact of uncertain threatening processes in the data-deficient Tasmanian masked owl Tyto novaehollandiae castanops. We addressed data-deficiency with a multi-parameter sensitivity analysis. This showed that reproductive output, adult mortality and juvenile mortality had the greatest impact on population size and growth. Using literature on a related but better studied species, the barn owl (Tyto alba), we then used population models to simulate the impacts of rodenticide exposure by increasing stochastic variation in reproductive output, adult, and juvenile mortality. We investigated rodenticide exposure because, although there is evidence of secondary poisoning of Tasmanian masked owls through consumption of contaminated prey, the effects of potentially widespread exposure on the population are unclear. The effect on population size and growth from increased stochasticity in the rodenticide sensitive parameters was negative. However, the magnitude of impacts depended on the baseline juvenile mortality rate used in each model, highlighting the importance of this uncertain parameter on our assessment of risk. Our study serves as an example of the use of population models for exploring hypothetical scenarios for data-deficient populations. Population models are an important tool for setting priorities for research and sounding a precautionary alarm where potential threats may be concealed by uncertainty.

Predation risk and landscape properties shape reproductive output of an endangered sea duck from two subpopulations with contrasting predation risk

Predation is the leading cause of avian reproductive failure and theory predicts clutch size reduction under high nest predation risk. However, the impact of nest predation on population dynamics is debated, and spatiotemporal variation in reproductive output is poorly understood due to the predominance of short-term, single-site studies. To this end, we investigated how island geography (size, forest cover, isolation), predation risk (White-tailed Eagle Haliaeetus albicilla abundance), climate (migration phenology, winter severity) and time trends affected early breeding success (inverse of early predation rate) and clutch size of endangered Baltic Common Eiders (Somateria mollissima). The study was conducted at two close sites (Tvärminne, Velkua) during 1991–2020. Local breeding numbers showed a similar annual decline. Interestingly, fecundity components were negatively correlated across sites: early breeding success was higher in Velkua and clutch size in Tvärminne. Island forest cover and exposure were the best determinants of early breeding success and clutch size (with only weak explanatory power for clutch size), but their effects were mediated by differential susceptibility to eagle predation risk. Clutch size increased in Tvärminne but decreased in Velkua. The former finding likely reflects increased breeder phenotypic quality due to selective disappearance at this high-predation site, whereas the latter finding may indicate increasingly compromised food intake. Only at the high-risk site did clutch size show the expected decline with increasing eagle predation risk, and the expected increase with increasing overhead protection (forest cover). We identify the least exposed forested islands, associated with the highest productivity, as prime targets of conservation.

Clutch Size, Clutch Frequency, and Egg Characteristics of Diamond-Backed Terrapins (Malaclemys terrapin) in Southwestern Louisiana

The reproductive output of Malaclemys terrapin (Diamond-backed Terrapin) is highly variable across its geographic range. While much of the literature is based on populations from the Atlantic coast of the United States, little reproductive-output data exists for the Gulf of Mexico populations. We captured female Diamond-backed Terrapins in southwestern Louisiana and assessed their reproductive output using radiographic- and ultrasound-imaging techniques. X-rays identified that average clutch size was 7.2 and average egg width was 21.9 mm. We revealed a positive relationship between female size (plastron length) and both clutch size and egg width, but no relationship between egg size and clutch size. Ultrasound imaging in a subset of individuals revealed large pre-ovulatory follicles and fully shelled eggs concurrently in females, indicating the potential for at least 2 clutches annually in this region. Our results suggest Diamond-backed Terrapins in southwestern Louisiana show variation in reproductive output compared to other populations at similar latitudes, indicating the need for additional study within and between populations in the region.

Measuring Annual Variation in Reproductive Output Reveals a Key Role of Maternal Body Condition in Determining the Size of Eggs in Snakes.

Simple SummaryWe measured female reproductive traits of a colubrid snake (Lycodon rufozonatus) from Zhejiang, East China in four years (1999, 2010, 2011, and 2014). After removing the influence of female size, postpartum body mass was greater in 2010 than in 2014, clutch mass was greater in 2010 than in 2011 and 2014, and egg size was greater in 2010 than in the other three years. Egg size was positively related to postpartum body condition in each year. Females laid larger eggs in 2010 than in other three years after removing the influence of maternal size and body condition. Our study does not follow the prediction that reproductive females with different amounts of resources to invest should give priority to adjusting the number rather than size of offspring.Long-term studies are especially suited for disentangling the effects of extrinsic and intrinsic factors on both total reproductive investment and reproductive allocation in offspring number versus offspring size. Female reproductive traits of the red-banded wolf snake (Lycodon rufozonatus) from Zhejiang, East China were studied in four years between 1999 and 2014. Egg-laying dates overall extended from late June to late July, and varied among years. Postpartum body mass, clutch size, clutch mass, and egg size were positively related to female size (snout vent length, SVL) in each year. Postpartum body mass, clutch mass, and egg size differed among years after accounting for female SVL, whereas clutch size did not. Setting female SVL at the same level, postpartum body mass was greater in 2010 than in 2014, clutch mass was greater in 2010 than in 2011 and 2014, and egg size was greater in 2010 than in the other three years. Females did not trade off egg size against number. Egg size was positively related to postpartum body condition in each year. Females laid larger eggs in 2010 than in other three years after removing the influence of maternal body condition. Our study provides evidence for the traditional view that reproductive output is highly linked to maternal body size in snakes, but not following Smith and Fretwell’s (1974) classic prediction that females with different amounts of resources to invest in reproduction should give priority to adjusting the number rather than size of their offspring. Maternal body size and condition both are important sources of variation in egg size, but factors other than these two variables may also affect the size of eggs produced by female L. rufozonatus.

Density-dependence and seasonal variation in reproductive output and sporophyte production in the kelp, Ecklonia radiata.

The kelp, Ecklonia radiata, is an abundant subtidal ecosystem engineer in southern Australia. Density-dependent changes in the abiotic environment engineered by Ecklonia may feedback to affect reproduction and subsequent recruitment. Here, we examined: 1) how the reproductive capacity of Ecklonia individuals in the field (zoospores released · mm-2 reproductive tissue) varied with adult density and time, and 2) how the recruitment of microscopic gametophytes and sporophytes was influenced by zoospore density at two times. Zoospore production did not vary with adult density, with only one month out of ten sampled over a 2-y period showing a significant effect of density. However, zoospore production varied hugely over time, being generally highest in mid-autumn and lowest in mid-late summer. There were strong effects of initial zoospore density on gametophyte and sporophyte recruitment with both a minimum and an optimum zoospore density for sporophyte recruitment, but these varied in time. Almost no sporophytes developed when initial zoospore density was <6.5 · mm-2 in spring or <0.5 · mm-2 in winter with optimum densities of 90-355 · mm-2 in spring and 21-261 · mm-2 in winter, which resulted in relatively high recruitment of 4-7sporophytes · mm-2 . Sporophyte recruitment declined at initial zoospore densities >335 · mm-2 in spring and >261 · mm-2 in winter and was zero at very high zoospore densities. These findings suggest that although adult Ecklonia density does not affect per-capita zoospore production, because there is a minimum zoospore density for sporophyte production, a decline in population-level output could feedback to impact recruitment.

Proximate drivers of population inter-annual variation in seed output for a masting conifer species

Assessing the drivers of population inter-annual variation in reproductive output (CVp) is key for conservation and management of forest resources, as these drivers determine variation in seed crops which are closely related to seedling recruitment (i.e. forest regeneration) and understanding the mechanisms by which they affect reproductive output sheds light into population-level resilience to changing abiotic conditions. Proximate drivers of CVp include weather conditions which act as cues for reproduction and resource-driven lagged negative autocorrelations between past and current reproduction. Increased temporal variability in weather cues and strong negative autocorrelations are both expected to increase CVp, but very few studies have robustly tested these predictions at the intra-specific level using long-term, multi-population datasets. Based on a published dataset, we used approximately 2,000 yearly observations spanning 130 years (1886–2015) and 61 populations to test for effects of temporal variability in weather cues and lagged autocorrelations on CVp in seed output for a masting conifer species (Picea abies). We found that lagged (lag –1) summer (June–July) mean temperature was the best predictor of population-level annual seed output. Contrary to expectations, however, we observed a significant negative (not positive) effect of the standard deviation of lag –1 summer mean temperature on CVp. In addition, we found a non-linear, hump-shaped relationship between lag –1 reproductive autocorrelation and CVp, suggesting a qualitative change in the effects of resource constraints on reproductive variability whereby expected positive effects change to negative when the strength of negative autocorrelations exceeds a certain level. These patterns point at unexpected mechanisms whereby temporal variability in weather cues dampens variability in reproductive output, whereas the non-linear association with the lagged autocorrelations suggest thresholds associated with resource availability leading to qualitative changes in temporal patterns of reproduction.

Variation in reproductive output as a function of maternal age and weather conditions in the cultured Asian yellow pond turtle, Mauremys mutica

Abstract Biotic factors (e.g., maternal age) and abiotic factors (e.g., weather) play vital roles in reproduction. However, there is little information about the combined effects of maternal age and weather on the reproductive output of cultured Asian yellow pond turtles, Mauremys mutica. To address this issue, we surveyed and compared the reproductive output of 13-year-old and 25-year-old female turtles on non-rainy and rainy days. The results showed that older females produced larger eggs than younger females regardless of the weather conditions. Females laid larger clutch sizes (number of eggs per nest) under non-rainy conditions compared with those under rainy conditions. However, the variation in clutch frequency (number of clutches per day) was independent of maternal age and weather. There was no effect of an interaction between maternal age and weather on egg mass, clutch size or clutch frequency. Our results suggest that maternal age and weather had significant effects on egg mass and clutch size, respectively. These results imply that maternal age, together with weather conditions (mainly conditions of rain), can affect the reproductive output of M. mutica. Our results provide useful information for the artificial breeding and stock management of M. mutica.

Reproduction in the pitviper Bothrops jararacussu: large females increase their reproductive output while small males increase their potential to mate

Reproductive traits vary widely within and among snake species, and are influenced by a range of factors. However, additional studies are needed on several species, especially on tropical snake faunas, to fully understand the patterns of reproductive variation in snakes. Here, we characterized the reproductive biology of B. jararacussu from southeastern and southern Brazil. We combined macroscopic and microscopic examinations of the reproductive system of museum specimens with observations of free-ranging snakes to characterize size at sexual maturity, sexual size dimorphism (SSD), reproductive output, and male and female reproductive cycles. We compared our data with published literature and discuss the factors that may play a role in shaping the reproductive patterns in the species and the genus. Bothrops jararacussu shares several characteristics with its congeners such as autumn mating season, obligatory sperm storage in the female reproductive tract, seasonal timing of parturition (summer-autumn), female-biased SSD, maturity at larger body sizes in females, and a positive relationship between body size and litter size. These characteristics seem phylogenetically conserved in Bothrops. On the other hand, B. jararacussu exhibits some unique characteristics such as a high degree of SSD (one of the highest values recorded in snakes), a large female body size, and a large litter and offspring size, which are among the largest recorded in the genus. Moreover, larger females reproduce more frequently than smaller conspecifics. These characteristics may be collectively interpreted as the result of a strong selection for increased fecundity. Other peculiarities of the species include an asynchrony between spermiogenesis (summer-autumn) and the peak of SSK hypertrophy (autumn to spring) and a prolonged production of SSK granules. Because SSK hypertrophy and mating are androgen-dependent in snakes, the prolonged SSK hypertrophy suggests that male B. jararacussu may prolong their potential to mate (compared with its congeners), which may increase their reproductive success. Our results and previous literature collectively suggest that, in Bothrops, the evolution of SSD is driven by fecundity selection, variation in reproductive output is influenced by variation in female body size, and the timing of spermiogenesis is influenced by other factors in addition to temperature. We also suggest that male Bothrops have undergone multiple evolutionary shifts in the timing of spermiogenesis.

Effectiveness of native nectar-feeding birds and the introduced Apis mellifera as pollinators of the kangaroo paw, Anigozanthos manglesii (Haemodoraceae)

Plants pollinated by vertebrates are often visited by native and exotic insects foraging for pollen and nectar. We compared flower visitation rates, foraging behaviour, and the contribution to reproduction of nectar-feeding birds and the introduced honeybee Apis mellifera in four populations of the bird-pollinated Anigozanthos manglesii (Haemodoraceae). The behaviour of floral visitors was quantified with direct observations and motion-triggered and hand-held cameras. Pollinator access to flowers was manipulated by enclosure in netting to either exclude all visitors or to exclude vertebrate visitors only. Apis mellifera was the only insect observed visiting flowers, and the most frequent flower visitor, but primarily acted as a pollen thief. Although birds visited A. manglesii plants only once per week on average, they were 3.5 times more likely to contact the anther or stigma as foraging honeybees. Exclusion of birds resulted in 67% fewer fruits and 81% fewer seeds than flowers left open and unmanipulated. Unnetted flowers that were open to bird and insect pollinators showed pollen-limitation and a large variation in reproductive output within and between sites. Although honeybees have been shown to pollinate other Australian plants, compared to birds, they are highly inefficient pollinators of A. manglesii.

Effects of breeding chronology on white‐tailed deer productivity in Alabama

ABSTRACTFollowing declines in white‐tailed deer (Odocoileus virginianus) populations during the 19th century, many areas throughout the southeastern United States were restocked from various sources. As a result, some populations remain genetically distinct, and phenotypic traits of source populations, including breeding chronology, have been conserved. For example, average conception dates vary by ≥60 days between populations within some Alabama, USA, counties. Although deer have achieved and maintained sustainable densities across much of the southeastern United States for several decades, it is unclear whether this restocking legacy has demographic consequences relevant to management. Therefore, we analyzed a data set containing information on 270 yearling (1.5 yr old) and 2,116 adult (≥2.5 yr old) female deer collected during 1995–2017 to determine potential effects of breeding chronology on in utero productivity. Parameter estimates from a generalized linear mixed model indicated yearling productivity decreased approximately 16% (95% CL = 0–29%) for each 30‐day increase in mean site‐specific parturition date. We did not observe a similar relationship for adults. We believe the relationships we observed for yearlings may result from an interaction between parturition and plant phenology. Specifically, on sites with relatively late parturition dates, fawns are born near the end of the growing season when suboptimal nutritional conditions may negatively affect productivity during their first year of life. Variation in reproductive output of large ungulates is primarily driven by young females, so managers should be aware that productivity of late‐breeding deer populations may be less than average, especially if those populations are behaving in a density‐dependent manner. In addition, these findings emphasize the importance of considering the potential demographic implications of wildlife translocations resulting from differences in timing of life‐history traits. © 2019 The Wildlife Society.

Demographic and life history variation in two sky‐island populations of an endangered alpine lizard

AbstractA species’ life history is a strong determinant of its risk of extinction; traits such as body size, growth rate, age at maturity and fecundity influence population viability and persistence, as well as capacity for dispersal and colonisation of new habitats. Yet, despite the potential for substantial geographic variation in life history, most conservation programmes rely upon the species average rather than information specific to individual populations. We use the Guthega Skink (Liopholis guthega), a threatened alpine endemic lizard restricted to two geographically isolated locations in south‐eastern Australia, as a case study to demonstrate how geographic variation in life history traits may better inform conservation management. Liopholis guthega has a relatively short life span, with only a few years of reproductive activity, inter‐annual variation in reproductive output, and less‐than‐annual reproduction. We show that the Victorian population has a significantly slower growth rate, attains a smaller maximum size, reaches reproductive maturity later, and produces significantly smaller litters, despite no difference in longevity suggesting that it may be more vulnerable to extinction. We, therefore, suggest evaluating genetic rescue from the New South Wales population to improve recruitment and longevity of Victorian L. guthega, ongoing population monitoring in both locations, and a dedicated pest control programme to reduce pressure on this population. Our study has far reaching impacts; primarily demonstrating how knowledge of geographic variation in life history has the potential to improve conservation management of threatened species.

Associations between duck harvest, hunting wing ratios and measures of reproductive output in Northern Europe

Ducks are important game species, hunted in several countries throughout their annual cycle. We investigated whether the size of the annual duck harvest in Finland and Denmark reflected annual reproductive output in three common quarry duck species. Finland represents an important breeding area and Denmark important staging/wintering grounds for common teal (Anas crecca), Eurasian wigeon (Mareca penelope) and common goldeneye (Bucephala clangula). We assessed whether (i) annual duck harvest in these two countries correlated with variation in Finnish reproductive output or adult population size during 1990–2016 and (ii) variation in reproductive output of Finnish ducks was reflected in the juvenile ratios of birds harvested in Finland (2005–2007, 2014–2016) or Denmark (1990–2016). We hypothesised that variation in Finnish reproductive output would positively affect the size and juvenile ratio of the harvest, and that this effect would be stronger closer to the breeding grounds. Our data showed that the annual harvest of goldeneye in Finland was positively correlated with reproductive output, a desirable basis for applying sustainable management to this species. Teal and wigeon have much longer, more complex flyways, and their harvest did not mirror the annual production of young, although the wigeon harvest in Denmark increased with increasing juvenile ratio there. For these populations, we need to better define population units if we are to be able to assess harvest sustainability. We urgently need to monitor duck breeding success and harvest at larger spatial scales to support a comprehensive analysis of how well the harvest reflects reproductive output.

Prey productivity and predictability drive different axes of life-history variation in carnivorous marsupials.

Variation in life-history strategies has usually been characterized as a single fast-slow continuum of life-history variation, in which mean lifespan increases with age at maturity as reproductive output at each breeding event declines. Analyses of plants and animals suggest that strategies of reproductive timing can vary on an independent axis, with iteroparous species at one extreme and semelparous species at the other. Insectivorous marsupials in the Family Dasyuridae have an unusually wide range of life-history strategies on both purported axes. We test and confirm that reproductive output and degree of iteroparity are independent in females across species. Variation in reproductive output per episode is associated with mean annual rainfall, which predicts food availability. Position on the iteroparity-semelparity axis is not associated with annual rainfall, but species in regions of unpredictable rainfall have longer maximum lifespans, more potential reproductive events per year, and longer breeding seasons. We suggest that these two axes of life-history variation arise because reproductive output is limited by overall food availability, and selection for high offspring survival favours concentrated breeding in seasonal environments. Longer lifespans are favoured when reproductive opportunities are dispersed over longer periods in environments with less predictable food schedules.

Incidence and biomarkers of pregnancy, spontaneous abortion, and neonatal loss during an environmental stressor: Implications for female reproductive suppression in the cooperatively breeding meerkat

Meerkats are group-living, insectivorous herpestids in which subordinate members provide extensive care for the dominant female's young. In contrast to some cooperative breeders, subordinate female meerkats are physiologically able to reproduce and occasionally do so successfully; their attempts are more frequently ‘suppressed’ via eviction or infanticide by the dominant female. Spontaneous abortion and neonatal loss occur with some regularity, further negatively impacting reproductive success. Here, we compared the reproductive outcomes and endocrine profiles, including of serum progesterone (P4), serum estradiol (E2), and fecal glucocorticoid metabolites (fGCm), of dominant and subordinate dams residing within their clans in the Kalahari Desert of South Africa. Our study spanned years of drought, which reduced insect abundance and represented a substantial environmental stressor. Meerkat pregnancies were identified at mid-term and culminated either in spontaneous abortions or full-term deliveries, after which pups were either lost prior to emergence from the natal den (usually within 2days of birth) or emerged at 2–3weeks. Neonatal loss exceeded fetal loss for all females, and contributed to narrowing the status-related disparity in female reproductive output seen during less arid periods. Although E2 concentrations were significantly lower in subordinate than dominant females, they were sufficient to support gestation. Absolute E2 concentrations may owe to androgenic precursors that also attain highest concentrations in dominant dams and may mediate aggression underlying female reproductive skew. Pregnancies terminating in fetal loss were marked by significantly lower P4 concentrations in mid-gestation and modestly lower E2 concentrations overall. Consistently high fGCm concentrations further increased across trimesters, particularly (but not consistently) in subordinates and in aborted pregnancies. Environmental stressors may modulate reproductive outcomes in meerkats through their influence on sex steroids and their effects on intragroup competition. The social and eco-physiological factors affecting intraspecific variation in reproductive output, even in obligate cooperative breeders, may be most apparent during extreme conditions, reflecting the benefits of long-term studies for assessing the impact of climate change.

The effects of climate on annual variation in reproductive output in Snapping Turtles (Chelydra serpentina)

Reptiles are highly dependent on climatic patterns to regulate their behavior and physiology, and studies of the effects of climate on the biology of organisms are increasingly important given expected climate change. Our study examined the effects of climate variation over 15 of the 26 years between 1990 and 2015 on the reproductive output of the Snapping Turtle (Chelydra serpentina (Linnaeus, 1758)). Egg mass, clutch size, and clutch mass (relative to body size) were significantly higher in years following warmer temperatures in September and October of the year before reproduction, but not related to temperatures in April and May just before reproduction. Of the above life-history traits, egg mass varied the least across years, and after warm autumns small turtles (225–285 mm carapace length) increased clutch mass by increasing clutch size but not egg mass. In contrast, under the same conditions, large turtles increased clutch mass by increasing egg mass but not clutch size. Our data suggest optimal egg mass may vary with female size. Climate change may already have impacted reproductive output in Snapping Turtles at the site because temperatures during September and October have increased about 0.5 °C each decade for the last 45 years.

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

Abstract The consequences of individual variation in life‐history traits have been well studied due to their importance in evolutionary ecology. However, a trait that has received little empirical attention is the rate of indeterminate growth. In long‐lived ectotherms, subtle variation in growth after maturity could have major effects over the animals’ lifetimes. These effects are difficult to measure due to the challenges involved in reliably estimating individual variation in the face of environmental stochasticity, and the need to account for trade‐offs among growth, reproduction and survival. However, modelling advances have made such analysis possible if long‐term high‐quality datasets are available. We used an integrated state‐space modelling framework to reveal relationships between indeterminate growth, reproduction and survival in a population of North American snapping turtles (Chelydra serpentina) using a 41‐year dataset for 298 adult females. A hierarchical version of the von Bertalanffy model fitted to data on carapace lengths showed substantial individual variation in growth trajectories, and hierarchical models fitted to clutch‐mass data and recapture histories showed that reproductive output and survival probability increased with size. Integration of these models revealed no detectable trade‐offs—i.e., individual growth parameters were not correlated with size‐specific survival or reproduction rates, and individual variation in reproductive output did not affect the size‐specific survival rate. Consequently, individual variation in growth parameters was estimated to result in &gt;2‐fold variation in post‐maturity life expectancy and &gt;4‐fold variation in expected lifetime reproductive output. These results illustrate that indeterminate growth can have major fitness consequences in long‐lived species. We suggest that the individual variation in growth rates reflects variation in environments experienced during development or later life. An understanding of this variation may be essential for predicting the population dynamics of long‐lived species under threat and identifying the most important environments to protect. A plain language summary is available for this article.

Variation in Reproductive Output of the Red-crowned Roofed Turtle (Batagur kachuga) and the Three-striped Roofed Turtle (Batagur dhongoka) in the Chambal River of North India

Abstract Characterizing variation in reproductive output is foundational to understanding the demography of a population and determining management strategies. Doing so is paramount when the species of interest is threatened with extinction. The red-crowned roofed turtle (Batagur kachuga) and the three-striped roofed turtle (Batagur dhongoka) are severely threatened by overharvesting and habitat loss. Despite their imperiled status, there are very few published studies on species ecology and life history to enable effective conservation; the 3 published studies that are available were completed nearly 3 decades ago. We herein provide information on variation in reproductive output for these turtles in the Chambal River of North India. Generalized linear models and analyses of variance were fitted to data on nesting density, fecundity, and egg volume. The number of nests showed an overall decline across 3 seasons (2007, 2008, and 2010) over a 4-yr duration with the highest number of nests observed in the m...

Female reproductive success and calf survival in a North Sea coastal bottlenose dolphin (Tursiops truncatus) population.

Between-female variation in reproductive output provides a strong measure of individual fitness and a quantifiable measure of the health of a population which may be highly informative to management. In the present study, we examined reproductive traits in female bottlenose dolphins from the east coast of Scotland using longitudinal sightings data collected over twenty years. From a total of 102 females identified between 1997 and 2016, 74 mothers produced a collective total of 193 calves. Females gave birth from 6 to 13 years of age with a mean age of 8. Calves were produced during all study months, May to October inclusive, but showed a seasonal birth pulse corresponding to the regional peak in summer water temperatures. Approximately 83% (n = 116) of the calves of established fate were successfully raised to year 2–3. Of the known mortalities, ~45% were first-born calves. Calf survival rates were also lower in multiparous females who had previously lost calves. A mean inter-birth interval (IBI) of 3.80 years (n = 110) and mean fecundity of 0.16 was estimated for the population. Calf loss resulted in shortened IBIs, whilst longer IBIs were observed in females assumed to be approaching reproductive senescence. Maternal age and size, breeding experience, dominance, individual associations, group size and other social factors, were all concluded to influence reproductive success (RS) in this population. Some females are likely more important than others for the future viability of the population. Consequently, a better knowledge of the demographic groups containing those females showing higher reproductive success would be highly desirable for conservation efforts aimed at their protection.

Rural populations of the red fox Vulpes vulpes show little evidence of reproductive senescence

The ageing theory predicts fast and early senescence for fast-living species. We investigated whether the pattern of senescence of a medium-sized, fast-living and heavily-culled mammal, the red fox (Vulpes vulpes), fits this theoretical prediction. We used cross-sectional data from a large-scale culling experiment of red fox conducted over six years in five study sites located in two regions of France to explore the age-related variation in reproductive output. We used both placental scars and embryos counts from 755 vixens’ carcasses aged by the tooth cementum method (age range: 1–10), as proxies for litter size. Mean litter size per vixen was 4.7±1.4. Results from Generalized Additive Mixed Models revealed a significant variation of litter size with age. Litter size peaked at age 4 with 5.0±0.2 placental scars and decreased thereafter by 0.5 cubs per year. Interestingly, we found a different age-specific variation when counting embryos which reached a plateau at age 5–6 (5.5±0.2) and decreased slower than placental scars across older ages, pointing out embryo resorption as a potential physiological mechanism of reproductive senescence in the red fox. Contrary to our expectation, reproductive senescence is weak, occurs late in life and takes place at an age reached by less than 11.7% of the population such that very few females exhibit senescence in these heavily culled populations.