Measures Of 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 tradeoffs 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 conditions 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, and 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 conditions during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter.

Decline and Extinction of the Italian Agile Frog Rana latastei from Core Areas of Its Range.

Detecting the trends of species and populations is fundamental to identifying taxa with high conservation priority. Unfortunately, long-term monitoring programs are challenging and often lacking. The Italian agile frog Rana latastei is endemic to Northern Italy and adjacent countries, is considered vulnerable by the IUCN, and is protected at the European level. However, quantitative estimates of its decline are extremely scarce. In this study, we document the trends in abundance and distribution of Rana latastei within Monza Park, which currently represents the area closer to the type locality of the species and holds unique genetic features. Wetlands within the park were monitored from 2000 to 2023; counts of egg clutches were taken as a measure of reproductive output and the abundance of breeding females. In 2000, the species occurred over a significant proportion of the park. Total abundance showed strong yearly variation but remained rather constant from 2000 to 2019. However, Rana latastei disappeared from the park around 2021 and was never detected in 2022-2023. The decline is probably related to the joint effect of multiple factors, including the conversion of breeding sites for farming, inappropriate water management, invasive alien species, and severe drought. The local extinction of Rana latastei occurred despite legal protection, highlighting the need for more effective and stringent tools for the conservation of European biodiversity.

Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

Biotic and abiotic stressors impose various fitness costs on individuals across a variety of taxa. In vertebrates, these stressors typically trigger complex neuroendocrine responses that stimulate glucocorticoid (GC) secretion from the adrenal cortex. Short-term elevation of GCs can be adaptive as it shifts energy toward physiological processes that cope with acute stressors; however, chronic increases in GC levels could have detrimental effects on fitness. Parasitism can be considered an important biotic stressor in nature and a possible cause of reproductive failure that could substantially affect an individual’s fitness. Thus, we aimed to test the effects of parasitism and maternal stress, as measured by GCs, during pregnancy and the relationship between these variables and measures of reproductive output using a rodent-flea system. Female Egyptian spiny mice (Acomys cahirinus) were randomly assigned to flea (Parapulex chephrenis) infested or uninfested treatments before and during pregnancy. The offspring of these females were flea-free. Feces were collected at five time points during the experiment to determine maternal fecal glucocorticoid metabolite (FGCM) concentrations. Overall, infested females had lower FGCM levels during gestation but higher FGCM levels post-parturition and larger mass changes than uninfested females. Additionally, models related to pup quality and quantity often included some measure of maternal investment or body condition moderating relationships between infestation and stress. This suggests that flea parasitism or high GC levels alone might not significantly impact host reproduction but rather females can experience different effects depending on their level of investment, which could be limited by body condition and/or the number of pups present in a litter.

Understanding reproductive allometry in turtles: A slippery "slope".

Measures of reproductive output in turtles are generally positively correlated with female body size. However, a full understanding of reproductive allometry in turtles requires logarithmic transformation of reproductive and body size variables prior to regression analyses. This allows for slope comparisons with expected linear or cubic relationships for linear to linear and linear to volumetric variables, respectively. We compiled scaling data using this approach from published and unpublished turtle studies (46 populations of 25 species from eight families) to quantify patterns among taxa. Our results suggest that for log–log comparisons of clutch size, egg width, egg mass, clutch mass, and pelvic aperture width to shell length, all scale hypoallometrically despite theoretical predictions of isometry. Clutch size generally scaled at ~1.7 to 2.0 (compared to an isometric expectation of 3.0), egg width at ~0.5 (compared to an expectation of 1.0), egg mass at ~1.1 to 1.3 (3.0), clutch mass at ~2.5 to 2.8 (3.0), and pelvic aperture width at 0.8–0.9 (1.0). We also found preliminary evidence that scaling may differ across years and clutches even in the same population, as well as across populations of the same species. Future investigators should aspire to collect data on all these reproductive parameters and to report log–log allometric analyses to test our preliminary conclusions regarding reproductive allometry in turtles.

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.

Age‐dependence and individual heterogeneity in reproductive success of greater sage‐grouse

Research on iteroparous species has shown that reproductive success may increase with age until the onset of senescence. However, from the population perspective, increased reproductive success with age could be a consequence of within‐individual variation (e.g. ageing, breeding experience, foraging ability hypotheses), between‐individual variation (e.g. individual heterogeneity, frailty, selection, delayed breeding hypotheses), or a combination thereof. We evaluated within‐ and between‐individual variation in reproductive success of greater sage‐grouse (Centrocercus urophasianus; sage‐grouse), a galliforme of conservation concern throughout western North America. We monitored female reproductive activity from 1998–2010 and used generalized linear mixed models incorporating within‐subject centering to evaluate and separate within‐ and between‐individual effects. We detected positive effects of within‐individual variation on nest initiation and success where ageing increased the likelihood of both parameters, which appears to support the breeding experience and/or foraging ability hypotheses. However, nest initiation was also affected by between‐individual variation whereby the likelihood of initiation was higher for individuals with higher mean age (i.e. survived longer), as is predicted by the frailty and selection hypotheses. Our results indicate both within‐ and between‐individual variation affect reproductive output of sage‐grouse, but the effects of each varied by measure of reproductive output. Our results corroborate previous findings that suggest population age parameters (i.e. cross‐sectional) should be interpreted with caution due to potential entanglement of within‐ and between‐individual processes. Moreover, the relative role and strength of within‐ and between‐individual processes appeared to vary by measure of reproductive output in our results, which further emphasizes the need for longitudinal analysis of age effects, even in relatively short‐lived iteroparous animals, to adequately interpret biological processes.

Hot males live fast and die young: habitat segregation, reproductive output, and lifespan of sympatric Mnais damselflies

The Japanese damselflies Mnais costalis and Mnais pruinosa show microhabitat segregation in response to forest sunlight conditions in their sympatric habitat: M. costalis prefers sunny sites while M. pruinosa prefers semi-shady sites. We tested whether sunlight conditions at territorial sites influenced reproductive output, territory occupancy, and/or reproductive lifespan of males of the two species differently. Oviposition duration of females after copulation was used as the measure of reproductive output of individual males. We recorded illuminance at each territorial site on sunny days during the behavioral observation periods. M. costalis males at sites with higher illuminance had a higher reproductive output than other territorial males, while M. pruinosa males had a relatively lower reproductive output at such sites. During a reproductive season, we performed population censuses in a 500-m area of stream, which contained at least 112 potential territorial sites. Using a fish-eye converter, we took a hemispherical photograph to estimate canopy openness as a measure of insolation at each territorial site and examined whether males incur higher survival costs by holding territories at sunnier sites. Minimum reproductive lifespan, estimated as days between the first and the last sightings, showed that M. costalis males that occupied sunnier sites had a shorter lifespan than those occupying shadier sites, while M. pruinosa males did not show such a relationship. These results suggest that microhabitat segregation of these two Mnais damselflies reflects a species difference in the tradeoff between the benefit of mating rate and cost of survival in the sun. We report a field study on the relationships among thermal environment, temperature tolerance, reproductive success, and character displacement in the mating systems of two species of territorial Mnais damselflies. Allopatric populations of these two species are forest dwellers, and males of each species show wing color polymorphism linked to alternative mating behaviors. When these species are sympatric, males lose their polymorphisms and change their habitat preferences: M. pruinosa prefers shady parts of a stream, while M. costalis prefers sunnier parts. We showed the costs and benefits of character displacement coupled to microhabitat preference shift. The findings of this study may highlight an underappreciated area of study, namely, the interplay between behavioral and physiological ecology in insects.

High levels of maternally transferred mercury do not affect reproductive output or embryonic survival of northern watersnakes (Nerodia sipedon)

Maternal transfer is an important exposure pathway for contaminants because it can directly influence offspring development. Few studies have examined maternal transfer of contaminants, such as mercury (Hg), in snakes, despite their abundance and high trophic position in many ecosystems where Hg is prevalent. The objectives of the present study were to determine if Hg is maternally transferred in northern watersnakes (Nerodia sipedon) and to evaluate the effects of maternal Hg on reproduction. The authors captured gravid female watersnakes (n = 31) along the South River in Waynesboro, Virginia, USA, where an extensive Hg-contamination gradient exists. The authors measured maternal tissue and litter Hg concentrations and, following birth, assessed (1) reproductive parameters (i.e., litter size and mass, neonate mass); (2) rates of infertility, death during development, stillbirths, malformations, and runts; and (3) the overall viability of offspring. Mercury concentrations in females were strongly and positively correlated with concentrations in litters, suggesting that N. sipedon maternally transfer Hg in proportion to their tissue residues. Maternal transfer resulted in high concentrations (up to 10.10 mg/kg dry wt total Hg) of Hg in offspring. The authors found little evidence of adverse effects of Hg on these measures of reproductive output and embryonic survival, suggesting that N. sipedon may be more tolerant of Hg than other vertebrate species. Given that this is the first study to examine the effects of maternally transferred contaminants in snakes and that the authors did not measure all reproductive endpoints, further research is needed to better understand factors that influence maternal transfer and associated sublethal effects on offspring.

Colony life history and lifetime reproductive success of red harvester ant colonies

1. We estimate colony reproductive success, in numbers of offspring colonies arising from a colony's daughter queens, of colonies of the red harvester ant, Pogonomyrmex barbatus. 2. A measure of lifetime reproductive success is essential to understand the relation of ecological factors, phenotype and fitness in a natural population. This was possible for the first time in a natural population of ant colonies using data from long-term study of a population of colonies in south-eastern Arizona, for which ages of all colonies are known from census data collected since 1985. 3. Parentage analyses of microsatellite data from 5 highly polymorphic loci were used to assign offspring colonies to maternal parent colonies in a population of about 265 colonies, ages 1-28 years, sampled in 2010. 4. The estimated population growth rate Ro was 1.69 and generation time was 7.8 years. There was considerable variation among colonies in reproductive success: of 199 possible parent colonies, only 49 (˜ 25%) had offspring colonies on the site. The mean number of offspring colonies per maternal parent colony was 2.94 and ranged from 1 to 8. A parent was identified for the queen of 146 of 247 offspring colonies. There was no evidence for reproductive senescence; fecundity was about the same throughout the 25-30 year lifespan of a colony. 5. There were no trends in the distance or direction of the dispersal of an offspring relative to its maternal parent colony. There was no relationship between the number of gynes produced by a colony in 1 year and the number of offspring colonies subsequently founded by its daughter reproductive females. The results provide the first estimate of a life table for a population of ant colonies and the first estimate of the female component of colony lifetime reproductive success. 6. The results suggest that commonly used measures of reproductive output may not be correlated with realized reproductive success. This is the starting point for future investigation asking whether variation in reproductive success is related to phenotypic variation among colonies in behavioural and ecological traits.

Population vigor of a rare, wetland, understory herb in relation to light and hydrology1

Light and hydrology are believed to have important effects on the population vigor of the globally rare and declining plant Trollius laxus (Ranunculaceae), which occurs in both open and forested geogenous, calcareous wetlands (e.g., rich fens, northern white-cedar swamps) in the northeastern United States. In a forested peatland that supports the largest population of T. laxus worldwide, we explored the relationships between T. laxus vigor and both light (photosynthetic photon flux density) and hydrology at 30 subpopulations. Subpopulation vigor was quantified as abundance (plant and seedling counts), size (stem counts), and reproductive output (flower and follicle counts), and these 5 vigor variables were regressed on 14 light environment and 6 hydrology predictor variables. The two measures of reproductive output were related to a number of the predictor variables, but subpopulation size and abundance were not. Although T. laxus emerges and blooms early in the spring, subpopulation vigor showed similar positive relationships between the spring and summer light environment variables. Vigor had stronger relationships with diffuse light than with direct light. Higher spring groundwater level, the only hydrology variable related to any component of subpopulation vigor, was related to greater follicle production. Because canopy gaps can cause small-scale changes in both light transmittance and hydrology in forested peatlands, our results indicate that gaps may be key to the persistence of T. laxus and other rich fen species during secondary succession.

Increased reproductive output in stereotypic captive Rhabdomys females: Potential implications for captive breeding

Captive animal populations can diverge considerably from populations in the wild, despite the animals not being deliberately domesticated. If the phenotypes which are of benefit in captivity are heritable, the genotypes of captive-stock can diverge swiftly and substantially from wild-stock. Using striped mice, Rhabdomys, we tested the relationship between reproductive output and stereotypic behaviour, a heritable repetitive abnormal behaviour common in captive wild animals. Individuals ( n = 120; 60♂, 60♀) were assigned to pairs in one of four treatment groups formed from combinations of non-stereotypic and stereotypic mothers and fathers, and various measures of reproductive output were recorded. Reproductive output (e.g. total number of offspring) for stereotypic females (but not stereotypic males) was significantly greater than for non-stereotypic striped mice. We suggest that, overall, unintended selection is likely to increase the incidence of stereotypic behaviour in a captive striped mouse population because (1) stereotypic females breed more successfully than non-stereotypic striped mice, and (2) genetic variance underlies the trait. The potential implications of these findings for the validity of behavioural studies using captive-bred wild animals and for conservation breeding programmes are discussed.

The effects of a coral disease on the reproductive output of Montastraea faveolata (Scleractinia: Faviidae).

The direct impacts of coral diseases on coral populations have been assessed by quantifying coral tissue loss and colony mortality, but the determination of the indirect effects of diseases, such as disruptions in life history functions (e.g. reproduction, growth and maintenance), are more difficult to ascertain and have been scant. This study involved a comparison of various measures of reproductive output from histological slides of healthy tissue samples of Montastraea faveolata and tissue samples from colonies with white plague (WP) infections in Dominica (West Indies). Although the variability in the reproductive data was high, WP had significant negative impacts on the percentage of reproductive polyps per cm2, the percentage of reproductive mesenteries within a polyp, oocyte quantity per polyp, mean oocyte volume (mm3), and fecundity (oocyte volume per cm2 of tissue). However, these effects were only observed in the tissue directly impacted by the WP disease "band" and were not observed in tissue samples taken 20 cm away from the lesion. Therefore, the effects of a coral disease (WP) on reproductive output are localized and not expressed colony-wide.

A database of vertebrate longevity records and their relation to other life‐history traits

Longevity is a major characteristic of animals that has long fascinated scientists. In this work, we present a comprehensive database of animal longevity records and related life-history traits entitled AnAge, which we compiled and manually curated from an extensive literature. AnAge started as a collection of longevity records, but has since been expanded to include quantitative data for numerous other life-history traits, including body masses at different developmental stages, reproductive data such as age at sexual maturity and measurements of reproductive output, and physiological traits related to metabolism. AnAge features over 4000 vertebrate species and is a central resource for applying the comparative method to studies of longevity and life-history evolution across the tree of life. Moreover, by providing a reference value for longevity and other life-history traits, AnAge can prove valuable to a broad range of biologists working in evolutionary biology, ecology, zoology, physiology and conservation biology. AnAge is freely available online (http://genomics.senescence.info/species/).

Declines in reproductive output in two dolphin populations depleted by the yellowfin tuna purse-seine fishery

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 369:273-285 (2008) - DOI: https://doi.org/10.3354/meps07606 Declines in reproductive output in two dolphin populations depleted by the yellowfin tuna purse-seine fishery Katie L. Cramer1,*, Wayne L. Perryman2, Tim Gerrodette2 1Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0208, USA 2NOAA Fisheries, Southwest Fisheries Science Center, 3333 North Torrey, Pines Court, La Jolla, California 92037-1023, USA *Email: kcramer@ucsd.edu ABSTRACT: Reproductive data for 2 pelagic dolphin subspecies in the eastern tropical Pacific, the eastern spinner (ES) dolphin Stenella longirostris orientalis and northeastern pantropical spotted (NEPS) dolphin S. attenuata attenuata, were obtained from aerial photographs taken between 1987 and 2003. Two measures of reproductive output were estimated: proportion of adult dolphins with calves (‘proportion with calves’) and length at which calves disassociated from their mothers (‘length at disassociation’). Trends in length at disassociation were investigated to determine if the proportion with calves was affected by possible changes in calving interval, but no changes were found. Proportion with calves for ES dolphins was stable from 1987 to 1993, then declined from 1993 to 2003; proportion with calves for NEPS dolphins decreased steadily from 1987 to 2003. For both species, proportion with calves was related to number of dolphins in the school of the focal species and/or proportion of the school made up of the focal species. For NEPS dolphins, annual number of purse-seine sets on dolphins was a predictor of both proportion with calves and length at disassociation. Because NEPS dolphins are the main species targeted by the fishery, the link between fishing activity and both measures of reproductive output indicates that the fishery has population-level effects beyond reported direct kill. Decline in reproductive output is the proximate cause or one of the proximate causes of the failure of dolphin populations to recover at rates expected after reduction of high bycatch levels. KEY WORDS: Tuna–dolphin issue · Bycatch · Stenella attenuata · Stenella longirostris · Dolphin reproduction · Fishery effects · El Niño effects Full text in pdf format PreviousNextCite this article as: Cramer KL, Perryman WL, Gerrodette T (2008) Declines in reproductive output in two dolphin populations depleted by the yellowfin tuna purse-seine fishery. Mar Ecol Prog Ser 369:273-285. https://doi.org/10.3354/meps07606 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 369. Online publication date: October 13, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Heterozygosity and fitness in a California population of the labyrinth spider Metepeira ventura (Araneae, Araneidae)

Abstract. The relationship between individual heterozygosity and characteristics likely to be associated with fitness was investigated in the labyrinth spider Metepeira ventura. Adult females and their egg sacs were collected at a coastal site in southern California, and three measures of bodily condition (carapace width, weight, residual index) and six measures of reproductive output (number of egg sacs, variation in egg number among sacs [coefficient of variation], total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were determined for each spider. The sample was polymorphic at three allozyme loci that were in Hardy–Weinberg equilibrium, and individual females were heterozygous at up to two of the three loci, forming three heterozygosity classes (0, 1, and 2). None of the bodily condition measures were significantly related to the number of heterozygous loci, while four of the reproductive output estimators (total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were significantly influenced by heterozygosity. In each significant case, values for class 2 females were less than those for class 0 and 1 females, whose values were usually more similar. Thus, while female bodily condition was comparable among classes, the most heterozygous females produced fewer total eggs and eggs per sac than their less heterozygous peers. The fact that females of M. ventura engage in a reproductive investment‐number trade‐off suggests that high‐variability and low‐variability females may be pursuing distinct reproductive strategies in the wild, with more heterozygous females being K‐selected (smaller clutches, heavier eggs) and more homozygous females being r‐selected (larger clutches, lighter eggs). Further investigation will be needed to assess more fully the fitness value of heterozygosity in M. ventura.

Male sexual attractiveness and parental effort in blue tits: a test of the differential allocation hypothesis

When the reproductive value of a breeding attempt is related to attributes of the breeding partner, an individual is expected to allocate more resources to parental care when mated to a high-quality partner. We tested predictions of the differential allocation hypothesis, by experimentally increasing and decreasing male blue tit, Parus caeruleus, sexual attractiveness and recording subsequent measures of male and female parental effort during the chick-feeding period. We used marker pens, to create two distinct male phenotypes: one more attractive phenotype with a shift in peak reflectance towards the ultraviolet (UV) part of the spectrum (UV+) and one less attractive phenotype with a shift towards the human-visible part of the spectrum (UV−). There was no significant difference in absolute or relative female feeding rate with respect to treatment. However, there were significant interaction effects between treatment and female age on female feeding rate, indicating that 1-year-old females provisioned more when mated to a UV+ male than a UV− male. UV− males fed their chicks at a higher rate than UV+ males, but there was no significant difference between the groups in total feeding rate. Females contributed less to nest defence relative to their mates when they were mated to UV− males, whereas the opposite was true for females mated to UV+ males. The behavioural responses did not translate into differences in measures of reproductive output. Our study suggests that male phenotypic appearance at the chick-feeding stage influences female decisions about level of parental effort.

Effects of intestinal nematodes during lactation: consequences for host morphology, physiology and offspring mass.

Sublethal parasites are often assumed to have no detrimental effects on their host. However, the sublethal intestinal nematode Heligmosomoides polygyrus affects both the morphology and the physiology of its laboratory mouse (Mus musculus) host and therefore has the potential to affect host life history. The objectives of the present study were to determine (1) whether lactating and non-lactating mice responded similarly to experimental infection with H. polygyrus and (2) whether the changes in morphology and physiology that occurred with parasite infection affected host reproductive performance. Parasitized mice had greater whole body mass as a result of greater lean mass compared with unparasitized mice. Parasitized mice had larger organs (spleen, stomach, cecum and small intestine) and a diminished rate of glucose transport by the small intestine compared with unparasitized mice. Lactating mice had larger organs (liver, kidney, spleen, heart, stomach, large intestine, cecum and small intestine), lean mass and whole body mass, but a similar rate of glucose transport compared with virgin mice. Resting metabolism increased with lactation but not with parasitism. Lactating and non-lactating mice responded similarly to parasite infection for most measured variables. Production of large litters was followed by production of small litters for parasitized but not unparasitized females. After adjusting for parity and litter size, parasitized mothers produced female pups that were 6% smaller at weaning than female pups from unparasitized mothers, but there was no effect of maternal parasite infection on mass at weaning for male pups. Other measures of reproductive output were not affected by parasite infection.

Low costs, high output: reproduction in an insular pit‐viper (Gloydius shedaoensis, Viperidae) from north‐eastern China

AbstractCurrent life‐history paradigms predict that an organism's total reproductive output is determined by its intrinsic level of ‘reproductive effort’ (RE), interacting with local resource availability. In turn, RE is driven by ‘costs of reproduction’. Within the total allocation, selective forces on offspring size ultimately determine both the number and size of offspring (because of a trade‐off between these two traits). Although patterns of life‐history variation are broadly consistent with this scenario, the evidence is weak: it is generally difficult to measure ‘costs’ or selective forces on offspring size. To test this paradigm, we need a study organism which differs in these respects from related taxa, so that we can unequivocally generate predictions about life‐history traits. A remarkable island population of Asian pit‐vipers Gloydius shedaoensis was studied for which (unlike mainland conspecifics) ‘costs of reproduction’ are low, food availability is high, and there is intense selection for large offspring size. Maternal body sizes and condition, and offspring numbers and sizes were quantified for 79 litters over 2 years. As predicted, the snakes display high reproductive output per female (relative to maternal body mass, litter mass is about twice as high as in related taxa), large offspring size (about three times the mass of related taxa) and a strong trade‐off between offspring size and litter size. Reproductive output was only weakly correlated with maternal body size, and output was adjusted mostly by manipulating litter size rather than offspring size. Reproductive output varied between years, but maternal body condition after parturition did not. Measures of reproductive output (such as the mass or energy content of the litter) bear little relationship to ‘costs of reproduction’ in this system.

Life histories of the Insectivora: the role of phylogeny, metabolism and sex differences

AbstractLife‐history data for 63 species from the mammalian order Insectivora have been collated from the literature. These data were analysed for covariation and for correlations with body mass, brain mass and mass‐specific resting metabolic rate. An independent contrasts method has been used to remove the effect of phylogeny. Due to uncertainties surrounding their evolutionary relationships, 22 different phylogenies of insectivores have been used as a basis for comparative analysis. The results show that several key correlations between life‐history variables are only significant when certain phylogenies are used, highlighting the problems of such analyses when the phylogeny used is inaccurate. After removing the effect of phylogeny, relatively few significant correlations remain. Insectivores that have a high body mass have relatively lower metabolic rates, longer lifespans and longer gestation lengths. There is some support for a fast–slow continuum in insectivore life‐history evolution: there are some significant positive correlations between measures of growth rates (e.g. gestation length and age at weaning) and lifespan, and some negative correlations between growth rates and measures of reproductive output. It is suggested that the seasonality of life of many insectivores may have played an influential role in the evolution of the group, in particular in delaying the onset of sexual maturity. There is little indication that brain size influences life‐history evolution in this order, but metabolism may play an important role. The energetic requirements of maintaining high metabolic rates in small mammals such as insectivores may be constraining life histories to a greater extent than occurs in larger mammals. This effect may have obscured the relationship between metabolic rate and life histories in wider inter‐order analyses. Finally, there is considerable evidence that sex differences play a large role in shaping insectivore evolution, and it is suggested that this factor must be considered more often in future studies of mammalian life histories in general.

Quantity or quality? Determinants of maternal reproductive success in tropical pythons (Liasis fuscus)

A female9s reproductive output (size and number of offspring) may say little about her reproductive success; the ‘quality’ of her progeny and the time that they are produced may be more important in this respect. We marked and released 1224 hatchling water pythons ( Liasis fuscus ) from 116 clutches of laboratory–incubated eggs, in a study site in tropical Australia. Clutches varied widely in the number of eggs, mean offspring sizes, the proportion of eggs that hatched, and recapture rates of offspring. Clutch size was not significantly correlated with the number of recaptured hatchlings in either year, nor was mean offspring size related to recapture probability. Instead, offspring recapture rates varied as a function of the time of hatching. Recapture rates were higher for hatchlings released in a year with high prey availability than in a year with few prey. In addition, recapture rates were higher for earlier–hatching clutches in the year with few prey. The other significant effect on recapture rates involved offspring viability: some clutches had a much higher proportion of surviving offspring than did others, and recapture rates were higher from clutches with higher hatching success (i.e. proportion of eggs hatching). Hence, the usual measures of reproductive output (clutch size and offspring size) offer only a poor index of a female9s reproductive success in this system.