Measures Of Reproductive Effort Research Articles

Reproductive effort in two viviparous species of blue-tailed skinks (Squamata: Scincidae: Plestiodon) from Mexico

The relative allocation of energy organisms devote to reproductive processes (aka reproductive effort) constitutes a central topic in life history theory. We document some aspects of the reproductive ecology and investment of 2 viviparous skinks of the genus Plestiodon from Mexico: an undescribed species previously assigned to P. brevirostris(Plestiodon sp., La Malinche, Tlaxcala, 2,700-3,000 m) and P. dugesii (2 populations, Mazamitla and Tapalpa, Jalisco; 2,400-2,500 m). We used relative litter mass (RLM) as a measure of reproductive effort and calculated a body condition index (BCI) as a proxy of the energy status of non-pregnant females, post-parturient females, and neonates. There were no differences in any of the reproductive characteristics between the 2 populations of P. dugesii. Both species lacked sexual size dimorphism, and female body size did not influence RLM, litter size nor litter mass. However, female BCI influenced RLM and, in P. dugesii, a larger litter size correlated with a lower BCI of neonates. Despite their overall similarities in reproductive investment, there seem to be differential selective pressures shaping offspring characteristics of these 2 lizard species.

Reproductive Ecology and Nesting Site Characteristics of Four-Toed Salamanders (Hemidactylium scutatum) in Natural and Constructed Upland-Embedded Wetlands on the Appalachian Plateau, Kentucky

Many forested freshwater wetlands have been altered or destroyed, and wetlands are constructed to offset loss. However, they do not always replace the function of natural wetlands. It is important to understand how features of the habitat differ between types of wetlands and whether constructed wetlands provide an adequate habitat for species adapted to natural wetlands. Our objectives were to measure the characteristics of Four-toed Salamanders’ nesting habitat and determine which factors contribute to the abundance of eggs and nests in natural and constructed upland-embedded wetlands within a ridgetop ecosystem in eastern Kentucky. We located and examined characteristics for 207 nests in twelve wetlands and measured variables at the nest level and at the wetland level. The best predictor of the number of eggs and number of nests was amount of moss at the wetland. These measures of reproductive effort were similar between types of wetlands, but the number of eggs per nest was higher in constructed wetlands and inversely related to amount of moss, highlighting a deficit in nesting habitat. Research of embryonic and larval survival is needed but based on data from other amphibian species in this system, we predict that the survival of Four-toed Salamanders’ larvae is low in constructed wetlands with permanent hydrology. Restoration of constructed wetlands should address the need for moss as nesting substrate and drying of the wetland to reduce the abundance and diversity of predators of larvae.

Young and mature males have similar energy expenditure during the rut in a trophy-hunted population of Mediterranean mouflon

In polygynous ungulates, males invest time and energy to reproductive activities during the rut and this involvement is expected to increase with age due to different mating tactics in young versus adult males. In contrast, mating period is expected to be less costly for females for which late gestation and lactation are the most energetically demanding periods. However, empirical supports of these hypotheses through direct measures of reproductive effort are still limited in ungulate species, particularly in males. In addition, this general pattern may be modified in populations facing selective harvesting on adult males, where young males may experience less competition to mate and invest more energy during the rut. We investigated these hypotheses by studying the age- and sex-specific variations of kidney fat reserves from pre- to post-rut periods in a trophy-hunted population of Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.), a polygynous dimorphic mountain ungulate. Females were found to build up energy from the pre-rut to the post-rut periods, most likely to face with the subsequent costs of gestation/lactation that occur few months later. Conversely, kidney fat mass strongly decreased similarly in both young and mature males, and with the same magnitude, suggesting a strong investment of males of all ages in this population. This might be related to the selective hunting pressure on mature males this population is facing with. This result supports the need for more empirical and comparative studies to better grasp the influence of trophy hunting on reproductive effort in male ungulates.

Variation in reproductive effort, genetic diversity and mating systems across Posidonia australis seagrass meadows in Western Australia.

Populations at the edges of their geographical range tend to have lower genetic diversity, smaller effective population sizes and limited connectivity relative to centre of range populations. Range edge populations are also likely to be better adapted to more extreme conditions for future survival and resilience in warming environments. However, they may also be most at risk of extinction from changing climate. We compare reproductive and genetic data of the temperate seagrass, Posidonia australis on the west coast of Australia. Measures of reproductive effort (flowering and fruit production and seed to ovule ratios) and estimates of genetic diversity and mating patterns (nuclear microsatellite DNA loci) were used to assess sexual reproduction in northern range edge (low latitude, elevated salinities, Shark Bay World Heritage Site) and centre of range (mid-latitude, oceanic salinity, Perth metropolitan waters) meadows in Western Australia. Flower and fruit production were highly variable among meadows and there was no significant relationship between seed to ovule ratio and clonal diversity. However, Shark Bay meadows were two orders of magnitude less fecund than those in Perth metropolitan waters. Shark Bay meadows were characterized by significantly lower levels of genetic diversity and a mixed mating system relative to meadows in Perth metropolitan waters, which had high genetic diversity and a completely outcrossed mating system. The combination of reproductive and genetic data showed overall lower sexual productivity in Shark Bay meadows relative to Perth metropolitan waters. The mixed mating system is likely driven by a combination of local environmental conditions and pollen limitation. These results indicate that seagrass restoration in Shark Bay may benefit from sourcing plant material from multiple reproductive meadows to increase outcrossed pollen availability and seed production for natural recruitment.

The cost of reproduction in women: Reproductive effort and oxidative stress in premenopausal and postmenopausal American women

Life history theory predicts a trade-off between female investment in reproduction and somatic maintenance, which can result in accelerated senescence. Oxidative stress has been shown to be a causal physiological mechanism for accelerated aging and a possible contributor to this trade-off. We aimed to test the hypothesis for the existence of significant associations between measures of reproductive effort and the level of oxidative stress biomarkers in premenopausal and postmenopausal American women. Serum samples and questionnaire data were collected from 63 premenopausal and postmenopausal women (mean age 53.4 years), controls in the Connecticut Thyroid Health Study, between May 2010 and December 2013. Samples were analyzed for levels of 8-OHdG and Cu/Zn-SOD using immunoassay method. Levels of oxidative damage (8-OHdG) but not oxidative defense (Cu/Zn-SOD) were negatively associated with parity and number of sons in premenopausal women (r = -0.52 for parity, r = -0.52 for number of sons, P < .01). Together, measures of reproductive effort, women's BMI, age, and menopausal status explained around 15% of variance in level of 8-OHdG. No association between reproductive effort characteristics and oxidative damage was found for postmenopausal women. We found no evidence of a trade-off between somatic maintenance as measured by 8-OHdG and reproductive effort in women from this American population. On the contrary, higher gravidity and parity in premenopausal women was associated with lower damage to cellular DNA caused by oxidative stress. These results highlight the importance of population variation and environmental conditions when testing the occurrence of life-history trade-offs.

Flower power: Floral and resource manipulations reveal how and why reproductive trade-offs occur for lowbush blueberry (Vaccinium angustifolium).

Plant reproductive trade‐offs are thought to be caused by resource limitations or other constraints, but more empirical support for these hypotheses would be welcome. Additionally, quantitative characterization of these trade‐offs, as well as consideration of whether they are linear, could yield additional insights. We expanded our flower removal research on lowbush blueberry (Vaccinium angustifolium) to explore the nature of and causes of its reproductive trade‐offs. We used fertilization, defoliation, positionally biased flower removal, and multiple flower removal levels to discern why reproductive trade‐offs occur in this taxon and to plot these trade‐offs along two continuous axes. We found evidence through defoliation that vegetative mass per stem may trade off with reproductive effort in lowbush blueberry because the two traits compete for limited carbon. Also, several traits including ripe fruit production per reproductive node and fruit titratable acidity may be “sink‐limited”—they decline with increasing reproductive effort because average reproductive structure quality declines. We found no evidence that reproductive trade‐offs were caused by nitrogen limitation. Use of reproductive nodes remaining per stem as a measure of reproductive effort indicated steeper trade‐offs than use of the proportion of nodes remaining. For five of six traits, we found evidence that the trade‐off could be concave down or up instead of strictly linear. Synthesis. To date, studies have aimed primarily at identifying plant reproductive trade‐offs. However, understanding how and why these trade‐offs occur represent the exciting and necessary next steps for this line of inquiry.

The challenges of asymmetric mating - the influence of male and female size on the reproductive output of Acanthochondria cornuta (Chondracanthidae).

The reproductive strategy of Acanthochondria cornuta, a parasitic copepod with dwarf, hyperparasitic males, is described in detail. The potential impact of male parasitism on the reproductive output was evaluated by determining the size of each sex and the female's fecundity, egg size and total reproductive effort for each pair/trio throughout the four seasons of the year. Marked seasonal differences were observed in female size and reproductive output, suggesting two distinct generations, but no differences were observed for male size. No statistically significant correlations were observed between male size and any measure of reproductive effort, but females with larger males had lower fecundity. A trade-off between egg number and egg size was recorded. Overall, the reproductive effort in A. cornuta seems to be determined mostly by female size, and larger females do not hold smaller males.

Milk immunity and reproductive status among Ariaal women of northern Kenya

Background: The immune factors in human milk protect infants from infection and promote immune development. Evidence suggests that the production of milk-specific immunoproteins is energetically costly, making them a form of maternal investment in offspring health that is subject to life history trade-offs.Aim: This research tests the relationship between measures of reproductive effort and the production of milk immunoglobulin A (IgA) among Ariaal women, a settled northern Kenyan pastoralist population that experiences nutritional and disease stress.Subjects and methods: Two hundred and forty-three lactating Ariaal women participated in a questionnaire, anthropometric measurement and milk collection. Milk IgA was analysed using ELISA.Results: There was a significant U-shaped relationship between post-partum months and milk IgA, reflecting decreasing investment in the current offspring over the early post-partum period and subsequent recovery of maternal energy status near the end. There was also a significant inverse U-shaped relationship between milk IgA and parity, with high parity women showing a drop in milk IgA. In contrast, anthropometric measures of energy status were not associated with the production of milk IgA.Conclusion: This research shows that patterns of reproductive investment can be demonstrated in milk IgA in the absence of measured energy changes.

Egg number–egg size: an important trade-off in parasite life history strategies

Parasites produce from just a few to many eggs of variable size, but our understanding of the factors driving variation in these two life history traits at the intraspecific level is still very fragmentary. This study evaluates the importance of performing multilevel analyses on egg number and egg size, while characterising parasite life history strategies. A total of 120 ovigerous females of Octopicola superba (Copepoda: Octopicolidae) (one sample (n=30) per season) were characterised with respect to different body dimensions (total length; genital somite length) and measures of reproductive effort (fecundity; mean egg diameter; total reproductive effort; mean egg sac length). While endoparasites are suggested to follow both an r- and K-strategy simultaneously, the evidence found in this and other studies suggests that environmental conditions force ectoparasites into one of the two alternatives. The positive and negative skewness of the distributions of fecundity and mean egg diameter, respectively, suggest that O. superba is mainly a K-strategist (i.e. produces a relatively small number of large, well provisioned eggs). Significant sample differences were recorded concomitantly for all body dimensions and measures of reproductive effort, while a general linear model detected a significant influence of season*parasite total length in both egg number and size. This evidence suggests adaptive phenotypic plasticity in body dimensions and size-mediated changes in egg production. Seasonal changes in partitioning of resources between egg number and size resulted in significant differences in egg sac length but not in total reproductive effort. Evidence for a trade-off between egg number and size was found while controlling for a potential confounding effect of parasite total length. However, this trade-off became apparent only at high fecundity levels, suggesting a state of physiological exhaustion.

Effects of radiotransmitters and breeding effort on harvest and survival rates of female mallards

AbstractThere has been widespread speculation that breeding activity places adult female mallards (Anas platyrhynchos) at heightened risk of harvest due to insufficient time to complete the wing molt or recover body condition prior to onset of hunting and autumn migration. We tested the hypotheses that breeding females have higher rates of harvest and reduced prospects for survival by estimating band recovery rates (f) and annual survival (S) in relation to individual measures of breeding effort for 3,055 adult female mallards that had been banded and radiomarked during the breeding season in the Prairie‐Parkland Region of Canada, 1993–2000. Birds that had been marked with external prong‐and‐suture transmitters had lower estimated survival rates (S = 0.518, SE = 0.118) than birds marked with implant transmitters (S = 0.731, SE = 0.061), but rates for birds marked with implant transmitters did not differ from expectations based on other studies for females marked only with legbands. After excluding external transmitters, we found that recovery rates were unaffected by any measures of reproductive effort, but annual survival was lower for females that tended broods to 60 days of age (S = 0.474 ± 0.115) versus females that never hatched a nest (S = 0.654 ± 0.042). Telemetry data indicated that brood‐rearing females experienced extremely low mortality, so reduced survival of females that raised broods presumably resulted from insufficient time to molt and prepare for autumn migration. Management efforts that promote successful early nesting attempts may also improve adult female survival by allowing females more time to molt and prepare for autumn migration, whereas hunting regulations designed to protect late‐breeding females may prove ineffective if such individuals have higher natural mortality. © 2012 The Wildlife Society.

The trade-off of reproduction and survival in slow-breeding seabirds

A trade-off between reproduction and survival is one of the most consistent empirical aspects of life-history diversification. One explanation for this interspecific pattern is evolved differences in the balance of allocation to reproduction versus individual maintenance and survival. The same pattern is expected, however, simply as a result of differences among species in body size. We tested these alternatives using original data from 44 species of albatrosses and petrels, long-lived seabirds that breed very slowly. After application of regression techniques to remove the effects of body size and phylogeny, annual reproduction and survival exhibited a significant trade-off. Our measures of reproductive effort also exhibited significant trade-offs with age at maturity, the latter strongly associated with survival. Feeding rate of chicks, success at fledging chicks, and annual chick production were also significantly associated. In conclusion, after removing the effects of body size, we found a significant trade-off of reproduction and survival, in spite of the fact that these long-lived birds lay only one egg at a time. Our examination of the pattern among life-history traits of these slow breeders and their pelagic feeding ecology provide support for the evolutionary explanation of a trade-off of reproduction and survival.

Patterns of reproductive effort in male ungulates

AbstractIn ungulates, males and females have contrasting life histories, as usually only the females raise the young. How reproductive effort in males varies with individual level and population level characteristics has received little attention in the literature. Using published information on direct (weight loss during the rut) and indirect (rut‐related changes in activity budgets, fighting frequency, etc.) measures of reproductive effort, we tested whether effort in males increased with (H1) increasing age, (H2) increasing body size, (H3) decreasing population density, (H4) increasingly female‐biased sex ratio and with a younger male age structure. Consistent with H1, reproductive effort was consistently higher in prime‐aged than in younger males in a large number of studies. Among younger males, sub‐adult males had an equal or higher effort than yearling males. Prime‐aged males had more typical rutting behaviour (e.g. roaring, tending, fighting and chasing frequencies) and they often lowered their intake of forage during the rut. However, reproductive effort usually declined for very old age classes. Reproductive effort increased with size (H2) also after accounting for age. Data on effort vs (H3) density and (H4) sex ratio/male age structure were inconclusive. Clearly, far more studies relating effort to population characteristics are needed before the rutting ecology of male ungulates can be understood.

Dominance, reproduction and survival in banded mongooses: towards an egalitarian social system?

The banded mongoose, Mungos mungo, is a social species that forms multimale and multifemale family groups. Earlier studies suggest these family groups are relatively egalitarian with small differences in reproductive opportunities among individuals of different rank. In contrast, previous studies of other social mongooses have focused on species with more despotic control of reproduction (meerkats, Suricata suricatta, dwarf mongooses, Helogale parvula). In these species, the distribution of reproductive opportunities amongst individuals of different rank has met the predictions of reproductive skew theory: dominant individuals accrue greater reproductive benefits than subordinates, with subordinates breeding less often than dominants. In this paper we test how well two predictions of reproductive skew theory explain variance in measures of reproductive effort, and its correlates, in a wild population of banded mongooses in Queen Elizabeth National Park, Uganda. We measure dominance rank in males and females, and we investigate whether individuals of higher social rank accrue greater benefits than subordinates in terms of survival and reproduction. Banded mongoose dominance hierarchies showed linearity, but low reproductive skew. Rank was not significantly correlated with age. Furthermore, there were only small effects of dominance rank on nutritional levels, and no effects on reproduction and survival, suggesting that banded mongoose societies are indeed relatively egalitarian. No evidence of reproductive suppression was found and other forms of reproductive control were not observed. However, we do not exclude the possibility of increased reproductive competition in circumstances of higher ecological constraints. These findings show that reproductive skew theory is equally useful in explaining variation in reproduction in societies with low reproductive skew, as it is in explaining the allocation of reproductive effort in despotic social systems.

Age-Related Changes in Efficiency among Breeding Common Terns Sterna hirundo: Measurement of Energy Expenditure Using Doubly-Labelled Water

We used doubly-labelled water to measure field metabolic rates of breeding Common Terns Sterna hirundo, and hence to investigate differences in reproductive efficiency among birds of different ages. Field metabolic rates, activity patterns, changes in body mass, chick provisioning rates, and chick growth rates were measured for 14 males of known age (6-24 yr) during a 48-h period immediately after hatching of the first chick, when males provide most of the food. Males expended energy at high rates (3.3-6.3 x estimated basal metabolic rates). We found no significant relationship between male age and energy expenditure. Some aspects of male performance (feeding rates and food provisioning rates) were age-related due to changes in efficiency. Efficiency in the use of time and energy was low in the youngest breeding males, increased thereafter to peak at about 12 years of age, but appeared to decline again amongst the oldest breeding males. Changes in body mass and measures of activity were not correlated with energy expenditure and hence were not appropriate measures of reproductive effort.

Fecundity, reproductive effort, and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 μg egg−1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.

The reproductive performance of black-billed magpies: is it related to mate choice?

The influence of age and dominance on measures of reproductive effort were investigated in 26 breeding pairs of captive black-billed magpies, Pica pica. Pairs with adult males constructed nests faster, initiated clutches earlier, and produced larger clutches than pairs with juvenile males. Age of females did not influence these variables. The results suggest that the reproductive output of males varies with age more than that of females. Thus when choosing a mate, females have a wider range of parental quality to choose from than do males. This may explain why females are more discriminant than males in mate choice. Paternal quality of breeding males was tested experimentally. During incubation, adult males searched longer for food, approached a potential predator more closely, and attacked a territory intruder more often than did juvenile males. This suggests that adult males invest more in parental care than juvenile males. It may also be a reason for female preference of adult males. There were no differences in the above variables between dominance classes of males in either age group. However, since competition among individuals was excluded by the captive situation, the significance of dominance status was probably minimized.

Reproductive Energetics of Two Tropical Bird Species

Abstract Daily energy expenditure (DEE) during breeding was studied in Pacific Swallows (Hirundo tahitica) and Blue-throated Bee-eaters (Merops viridis) in Malaysia. DEE was measured directly by the doubly labelled water (D218O) technique and indirectly by TAL (time-activity-laboratory) methods during the time adults were feeding their young at the nest. DEE was 76.6 kJ/day in the Pacific Swallow and 77.4 kJ/day in the larger Blue-throated Bee-eater (D218O results). The relatively low DEE, compared to temperate-zone insectivores that also feed in flight, was attributed to the action of proximate factors, namely a more favorable thermal environment and shorter days (which results in less daytime activity). In bee-eaters, partial use of a low-cost foraging technique also contributed to their lower DEE. The suitability of DEE as a measure of reproductive effort is discussed.

Reproductive Tactics and Female Body Size in Butler's Garter Snake, Thamnophis butleri

Reproductive strategies of snakes are complicated by the fact that these animals have indeterminate growth. Larger females can produce more offspring, but whether female size affects the size of individual offspring has not been carefully examined. In the viviparous garter snake, Thamnophis butleri, measures of neonate size (snout-vent length, mass or mass/SVL) were posi- tively correlated with measures of female size (length, mass, or mass/SVL) and negatively correlated to clutch size. Relative clutch mass (RCM: total clutch mass/female mass, an operational measure of reproductive effort) did not change with increase in female size. However, RCM per progeny decreased with female size, which would allow larger females to produce clutches of larger numbers with less effect on neonate size.

Intraseasonal Reproductive Costs for the House Sparrow (Passer domesticus)

Abstract House Sparrows (Passer domesticus) near Calgary, Alberta begin breeding in early spring and continue through to late summer. High productivity from previous broods is negatively correlated with fledgling production from second and third broods. Although fat reserves may limit the ability of females to raise young, there is no concomitant drop in clutch size or in the probability of renesting. Pairs that fledge many young in a year space fledgling production evenly over the breeding season but are most productive in mid-season. The interval between fledging and the initiation of the next clutch increases with the number fledged. This delay, an indication of the physiological strain involved in rearing young, is greater for later broods and for females nesting in trees. Measures of reproductive effort (clutch size, number fledged, length of the nestling period) vary seasonally but give no indication of peaking for last broods. Thus, reproductive effort is not adjusted to parallel changes in the probability of surviving to the next breeding attempt.

Lizard Reproductive Effort: Caloric Estimates and Comments on Its Evolution

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.