A model for estimating the minimum number of offspring to sample in studies of reproductive success

Molecular parentage permits studies of selection and evolution in fecund species with cryptic mating systems, such as fish, amphibians, and insects. However, there exists no method for estimating the number of offspring that must be assigned parentage to achieve robust estimates of reproductive success when only a fraction of offspring can be sampled. We constructed a 2-stage model that first estimated the mean (μ) and variance (v) in reproductive success from published studies on salmonid fishes and then sampled offspring from reproductive success distributions simulated from the μ and v estimates. Results provided strong support for modeling salmonid reproductive success via the negative binomial distribution and suggested that few offspring samples are needed to reject the null hypothesis of uniform offspring production. However, the sampled reproductive success distributions deviated significantly (χ(2) goodness-of-fit test p value < 0.05) from the known simulated reproductive success distribution at rates often >0.05 and as high as 0.24, even when hundreds of offspring were assigned parentage. In general, reproductive success patterns were less accurate when offspring were sampled from cohorts with larger numbers of parents and greater variance in reproductive success. Our model can be reparameterized with data from other species and will aid researchers in planning reproductive success studies by providing explicit sampling targets required to accurately assess reproductive success.     

Assessing the contributions of multiple interacting traits to plant reproductive success: environmental dependence

The reproductive success of sibling cocklebur plants (Compositae: Xanthium strumarium) was monitored after growth at different levels of availability of water and nutrient resources. Variation in reproductive success among individual plants was related to physiological, structural, and phenological characteristics. Reproductive success increased with increased availability of resources, but the relative contribution of particular traits to reproductive success varied with resource availability. Allocation of biomass to different vegetative tissues, time to seedling emergence, degree of branching, transpiration rates, water use efficiency, the rate of decline in height growth after seedling emergence and final plant size all varied significantly with resource availability. However, the changes in each of these phenotypic traits across three garden environments did not always correlate with reproductive success. The shifts across environments in the apparent importance of somatic traits for reproductive success were attributed to plastic changes in the traits but also to changes in the phenotypic correlations of the traits with reproductive success.     

Group size and composition influence male and female reproductive success in black howler monkeys (Alouatta pigra)

It has been argued that grouping patterns might influence the reproductive performance of individuals. Increasing group size results in greater travel costs and competition over depletable food resources, which could lead to reduced individual reproductive success. However, in groups with an increasing number of males, female reproductive success is predicted to augment because larger male groups might better protect immatures from infanticidal attacks. In contrast, male reproductive success is predicted to decrease with number of males in a group because fertilization cannot be shared between males. In this paper, we test these predictions on the Mesoamerican black howler monkey (Alouatta pigra) with data on group size and composition for 120 groups from eight populations of black howler monkeys existing in eight protected forests in Mexico and Guatemala. Male and female reproductive success were calculated as a deviation of the observed number of infants (or immatures) from the expected number of infants (or immatures), relative to the number of males and females in a group. Results indicate that both male and female reproductive success decreased with group size. Male reproductive success decreased with an increasing number of males in a group and with increasing proportion of males relative to females in a group. Decreased female reproductive success was associated with increasing number of females in a group, and female reproductive success had a tendency to increase with increasing number of males in a group. These results suggest that in black howler monkeys, living in larger groups might negatively affect the reproductive success of each member. Our findings are similar to those reported for a population of a sister species, Alouatta palliata, living in larger groups.     

Determinants of reproductive success in female Columbian ground squirrels

Summary We studied the reproductive success of female Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta for nine years. We defined reproductive success as the number of offspring surviving their first hibernation, classified as yearlings. The number of weaned juveniles explained one third of the variance in number of yearlings at emergence from their first hibernation the following spring, and much of the variance in individual reproductive success originated after weaning. Weight of adult females at emergence from hibernation was correlated with annual reproductive success. The mother's survival beyond weaning and the subsequent winter's snow accumulation had positive effects on annual reproductive success, whereas population density and summer temperature had negative effects. We found no effects on annual reproductive success of date of litter emergence, weight at emergence as a yearling, presence or absence of adult kin, distance from the natal site, location within the study area, winter temperature or summer precipitation. Age of first breeding did not affect lifetime reproductive success, which ranged from 0 to 19 yearlings produced over a lifetime. The greatest source of variation in lifetime reproductive success for females surviving to breeding age was offspring survival, followed by reproductive lifespan.     

Longevity in cheetahs: the key to success?

An understanding of the factors governing reproductive success has fundamental implications for population demography, conservation, selection and adaptation. Although a consistent positive correlation between lifetime reproductive success and longevity has been reported for many iteroparous organisms, few studies have explored how longevity influences annual individual performance. In this study we show (1) that longevity and lifetime reproductive success are positively but not linearly correlated, (2) that short-lived individuals have higher annual reproductive success, (3) that the generally lower success of the last breeding occasion increased with females' longevity, and (4) that long-lived females have higher chances of rearing long-lived females. We suggest that experience and the increase in the number of reproductive events with longevity are key processes leading to a strong correlation between (1) lifetime reproductive success and longevity and (2) mother and daughter longevities. Our results demonstrate the importance of long term studies that follow multiple generations in gaining a full understanding of the factors affecting reproductive success.     

Effects of extra-pair and within-pair reproductive success on the opportunity for selection in birds

The number of mates, their fecundity, and the number of extra-pairfertilizations can all affect male reproductive success in biparentalspecies. Extra-pair mating in birds has been of particular interest,because it could generate strong levels of sexual selectioneven when a species is socially monogamous. We examined howextra-pair fertilizations affect the opportunity for selectionin the sexually dimorphic common yellowthroat (Geothlypis trichas)and the sexually monomorphic house wren (Troglodytes aedon).We were able to identify sires for at least 95% of all nestlings,and, thus, we were able to make a nearly complete accountingof male reproductive success. Although extra-pair fertilizationswere common in yellowthroats (26% of young) it contributed little(21%) to the total variance in male reproductive success. Mostof the variance in reproductive success (58%) was attributableto the male's within-pair success, which was influenced primarilyby the number of young produced by each mate and the proportionof within-pair young sired. Despite a moderate level of extra-pairfertilizations (10% of young) in house wrens, almost all ofthe variance in male reproductive success (97%) was attributableto within-pair success, particularly the number of social mates.Although extra-pair fertilizations generally increase the variancein male reproductive success, within-pair reproductive successmay be the major source of variation in male reproductive success.Thus, sexual dimorphism in monogamous birds may be influencedmore by the number of mates and their fecundity than by extra-pairmatings.     

Wealth, Status, and Reproductive Success among the Mukogodo of Kenya

The evolutionary biological hypothesis that culturally defined values and goals are proximate means of enhancing reproductive success is tested on data from the Mukogodo, a small group of Maa-speaking pastoralists in north-central Kenya who value the accumulation of livestock. The results support the prediction that, at least among males, livestock wealth should correlate with reproductive success. This correlation appears to be due mainly to greater polygyny among wealthier men. Lower age at first marriage among wealthier men may also contribute to the correlation between livestock wealth and reproductive success. The association between livestock wealth and reproductive success does not appear to be due to the productivity of wives and children, to bridewealths obtained when daughters marry, or to the effects of wealth on the reproductive success of men's wives.     

Validity of an estimator of reproductive success

Lifetime reproductive success is a major component of individual fitness and a central dependent variable for the study of natural selection. For long-lived animals, such as apes or baboons, assessment of lifetime reproductive success requires observations of identified individuals in continuous, long-term studies from which it is difficult and often impossible to obtain an adequate sample of necessary reproductive and survival data. This situation can be alleviated by the availability of a valid measure that uses incomplete reproductive histories to estimate the lifetime reproductive success of individuals. The validity of one such estimator was tested by determining if, after 10.5 years of studying free-ranging female baboons, it predicted lifetime reproductive success obtained from full reproductive histories after 21.5 years. Validity was evaluated for seven criteria of success, ranging from the number of a female's live births to the number of her offspring that reached the age of 72 months. Moderate to good prediction of lifetime reproductive success by the estimator was found for criteria of offspring living to 36 months or more. After 10.5 years, complete reproductive life spans were available for only eight females. Using the estimator, analytic potential, via sample representativeness and size, was improved at 10.5 years by an increase from a sample of eight to between 34 and 62, depending upon the criterion used, and at 21.5 years from 39 to 70. With a valid estimator, the opportunity to study lifetime reproductive success of a long-lived species is substantially improved without having to depend upon rarely available, uninterrupted data collection for 20–60 years. Am. J. Primatol. 44:137–145, 1998. © 1998 Wiley-Liss, Inc.     

Male reproductive success in plateau pikas (Ochotona curzoniae): A microsatellite analysis

In many social species, competition and cooperation between group members may lead to a large variance in reproductive success among individuals, especially for adult male. From April to August 2002, we studied the adult male reproductive success of plateau pikas in Haibei Alpine Meadow Ecosystem Research Station, Chinese Academy of Science, using microsatellite analysis of paternity, mark-recapture and behavioral observations. Our result indicated that the reproductive success of adult males had a large variance. Its average was 6 individuals and range was from 0 to 13 individuals. One-third of males sired 63.22% offspring. There was a hierarchy system in polygynandrous families. Although the reproductive success of dominant males was higher than that of subordinate males, subordinate males still play an important role in the reproductive success of the population.     

VARIATION IN MALE REPRODUCTIVE INVESTMENT AND MALE REPRODUCTIVE SUCCESS IN WHITE SPRUCE

An experimental population composed of ramets of white spruce clones was studied to determine the influence of different levels of clonal male reproductive investment on clonal male reproductive success, where the male reproductive success of different clones in the population was defined as the proportion of the seed crop sired by each clone. We present a multilocus estimation procedure which provides unbiased estimates of the proportion of seed sired by each parental genotypic class from pollen gamete frequency data, whenever gametic segregation frequencies are known. Significant linear and quadratic components were found for the relationship between the number of male cones produced and the estimated proportion of the seed crop sired. A clone that produced an exceptionally large number of male cones, however, did not have the greatest male reproductive success. In general, the results support an assumption made in theoretical models of selection on mating system modifiers regarding the relationship between male investment and male reproductive success. They also support the hypothesis that male reproductive success in wind-pollinated species continues to increase substantially with increasing male reproductive investment.     

Factors affecting the reproductive success of dominant male meerkats

Identifying traits that affect the reproductive success of individuals is fundamental for our understanding of evolutionary processes. In cooperative breeders, a dominant male typically restricts mating access to the dominant female for extended periods, resulting in pronounced variation in reproductive success among males. This may result in strong selection for traits that increase the likelihood of dominance acquisition, dominance retention and reproductive rates while dominant. However, despite considerable research on reproductive skew, few studies have explored the factors that influence these three processes among males in cooperative species. Here we use genetic, behavioural and demographic data to investigate the factors affecting reproductive success in dominant male meerkats (Suricata suricatta). Our data show that dominant males sire the majority of all offspring surviving to 1 year. A male's likelihood of becoming dominant is strongly influenced by age, but not by weight. Tenure length and reproductive rate, both important components of dominant male reproductive success, are largely affected by group size and composition, rather than individual traits. Dominant males in large groups have longer tenures, but after this effect is controlled, male tenure length also correlates negatively to the number of adult females in the group. Male reproductive rate also declines as the number of intra- and extra-group competitors increases. As the time spent in the dominant position and reproductive rate while dominant explain > 80% of the total variance in reproductive success, group composition thus has major implications for male reproductive success.     

Condition dependence of male and female reproductive success: insights from a simultaneous hermaphrodite

Sexually selected traits are predicted to show condition dependence by capturing the genetic quality of its bearer. In separate‐sexed organisms, this will ultimately translate into condition dependence of reproductive success of the sex that experiences sexual selection, which is typically the male. Such condition dependence of reproductive success is predicted to be higher in males than females under conditions promoting intense sexual selection. For simultaneous hermaphrodites, however, sex allocation theory predicts that individuals in poor condition channel relatively more resources into the male sex function at the expense of the female function. Thus, male reproductive success is expected to be less condition dependent than female reproductive success. We subjected individuals of the simultaneously hermaphroditic snail Physa acuta to two feeding treatments to test for condition dependence of male and female reproductive success under varying levels of male–male competition. Condition dependence was found for female, but not for male, reproductive success, meaning that selection on condition is relatively stronger through the female sex function. This effect was consistent over both male–male competition treatments. Decomposition of male and female reproductive performance revealed that individuals in poor condition copulated more in their male role, indicating an increased male allocation to mate acquisition. These findings suggest that sex‐specific condition dependence of reproductive success is at least partially driven by condition‐dependent sex allocation. We discuss the implications of condition‐dependent sex allocation for the evolution of sexually selected traits in simultaneous hermaphrodites.     

Plant size,flowering synchrony and edge effects: What,how and where they affect the reproductive success of a Neotropical tree species

Plant reproductive success is supposedly influenced by phenology and individual size, which may be modified under edge effects. We tested if reproductive success, estimated by fruit set, in Senefeldera verticillata (Euphorbiaceae) is related to flowering synchrony and tree size, including plant height and circumference at breast height. The study was carried out in the interior and in edges of clearings for gas pipelines and electric lines of a lowland rainforest in south‐eastern Brazil. Monthly observations were performed during one reproductive season, of 19 individuals that grew at edges of electric lines and gas pipelines and at forest interior. Reproductive success was significantly higher at forest interior than at gas pipeline area; there was no significant difference between gas pipeline and electric line areas or between forest interior and electric line area. In the forest edges, only plant height was positively related to plant reproductive success. This is probably related to crown exposure to sunlight, which enhances flower production. At forest interior, reproductive success was positively influenced by the synchrony of flowering activity among neighbouring individuals. In contrast, flowering synchrony based on phenophase intensity negatively impacted reproductive success. Senefeldera verticillata shows temporal dioecy and is mainly pollinated by small social bees, and the high degree of flowering synchrony at low intensity may increase the number of mating partners and therefore enhance its reproductive success. Inside the forest fragments, individuals with thicker trunks showed lower reproductive success, which may be related to a loss of reproductive capacity of older individuals. Our results evidenced the complexity of responses experienced by tropical plants subjected to forest fragmentation because of linear clearings.     

Marker-assisted determination of the relationship between body size and reproductive success and consequences for evaluation of adaptive life histories

We tested for differences in the predicted optimal ages at first maturity in brook charr ( Salvelinus fontinalis ) in Freshwater River, Newfoundland, when life-history data were collated based on the marker-assisted estimation of the relationship between body size and reproductive success rather than using fecundity as a surrogate for reproductive success. Jointly with capture–recapture data to estimate the growth and survival costs of reproduction, we found that weak relationships between body size and reproductive success generate selection against delayed maturation. This finding would not have held for females if the relationship between body size and fecundity had been used as a surrogate for the relationship between body size and reproductive success. This shows that predictions of optimal life histories can be qualitatively changed when using molecular markers to directly evaluate age- and/or size-specific effects of body size on reproductive success.     

Physical attractiveness influences reproductive success of modern men

Theory suggests that reproductive success is positively associated with an individual’s genetic quality. However, the association between physical attractiveness and reproductive success (i.e., number of offspring) in modern humans remains less clear. Here we examined associations between men’s reproductive success and physical attractiveness from retrospective data obtained from married, divorced, and single samples of Slovakian men. As predicted, facially more attractive and taller men were more likely to engage in marriage. In turn, married men had higher reproductive success than single men. Even when men’s marital status was considered, facially more attractive men had higher reproductive success than their less attractive counterparts. This supports the importance of physical attractiveness in sexual selection in modern humans.     

The association between rank,mating effort,and reproductive success in male Barbary macaques (Macaca sylvanus)

The association between social rank, mating effort, and reproductive success of male Barbary macaques (Macaca sylvanus) has been evaluated by longterm behavioral observations and subsequent paternity determination via oligonucleotide DNA fingerprinting in a large semifreeranging group. All offspring born between 1985 and 1988 that survived to at least 1 year of age (n=75) were available for paternity testing. The exclusion of all but one of the potential fathers from paternity was possible in 70 cases (93%). Mating activities were recorded using ad lib. and focal female sampling techniques. The analysis of male mating effort was restricted to the most likely days of conception. Male rank correlated significantly with male mating success in all four breeding seasons and with male reproductive success in three of the four seasons. Mating success and reproductive success also showed a significant correlation, with the exception of one breeding season, in which the proportion of males per fertilizable female was especially high. Poor mating success was almost always associated with poor reproductive success, while good mating success was less predictive for a male's actual reproductive success. This was apparently a consequence of sperm competition, resulting from the promiscuous mating system. Male mating success is not necessarily an unreliable indicator for reproductive success, provided that sufficient sample sizes are available and that conception periods can be determined. Sperm competition and other factors may weaken the association, however.     

Accurate Alternative Measurements for Female Lifetime Reproductive Success in Drosophila melanogaster

Fitness is an individual’s ability to survive and reproduce, and is an important concept in evolutionary biology. However, accurately measuring fitness is often difficult, and appropriate fitness surrogates need to be identified. Lifetime reproductive success, the total progeny an organism can produce in their lifetime, is thought to be a suitable proxy for fitness, but the measure of an organism’s reproductive output across a lifetime can be difficult or impossible to obtain. Here we demonstrate that the short-term measure of reproductive success across five days provides a reasonable prediction of an individual''s total lifetime reproductive success in Drosophila melanogaster. However, the lifetime reproductive success of a female that has only mated once is not correlated to the lifetime reproductive success of a female that is allowed to mate multiple times, demonstrating that these measures should not serve as surrogates nor be used to make inferences about one another.     

From endosymbionts to host communities: factors determining the reproductive success of arthropod vectors

Elucidating the factors determining reproductive success has challenged scientists since Darwin, but the exact pathways that shape the evolution of life history traits by connecting extrinsic (e.g., landscape structure) and intrinsic (e.g., female’s age and endosymbionts) factors and reproductive success have rarely been studied. Here we collected female fleas from wild rodents in plots differing in their densities and proportions of the most dominant rodent species. We then combined path analysis and model selection approaches to explore the network of effects, ranging from micro to macroscales, determining the reproductive success of these fleas. Our results suggest that female reproductive success is directly and positively associated with their infection by Mycoplasma bacteria and their own body mass, and with the rodent species size and total density. In addition, we found evidence for indirect effects of rodent sex and rodent community diversity on female reproductive success. These results highlight the importance of exploring interrelated factors across organization scales while studying the reproductive success of wild organisms, and they have implications for the control of vector-borne diseases.     

Cues to fertility: perceived attractiveness and facial shape predict reproductive success

Attractive facial features in women are assumed to signal fertility, but whether facial attractiveness predicts reproductive success in women is still a matter of debate. We investigated the association between facial attractiveness at young adulthood and reproductive life history—number of children and pregnancies—in women of a rural community. For the analysis of reproductive success, we divided the sample into women who used contraceptives and women who did not. Introducing two-dimensional geometric morphometric methodology, we analysed which specific characteristics in facial shape drive the assessment of attractiveness and covary with lifetime reproductive success. A set of 93 (semi)landmarks was digitized as two-dimensional coordinates in postmenopausal faces. We calculated the degree of fluctuating asymmetry and regressed facial shape on facial attractiveness at youth and reproductive success. Among women who never used hormonal contraceptives, we found attractive women to have more biological offspring than less attractive women. These findings are not affected by sociodemographic variables. Postmenopausal faces corresponding to high reproductive success show more feminine features—facial characteristics previously assumed to be honest cues to fertility. Our findings support the notion that facial attractiveness at the age of mate choice predicts reproductive success and that facial attractiveness is based on facial characteristics, which seem to remain stable until postmenopausal age.     

Group Structure,Nest Size and Reproductive Success in the Cooperatively Breeding Cichlid Julidochromis ornatus: A Correlation Study

The effect of group size on reproductive success has long been studied in cooperatively breeding species, as it might provide an adaptive explanation for group‐living in social species. Numerous studies have shown positive effects of subordinates on reproductive success (‘helper effect’), but these studies have also revealed the importance of controlling statistically, or experimentally, for the effect of other factors that might affect reproductive success. Here, we first examine the relationships between group size, body size of group members and nest size in the cooperatively breeding cichlid Julidochromis ornatus, in which unrelated helpers frequently participate in reproduction and their breeding nests inside rock crevices may be crucial for reproduction and survival of all group members. Then, we subsequently investigate the relationship between group size and reproductive success, while controlling for these factors. The results showed that group size was significantly related to body size of group members rather than nest size; and larger breeders had larger helpers. It was found that group size significantly increased group reproductive output. More importantly, reproductive success of male breeders did not depend on the presence of mature helpers, whereas female reproductive success increased when two males assisted her and tended to decrease when two females bred cooperatively. We conclude that breeding groups of J. ornatus have size hierarchical societies that relate to group size, and group composition of genetically unrelated and co‐breeding members affects their reproductive success.