Relative Reproductive Success Research Articles

Ontogeny of social skills: social complexity improves mating and competitive strategies in male brown-headed cowbirds

Social individuals require a suite of skills to outcompete groupmates and gain reproductive advantage. Recently we showed that adult male cowbirds (Molothrus ater) exposed to enhanced social-learning opportunities (living in ‘dynamic’ social conditions) became more reproductively successful than males living in ‘stable’ conditions (White et al. 2010a, Animal Behaviour, 79, 385–390). The experiment left open important questions about how subjects turned the experiences they gained in the dynamic condition into a reproductive advantage. Here, 1 year later, we examined the within-individual plasticity of the effect by exposing some of the same subjects to opposite social conditions, followed by another opportunity to measure their relative reproductive success. Again, dynamic-condition birds outcompeted stable-condition birds, reversing individuals’ performances from the year before. We investigated the constituents of the dynamic-condition birds’ advantage, and found that they succeeded by using aggression to increase dominance rank, and by focusing courtship singing on forming consortships with particular females. Stable-condition birds adhered to no discernible strategy. This work affirms that adult experience can modify reproductive success, and suggests a mechanism for that modification: individuals that experience a wider array of social environments may improve their ‘behavioural control’, the ability to modulate behaviour to suit the competitive context. Natural selection may act on groups of traits that facilitate the development of behavioural control, including faculties for expressing or inhibiting behaviours and traits that regulate individuals’ exposure and attention to social experience.

Seaside sparrow reproductive success in relation to prescribed fire

AbstractIn North American tidal marshes, prescribed burning has been used to manage waterfowl, furbearers, invasive plants, and fuels, but its effects on non‐target species, such as marsh birds, are relatively unknown, particularly in the mid‐Atlantic region. To address this informational need, we studied seaside sparrows (Ammodramus maritimus) in Dorchester County, Maryland, where prescribed marsh burning has been conducted since at least the 1930s. We compared the effects of 4 fire treatments (<1 yr since burn, 1–2 yr since burn, 3–4 yr since burn, and ≥5 yr since burn) on seaside sparrow density and reproductive output, and examined the impact of fire treatment, nest‐site characteristics, and weather on nest survival from 2007 to 2009. We found that nest and territory densities were greatest on marshes <1 year post‐burn, indicating that burning did not displace seaside sparrows. Nest and territory densities also declined as time since burn increased, and were about 50% less on marshes that were ≥5 years post‐burn compared to marshes <1 year post‐burn. Egg density (the number of eggs produced per ha) was 50% greater on marshes burned <1 year ago than on marshes burned 3–4 years ago, but we found no difference in fledgling density, indicating that predation may have disproportionately affected recently‐burned marshes. Study year and percent cover of smooth cordgrass (Spartina alterniflora) best explained nest survival, which was lowest in 2009, a year with high precipitation and tides. We recommend that prescribed burning continue to be used at 1–4 year intervals to maintain habitat quality for breeding seaside sparrows in the mid‐Atlantic, but suggest that the effects of fire management may be less influential than predicted impacts of global climate change. © 2012 The Wildlife Society.

Dependence on sunbird pollination for fruit set in three West African montane mistletoe species

Abstract:Theory predicts that not all plant species will be equally affected by disruption to their pollinator mutualisms because traits such as breeding system and mutualism strength can affect their response. We investigated these traits in three species of Afromontane mistletoe Globimetula braunii, Agelanthus brunneus and A. djurensis in Ngel Nyaki Forest Reserve, Nigeria, to test whether the traits were reliable indicators of relative reproductive success and could be used to predict relative vulnerability to pollinator loss. For each mistletoe species, insect and bird visitors were identified during a 160–240-min observation period of 4–10 plants and their roles in flower opening and fruit set were investigated using exclusion experiments applied to 250–500 flowers. We found that all three mistletoes are self-compatible but not capable of autonomous self-fertilization. The pollinator assemblage comprised four species of sunbird (Cyanomitris spp., Cinnyris spp.) and a small social wasp (Vespinae). None of the mistletoes requires birds for flower opening: G. braunii flowers self-opened in the absence of pollinators, whereas insects opened both Agelanthus spp. Irrespective of flower opening, each mistletoe species requires sunbirds for effective pollination and fruit set. Only G. braunii demonstrated pollen limitation (pollen limitation index = 0.504) which may be an early indication of mutualism breakdown. We suggest that mistletoes be considered as indicators of habitat condition and functioning within Afromontane forest ecosystems.

Nest positioning by male Daito White‐eyes Zosterops japonicus daitoensis improves with age to reduce nest predation risk

Age‐related improvement in reproductive success is widely observed in birds, and the mechanisms by which productivity is enhanced have received considerable attention. However, little is known about how parental age affects the loss of eggs or nestlings despite the fact that age effects on nesting success are often reported. We examined parental age effects on reproductive success in relation to the avoidance of nest predation in an island subspecies of the Japanese White‐eye, the Daito White‐eye Zosterops japonicus daitoensis. Clutch size and annual number of breeding attempts did not differ between parental age classes. Reproductive success was affected only by male age through an increase in nesting success. Nest failure was attributed only to predation in this species and nest concealment and nest height were important nest characteristics promoting successful fledging. Older males built their nests in more concealed and higher positions than first‐year birds, regardless of vegetation status around the nest. Analysis of individual birds suggested that by shifting the nest to a safer position, male White‐eyes achieved higher nesting success than in the previous year. Of three hypotheses of age‐related improvement in reproductive success considered, our data favoured the hypothesis that as individuals grow older, their breeding competence improves.

Bias and significance of relative reproductive success estimates based on steelhead trout (Oncorhynchus mykiss) data: a Bayesian meta-analysis

The evaluation of the reproductive success (RS) of hatchery fish in the wild is one of the most important issues in hatchery supplementation, aquaculture, and conservation. Estimates of the relative reproductive success (RRS) have been used to evaluate RS. Because RRS may vary greatly depending on cross, years of release, and environmental conditions, we introduced a log-normal distribution to quantify the variation. The classical estimator of RRS based on multiple measurements is contrasted with the mean of this distribution. We derived the mean, variance, and relative bias and applied our Bayesian hierarchical model to 42 empirical RRS estimates of steelhead trout ( Oncorhynchus mykiss ) in the Hood River, Oregon, USA. The RRS estimate generally had an upward bias. Although the average level of RRS implied the reproductive decline of hatchery fish and wild-born hatchery descendants, we could not reject the null hypothesis that hatchery fish and their descendants have the same chance of having smaller RS than wild fish as they do of having larger RS than wild fish.

Diminished Reproductive Success of Steelhead from a Hatchery Supplementation Program (Little Sheep Creek, Imnaha Basin, Oregon)

AbstractHatchery supplementation programs are designed to enhance natural production and maintain the fitness of the target population; however, it can be difficult to evaluate the success of these programs. Key to the success of such programs is a relatively high reproductive success of hatchery fish. This study investigated the relative reproductive success (RRS) of steelhead Oncorhynchus mykiss (anadromous rainbow trout) by creating pedigrees for hatchery and natural spawning steelhead. We genotyped adult steelhead that returned to a weir and were released upstream to spawn in Little Sheep Creek, a tributary to the Imnaha River in eastern Oregon. The broodstock for this supplementation program were originally chosen from natural‐origin steelhead returning to the weir and in subsequent years consisted of both natural‐ and hatchery‐origin individuals. Microsatellite analyses showed the broodstock to be genetically similar to the natural population across years. We also genotyped adult resident rainbow trout from multiple locations upstream of the weir and determined the parentage of progeny collected at various life history stages, including returning adults in subsequent years. Analysis of progeny sampled at both the juvenile and adult life stages suggested that the RRS of hatchery‐origin fish was 30–60% that of their natural‐origin counterparts. Using generalized linear models to address the importance of various factors associated with reduced reproductive success, we found that the greatest effects on RRS were origin (natural versus hatchery), length, return date, and the number of same‐sex competitors. Natural parents were less negatively affected by same‐sex competitors. Differential survival of juveniles and the behavior of offspring and/or spawning adults may all contribute to diminished fitness in hatchery‐reared salmon, although it could not be determined to what extent these effects were of a persistent, heritable nature as distinct from an environmental effect associated with hatchery rearing and release strategies.

Female competition and its evolutionary consequences in mammals

Following Darwin's original insights regarding sexual selection, studies of intrasexual competition have mainly focused on male competition for mates; by contrast, female reproductive competition has received less attention. Here, we review evidence that female mammals compete for both resources and mates in order to secure reproductive benefits. We describe how females compete for resources such as food, nest sites, and protection by means of dominance relationships, territoriality and inter-group aggression, and by inhibiting the reproduction of other females. We also describe evidence that female mammals compete for mates and consider the ultimate causes of such behaviour, including competition for access to resources provided by mates, sperm limitation and prevention of future resource competition. Our review reveals female competition to be a potentially widespread and significant evolutionary selection pressure among mammals, particularly competition for resources among social species for which most evidence is currently available. We report that female competition is associated with many diverse adaptations, from overtly aggressive behaviour, weaponry, and conspicuous sexual signals to subtle and often complex social behaviour involving olfactory signalling, alliance formation, altruism and spite, and even cases where individuals appear to inhibit their own reproduction. Overall, despite some obvious parallels with male phenotypic traits favoured under sexual selection, it appears that fundamental differences in the reproductive strategies of the sexes (ultimately related to parental investment) commonly lead to contrasting competitive goals and adaptations. Because female adaptations for intrasexual competition are often less conspicuous than those of males, they are generally more challenging to study. In particular, since females often employ competitive strategies that directly influence not only the number but also the quality (survival and reproductive success) of their own offspring, as well as the relative reproductive success of others, a multigenerational view ideally is required to quantify the full extent of variation in female fitness resulting from intrasexual competition. Nonetheless, current evidence indicates that the reproductive success of female mammals can also be highly variable over shorter time scales, with significant reproductive skew related to competitive ability. Whether we choose to describe the outcome of female reproductive competition (competition for mates, for mates controlling resources, or for resources per se) as sexual selection depends on how sexual selection is defined. Considering sexual selection strictly as resulting from differential mating or fertilisation success, the role of female competition for the sperm of preferred (or competitively successful) males appears particularly worthy of more detailed investigation. Broader definitions of sexual selection have recently been proposed to encompass the impact on reproduction of competition for resources other than mates. Although the merits of such definitions are a matter of ongoing debate, our review highlights that understanding the evolutionary causes and consequences of female reproductive competition indeed requires a broader perspective than has traditionally been assumed. We conclude that future research in this field offers much exciting potential to address new and fundamentally important questions relating to social and mating-system evolution.

An integrated approach for the conservation of threatened plants: The case of Arabis kennedyae (Brassicaceae)

The aim of this paper is to propose an integrated approach (including population and habitat monitoring and the study of reproductive biology and genetic diversity) for the comprehensive study of threatened plants, for which conservation measures are imperative. We applied this model to the plant species Arabis kennedyae which is classified as endangered according to the IUCN criteria. The current population of the species consists of three small subpopulations (AR1, AR2, and AR3) at three locations. Population size was characterized by considerable annual fluctuations. The distribution pattern of the plant followed habitat availability. Relative Reproductive Success remained stable but moderate. Germination of dormant seeds was promoted by light and was optimal at 15 and 20 °C. Genetic analysis showed low interpopulation variability and detected two groups: haplotype I (AR1 and AR3) and haplotype II (AR2), which may represent two altitudinal ecotypes. The direct threats identified were related to recreation activities, road construction and fire. The subpopulations of the plant are regulated by density and depend on fecundity and on the soil seedbank while their persistence depends mainly on habitat availability. Low genetic diversity combined with small population size and a possible reduction in fitness suggest increased susceptibility to loss of genetic variation. The overall results suggest that ex situ conservation in a seed bank, and in situ conservation in the form of population restoration, are suitable conservation measures and the study of the different aspects of the species’ biology has provided the data required for their implementation.

Flowering Phenology, Floral Display and Reproductive Success in the GenusSirindhornia(Orchidaceae): A Comparative Study of Three Pollinator-Rewarding Species

Numbers of flowers and their arrangement in time and space greatly influence levels of pollination and fruit set in natural populations of flowering plants. We examined relations between flowering phenology, floral display and reproductive success in the nectar-producing orchids Sirindhornia mirabilis, S. monophylla and S. pulchella in Thailand. We found each species to be self-compatible and dependent on insects for pollination. Sirindhornia mirabilis exhibited prolonged longevity of individual flowers and produced more flowers per inflorescence — features that may have evolved in response to low visitation rates. Patterns of reproductive success in relation to floral display suggest selection for increased inflorescence size in S. mirabilis and S. monophylla, but this may be counterbalanced by selection for a sustainable annual fruit set. In all three species, the female (and in S. mirabilis also the male) reproductive success decreased from the basal to the apical part of the inflorescence. Against this background, we propose a hypothesis for explaining differential fruit set in polinator-rewarding orchid species.

Factors influencing the relative fitness of hatchery and wild spring Chinook salmon (Oncorhynchus tshawytscha) in the Wenatchee River, Washington, USA

Understanding the relative fitness of naturally spawning hatchery fish compared with wild fish has become an important issue in the management and conservation of salmonids. We used a DNA-based parentage analysis to measure the relative reproductive success of hatchery- and natural-origin spring Chinook salmon ( Oncorhynchus tshawytscha ) in the natural environment. Size and age had a large influence on male fitness, with larger and older males producing more offspring than smaller or younger individuals. Size had a significant effect on female fitness, but the effect was smaller than on male fitness. For both sexes, run time had a smaller but still significant effect on fitness, with earlier returning fish favored. Spawning location within the river had a significant effect on fitness for both sexes. Hatchery-origin fish produced about half the juvenile progeny per parent when spawning naturally than did natural-origin fish. Hatchery fish tended to be younger and return to lower areas of the watershed than wild fish, which explained some of their lower fitness.

REMATING IN DROSOPHILA MELANOGASTER: ARE INDIRECT BENEFITS CONDITION DEPENDENT?

By measuring the direct and indirect fitness costs and benefits of sexual interactions, the feasibility of alternate explanations for polyandry can be experimentally assessed. This approach becomes more complicated when the relative magnitude of the costs and/or benefits associated with multiple mating (i.e., remating with different males) vary with female condition, as this may influence the strength and direction of sexual selection. Here, using the model organism Drosophila melanogaster, we test whether the indirect benefits that a nonvirgin female gains by remating (“trading-up”) are influenced by her condition (body size). We found that remating by small-bodied, low-fecundity females resulted in the production of daughters of relatively higher fecundity, whereas the opposite pattern was observed for large-bodied females. In contrast, remating had no measurable effect on the relative reproductive success of sons from dams of either body size. These results are consistent with a hypothesis based on sexually antagonistic genetic variation. The implications of these results to our understanding of the evolution and consequences of polyandry are discussed.

A two level mutation-selection model of cultural evolution and diversity

Cultural evolution is a complex process that can happen at several levels. At the level of individuals in a population, each human bears a set of cultural traits that he or she can transmit to its offspring (vertical transmission) or to other members of his or her society (horizontal transmission). The relative frequency of a cultural trait in a population or society can thus increase or decrease with the relative reproductive success of its bearers (individual’s level) or the relative success of transmission (called the idea’s level). This article presents a mathematical model on the interplay between these two levels. The first aim of this article is to explore when cultural evolution is driven by the idea’s level, when it is driven by the individual’s level and when it is driven by both. These three possibilities are explored in relation to (a) the amount of interchange of cultural traits between individuals, (b) the selective pressure acting on individuals, (c) the rate of production of new cultural traits, (d) the individual’s capacity to remember cultural traits and to the population size. The aim is to explore the conditions in which cultural evolution does not lead to a better adaptation of individuals to the environment. This is to contrast the spread of fitness-enhancing ideas, which make individual bearers better adapted to the environment, to the spread of “selfish” ideas, which spread well simply because they are easy to remember but do not help their individual bearers (and may even hurt them). At the same time this article explores in which conditions the adaptation of individuals is maximal. The second aim is to explore how these factors affect cultural diversity, or the amount of different cultural traits in a population. This study suggests that a larger interchange of cultural traits between populations could lead to cultural evolution not improving the adaptation of individuals to their environment and to a decrease of cultural diversity.

German cockroach males maximize their inclusive fitness by avoiding mating with kin

Conventional sex roles imply choosy females and nondiscriminating males. However, growing evidence suggests that male choosiness is more common than expected. While male mate choice is clearly linked to high mating investment in sex role-reversed species, factors promoting male mate choice in conventional sex role species are still debated. We addressed this fundamental issue in the German cockroach, Blattella germanica (L.), a group-living species where members of both sexes exercise mutual mate choice to avoid inbreeding. We focused on (1) male potential reproductive rate, (2) male effective reproductive rate, and (3) male reproductive success in relation to female quality. Males tested in situations with unrestrained female availability were able to mate throughout their life, thus revealing a high potential reproductive rate. However, their effective reproductive rate was much more limited under ecologically realistic conditions with restrained female availability. In contradiction with general predictions of sex role theory, mate choice by B. germanica males occurs despite an apparent low mating investment and a male-biased operational sex ratio. The finding that inbred matings were less fertile than outbred matings reveals that kinship is the key factor promoting male choice in this particular case. In the light of inbreeding avoidance theory, we propose that by being choosy cockroach males avoid imposing inbreeding costs on their sisters, thus maximizing their own inclusive fitness via kin selection.

Survival and life history characteristics among wild and hatchery coho salmon (Oncorhynchus kisutch) returns: how do unfed fry differ from smolt releases?

Survival and life history characteristics were evaluated for a coho salmon ( Oncorhynchus kisutch ) integrated hatchery program using two stocking strategies. Fish were released as unfed fry or smolts and returned as adults, and then molecular analysis was employed to pedigree the entire population. We showed that mean adult survival of individuals released as unfed fry was less than that of individuals released as smolts (0.03% vs. 2.39%). The relative reproductive success (RRS) of the fry release strategy to wild spawning was significantly greater for one of two cohorts, whereas the smolt release strategy to wild RRS was significantly greater for both cohorts. Fish released as smolts were significantly smaller upon returning as adults than either those released as unfed fry or wild returns. Mean run timing was also significantly biased towards an earlier run time for hatchery-released fish when compared with the wild component. The incidence of jacking (males maturing at age 2) was greater among fish stocked as smolts than for fish stocked as fry. Differences in survival, RRS, and life history appeared to be the result of hatchery practices and indicated that a fry stocking strategy produced fish more similar to the wild component of the population than to that of fish released as smolts.

Investment in mate choice depends on resource availability in female Galápagos marine iguanas (Amblyrhynchus cristatus)

Changes in mate selectivity can significantly alter the direction and strength of sexual selection. When the direct cost of mate search increases selectivity often declines; however, little is known about how the relative cost of mate search affects investment in mate choice. Here, I investigate whether male and female Galapagos marine iguanas (Amblyrhynchus cristatus) alter their investment in mate choice behaviors when resources are limited and the relative cost of mate search is increased. Moderate resource limitation had little effect on male reproductive behavior: in both years, a similar number of males were territorial, and the mean display rate and copulation success of territorial males did not differ. In contrast, female mate search appeared to be affected by the prevailing environmental conditions. During the reproductive season following a moderate El Nino event, when food availability declined, females were in poorer body condition, assessed fewer territorial males, and mated with a male with lower relative reproductive success. Circulating hormone levels also differed between years: when resource availability was limited, receptive females had higher levels of testosterone and stress-induced corticosterone. The frequency and magnitude of climatic fluctuations are expected to increase in the future across many regions of the globe. Determining how sexual selection is shaped by changes in resource availability is vital for predicting the impact of climate change.

Reproductive behavior and relative reproductive success of natural- and hatchery-origin Hood Canal summer chum salmon (Oncorhynchus keta)

Estimates of the relative fitness of hatchery- and natural-origin salmon can help determine the value of hatchery stocks in contributing to recovery efforts. This study compared the adult to fry reproductive success of natural-origin summer chum salmon ( Oncorhynchus keta ) with that of first- to third-generation hatchery-origin salmon in an experiment that included four replicate breeding groups. Hatchery- and natural-origin chum salmon exhibited similar reproductive success. Hatchery- and natural-origin males obtained similar access to nesting females, and females of both types exhibited similar breeding behaviors and durations. Male body size was positively correlated with access to nesting females and reproductive success. The estimates of relative reproductive success (hatchery/natural = 0.83) in this study were similar to those in other studies of other anadromous salmonids in which the hatchery population was founded from the local natural population and much higher than those in studies that evaluated the lifetime relative reproductive success of nonlocal hatchery populations.

It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird.

Variance in reproductive success among individuals is a defining characteristic of many social vertebrates. Yet, our understanding of which male attributes contribute to reproductive success is still fragmentary in most cases. Male-male reproductive coalitions, where males jointly display to attract females, are of particular interest to evolutionary biologists because one male appears to forego reproduction to assist the social partner. By examining the relationship between social behaviour and reproductive success, we can elucidate the proximate function of coalitions in the context of mate choice. Here, we use data from a 4-year study of wire-tailed manakins (Pipra filicauda) to provide molecular estimates of reproductive skew and to test the hypothesis that male-male social interactions, in the context of coordinated displays, positively influence a male's reproductive success. More specifically, we quantify male-male social interactions using network metrics and predict that greater connectivity will result in higher relative reproductive success. Our data show that four out of six leks studied had significant reproductive skew, with success apportioned to very few individuals in each lek. Metrics of male social affiliations derived from our network analysis, especially male connectivity, measured as the number of males with whom the focal male has extended interactions, were strong predictors of the number of offspring sired. Thus, network connectivity is associated with male fitness in wire-tailed manakins. This pattern may be the result of shared cues used by both sexes to assess male quality, or the result of strict female choice for coordinated display behaviour.

ON THE OPPORTUNITY FOR SEXUAL SELECTION, THE BATEMAN GRADIENT AND THE MAXIMUM INTENSITY OF SEXUAL SELECTION

Bateman's classic paper on fly mating systems inspired quantitative study of sexual selection but also resulted in much debate and confusion. Here, I consider the meaning of Bateman's principles in the context of selection theory. Success in precopulatory sexual selection can be quantified as a "mating differential," which is the covariance between trait values and relative mating success. The mating differential is converted into a selection differential by the Bateman gradient, which is the least squares regression of relative reproductive success on relative mating success. Hence, a complete understanding of precopulatory sexual selection requires knowledge of two equally important aspects of mating patterns: the mating differential, which requires a focus on mechanisms generating covariance between trait values and mating success, and the Bateman gradient, which requires knowledge of the genetic mating system. An upper limit on the magnitude of the selection differential on any sexually selected trait is given by the product of the standard deviation in relative mating success and the Bateman gradient. This latter view of the maximum selection differential provides a clearer focus on the important aspects of precopulatory sexual selection than other methods and therefore should be an important part of future studies of sexual selection.

Retrospective investigation of captive red wolf reproductive success in relation to age and inbreeding

The critically endangered red wolf (Canis rufus) has been subject to a strictly managed captive breeding program for three decades. A retrospective demographic analysis of the captive population was performed based on data from the red wolf studbook. Data analyses revealed a decrease in the effective population size relative to the total population size, and changes in age structure and inbreeding coefficients over time. To varying degrees, the probability of successful breeding and litter sizes declined in association with increasing dam age and sire inbreeding coefficients. Neonate survival also declined with increasing dam age. Recent changes in strategies regarding breed-pair recommendations have resulted in moderate increases in reproductive success.

Diploid Amazon mollies (Poecilia formosa) show a higher fitness than triploids in clonal competition experiments

The gynogenetic livebearing Amazon molly (Poecilia formosa) is a sexual parasite that exploits males of closely related species for sperm. This is needed as physiological stimulus for embryo development; however, none of the male’s genes are normally incorporated into the genome of the gynogenetic offspring. Mostly diploid individuals were reported from the natural habitats in North-Eastern Mexico and South-Eastern Texas but stable populations of triploids have been reported from the Rio Soto la Marina drainage and in the Rio Guayalejo in North-Eastern Mexico. Triploidy is the result of defects in the mechanisms that normally clear the host sperm from the ameiotic diploid egg. Triploids also reproduce gynogenetically and their frequencies fluctuate markedly between years, seasons, and localities. To understand the dynamics of this mating system, it is important to understand the relative reproductive success of triploids and diploids. We hypothesize that triploids should have a selective advantage over diploids due to heterosis and/or gene redundancy based on the additional genetic material from the sexual host. However, clonal competition experiments revealed a clear reproductive advantage of diploids competing with triploids. This result contradicts not only our hypothesis but also the stable co-existence of diploids and triploids in natural habitats. Frequency dependent selection, niche partitioning and environmental heterogeneity are discussed as possible explanations.