Individual Reproductive Success Research Articles

Concurrent habitat and life history influences on effective/census population size ratios in stream‐dwelling trout

Lower effective sizes (Ne) than census sizes (N) are routinely documented in natural populations, but knowledge of how multiple factors interact to lower Ne/N ratios is often limited. We show how combined habitat and life-history influences drive a 2.4- to 6.1-fold difference in Ne/N ratios between two pristine brook trout (Salvelinus fontinalis) populations occupying streams separated by only 750 m. Local habitat features, particularly drainage area and stream depth, govern trout biomass produced in each stream. They also generate higher trout densities in the shallower stream by favoring smaller body size and earlier age-at-maturity. The combination of higher densities and reduced breeding site availability in the shallower stream likely leads to more competition among breeding trout, which results in greater variance in individual reproductive success and a greater reduction in Ne relative to N. A similar disparity between juvenile or adult densities and breeding habitat availability is reported for other species and hence may also result in divergent Ne/N ratios elsewhere. These divergent Ne/N ratios between adjacent populations are also an instructive reminder for species conservation programs that genetic and demographic parameters may differ dramatically within species.

Temporal variation in selection on body length and date of return in a wild population of coho salmon, Oncorhynchus kisutch

BackgroundA number of studies have measured selection in nature to understand how populations adapt to their environment; however, the temporal dynamics of selection are rarely investigated. The aim of this study was to assess the temporal variation in selection by comparing the mode, direction and strength of selection on fitness-related traits between two cohorts of coho salmon (Oncorhynchus kisutch). Specifically, we quantified individual reproductive success and examined selection on date of return and body length in a wild population at Big Beef Creek, Washington (USA).ResultsReproductive success and the mode, direction and strength of selection on date of return and body length differed between two cohorts sampled in 2006 and 2007. Adults of the first brood year had greater success over those of the second. In 2006, disruptive selection favored early and late returning individuals in 2-year-old males, and earlier returning 3-year-old males had higher fitness. No evidence of selection on date of return was detected in females. In 2007, selection on date of return was not observed in males of either age class, but stabilizing selection on date of return was observed in females. No selection on body length was detected in males of both age classes in 2006, and large size was associated with higher fitness in females. In 2007, selection favored larger size in 3-year-old males and intermediate size in females. Correlational selection between date of return and body length was observed only in 2-year-old males in 2006.ConclusionsWe found evidence of selection on body length and date of return to the spawning ground, both of which are important fitness-related traits in salmonid species, but this selection varied over time. Fluctuation in the mode, direction and strength of selection between two cohorts was likely to be due to factors such as changes in precipitation, occurrence of catastrophic events (flooding), the proportion of younger- versus older-maturing males, sex ratio and densities of spawners.

Phenotypic plasticity in temperature stress resistance is triggered by photoperiod in a fly

Temperature variation poses a substantial challenge for individual survival and reproductive success, warranting effective means to counter negative effects of temperature extremes. Phenotypic plasticity offers a particularly powerful mechanism to cope with short-time temperature fluctuations. While temperature-induced plasticity in thermal tolerance has been widely explored, effects of other environmental factors have received much less attention. Using a full-factorial design we here show that variation in temperature stress resistance can be triggered by photoperiod (and temperature) in the fly Protophormia terraenovae, with shorter day lengths inducing more cold- and longer day lengths more heat-tolerant phenotypes. Such plastic changes were not related to different developmental pathways (reproductive activity or reproductive diapause), and can be induced during development but also in the adult stage (at least for cold tolerance). We suggest that short-term, photoperiod-mediated changes in insect thermal tolerance represent a mechanism of adaptive seasonal plasticity. Photoperiod further affected development time and body size, the significance of which is currently unclear.

Mating Systems and Reproductive Success in Hermaphroditic Bay Scallop, Argopecten irradians irradians (Lamarck 1819), Inferred by Microsatellite‐based Parentage Analysis

In this study, we used microsatellite‐based parentage analysis to assess the mating system of a mass spawning bay scallop, Argopecten irradians irradians. Parental assignment was performed on 237 offspring and 14 candidate parents. Overall, 95% of all offspring were unambiguously allocated to their putative parents based on information from six highly polymorphic loci. Offspring from both the self‐fertilization and cross‐fertilization style were observed, the large variation of self‐fertilization rate among individuals displays a mixed mode of mating. The high variances in reproductive success resulted in a decline in effective breeding numbers (Nb/N = 0.71). The self‐fertilization rate was 32.89% for this mass spawning and the coefficient of inbreeding was estimated at around 16.5% per generation. When selfed larvae were removed, the relationship between relatedness and individual reproductive success was proved insignificant between half‐sibings and unrelated, which suggest that selection pressures other than avoidance of inbreeding may be responsible for the evolution and maintenance of the self‐compatible mating system of A. i. irradians. These results lend insight to A. i. irradians cultivation in present China and provide a genetic basis for the development of more effective spawning techniques.

Variation in annual and lifetime reproductive success of lance-tailed manakins: alpha experience mitigates effects of senescence on siring success

The causes of variation in individual reproductive success over a lifetime are not well understood. In long-lived vertebrates, reproductive output usually increases during early adulthood, but it is difficult to disentangle the roles of development and learning on this gain of reproductive success. Lekking lance-tailed manakins provide an opportunity to separate these processes, as the vast majority of male reproduction occurs after a bird obtains alpha status and maintains a display area in the lek, but the age at which males achieve alpha status varies widely. Using 11 years of longitudinal data on age, social status and genetic siring success, I assessed the factors influencing variation in siring success by individuals over their lifetimes. The data show increases in annual reproductive success with both age and alpha experience. At advanced ages, these gains were offset by senescence in fecundity. Individual ontogeny, rather than compositional change of the population, generated a nonlinear relationship of breeding tenure with lifetime success; age of assuming alpha status was unrelated to tenure as a breeder, or success in the alpha role. Importantly, these findings suggest that social experience can mitigate the negative effects of senescence in older breeders.

Paternal body size affects reproductive success in laboratory-held zebrafish (Danio rerio)

Across many fish species, large females tend to exhibit higher individual reproductive success due to elevated fecundity and the provisioning of better conditioned eggs and offspring compared to small females. By contrast, effects of paternal body size on reproductive success are less well understood. We disentangled the maternal- and paternal-size dependent effects on reproductive output and early life history in zebrafish (Danio rerio). In the laboratory, females and males from four size categories (small, medium-sized, large and very large) were allowed to spawn freely in a full factorial design with 10 replicates per size combination. As expected, larger females produced more eggs and better conditioned offspring compared to smaller females. Male body size further contributed to zebrafish reproductive success: offspring sired by large males exhibited higher hatching probability and these offspring also hatched earlier and larger than offspring fertilized by small males. However, the largest males experienced lower mating success and received fewer eggs than males of the smaller size classes. While male body size substantially affected reproductive success in zebrafish, it remained unclear whether and to what degree direct paternal effects (e.g., related to sperm quality) or indirect paternal effects stemming from differential allocation patterns by females were the mechanism behind our findings. Answering this question constitutes an important future research topic.

Delayed autumn migration in northern European waterfowl

Climate change is causing phenological shifts in the environment. Among birds, increasing temperatures have been shown to advance the spring migration and breeding, which in turn affect individual reproductive success. The autumn migration phenology has, however, been largely overlooked. Here, we study long-term changes in the timing of autumn migration in 15 northern European waterfowl species during 1979–2009. We hypothesised that waterfowl should delay their migration since they winter north of the Sahara desert. Our results show that 6 (Greylag Goose Anser anser, Eurasian Wigeon Anas penelope, Eurasian Teal Anas crecca, Tufted Duck Aythya fuligula, Velvet Scoter Melanitta fusca, and Common Goldeneye Bucephala clangula) of the 15 studied species have delayed at least one of the three phases of migration examined. The most marked delay in median migration dates was by more than a month over the past 31 years. Only the Bean Goose Anser fabalis exhibited an advanced beginning of its migration. We also analyse the timing of the entire waterfowl migration and show that the median and end of the migration have been significantly delayed. The results support our predictions and highlight how rapid phenological responses to climate change may be. Such delayed departures may be the cause for recently observed northward shifts of wintering ducks. Our results suggest that waterfowl to be a good indicator group for climate change. Changing migration times can also have population-level consequences due to differential hunting and natural predation pressures over the waterfowl flyway.

Review on hard coral recruitment (Cnidaria: Scleractinia) in Colombia

<p><strong>Abstract</strong></p><p>Recruitment, defined and measured as the incorporation of new individuals (i.e. coral juveniles) into a population, is a fundamental process for ecologists, evolutionists and conservationists due to its direct effect on population structure and function. Because most coral populations are self-feeding, a breakdown in recruitment would lead to local extinction. Recruitment indirectly affects both renewal and maintenance of existing and future coral communities, coral reef biodiversity (bottom-up effect) and therefore coral reef resilience. This process has been used as an indirect measure of individual reproductive success (fitness) and is the final stage of larval dispersal leading to population connectivity. As a result, recruitment has been proposed as an indicator of coral-reef health in marine protected areas, as well as a central aspect of the decision-making process concerning management and conservation. The creation of management plans to promote impact mitigation, rehabilitation and conservation of the Colombian coral reefs is a necessity that requires firstly, a review and integration of existing literature on scleractinian coral recruitment in Colombia and secondly, larger scale field studies. This motivated us to summarize and analyze all existing information on coral recruitment to determine the state of knowledge, isolate patterns, identify gaps, and suggest future lines of research.</p><p><strong>Key words: </strong>Recruitment, juvenile, coral, Scleractinia, structure, reef, Colombia, density, richness, monitoring.</p><p> </p>

Sweepstakes Reproductive Success in Highly Fecund Marine Fish and Shellfish: A Review and Commentary

Most marine animal species are very abundant, relatively long-lived, and late-maturing, with highly fecund adults adapted to spatially and temporally fluctuating ocean environments. Adults typically produce millions of small eggs that develop rapidly, without parental care, into planktonic larval stages that suffer high early mortality (Type III survivorship). Yet, large marine populations generally have only fractions of the genetic diversity expected from their sheer abundance, and despite widely dispersing larvae and geographically weakly structured adult populations, often show chaotic genetic heterogeneity on small spatial scales. These paradoxical observations can be explained by the hypothesis of Sweepstakes Reproductive Success (SRS), which posits extremely large variance in individual reproductive success, owing to sweepstakes-like chances of matching reproductive activity with oceanographic conditions conducive to gamete maturation, fertilization, larval development, settlement, and recruitment to the adult spawning population. The primary genetic consequence of SRS is reduction of Ne/N, the ratio of effective to actual population numbers, to a value usually much smaller than 0.01. Published nearly 30 yrs ago, SRS has gained traction, with numerous papers verifying specific predictions of the hypothesis in a broad array of marine animal taxa. Moreover, the hypothesis and empirical data from marine systems have stimulated modifications of coalescence population genetics theory, which can now account for low molecular diversity and chaotic patchiness. Here, we review the empirical and theoretical support for SRS, concluding that it plays a major role in shaping marine biodiversity, comment on issues related to hypothesis testing and data interpretation, and clarify some misconceptions.

Effects of selective harvest on antler size in white‐tailed deer: A modeling approach

AbstractSelective harvesting in wild deer (Odocoileus spp.) populations is a common practice that may influence antler size. However, in free‐ranging populations, response due to selection is unknown or difficult to quantify because antlers are influenced by nutrition and population demographics. We used quantitative genetic models to predict how white‐tailed deer (O. virginianus) antlers would respond to selection and what variables (i.e., population size, age structure, mating ratio, and heritability) most affected antler size. We validated our quantitative genetics program by comparing model results with a population of deer used for controlled breeding experiments; modeled antler points (AP) and score increased (2.2–4.3 AP and 48.5–97.7 cm, respectively) after 8 years of selection, similar to observed increases in AP (3.2) and score (92.3 cm) from the controlled population. In modeled free‐ranging populations, mating ratio, age structure, and heritability were more important in influencing antler size than size of the population. However, response to selection in free‐ranging populations was lower (0.1–0.9 AP) than controlled breeding populations even after 20 years of selection. These results show that selective harvesting of free‐ranging white‐tailed deer may be inefficient to change population‐level genetic characteristics related to antler size. Response of antlers in free‐ranging deer will be less than controlled populations, and possibly modeled free‐ranging simulations, because individual reproductive success of males is lower, breeding is done by a large group of males, and reproductive and survival rates are lower. These factors, and others, reduce the amount of improvement that can be made to antlers due to selection. Therefore, selective harvesting in free‐ranging populations should be justified for managing population demographics and dynamics, but not for changing the genetic characteristics of populations. © 2011 The Wildlife Society.

Success-driven distribution of public goods promotes cooperation but preserves defection

Established already in Biblical times, the Matthew effect refers to the fact that in societies the rich tend to get richer and the potent even more powerful. Here we investigate a game theoretical model describing the evolution of cooperation on structured populations where the distribution of public goods is driven by the reproductive success of individuals. Phase diagrams reveal that cooperation is promoted irrespective of the uncertainty by strategy adoptions and the type of interaction graph, yet the complete dominance of cooperators is elusive due to the spontaneous emergence of superpersistent defectors that owe their survival to extremely rare microscopic patterns. This indicates that success-driven mechanisms are crucial for effectively harvesting benefits from collective actions but that they may also account for the observed persistence of maladaptive behavior.

Manipulating individual state during migration provides evidence for carry-over effects modulated by environmental conditions

Despite observational evidence of carry-over effects (COEs, events occurring in one season that produce residual effects on individuals the following seasons), to our knowledge no experimental studies have been carried out to explore how COEs might affect reproductive output. We simulated an environmental perturbation affecting spring-staging migrants to investigate COEs in greater snow geese (Anser caerulescens atlanticus). During three consecutive years, 2037 females captured during spring staging (approx. 3000 km south of their Arctic breeding grounds) were maintained in captivity (with or without access to food) for 0-4 days. Duration of captivity (but not food treatment) negatively affected reproductive success, probably through stress response. Reproductive success was reduced by 45-71% in 2 years, but not in a third year with unusually favourable breeding conditions. This unprecedented manipulation indicates that COEs can have a strong effect on individual reproductive success in long-distance migrants, but that this effect can be partly compensated for by good environmental conditions on the breeding ground.

Juvenile hormone titer and advertised quality are associated with timing of early spring activity in Polistes dominulus foundresses

Timing of diapause termination has an important influence on individual reproductive success, but relatively little research has explored how individuals differ in their response to diapause termination cues. We tested individual variation in the timing of post-diapause activity in Polistes dominulus paper wasps. Wasps were overwintered in a temperature-controlled chamber. In the spring, ambient temperature was gradually increased and the time each foundress became active was recorded. Timing of post-diapause activity was most strongly associated with the facial patterns that function as a conventional signal of quality. Foundresses with facial patterns indicating high quality became active at lower temperatures than individuals with facial patterns indicating low quality. Early diapause termination is associated with dominance, so the relationship between diapause termination and facial patterns provides a mechanism linking facial patterns with dominance. Body weight and mating status did not influence timing of post-diapause activity. Juvenile hormone (JH) titer at the time of diapause termination was also measured in a subset of foundresses. There was no JH titer threshold for diapause termination. Instead, our results suggest that individuals may have different threshold responses to JH, as individuals that became active at a lower temperature had lower JH titers than individuals that became active at a higher temperature. Overall, there is substantial individual variation in response to diapause termination cues and the variation is likely to have important impacts on the fitness of nest-founding females.

Complex relationship between multiple measures of cognitive ability and male mating success in satin bowerbirds, Ptilonorhynchus violaceus

Many animal species have complex cognitive abilities previously assumed to be limited to humans. Explanations for how these abilities evolved have focused on ways in which cognitive performance may influence survival, such as solving ecological problems or navigating complex social environments. However, sexual selection (differences in the reproductive success of individuals) can also lead to the evolution of complex traits. This could occur, for example, if females prefer males with better cognitive ability. A common assumption of models of female choice for male cognitive ability is that performance scores on different cognitive tasks are intercorrelated. In the present study, we evaluated performance of male satin bowerbirds on six cognitive tasks. Although we found little intercorrelation amongst males’ performance scores of these tasks, males with better scores for two integrative measures of these cognitive tasks had higher mating success, which is a good indicator of reproductive success in this species. In addition, a multiple regression analysis suggested that performance on most cognitive tasks independently predicted mating success. Our results point to an important link between sexual selection and cognitive ability that has not been well appreciated and appears to be quite complex.

Exploring local borders of distribution in the shrub Daphne laureola: Individual and populations traits

Biogeographic models predict that marginal populations should be more geographically isolated and smaller than central populations, linked to more stressful conditions and likely also to a reduction in density of individuals, individual growth, survival and reproductive output. This variation in population features could have important consequences for different aspects of plant ecology such as individual reproductive success, population genetic structure or plant-animal interactions. In this study, we analyze if individuals of the evergreen shrub Daphne laureola at disjunt populations in a local border of its distribution area in southern Iberian Peninsula differ in individual size, shoot growth, reproductive output and the pollination environment from central continuous populations within the area. Plants of central continuous populations were larger and produced more flowers and fruits than plants of marginal disjunct populations suggesting more optimal conditions, although they had lower annual shoot growth. In contrast, fruit set was higher in plants at the local border, suggesting a more efficient pollinator service in these populations where the main pollinator in central continuous populations, the pollen beetle Meligethes elongatus, was not present. Our results do not support strong differences in the ecological stress between marginal disjunct and central continuous populations of D. laureola in the south of the Iberian Peninsula but indicate some changes in plant-pollinator interactions that could be relevant for the sexual polymorphism in this gynodioecious species.

Life history pattern and fitness of an endangered Hainan Eld's deer population

Understanding life history patterns, individual fitness and population fitness can assist with conservation of endangered species. Field data on life history traits (i.e. age specific fecundity, age specific mortality, age at first reproduction, litter size and adult life expectancy) were collected from 121 Hainan Eld's deer (Cervus eldi hainanus Thomas, 1918), an in situ herd of an endemic, rare and endangered cervid inhabiting Bangxi Natural Reserve of Hainan Island, from 1990 to 2002. First, we constructed a dynamic life table to analyze the life history pattern of the population, which showed that the difference between the average lifespan of males and females was not significant (P > 0.05), and that the difference between the average lifespan of the whole Hainan Eld's deer population and that of other Eld's deer populations living in South Asia (P > 0.05), North America (P > 0.05) and Europe (P > 0.05) was not significant. Second, we used individual reproductive success or number of offspring of a male over its lifetime to estimate male individual fitness. Statistic analysis showed that male individual fitness was not significantly correlated with total antler velvet mass. Third, we used the population intrinsic rate of increase to measure population fitness, and population fitness of Hainan Eld's deer was compared with similar indexes of 5 other cervid species. Hainan Eld's deer population fitness index was 0.012, the second lowest value relative to other cervids. Results indicated that this rare species is still endangered and is in need of additional protection.

Major histocompatibility complex heterozygosity enhances reproductive success

We investigated how heterozygosity at the major histocompatibility complex (MHC) affects fitness in wild-derived (F2) house mice (Mus musculus musculus). To compare and control for potential confounding effects from close inbreeding and genome-wide heterozygosity, we used mice that were systematically outbred. We assessed how heterozygosity at MHC and background loci (using 15 microsatellite markers on 11 different chromosomes) affects individual survival and reproductive success (RS) in large, semi-natural population enclosures. We found that overall heterozygosity significantly increased RS, and this correlation was entirely explained by heterozygosity at two MHC loci. Moreover, we found that the effects of MHC heterozygosity depend on the level of background heterozygosity, and the benefits of maximal MHC heterozygosity show a curvilinear effect with increasing background heterozygosity. The enhanced RS from MHC heterozygosity was not because of increased survival, and although MHC heterozygosity was correlated with body mass, body mass did not correlate with RS when heterozygosity is controlled. Breeders were more MHC heterozygous than nonbreeders for both sexes, indicating that MHC heterozygosity enhanced fecundity, mating success or both. Our results show that (i) MHC heterozygosity enhances fitness among wild, outbred as well as congenic laboratory mice; (ii) heterozygosity-fitness correlations can potentially be explained by a few loci, such as MHC; (iii) MHC heterozygosity can increase fitness, even without affecting survival, by increasing mating and RS; and (iv) MHC effects depend on background genes, and maximal MHC heterozygosity is most beneficial at intermediate or optimal levels of background heterozygosity.

Short-term temporal genetic investigation of two populations of Pagellus erythrinus (Linnaeus, 1758, Sparidae) from Western and Eastern Mediterranean basins off the Tunisian coast

Geographic and temporal genetic variation of allele frequencies at 21 isozyme loci were examined in two populations of common Pandora, Pagellus erythrinus (Linnaeus, 1758, Sparidae). Fishes were sampled from Western and Eastern Mediterranean basins off Tunisian coasts over one year at the beginning of each season. Analysis of genetic diversity showed a low level of heterozygosity for all populations (average H e=0.052). Fixation indices reflected a significant departure from Hardy–Weinberg equilibrium with heterozygote deficiencies, slight spatial differentiation between both sampling localities (F ST=0.003, P=0.017) and temporal genetic stability at seasonal and annual scales. Annual genetic variation was evaluated over a five-year period estimated indirectly from fish otoliths. Comparison of genetic diversity between year classes of both locations showed an increase of the H e values concurrent with age, supporting the hypothesis of the high variance in individual reproductive success. Finally, our results suggest that the effective population size of Pagellus erythrinus is large and genetic drift is weak but variable, especially between successive adult year classes for both sampling locations.

Comparative maturation schedules of two Columbia River sockeye salmon Oncorhynchus nerka populations

Age and size at maturation affect an individual's reproductive success and reflect both evolutionary adaptations and phenotypic responses to environmental conditions. We evaluated age and size at maturity of sockeye salmon Oncorhynchus nerka from 2 populations within the Columbia River drainage: the Okanagan River, British Columbia (Canada), population and the endangered population from Redfish Lake, Idaho, USA. We compared available data on wild fish to data on fish reared under controlled laboratory conditions. Data obtained from the wild revealed that Okanagan River fish smolted at younger ages and larger sizes and then matured at younger ages than Redfish Lake fish. In captivity, fish from both populations were grown at the same rate and all smolted at Age 1. Despite their similar lengths as smolts, a greater proportion of Redfish Lake (>90%) than Okanagan River sockeye salmon (68%) matured 1 yr after smolt transformation. Calculated proba- bilistic maturation reaction norm midpoints for the captive fish indicated that Redfish Lake sockeye salmon in this study may have lower maturation thresholds than Okanagan River fish. Expression of different life history traits in the 2 populations under controlled conditions is consistent with a genetic basis for these traits and countergradient variation in maturation thresholds. Understanding life history differences and local adaptation among populations is important for their conservation, including anticipating responses to captive breeding regimes and supplementation, changing environmental conditions, and selective harvest.

Behavioral and physiological factors associated with juvenile hormone in Polistes wasp foundresses

Although there is increasing interest in the evolution of endocrine systems, relatively little is known about the factors associated with natural endocrine variation in invertebrates. Here, we assess juvenile hormone (JH) titers among nest-founding queens of the wasp Polistes dominulus over 2 years. We allowed unfamiliar wasps to battle for dominance and examined the relationships between dominance rank, JH, ovarian development, and facial patterns. The relationship between JH-titer and dominance varied across years; there was a stronger relationship between JH-titer and dominance in 2006 than in 2008. Across years, wasps that won dominance contests had facial patterns with more broken black spots than wasps that lost dominance contests. There was no relationship between dominance rank and ovarian development. The individual characteristics associated with JH-titer were also tested; JH-titers were correlated with facial pattern brokenness and ovarian development. This study adds to previous work indicating that P. dominulus facial patterns function as a signal of fighting ability. Furthermore, the correlation between JH-titers and facial patterns parallels previous work on testosterone and vertebrate signals and suggests that links between signals of fighting ability and hormones that mediate fighting ability may be common across taxa. Overall, individual JH-titers vary, though they are typically associated with factors related to individual reproductive success, including dominance, fertility, and facial pattern brokenness. Future studies in additional contexts and taxa will be important to test how and why JH-titers vary.