Reproductive Fitness Components Research Articles

Maternal effects and fitness consequences of individual variation in bottlenose dolphins' ecological niche.

The niche describes the ecological and social environment that an organism lives in, as well as the behavioural tactics used to interact with its environment. A species niche is key to both ecological and evolutionary processes, including speciation, and has therefore been a central focus in ecology. Recent evidence, however, points to considerable individual variation in a species' or population's niche use, although how this variation evolves or is maintained remains unclear. We used a large longitudinal dataset to investigate the drivers and maintenance of individual variation in bottlenose dolphins' Tursiops aduncus niche. Specifically, we (a) characterised the extent of individual differences in habitat use, (b) identified whether there were maternal effects associated with this variation and (c) investigated the relationship between habitat use and calving success, a component of reproductive fitness. By examining patterns of habitat use, we provide evidence that individual dolphins vary consistently between one another in their niche. We further show that such individual variation is driven by a strong maternal effect. Finally, habitat use and calving success were not related, suggesting that use of different habitats results in similar fitness outcomes. Niche partitioning, maintained by maternal effects, likely facilitates the coexistence of multiple ecotypes within this population.

A non-coding indel polymorphism in the fruitless gene of Drosophila melanogaster exhibits antagonistically pleiotropic fitness effects.

The amount of genetic variation for fitness within populations tends to exceed that expected under mutation-selection-drift balance. Several mechanisms have been proposed to actively maintain polymorphism and account for this discrepancy, including antagonistic pleiotropy (AP), where allelic variants have opposing effects on different components of fitness. Here, we identify a non-coding indel polymorphism in the fruitless gene of Drosophila melanogaster and measure survival and reproductive components of fitness in males and females of replicate lines carrying each respective allele. Expressing the fruitless region in a hemizygous state reveals a pattern of AP, with one allele generating greater reproductive fitness and the other conferring greater survival to adulthood. Different fitness effects were observed in an alternative genetic background, which may reflect dominance reversal and/or epistasis. Our findings link sequence-level variation at a single locus with complex effects on a range of fitness components, thus helping to explain the maintenance of genetic variation for fitness. Transcription factors, such as fruitless, may be prime candidates for targets of balancing selection since they interact with multiple target loci and their associated phenotypic effects.

Costs of cold acclimation on survival and reproductive behavior in Drosophila melanogaster.

Fitness is determined by the ability of an organism to both survive and reproduce; however, the mechanisms that lead to increased survival may not have the same effect on reproductive success. We used nineteen natural Drosophila melanogaster genotypes from the Drosophila Genetic Reference Panel to determine if adaptive plasticity following short-term acclimation through rapid cold-hardening (RCH) affects mating behavior and mating success. We confirmed that exposure to the acclimation temperature is beneficial to survival following cold stress; however, we found that this same acclimation temperature exposure led to less efficient male courtship and a significant decrease in the likelihood of mating. Cold tolerance and the capacity to respond plastically to cold stress were not correlated with mating behavior following acclimation, suggesting that the genetic control of the physiological effects of the cold temperature exposure likely differ between survival and behavioral responses. We also tested whether the exposure of males to the acclimation temperature influenced courtship song. This exposure again significantly increased courtship duration; however, courtship song was unchanged. These results illustrate costs of short-term acclimation on survival and reproductive components of fitness and demonstrate the pronounced effect that short-term thermal environment shifts can have on reproductive success.

Field estimates of parentage reveal sexually antagonistic selection on body size in a population of Anolis lizards.

Sexual dimorphism evolves when selection favors different phenotypic optima between the sexes. Such sexually antagonistic selection creates intralocus sexual conflict when traits are genetically correlated between the sexes and have sex‐specific optima. Brown anoles are highly sexually dimorphic: Males are on average 30% longer than females and 150% heavier in our study population. Viability selection on body size is known to be sexually antagonistic, and directional selection favors large male size whereas stabilizing selection constrains females to remain small. We build on previous studies of viability selection by measuring sexually antagonistic selection using reproductive components of fitness over three generations in a natural population of brown anoles. We estimated the number of offspring produced by an individual that survived to sexual maturity (termed RSV), a measure of individual fitness that includes aspects of both individual reproductive success and offspring survival. We found directional selection on male body size, consistent with previous studies of viability selection. However, selection on female body size varied among years, and included periods of positive directional selection, quadratic stabilizing selection, and no selection. Selection acts differently in the sexes based on both survival and reproduction and sexual conflict appears to be a persistent force in this species.

Local adaptation to developmental density does not lead to higher mating success in Drosophila melanogaster.

In this study, we investigate the effect of local adaptation to developmental density on male mating success in laboratory populations of Drosophila melanogaster. Mating success is known to be influenced by body condition which can in turn be influenced by local adaptation. We test the hypothesis that males adapted to a given environment have higher mating success when assayed in that environment. We used males selected for adaptation to high larval density and their controls which are reared at low larval density. We grew assay males in low and high densities whereas the focal females (raised at low larval density) used for the experiment belonged to the common ancestor of selected and control populations. We considered selected males grown at high density and control males grown at low density as 'adapted'. Similarly, we considered selected males grown at low density and control males grown at high density as 'nonadapted'. Selected male belonging to a given treatment (larval density) was made to compete with control male of the same treatment for mating with ancestral female. We quantified components of reproductive fitness: mating latency, copulation duration, mating success and number of progeny sired by the 'adapted' and 'nonadapted' males. The results show that local adaptation does not lead to higher mating success in populations adapted to their own larval rearing environment.

Variation in style morph frequencies in tristylous Lythrum salicaria in the Iberian Peninsula: the role of geographical and demographic factors.

The balance between stochastic forces and negative frequency-dependent selection largely determines style morph frequencies in heterostylous populations. Investigation of morph frequencies at geographical range limits can provide insights into the forces maintaining the floral polymorphism, and the factors causing biased morph ratios. Here, we investigate style morph frequencies in populations at the south-western European range limit of tristylous Lythrum salicaria, to explore the role of demographic and geographical factors influencing morph ratios in its native range. We measured morph composition and evenness, and the size of 96 populations, along a north to south latitudinal transect from Galicia to Andalucia, Iberian Peninsula, traversing a steep climatic gradient. To examine the potential influence of morph-specific fitness components on morph ratios, we examined reproductive traits in 19 populations. Most populations of L. salicaria were trimorphic (94·79 %), the majority exhibiting 1 : 1 : 1 morph ratios (68·75 %). Populations with biased morph ratios had a deficiency of the short-styled morph. Population size and morph evenness were positively associated with latitude, with smaller populations and those with less even morph ratios occurring towards the south. Greater variance in morph evenness was evident at the southern range margin. There were no consistent differences in components of reproductive fitness among style morphs, but southern populations produced less fruit and seed than more northerly populations. Our results demonstrate the influence of finite population size on morph frequencies in L. salicaria. However, they also illustrate the resilience of Iberian populations to the factors causing deviations from isoplethy and morph loss, especially at the southern range limit where populations are smaller. The maintenance of tristyly in small populations of L. salicaria may be aided by the genetic connectivity of populations in agricultural landscapes resulting from gene flow through pollen and seed dispersal.

Egg Viability, Mating Frequency and Male Mating Ability Evolve in Populations of Drosophila melanogaster Selected for Resistance to Cold Shock.

BackgroundAbility to resist temperature shock is an important component of fitness of insects and other ectotherms. Increased resistance to temperature shock is known to affect life-history traits. Temperature shock is also known to affect reproductive traits such as mating ability and viability of gametes. Therefore selection for increased temperature shock resistance can affect the evolution of reproductive traits.MethodsWe selected replicate populations of Drosophila melanogaster for resistance to cold shock. We then investigated the evolution of reproductive behavior along with other components of fitness- larval survivorship, adult mortality, fecundity, egg viability in these populations.ResultsWe found that larval survivorship, adult mortality and fecundity post cold shock were not significantly different between selected and control populations. However, compared to the control populations, the selected populations laid significantly higher percentage of fertile eggs (egg viability) 24 hours post cold shock. The selected populations had higher mating frequency both with and without cold shock. After being subjected to cold shock, males from the selected populations successfully mated with significantly more non-virgin females and sired significantly more progeny compared to control males.ConclusionsA number of studies have reported the evolution of survivorship in response to selection for temperature shock resistance. Our results clearly indicate that adaptation to cold shock can involve changes in components of reproductive fitness. Our results have important implications for our understanding of how reproductive behavior can evolve in response to thermal stress.

Strong selection genome-wide enhances fitness trade-offs across environments and episodes of selection.

Fitness trade-offs across episodes of selection and environments influence life-history evolution and adaptive population divergence. Documenting these trade-offs remains challenging as selection can vary in magnitude and direction through time and space. Here, we evaluate fitness trade-offs at the levels of the whole organism and the quantitative trait locus (QTL) in a multiyear field study of Boechera stricta (Brassicaceae), a genetically tractable mustard native to the Rocky Mountains. Reciprocal local adaptation was pronounced for viability, but not for reproductive components of fitness. Instead, local genomes had a fecundity advantage only in the high latitude garden. By estimating realized selection coefficients from individual-level data on viability and reproductive success and permuting the data to infer significance, we examined the genetic basis of fitness trade-offs. This analytical approach (Conditional Neutrality-Antagonistic Pleiotropy, CNAP) identified genetic trade-offs at a flowering phenology QTL (costs of adaptation) and revealed genetic trade-offs across fitness components (costs of reproduction). These patterns would not have emerged from traditional ANOVA-based QTL mapping. Our analytical framework can be applied to other systems to investigate fitness trade-offs. This task is becoming increasingly important as climate change may alter fitness landscapes, potentially disrupting fitness trade-offs that took many generations to evolve.

Reproductive and post‐reproductive life history of wild‐caughtDrosophila melanogasterunder laboratory conditions

The life history of the fruit fly (Drosophila melanogaster) is well understood, but fitness components are rarely measured by following single individuals over their lifetime, thereby limiting insights into lifetime reproductive success, reproductive senescence and post-reproductive lifespan. Moreover, most studies have examined long-established laboratory strains rather than freshly caught individuals and may thus be confounded by adaptation to laboratory culture, inbreeding or mutation accumulation. Here, we have followed the life histories of individual females from three recently caught, non-laboratory-adapted wild populations of D.melanogaster. Populations varied in a number of life-history traits, including ovariole number, fecundity, hatchability and lifespan. To describe individual patterns of age-specific fecundity, we developed a new model that allowed us to distinguish four phases during a female's life: a phase of reproductive maturation, followed by a period of linear and then exponential decline in fecundity and, finally, a post-ovipository period. Individual females exhibited clear-cut fecundity peaks, which contrasts with previous analyses, and post-peak levels of fecundity declined independently of how long females lived. Notably, females had a pronounced post-reproductive lifespan, which on average made up 40% of total lifespan. Post-reproductive lifespan did not differ among populations and was not correlated with reproductive fitness components, supporting the hypothesis that this period is a highly variable, random 'add-on' at the end of reproductive life rather than a correlate of selection on reproductive fitness. Most life-history traits were positively correlated, a pattern that might be due to genotype by environment interactions when wild flies are brought into a novel laboratory environment but that is unlikely explained by inbreeding or positive mutational covariance caused by mutation accumulation.

Reproductive aspects of American minks (Neovison vison) in central Spain: Testing the effects of prey availability

Some reproductive components of fitness (breeding times, litter size and the proportion of breeding females per year) of two feral populations of American minks in central Spain were investigated by means of direct observation from 2006 to 2010. The effects of prey availability were explored. Mating season was from February to March. Parturition dates did not differ between the two sites and pooled births took place between April (33.3%) and July (2.8%), peaking in May (40.3%). Mean litter size (the number of small cubs following their mother) was 3.43±1.01 cubs (±SD; n=30) with statistical significant differences between the two study sites. The strong seasonality in births and differences in litter size were related to prey availability (i.e. these are food-limited life-history traits), but in a complex non-linear fashion. A minimum value of prey abundance is necessary to breed. While litter size rises with prey abundance, there is a point where increasing prey did not result in an increase in litter size. Up to 75% of the females in the breeding pool reared cubs each year in both areas, which represents a somewhat high pool of breeding females. Delayed implantation is shorter than a month or does not exist in these populations. Such a short time-span seems to emerge because longer delays would have an important fitness cost to females. The breeding calendar and the litter size were similar to that reported previously from other areas.

Short-term fitness and long-term population trends in the orchid Anacamptis morio

The conservation of endangered species critically depends on the understanding to which degree short-term fitness and long-term trends are affected by intrinsic local conditions and external global dynamics. However, studies combining long-term demographic data with population level analyses of site conditions, genetic variation, and reproduction as well as with climatic data are still rare. Here we studied the endangered orchid Anacamptis morio, representative for species with a sub-mediterranean distribution. For populations at the northern range edge, we combined long-term monitoring data (1977–2010) with climatic data and analyzed reproductive fitness components, genetic variation, and abiotic site conditions. Reproduction was generally low as expected from the deceptive pollination system, and was positively influenced by population size and xerothermic site quality. The majority of populations showed a positive population trend, which was paralleled by an increase in spring temperature and positively affected by site quality. High levels of genetic variation were found in the populations which were at gene flow-drift equilibrium. A. morio may profit from increasing spring temperatures because of increased reproductive output. Nevertheless, whether climate change results in fitness increase or not may depend on the maintenance and provision of optimal site quality, i.e., xerothermic and nutrient poor conditions.

Similar offspring production by normal and intersex females in two populations of Gammarus minus (Malacostraca, Amphipoda) with high levels of intersexuality

Two Virginia (U.S.A.) populations of the freshwater amphipod Gammarus minus (Say, 1818) exhibit high frequencies of females with male genital papillae (60 to 75% in one population and 100% in the other) that have been observed for over 30 years. This observation is surprising because sex-allocation theory predicts that such intersex individuals should have lower evolutionary fitness than ‘normal’ males or females. Here we tested this theory by comparing a major component of reproductive fitness (offspring production, as estimated by number and total mass of offspring in a brood) between intersex and normal females. Although intersex females tend to brood slightly fewer, but larger embryos than those of normal females, these differences were not significant overall, and moreover they resulted in nearly identical mean production of total offspring mass per brood. Maternal somatic investment (body mass and body condition) during brooding also did not differ significantly between intersex and normal females. These results suggest that intersex females may not have lower reproductive fitness than that of normal females, which may help explain their high frequencies in the Virginia populations. Consistent with this hypothesis, available literature data on four amphipod species show a positive association between intersex frequency and the offspring production of intersex females relative to that of normal females. However, this hypothesis needs to be tested further by examining other reproductive and survival traits related to fitness, and by examining other amphipod populations with varying intersex frequencies. Moreover, the cause(s) of the intersex condition in the Virginia populations (and most other amphipod populations) remains largely unknown.

What is Aging?

In 1991, the book Evolutionary Biology of Aging offered the following definition of aging: a persistent decline in the age-specific fitness components of an organism due to internal physiological deterioration (Rose, 1991). This definition has since been used by others a number of times. However, it was only a modest generalization of a definition proffered by Alex Comfort over three editions (1956–1979) of his key book The Biology of Senescence (Comfort, 1979): “a progressive increase throughout life, or after a given stadium, in the likelihood that a given individual will die, during the next succeeding unit of time, from randomly distributed causes.” The 1991 definition chiefly added reproductive fitness components to Comfort's definition, while adding the qualifiers that the fitness-component decline should be persistent and should be “due to internal physiological deterioration,” where the latter phrase was meant fairly broadly. Thus increases in mortality with age due to chronic infections such as HIV/AIDS were excluded by the 1991 definition.

Nest site selection in the European wool-carder bee, Anthidium manicatum, with methods for an emerging model species

For many organisms, choosing an appropriate nest site is a critical component of reproductive fitness. Here we examine nest site selection in the solitary, resource defense polygynous bee, Anthidium manicatum. Using a wood-framed screen enclosure outfitted with food sources, nesting materials, and bamboo trap nests, we show that female bees prefer to initiate nests in sites located high above the ground. We also show that nest sites located at higher levels are less likely to contain spiderwebs, suggesting an adaptive explanation for nest site height preferences. We report size differences between this study’s source populations in Boston, Massachusetts and Brooklyn, New York; male bees collected in Boston have smaller mean head widths than males collected in Brooklyn. Finally, we argue that methods for studying captive populations of A. manicatum hold great promise for research into sexual selection, alternative phenotypes, recognition systems, and the evolution of nesting behavior.

Cost of inbreeding in resistance to herbivores in Datura stramonium

Experiments show that inbred progenies are frequently more damaged by herbivores than outcrossed progenies, suggesting that selfing is costly when herbivores are present and can increase the magnitude of inbreeding depression in survival and reproductive components of fitness. The present study assesses whether inbreeding increases herbivory and estimates the magnitude of inbreeding depression on reproductive components of fitness in the annual plant Datura stramonium. Two experiments were performed under natural conditions of herbivory to assess the effect of inbreeding on plant damage in D. stramonium. In the first experiment, outcrossed progeny was generated using foreign pollen donors, whereas inbred progeny was produced by self-pollination. In both groups, survival, herbivore damage and reproductive components of fitness were measured. In the second experiment, inbred and outcrossed progenies were produced using only local pollen donors, and only damage by herbivores was measured. Despite yearly variation in damage caused by the same specialist herbivores, inbred progeny suffered consistently more damage than outcrossed progeny. There was a significant inbreeding depression for fruit number (delta = 0.3), seed number per fruit (delta = 0.19) and seed number per plant (delta = 0.43). Furthermore, significant genetic variation amongst families in the magnitude of inbreeding depression was observed. The results suggest that the plant's mating system modified the pattern of herbivory by specialist insects in D. stramonium. Inbred plants suffer not only from the genetic cost of low vigour but also from greater damage by herbivores. The mechanism by which inbreeding reduces plant resistance to herbivores remains unknown but is an interesting area for future research.

Existence of vigorous lineages of crop-wild hybrids in Lettuce under field conditions.

Plant to plant gene flow is a route of environmental exposure for GM plants specifically since crosses with wild relatives could lead to the formation of more vigorous hybrids, which could increase the rate of introgression and the environmental impact. Here, we test the first step in the process of potential transgene introgression: whether hybrid vigor can be inherited to the next generation, which could lead to fixation of altered, i.e., elevated, quantitative traits. The potential for a permanent elevated fitness was tested using individual autogamous progeny lineages of hybrids between the crop Lactuca sativa (Lettuce) and the wild species Lactuca serriola (Prickly Lettuce). We compared progeny from motherplants grown under either greenhouse or field conditions. The survival of young plants depended strongly on maternal environment. Furthermore, we observed that offspring reproductive fitness components were correlated with maternal fitness. Our study demonstrates that post-zygotic genotypic sorting at the young plants stage reduces the number of genotypes non-randomly, leading to inheritance of high levels of reproductive traits in the surviving hybrid lineages, compared to the pure wild relatives. Consequently, directional selection could lead to displacement of the pure wild relative and fixation of more vigorous genome segments originating from crops, stabilizing plant traits at elevated levels. Such information can be used to indentify segments which are less likely to introgress into wild relative populations as a target for transgene insertion.

Correlations among Fertility Components Can Maintain Mixed Mating in Plants

Classical models studying the evolution of self-fertilization in plants conclude that only complete selfing and complete outcrossing are evolutionarily stable. In contrast with this prediction, 42% of seed-plant species are reported to have rates of self-fertilization between 0.2 and 0.8. We propose that many previous models fail to predict intermediate selfing rates because they do not allow for functional relationships among three components of reproductive fitness: self-fertilized ovules, outcrossed ovules, and ovules sired by successful pollen export. Because the optimal design for fertility components may differ, conflicts among the alternative pathways to fitness are possible, and the greatest fertility may be achieved with some self-fertilization. Here we develop and analyze a model to predict optimal selfing rates that includes a range of possible relationships among the three components of reproductive fitness, as well as the effects of evolving inbreeding depression caused by deleterious mutations and of selection on total seed number. We demonstrate that intermediate selfing is optimal for a wide variety of relationships among fitness components and that inbreeding depression is not a good predictor of selfing-rate evolution. Functional relationships subsume the myriad effects of individual plant traits and thus offer a more general and simpler perspective on mating system evolution.

Water availability limits tolerance of apical damage in the Chilean tarweed Madia sativa

Plant tolerance is the ability to reduce the negative impact of herbivory on plant fitness. Numerous studies have shown that plant tolerance is affected by nutrient availability, but the effect of soil moisture has received less attention. We evaluated tolerance of apical damage (clipping that mimicked insect damage) under two watering regimes (control watering and drought) in the tarweed Madia sativa (Asteraceae). We recorded number of heads with seeds and total number of heads as traits related to fitness. Net photosynthetic rate, water use efficiency, number of branches, shoot biomass, and the root:shoot biomass ratio were measured as traits potentially related to tolerance via compensatory responses to damage. In the drought treatment, damaged plants showed ≈43% reduction in reproductive fitness components in comparison with undamaged plants. In contrast, there was no significant difference in reproductive fitness between undamaged and damaged plants in the control watering treatment. Shoot biomass was not affected by apical damage. The number of branches increased after damage in both water treatments but this increase was limited by drought stress. Net photosynthetic rate increased in damaged plants only in the control watering treatment. Water use efficiency increased with drought stress and, in plants regularly watered, also increased after damage. Root:shoot ratio was higher in the low water treatment and damaged plants tended to reduce root:shoot ratio only in this water treatment. It is concluded that water availability limits tolerance to apical damage in M. sativa, and that putative compensatory mechanisms are differentially affected by water availability.

Empirical assessment of the reproductive fitness components of the hybrid pine Pinus densata on the Tibetan Plateau

Pinus densata is distributed on the Tibetan Plateau, where it forms extensive forests at high elevations. Genetic studies have provided evidence that P. densata originated through hybridization between P. yunnanensis and P. tabuliformis. To clarify the relationships among these pines, and assess their reproductive fitness in their respective habitats, we conducted a comparative analysis of eight cone and seed morphometric traits and six reproductive traits in them. Among the eight morphometric traits examined, six appeared to be intermediate in P. densata between those of P. yunnanensis and P. tabuliformis. There were significant differences among the three pines in all of the morphometric traits, and P. densata showed greater variability in these traits than the other two pines. In contrast to the morphometric traits, the reproductive traits (including the proportions of filled and empty seeds, ovule abortion rate, seed efficiency, meiotic abnormalities during microsporogenesis and pollen viability) differed little among the three pines, indicating that they have similar overall rates of effective pollination and fertilization in their respective natural environments. Despite their location on the high plateau, natural populations of P. densata appeared to have normal levels of reproductive success, comparable to those of the two parental species in their natural habitats. This study provides empirical data characterizing the reproductive success and adaptation of a stabilized homoploid hybrid in a novel habitat that is ecologically and spatially inaccessible to its parental species.

Assessments of habitat preferences and quality depend on spatial scale and metrics of fitness

SummaryIdentifying the habitat features that influence habitat selection and enhance fitness is critical for effective management. Ecological theory predicts that habitat choices should be adaptive, such that fitness is enhanced in preferred habitats. However, studies often report mismatches between habitat preferences and fitness consequences across a wide variety of taxa based on a single spatial scale and/or a single fitness component.We examined whether habitat preferences of a declining shrub steppe songbird, the Brewer's sparrowSpizella breweri, were adaptive when multiple reproductive fitness components and spatial scales (landscape, territory and nest patch) were considered.We found that birds settled earlier and in higher densities, together suggesting preference, in landscapes with greater shrub cover and height. Yet nest success was not higher in these landscapes; nest success was primarily determined by nest predation rates. Thus landscape preferences did not match nest predation risk. Instead, nestling mass and the number of nesting attempts per pair increased in preferred landscapes, raising the possibility that landscapes were chosen on the basis of food availability rather than safe nest sites.At smaller spatial scales (territory and nest patch), birds preferred different habitat features (i.e. density of potential nest shrubs) that reduced nest predation risk and allowed greater season‐long reproductive success.Synthesis and applications.Habitat preferences reflect the integration of multiple environmental factors across multiple spatial scales, and individuals may have more than one option for optimizing fitness via habitat selection strategies. Assessments of habitat quality for management prescriptions should ideally include analysis of diverse fitness consequences across multiple ecologically relevant spatial scales.