Offspring Reproductive Success Research Articles

Trichopria anastrephae: A Promising Neotropical-Native Parasitoid for Drosophila suzukii Control

Trichopria anastrephae: A Promising Neotropical-Native Parasitoid for Drosophila suzukii Control

Moving from trends to benchmarks by using regression tree analysis to find inbreeding thresholds in a critically endangered bird.

Understanding how inbreeding affects endangered species in conservation breeding programs is essential for their recovery. The Hawaiian Crow ('Alalā) (Corvus hawaiiensis) is one of the world's most endangered birds. It went extinct in the wild in 2002, and, until recent release efforts starting in 2016, nearly all of the population remained under human care for conservation breeding. Using pedigree inbreeding coefficients (F), we evaluated the effects of inbreeding on Hawaiian Crow offspring survival and reproductive success. We used regression tree analysis to identify the level of inbreeding (i.e., inbreeding threshold) that explains a substantial decrease in 'Alalā offspring survival to recruitment. Similar to a previous study of inbreeding in 'Alalā, we found that inbreeding had a negative impact on offspring survival but that parental (vs. artificial) egg incubation improved offspring survival to recruitment. Furthermore, we found that inbreeding did not substantially affect offspring reproductive success, based on the assumption that offspring that survive to adulthood breed with distantly related mates. Our novel application of regression tree analysis showed that offspring with inbreeding levels exceeding F = 0.098 were 69% less likely to survive to recruitment than more outbred offspring, providing a specific threshold value for ongoing population management. Our results emphasize the importance of assessing inbreeding depression across all life history stages, confirm the importance of prioritizing parental over artificial egg incubation in avian conservation breeding programs, and demonstrate the utility of regression tree analysis as a tool for identifying inbreeding thresholds, if present, in any pedigree-managed population.

Older fathers' children have lower evolutionary fitness across four centuries and in four populations.

Higher paternal age at offspring conception increases de novo genetic mutations. Based on evolutionary genetic theory we predicted older fathers' children, all else equal, would be less likely to survive and reproduce, i.e. have lower fitness. In sibling control studies, we find support for negative paternal age effects on offspring survival and reproductive success across four large populations with an aggregate N > 1.4 million. Three populations were pre-industrial (1670–1850) Western populations and showed negative paternal age effects on infant survival and offspring reproductive success. In twentieth-century Sweden, we found minuscule paternal age effects on survival, but found negative effects on reproductive success. Effects survived tests for key competing explanations, including maternal age and parental loss, but effects varied widely over different plausible model specifications and some competing explanations such as diminishing paternal investment and epigenetic mutations could not be tested. We can use our findings to aid in predicting the effect increasingly older parents in today's society will have on their children's survival and reproductive success. To the extent that we succeeded in isolating a mutation-driven effect of paternal age, our results can be understood to show that de novo mutations reduce offspring fitness across populations and time periods.

Within-female plasticity in sex allocation is associated with a behavioural polyphenism in house wrens.

Sex allocation theory assumes individual plasticity in maternal strategies, but few studies have investigated within-individual changes across environments. In house wrens, differences between nests in the degree of hatching synchrony of eggs represent a behavioural polyphenism in females, and its expression varies with seasonal changes in the environment. Between-nest differences in hatching asynchrony also create different environments for offspring, and sons are more strongly affected than daughters by sibling competition when hatching occurs asynchronously over several days. Here, we examined variation in hatching asynchrony and sex allocation, and its consequences for offspring fitness. The number and condition of fledglings declined seasonally, and the frequency of asynchronous hatching increased. In broods hatched asynchronously, sons, which are over-represented in the earlier-laid eggs, were in better condition than daughters, which are over-represented in the later-laid eggs. Nonetheless, asynchronous broods were more productive later within seasons. The proportion of sons in asynchronous broods increased seasonally, whereas there was a seasonal increase in the production of daughters by mothers hatching their eggs synchronously, which was characterized by within-female changes in offspring sex and not by sex-biased mortality. As adults, sons from asynchronous broods were in better condition and produced more broods of their own than males from synchronous broods, and both males and females from asynchronous broods had higher lifetime reproductive success than those from synchronous broods. In conclusion, hatching patterns are under maternal control, representing distinct strategies for allocating offspring within broods, and are associated with offspring sex ratios and differences in offspring reproductive success.

What are the benefits of parental care? The importance of parental effects on developmental rate.

The evolution of parental care is beneficial if it facilitates offspring performance traits that are ultimately tied to offspring fitness. While this may seem self-evident, the benefits of parental care have received relatively little theoretical exploration. Here, we develop a theoretical model that elucidates how parental care can affect offspring performance and which aspects of offspring performance (e.g., survival, development) are likely to be influenced by care. We begin by summarizing four general types of parental care benefits. Care can be beneficial if parents (1) increase offspring survival during the stage in which parents and offspring are associated, (2) improve offspring quality in a way that leads to increased offspring survival and/or reproduction in the future when parents are no longer associated with offspring, and/or (3) directly increase offspring reproductive success when parents and offspring remain associated into adulthood. We additionally suggest that parental control over offspring developmental rate might represent a substantial, yet underappreciated, benefit of care. We hypothesize that parents adjust the amount of time offspring spend in life-history stages in response to expected offspring mortality, which in turn might increase overall offspring survival, and ultimately, fitness of parents and offspring. Using a theoretical evolutionary framework, we show that parental control over offspring developmental rate can represent a significant, or even the sole, benefit of care. Considering this benefit influences our general understanding of the evolution of care, as parental control over offspring developmental rate can increase the range of life-history conditions (e.g., egg and juvenile mortalities) under which care can evolve.

No evidence for sex biases in milk macronutrients, energy, or breastfeeding frequency in a sample of filipino mothers

Maternal reproductive investment includes both the energetic costs of gestation and lactation. For most humans, the metabolic costs of lactation will exceed those of gestation. Mothers must balance reproductive investment in any single offspring against future reproductive potential. Among mammals broadly, mothers may differentially invest in offspring based on sex and maternal condition provided such differences investment influence future offspring reproductive success. For humans, there has been considerable debate if there are physiological differences in maternal investment by offspring sex. Two recent studies have suggested that milk composition differs by infant sex, with male infants receiving milk containing higher fat and energy; prior human studies have not reported sex-based differences in milk composition. This study investigates offspring sex-based differences in milk macronutrients, milk energy, and nursing frequency (per 24 h) in a sample of 103 Filipino mothers nursing infants less than 18 months of age. We found no differences in milk composition by infant sex. There were no significant differences in milk composition of mothers nursing first-born versus later-born sons or daughters or between high- and low-income mothers nursing daughters or sons. Nursing frequency also showed no significant differences by offspring sex, sex by birth order, or sex by maternal economic status. In the Cebu sample, there is no support for sex-based differences in reproductive investment during lactation as indexed by milk composition or nursing frequency. Further investigation in other populations is necessary to evaluate the potential for sex-based differences in milk composition among humans.

Parental investment and the optimization of human family size.

Human reproductive behaviour is marked by exceptional variation at the population and individual level. Human behavioural ecologists propose adaptive hypotheses to explain this variation as shifting phenotypic optima in relation to local socioecological niches. Here we review evidence that variation in fertility (offspring number), in both traditional and modern industrialized populations, represents optimization of the life-history trade-off between reproductive rate and parental investment. While a reliance on correlational methods suggests the true costs of sibling resource competition are often poorly estimated, a range of anthropological and demographic studies confirm that parents balance family size against offspring success. Evidence of optimization is less forthcoming. Declines in fertility associated with modernization are particularly difficult to reconcile with adaptive models, because fertility limitation fails to enhance offspring reproductive success. Yet, considering alternative measures, we show that modern low fertility confers many advantages on offspring, which are probably transmitted to future generations. Evidence from populations that have undergone or initiated demographic transition indicate that these rewards to fertility limitation fall selectively on relatively wealthy individuals. The adaptive significance of modern reproductive behaviour remains difficult to evaluate, but may be best understood in response to rising investment costs of rearing socially and economically competitive offspring.

The genetic architecture of fitness in a seed beetle: assessing the potential for indirect genetic benefits of female choice

BackgroundQuantifying the amount of standing genetic variation in fitness represents an empirical challenge. Unfortunately, the shortage of detailed studies of the genetic architecture of fitness has hampered progress in several domains of evolutionary biology. One such area is the study of sexual selection. In particular, the evolution of adaptive female choice by indirect genetic benefits relies on the presence of genetic variation for fitness. Female choice by genetic benefits fall broadly into good genes (additive) models and compatibility (non-additive) models where the strength of selection is dictated by the genetic architecture of fitness. To characterize the genetic architecture of fitness, we employed a quantitative genetic design (the diallel cross) in a population of the seed beetle Callosobruchus maculatus, which is known to exhibit post-copulatory female choice. From reciprocal crosses of inbred lines, we assayed egg production, egg-to-adult survival, and lifetime offspring production of the outbred F1 daughters (F1 productivity).ResultsWe used the bio model to estimate six components of genetic and environmental variance in fitness. We found sizeable additive and non-additive genetic variance in F1 productivity, but lower genetic variance in egg-to-adult survival, which was strongly influenced by maternal and paternal effects.ConclusionOur results show that, in order to gain a relevant understanding of the genetic architecture of fitness, measures of offspring fitness should be inclusive and should include quantifications of offspring reproductive success. We note that our estimate of additive genetic variance in F1 productivity (CVA = 14%) is sufficient to generate indirect selection on female choice. However, our results also show that the major determinant of offspring fitness is the genetic interaction between parental genomes, as indicated by large amounts of non-additive genetic variance (dominance and/or epistasis) for F1 productivity. We discuss the processes that may maintain additive and non-additive genetic variance for fitness and how these relate to indirect selection for female choice.

P-714: Maternal biological age impacts first generation female offspring reproductive success during infertility treatment

During the early human life, somatic cells differentiate and specialize to certain functions through intense epigenetic modifications. The gametes’ genome also undergoes these epigenetic modifications, however, they are then later erased (except gonad specific imprinting) contributing to the preservation of their longevity and the potential to produce a new individual. Gametes in the female gonad present an age dependent decrease of quality and related decline of female fertility is also well described.

Individual mares bias investment in sons and daughters in relation to their condition

The Trivers–Willard hypothesis (TWH) predicts that a mother will treat a son or daughter differently depending on her ability to invest and the impact of her investment on offspring reproductive success. Although many studies have investigated the hypothesis, few have definitively supported or refuted it because of confounding factors or an inappropriate level of analysis. We studied maternal investment in sons and daughters in feral horses, Equus caballus, which meet the assumptions of the TWH with a minimum of confounding variables. Population level analyses revealed no differences in maternal behaviour towards sons and daughters. When we incorporated mare condition, we found that sons were more costly to mares in good condition, whereas daughters were more costly to mares in poor condition, although no differences in maternal behaviour were found. However, since the TWH makes predictions about individual mothers, we examined investment by mares who reared both a son and a daughter in different years of the study. Mares in good condition invested more in their sons in terms of maternal care patterns, costs to maternal body condition and costs to future reproduction. Conversely, mares in poor condition invested more in daughters. Therefore, with an appropriate level of analysis in a species in which confounding variables are minimal, the predictions of the Trivers–Willard hypothesis are supported.

Male sexual rest affects litter sex ratio of newborn Norway rats

Associations between male sexual rest and litter sex ratio have been reported in Norway rats, Rattus norvegicus, but the direction of the effect has been inconsistent. Female rats were paired with either a male that had copulated to satiety three weeks previously or a male that had copulated within the previous four days. Females were paired during both a cycling oestrus and a postpartum oestrus. Sex-ratio biases were only observed in litters conceived during a cycling oestrus. Litters sired by rested males had higher sex ratios than litters sired by unrested males. This relationship was mediated by differences in the timing of mating events, including length of post-ejaculatory interval and the time at which effective mating was completed. Sex ratio was negatively associated with time of mating completion, replicating earlier findings. Only litters that had fewer pups at birth than at implantation showed the relationship between sex ratio and rest-mediated mating behaviour. These litters were not smaller than litters without loss, however. Post-implantation loss was more likely to occur when uterine horns were crowded, suggesting that this type of sex-ratio biasing occurs in the context of adaptive litter reduction. This association between paternal behaviour, paternal condition and offspring sex ratio prompts the hypothesis that females use the timing of mating behaviour to evaluate heritable traits that might affect male mating success, and then adjust offspring sex ratio to maximize offspring reproductive success.

Clutch size, offspring performance, and intergenerational fitness

It is now generally recognized that clutch size affects more than offspring number. In particular, clutch size affects a suite of traits associated with offspring reproductive performance. Optimal clutch size is therefore determined not by the numerically most productive clutch but by the clutch that maximizes collective offspring reproductive success. Calculation of optimal clutch size thus requires a consideration of ecological factors operating during an intergenerational time frame, spanning the lifetime of the egglaying adult and the lifetimes of her offspring. The optimal clutch cannot define reproductive values in advance, but instead requires that the strategy chosen is the best response to the set of reproductive values that it itself generates. In this article, we introduce methods for solving this problem, based on an iterative solution of the equation characterizing expected lifetime reproductive success. We begin by considering a semelparous organism, in which case lifetime reproductive success is a function only of the state of the organism. For an iteroparous organism, lifetime reproductive success depends upon both state and time, so that our methods extend the usual stochastic dynamic programming approach to the evaluation of lifetime reproductive success. The methods are intuitive and easily used. We consider both semelparous and iteroparous organisms, stable and varying environments, and describe how our methods can be employed empirically.

Baboons adjust secondary sex ratio in response to predictors of sex-specific offspring survival

Most theories of sex ratio adjustment assume that parents will adjust the sex ratio of births (secondary sex ratio) in a manner that maximizes offspring reproductive success (as long as this does not jeopardize parental reproductive success). Survival to maturity is typically the largest component of variance in offspring reproductive success. This should make environmental predictors of sex-specific offspring survival strong predictors of secondary sex ratio adjustment. We tested this survivorship maximization hypothesis for secondary sex ratio adjustment using data from a 17-year demographic study of 315 yellow baboon infants at Mikumi National Park, Tanzania. Sex differences were found in the degree to which several social and ecological conditions affected infant survival to 1 year. Female, but not male, infant survival was inversely correlated with birth order and the proportion of infant females in their birth cohort. Male, but not female, infant survival was inversely correlated with the amount of rainfall early in the year (January) and the proportion of infant males in their birth cohort; male survival also was positively correlated with maternal dominance rank. The consistency and timing of these effects across years suggested that such information was, in fact, available to females around the time of conception. Most importantly, social and ecological conditions that predicted improved survivorship of a given sex also were positively correlated with production of that sex. Early births were female-biased; and low January rainfall was correlated with a male-biased sex ratio, becoming increasingly female-biased as January rainfall increased. However, no sex ratio effects were correlated with maternal rank. Data supported the hypothesis that females adjusted secondary sex ratio in a manner that maximized sex-specific infant survival. This hypothesis also offered a plausible explanation for some of the contradictory data that have arisen from studies of maternal rank effects on sex ratio both within and between species.

Mycorrhizal infection of wild oats: maternal effects on offspring growth and reproduction.

The objective of this study was to determine whether infection of Avena fatua L. plants by the mycorrhizal fungus Glomus intraradices Schenck & Smith could influence the vigor of the offspring generation. Two experiments demonstrated that mycorrhizal infection of the maternal generation had slight but persistent positive effects on offspring leaf expansion in the early stages of growth. In two other experiments, mycorrhizal infection of mother plants had several long lasting effects on their offspring. Offspring produced by mycorrhizal mother plants had greater leaf areas, shoot and root nutrient contents and root:shoot ratios compared to those produced by non-mycorrhizal mother plants. Moreover, mycorrhizal infection of mother plants significantly reduced the weight of individual seeds produced by offspring plants while it increased the P concentrations of the seeds and the number of seeds per spikelet produced by offspring plants. The effects of mycorrhizal infections of maternal plants on the vigor and performance of offspring plants were associated with higher seed phosphorus contents but generally lighter seeds. The results suggest that mycorrhizal infection may influence plant fitness by increasing offspring vigor and offspring reproductive success in addition to previously reported increases in maternal fecundity.

Mating System and Reproductive Success: a Comparison of Two African Forest Monkeys (Colobus Badius and Cercopithecus Ascanius)

Reproductive success was compared between two species of rainforest monkeys. The folivorous red colobus lived in patrilineal, multi-male groups, whereas the omnivorous, redtail had matrilineal groups usually with only one adult male, but occasionally experiencing temporary multi-male influxes. Maternal investment by red colobus in offspring was demonstrated in two ways. Offspring survival was positively correlated with interbirth interval even when cases of neonatal mortality were excluded. Among male red colobus surviving to at least 24 months, the interbirth interval following their birth was positively correlated with the age at which they disappeared or became breeders. Female red colobus appear to invest more in sons than daughters. Among the primate species examined, females invested more in their sons and daughters depending upon variables such as intersexual differences in variance in reproductive success, the dispersing sex, and maternal dominance rank as it influenced the offspring's reproductive success. Lifetime reproductive success (LRS) of female red colobus was influenced most by offspring survivorship and less so by birth rate. In contrast, LRS of male red colobus was largely a function of reproductive rate and lifespan, with offspring survivorship playing a much smaller role. Variance in LRS was higher in males than females. This difference was much more pronounced in the one-male groups of redtails than the multi-male groups of red colobus. The coefficient of variation in male reproductive success in these two species was similar to that in other polygynous mammals, except elephant seals. Although offspring mortality and estimated reproductive lifespan were nearly identical for males of the two species, the harem breeding system and highly skewed adult sex ratio lead to greater, more variable LRS in redtail males. Male red colobus within groups produced about 20% more offspring per year than male redtails, but the large proportion of red colobus males with zero breeding success reduced mean LRS to 40% less than redtails. While annual fecundity among adult females of both species was similar, variance in annual fecundity among female redtails was over five times greater than in female red colobus. This, accompanied by a longer reproductive lifespan in red colobus females, lead to a higher LRS in female red colobus and a lower coefficient of variation than in female redtails. Although females are the primary dispersers in red colobus, they did not have a greater coefficient of variation in LRS than in species where females rarely disperse. This is because female red colobus were readilty accepted into new groups and their intergroup transfer was relatively rapid with little time, if any, spent as a solitary. In both red colobus and redtails adult males contributed, on average, more offspring to the succeeding generation than adult females, as in other polygynous mammals. This is because fewer males survived to adulthood, but once they reached adulthood, their estimated reproductive lifespans were similar to females.

Sibling Competition and Evolution of Pollen Unit, Ovule Number, and Pollen Vector in Angiosperms

The pollination biology of angiosperms affects the quantity and qual- ity of seeds produced by an individual. The amount of genetic variability present in the seeds of a single fruit is dependent on the number of male parents involved in fertilization. The variation in genetic relatedness of developing siblings in an ovary may lead to varying degrees of competition among young seeds for maternal nu- trients. Kin selection theory predicts that closely related seeds resulting from fertil- ization by a single paternal parent will compete less with each other than seeds fertilized by different fathers. Ramdom dispersal of single pollen grains character- istic of wind pollination tends to produce less closely related seeds in multi-ovulate ovaries. Pollen transferred between flowers in large aggregations by specialized an- imal pollinators gives rise to seeds that are full siblings. The evolution of animal pollination, large pollen unit size, and multi-ovulate ovaries in some angiosperms may be understood in terms of competitive interactions among the developing seeds. The multi-seeded angiosperm fruit contains a unique collection of in- dividuals. These individuals are young sporophytes that share a common maternal parent. The group is special because of the relatively high ge- netic relatedness of its members. The high genetic similarity is important in two ways. First, within a single fruit it sets an upper limit to the amount of genetic variation controlling the rate and quality of seed development. Second, the large number of genes by descent shared by these sporophytes will augment the inclusive fitness component of offspring reproductive success and influence their competitive interactions. Inclu- sive fitness is defined here as the total reproductive value of an individual including personal production of offspring plus the individual's effects on the reproduction of relatives (Hamilton 1964; West Eberhard 1975). Haldane (1923) originally noted that the pollination system in angio- sperms determines the number of paternal parents involved in fertiliza- tion. Later Hamilton (1964) suggested that seeds in the flowering plant ovary can be half-sibs, full-sibs, or genetically identical individuals de- pending on the manner in which pollen is transferred between plants. He also pointed out that the variation in genetic relatedness of sibs might influence the degree of competition and cooperation among them. To date there has been no experimental confirmation of the hypothesis that kin selection has led to the evolution of cooperative interactions among fertilized ovules in the angiosperm ovary. The difficulties encountered in studying kin selection as an evolutionary process in the laboratory have been pointed out by Wade (1980). In the present paper I attempt