Inbreeding depression and a poor start in life

Inbreeding is a widespread phenomenon that can decrease fitness. Inbreeding depression occurs because matings between relatives lead to an increase in homozygosity. Inbreeding is a pervasive force in evolutionary ecology driving the evolution of different traits, mating systems, and influencing population dynamics. It is generally assumed that the negative effects of inbreeding are exacerbated in stressful environments. In this thesis, I present seven experimental studies that explore whether life history, morphological, and sexual traits show inbreeding depression, and if this effect is increased by an interaction with an early stressful environment. Chapter 1 explores the preference for novel mates by males and females depending on the choosers’ previous sexual experience. I discuss the potential adaptive significance of these preferences and the likelihood of there being benefits of mating with multiple partners for both males and females. In the second chapter I look at the effects of mating with relatives on offspring fitness. I highlight the importance of considering the potential role of maternal effects when studying inbreeding depression, and the relative importance of genetic and maternal effects on reproductive traits and offspring performance. Chapter 3 addresses the interaction between inbreeding depression and an environmental stress, in the form of restricted food availability early in life. I test whether diet restriction during early development influences subsequent growth trajectories in ways that depend on the level of inbreeding. I then discuss potential hidden long-term costs that could affect reproductive success. In the fourth chapter I investigate the effects of limited food availability on sexually selected traits. I present a study testing whether a poor early diet is costly due to the reduced expression of sexually selected male characters. I aim to understand whether individuals are able to compensate for a poor start in life in various ways, or if they still incur costs that are evident after maturation. Chapter 5 investigates how differences in inbreeding and an early stressful environment influence the actual reproductive success of males. I argue about the extent to which inbreeding depression in males is due to natural or sexual selection. In Chapter 6 I explore how key factors act and interact to determine the strength of parental effects and whether these factors differ between mothers and fathers, and between their effects on sons and daughters. I discuss the multifaceted role of parental effects in a species lacking parental care. Finally, in the seventh chapter I provide a test of the effects of early life environment on the expression of genetic and maternal effects variance for a range of adult traits. I argue that maternal by-environment interactions are an under-appreciated component of phenotypic diversity

Evidence for inbreeding depression in a species with limited opportunity for maternal effects

It is often assumed that mating with close relatives reduces offspring fitness. In such cases, reduced offspring fitness may arise from inbreeding depression (i.e., genetic effects of elevated homozygosity) or from post-mating maternal investment. This can be due to a reduction in female investment after mating with genetically incompatible males ("differential allocation") or compensation for incompatibility ("reproductive compensation"). Here, we looked at the effects of mating with relatives on offspring fitness in mosquitofish, Gambusia holbrooki. In this species, females are assumed to be nonplacental and to allocate resources to eggs before fertilization, limiting differential allocation. We looked at the effects of mating with a brother or with an unrelated male on brood size, offspring size, gestation period, and early offspring growth. Mating with a relative reduced the number of offspring at birth, but there was no difference in the likelihood of breeding, gestation time, nor in the size or growth of these offspring. We suggest that due to limited potential for maternal effects to influence these traits that any reduction in offspring fitness, or lack thereof, can be explained by inbreeding depression rather than by maternal effects. We highlight the importance of considering the potential role of maternal effects when studying inbreeding depression and encourage further studies in other Poeciliid species with different degrees of placentation to test whether maternal effects mask or amplify any genetic effects of mating with relatives.This work was supported bythe Australian Research Council (DP120100339). R.V.-T. is supported by fellowships from Consejo Nacion-al de Ciencia y Tecnologıa-Mexico and the ResearchSchool of Biology

Meta-analysis shows no consistent evidence for senescence in ejaculate traits across animals

Male reproductive traits such as ejaculate size and quality, are expected to decline with advancing age due to senescence. It is however unclear whether this expectation is upheld across taxa. We perform a meta-analysis on 379 studies, to quantify the effects of advancing male age on ejaculate traits across 157 species of non-human animals. Contrary to predictions, we find no consistent pattern of age-dependent changes in ejaculate traits. This result partly reflects methodological limitations, such as studies sampling a low proportion of adult lifespan, or the inability of meta-analytical approaches to document non-linear ageing trajectories of ejaculate traits; which could potentially lead to an underestimation of senescence. Yet, we find taxon-specific differences in patterns of ejaculate senescence. For instance, older males produce less motile and slower sperm in ray-finned fishes, but larger ejaculates in insects, compared to younger males. Notably, lab rodents show senescence in most ejaculate traits measured. Our study challenges the notion of universal reproductive senescence, highlighting the need for controlled methodologies and a more nuanced understanding of reproductive senescence, cognisant of taxon-specific biology, experimental design, selection pressures, and life-history

Supplementary material from "Experimental translocations to low predation lead to non-parallel increases in relative brain size"

Predation is a near ubiquitous factor of nature and a powerful selective force on prey. Moreover, it has recently emerged as an important driver in the evolution of brain anatomy, though population comparisons show ambiguous results with considerable unexplained variation. Here, we test the reproducibility of reduced predation on evolutionary trajectories on brain evolution. We make use of an introduction experiment, whereby guppies (Poecilia reticulata) from a single high predation stream were introduced to four low predation streams. After 8–9 years of natural selection in the wild and two generations of common garden conditions in the laboratory, we quantified brain anatomy. Relative brain region sizes did not differ between populations. However, we found a general increase and striking variation in relative brain size of introduced populations, which varied from no change to a 12.5% increase in relative brain weight, relative to the ancestral high predation population. We interpret this as evidence for non-parallel evolution, which implies a weak or inconsistent association of relative brain size with fitness in low predation sites. The evolution of brain anatomy appears sensitive to unknown environmental factors, or contingent on either chance events or historical legacies of environmental change

Experimental translocations to low predation lead to non-parallel increases in relative brain size

Predation is a near ubiquitous factor of nature and a powerful selective force on prey. Moreover, it has recently emerged as an important driver in the evolution of brain anatomy, though population comparisons show ambiguous results with considerable unexplained variation. Here, we test the reproducibility of reduced predation on evolutionary trajectories of brain evolution. We make use of an introduction experiment, whereby guppies (Poecilia reticulata) from a single high predation stream were introduced to four low predation streams. After 8-9 years of natural selection in the wild and two generations of common garden conditions in the laboratory, we quantified brain anatomy. Relative brain region sizes did not differ between populations. However, we found a general increase and striking variation in relative brain size of introduced populations, which varied from no change to a 12.5% increase in relative brain weight, relative to the ancestral high predation population. We interpret this as evidence for non-parallel evolution, which implies a weak or inconsistent association of relative brain size with fitness in low predation sites. The evolution of brain anatomy appears sensitive to unknown environmental factors, or contingent on either chance events or historical legacies of environmental change.</p

Data from: Inbreeding depression does not increase after exposure to a stressful environment: a test using compensatory growth

Background: Inbreeding is often associated with a decrease in offspring fitness (‘inbreeding depression’). Moreover, it is generally assumed that the negative effects of inbreeding are exacerbated in stressful environments. This G × E interaction has been explored in many taxa under different environmental conditions. These studies usually manipulate environmental conditions either in adulthood or throughout an individual’s entire life. Far fewer studies have tested how stressful environments only experienced during development subsequently influence the effects of inbreeding on adult traits. Results: We experimentally manipulated the diet (control versus low food) of inbred and outbred juvenile Eastern mosquitofish (Gambusia holbrooki) for three weeks (days 7-28) to test whether experiencing a presumably stressful environment early in life influences their subsequent growth and adult phenotypes. The control diet was a standard laboratory food regime, while fish on the low food diet received less than 25 % of this amount of food. Unexpectedly, despite a large sample size (237 families, 908 offspring) and a quantified 23 % reduction in genome-wide heterozygosity in inbred offspring from matings between full-siblings (f = 0.25), neither inbreeding nor its interaction with early diet affected growth trajectories, juvenile survival or adult size. Individuals did not mitigate a poor start in life by showing ‘compensatory growth’ (i.e. faster growth once the low food treatment ended), but they showed ‘catch-up growth’ by delaying maturation. There was, however, no effect of inbreeding on the extent of catch-up growth. Conclusions: There were no detectable effects of inbreeding on growth or adult size, even on a low food diet that should elevate inbreeding depression. Thus, the long-term costs of inbreeding due to lower male reproductive success we have shown in another study appear to be unrelated to inbreeding depression for adult male size or the growth rates that are reported in the current study

Vega-Trejo et.al.2015.Ecol and Evol.Dryad

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