Does inbreeding distort sex-ratios?

Frankham, Richard; Wilcken, Jonathan

doi:10.1007/s10592-006-9129-6

Cited by 22 publications

(39 citation statements)

References 36 publications

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“…However, although significant effects of inbreeding have been found within this population for a number of traits (e.g. [47,48]), and one would expect to find an effect of inbreeding on sex ratio in at least some populations and species [26], the absence of any extra-binomial variation implies that there is no room for non-additive genetic effects shaping variation in sex ratio. Similarly, the lack of extra-binomial variation suggests that, in contrast to a Figure 2.…”

Section: Discussionmentioning

confidence: 82%

Disentangling the effect of genes, the environment and chance on sex ratio variation in a wild bird population

et al. 2011

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Sex ratio theory proposes that the equal sex ratio typically observed in birds and mammals is the result of natural selection. However, in species with chromosomal sex determination, the same 1 : 1 sex ratio is expected under random Mendelian segregation. Here, we present an analysis of 14 years of sex ratio data for a population of song sparrows (Melospiza melodia) on Mandarte Island, at the nestling stage and at independence from parental care. We test for the presence of variance in sex ratio over and above the binomial variance expected under Mendelian segregation, and thereby quantify the potential for selection to shape sex ratio. Furthermore, if sex ratio variation is to be shaped by selection, we expect some of this extra-binomial variation to have a genetic basis. Despite ample statistical power, we find no evidence for the existence of either genetic or environmentally induced variation in sex ratio, in the nest or at independence. Instead, the sex ratio variation observed matches that expected under random Mendelian segregation. Using one of the best datasets of its kind, we conclude that female song sparrows do not, and perhaps cannot, adjust the sex of their offspring. We discuss the implications of this finding and make suggestions for future research.

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Section: Discussionmentioning

confidence: 82%

Disentangling the effect of genes, the environment and chance on sex ratio variation in a wild bird population

et al. 2011

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“…Sex-specific inbreeding depression observed in early life stages suggests an indirect physiological mechanism. Direct phenotypic consequences of inbreeding should not differ between females and males unless key loci are sex-linked (Frankham & Wilcken 2006). If highly inbred females are dying at the very early embryo stage beyond the detection capability of this study, then this may suggest a direct physiological mechanism in which the heterogametic sex is more vulnerable owing to sexlinked recessive genes (Haldane 1922).…”

Section: Discussionmentioning

confidence: 82%

Sensitive males: inbreeding depression in an endangered bird

et al. 2010

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Attempts to conserve threatened species by establishing new populations via reintroduction are controversial. Theory predicts that genetic bottlenecks result in increased mating between relatives and inbreeding depression. However, few studies of wild sourced reintroductions have carefully examined these genetic consequences. Our study assesses inbreeding and inbreeding depression in a free-living reintroduced population of an endangered New Zealand bird, the hihi (Notiomystis cincta). Using molecular sexing and marker-based inbreeding coefficients estimated from 19 autosomal microsatellite loci, we show that (i) inbreeding depresses offspring survival, (ii) male embryos are more inbred on average than female embryos, (iii) the effect of inbreeding depression is male-biased and (iv) this population has a substantial genetic load. Male susceptibility to inbreeding during embryo and nestling development may be due to size dimorphism, resulting in faster growth rates and more stressful development for male embryos and nestlings compared with females. This work highlights the effects of inbreeding at early life-history stages and the repercussions for the long-term population viability of threatened species.

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“…Nevertheless, the possibility that after insemination or during gestation maternal effects also moderate sex ratio cannot be ruled out. However, these effects would The individual-and population-level mechanisms underlying the effects of inbreeding on sex ratio allocation in vertebrates remain far from being understood [42]. Partly, this may be because males' role on sex ratio bias has been consistently dismissed.…”

Section: Discussionmentioning

confidence: 99%

A father effect explains sex-ratio bias

et al. 2017

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Sex ratio allocation has important fitness consequences, and theory predicts that parents should adjust offspring sex ratio in cases where the fitness returns of producing male and female offspring vary. The ability of fathers to bias offspring sex ratios has traditionally been dismissed given the expectation of an equal proportion of X-and Y-chromosome-bearing sperm (CBS) in ejaculates due to segregation of sex chromosomes at meiosis. This expectation has been recently refuted. Here we used Peromyscus leucopus to demonstrate that sex ratio is explained by an exclusive effect of the father, and suggest a likely mechanism by which male-driven sex-ratio bias is attained. We identified a male sperm morphological marker that is associated with the mechanism leading to sex ratio bias; differences among males in the sperm nucleus area (a proxy for the sex chromosome that the sperm contains) explain 22% variation in litter sex ratio. We further show the role played by the sperm nucleus area as a mediator in the relationship between individual genetic variation and sexratio bias. Fathers with high levels of genetic variation had ejaculates with a higher proportion of sperm with small nuclei area. This, in turn, led to siring a higher proportion of sons (25% increase in sons per 0.1 decrease in the inbreeding coefficient). Our results reveal a plausible mechanism underlying unexplored male-driven sex-ratio biases. We also discuss why this pattern of paternal bias can be adaptive. This research puts to rest the idea that father contribution to sex ratio variation should be disregarded in vertebrates, and will stimulate research on evolutionary constraints to sex ratios-for example, whether fathers and mothers have divergent, coinciding, or neutral sex allocation interests. Finally, these results offer a potential explanation for those intriguing cases in which there are sex ratio biases, such as in humans.

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Does inbreeding distort sex-ratios?

Cited by 22 publications

References 36 publications

Disentangling the effect of genes, the environment and chance on sex ratio variation in a wild bird population

Disentangling the effect of genes, the environment and chance on sex ratio variation in a wild bird population

Sensitive males: inbreeding depression in an endangered bird

A father effect explains sex-ratio bias

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