[New Paper] Sex-biased demography modulates male harm across the genome

Hitchcock TJ & Gardner A (2021) Sex-biased demography modulates male harm across the genome. Proceedings of the Royal Society of London Series B – Biological Sciences 288, 20212237.

Image created at https://app.wombo.art

Recent years have seen an explosion of theoretical and empirical interest in the role that kin selection plays in shaping patterns of sexual conflict, with a particular focus on male harming traits. However, this work has focused solely on autosomal genes, and as such it remains unclear how demography modulates the evolution of male harm loci occurring in other portions of the genome, such as sex chromosomes and cytoplasmic elements. To investigate this, we extend existing models of sexual conflict for application to these different modes of inheritance. We first analyse the general case, revealing how sex-specific relatedness, reproductive value and the intensity of local competition combine to determine the potential for male harm. We then analyse a series of demographically explicit models, to assess how dispersal, overlapping generations, reproductive skew and the mechanism of population regulation affect sexual conflict across the genome, and drive conflict between nuclear and cytoplasmic genes. We then explore the effects of sex biases in these demographic parameters, showing how they may drive further conflicts between autosomes and sex chromosomes. Finally, we outline how different crossing schemes may be used to identify signatures of these intragenomic conflicts.

[New Paper] Reproductive value and the evolution of altruism

Rodrigues AMM & Gardner A (in press) Reproductive value and the evolution of altruism. Trends in Ecology and Evolution doi: https://doi.org/10.1016/j.tree.2021.11.007

Altruism is favored by natural selection provided that it delivers sufficient benefits to relatives. An altruist’s valuation of her relatives depends upon the extent to which they carry copies of her genes – relatedness – and also on the extent to which they are able to transmit their own genes to future generations – reproductive value. However, although relatedness has received a great deal of attention with regard to altruism, reproductive value has been surprisingly neglected. We review how reproductive value modulates patterns of altruism in relation to individual differences in age, sex, and general condition, and discuss how social partners may manipulate each other’s reproductive value to incentivize altruism. This topic presents opportunities for tight interplay between theoretical and empirical research.

[New Paper] Sexual antagonism in haplodiploids.

Hitchcock TJ, Gardner A & Ross L (in press) Sexual antagonism in haplodiploids. Evolution doi: https://doi.org/10.1111/evo.14398 

Females and males may face different selection pressures, such that alleles conferring a benefit in one sex may be deleterious in the other. Such sexual antagonism has received a great deal of theoretical and empirical attention, almost all of which has focused on diploids. However, a sizeable minority of animals display an alternative haplodiploid mode of inheritance, encompassing both arrhenotoky, whereby males develop from unfertilized eggs, and paternal genome elimination (PGE), whereby males receive but do not transmit a paternal genome. Alongside unusual genetics, haplodiploids often exhibit social ecologies that modulate the relative value of females and males. Here we develop a series of evolutionary-genetic models of sexual antagonism for haplodiploids, incorporating details of their molecular biology and social ecology. We find that: 1) PGE promotes female-beneficial alleles more than arrhenotoky, and to an extent determined by the timing of elimination – and degree of silencing of – the paternal genome; 2) sib-mating relatively promotes female-beneficial alleles, as do other forms of inbreeding, including limited male-dispersal, oedipal-mating, and the pseudo-hermaphroditism of Icerya purchasi; 3) resource competition between related females inhibits the invasion of female-beneficial alleles; and 4) sexual antagonism foments conflicts between parents and offspring, endosymbionts and hosts, and maternal-origin and paternal-origin genes.

(Photo: https://commons.wikimedia.org/wiki/File:Sminthurides_malmgreni_courtship_(7178213310).jpg)

[New Group Member] Bing Dong

Bing Dong has joined us to undertake a PhD. He’ll be working on genomic imprinting. Welcome to the lab, Bing!

[PhD opportunity] Social evolution: cooperation & conflict between genes, individuals & groups

Social evolution: cooperation and conflict between genes, individuals and groups

Natural selection explains the appearance of design in the living world. But at what level is this design expected to manifest – gene, individual or group – and what is its function? Social evolution provides a window on this problem, because it is in the context of social interaction that the interests of genes, individuals and groups come into conflict with each other.

I invite applications for a PhD studentship in my research group at the School of Biology, University of St Andrews, Scotland, to develop new theory on the topic of social evolution. The project will suit a Biology graduate with a strong interest in social evolution, but applications from graduates with other backgrounds are also encouraged, and although prior experience in mathematical modelling would be helpful this is certainly not required as the requisite training will be provided.

Current research in my lab involves development of general theory – using kin selection, multilevel selection, game theory and theoretical population genetics approaches – as well as more specific mathematical and computer simulation models that are tailored to the biology of particular organisms, from microbes to insects to humans. Much of our ongoing work is focused on intragenomic conflicts and associated clinical pathologies, plus the role of sex and gender in social evolution.

This studentship is funded by the European Research Council and the School of Biology at the University of St Andrews for a duration of 3.5 years. There are no nationality restrictions on who can apply, and the studentship will cover both Home and Overseas tuition fees, as well as providing a living allowance and covering the costs of the research. (Chinese nationals are particularly encouraged to apply, as they will also be eligible for additional funding opportunities at the University of St Andrews.)

If evolutionary biology really fascinates you, and you are a careful thinker, then you will flourish in the kind of project that I enjoy supervising. Please direct informal enquiries to Prof Andy Gardner (andy.gardner@st-andrews.ac.uk).

The deadline for applications is 3 Dec 2021. Details on how to apply are given here.

[New Paper] Sex, males, and hermaphrodites in the scale insect Icerya purchasi

Mongue AJ, Michaelides S, Coombe O, Tena A, Kim D-S, Normark B, Gardner A, Hoddle MS & Ross L (2021) Sex, males, and hermaphrodites in the scale insect Icerya purchasi. Evolution doi: https://doi.org/10.1111/evo.14233

Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Here we investigate the cottony cushion scale, Icerya purchasi, one of only three reported cases of androdioecy in insects. In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, males are rarely observed too. In a large genetic analysis, we show for the first time that, although self-fertilization appears to be the primary mode of reproduction, rare outbreeding events between do occur in natural populations, supporting the hypothesis that hermaphrodites mate with males and androdioecy is the mating system of I. purchasi. Thus, this globally invasive pest insect appears to have the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males.

(Photo: https://commons.wikimedia.org/wiki/Category:Icerya_purchasi#/media/File:Icerya_purchasi_1.JPG)

[PhD opportunity] Explaining human handedness: the role of parental genes

Explaining human handedness: the role of parental genes

This project will be co-supervised by myself and Dr Silvia Paracchini, jointly between the Schools of Biology and Medicine at the University of St Andrews. The PhD studentship is funded by the European Research Council and the School of Biology, University of St Andrews, and covers tuition fees (at both Home and Overseas rates), living allowance and research costs. Full details are given here. The deadline is 5 Jan 2021.

[New Paper] Adjustment of sex allocation to co‐foundress number and kinship under local mate competition: An inclusive‐fitness analysis

Gardner A & Hardy ICW (in press) Adjustment of sex allocation to co-foundress number and kinship under local mate competition: an inclusive-fitness analysis. Journal of Evolutionary Biology.

Hamilton’s theory of local mate competition (LMC) describes how competition between male relatives for mating opportunities favours a female‐biased parental investment. LMC theory has been extended in many ways to explore a range of genetic and life‐history influences on sex allocation strategies, including showing that increasing genetic homogeneity within mating groups should favour greater female bias. However, there has been no quantitative theoretical prediction as to how females should facultatively adjust their sex allocation in response to co-foundress number and kinship. This shortfall has been highlighted recently by the finding that sex ratios produced by sub‐social parasitoid wasps in the family Bethylidae are affected by the number of co‐foundresses and by whether these are sisters or unrelated females. Here we close this gap in LMC theory by taking an inclusive‐fitness approach to derive explicit theoretical predictions for this scenario. We find that, in line with the recent empirical results, females should adopt a more female‐biased sex allocation when their co‐foundresses are less numerous and are their sisters. Our model appears to predict somewhat more female bias than is observed empirically; we discuss a number of possible model extensions that would improve realism and that would be expected to result in a closer quantitative fit with experimental data.

[New Paper] A gene’s-eye view of sexual antagonism

Hitchcock TJ & Gardner A (2020) A gene’s-eye view of sexual antagonism. Proceedings of the Royal Society of London Series B — Biological Sciences 287, 20201633.

Females and males may face different selection pressures. Accordingly, alleles that confer a benefit for one sex often incur a cost for the other. Classic evolutionary theory holds that the X chromosome, whose sex-biased transmission sees it spending more time in females, should value females more than males, whereas autosomes, whose transmission is unbiased, should value both sexes equally. However, recent mathematical and empirical studies indicate that male-beneficial alleles may be more favoured by the X chromosome than by autosomes. Here we develop a gene’s-eye-view approach that reconciles the classic view with these recent discordant results, by separating a gene’s valuation of female versus male fitness from its ability to induce fitness effects in either sex. We use this framework to generate new comparative predictions for sexually antagonistic evolution in relation to dosage compensation, sex-specific mortality and assortative mating, revealing how molecular mechanisms, ecology and demography drive variation in masculinization versus feminization across the genome.