Chedhawat (Tim) Chokechaipaisarn has begun his PhD with us in the last few days; he’ll be working on theory of sex allocation. Welcome to the lab, Tim!
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 (email@example.com).
The deadline for applications is 3 Dec 2021. Details on how to apply are given here.
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.
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.
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.
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.
Faria GS, Gardner A & Carazo P (in press) Kin discrimination and demography modulate patterns of sexual conflict. Nature Ecology & Evolution. doi: 10.1038/s41559-020-1214-6
(Image: Africa Gómez)
Recent years have seen an explosion of interest in the overlap between kin selection and sexual selection, particularly concerning how kin selection can put the brakes on harmful sexual conflict. However, there remains a significant disconnect between theory and empirical research. Whilst empirical work has focused on kin-discriminating behaviour, theoretical models have assumed indiscriminating behaviour. Additionally, theoretical work makes particular demographic assumptions that constrain the relationship between genetic relatedness and the scale of competition, and it is not clear that these assumptions reflect the natural setting in which sexual conflict has been empirically studied. Here, we plug this gap between current theoretical and empirical understanding by developing a mathematical model of sexual conflict that incorporates kin discrimination and different patterns of dispersal. We find that kin discrimination and group dispersal inhibit harmful male behaviours at an individual level, but kin discrimination intensifies sexual conflict at the population level.
Faria GS & Gardner A (2020) Does kin discrimination promote cooperation? Biology Letters 16, 20190742.
Genetic relatedness is a key driver of the evolution of cooperation. One mechanism that may ensure social partners are genetically related is kin discrimination, in which individuals are able to distinguish kin from non-kin and adjust their behaviour accordingly. However, the impact of kin discrimination upon the overall level of cooperation remains obscure. Specifically, while kin discrimination allows an individual to help more-related social partners over less-related social partners, it is unclear whether and how the population average level of cooperation that is evolutionarily favoured should differ under kin discrimination versus indiscriminate social behaviour. Here, we perform a general mathematical analysis in order to assess whether, when and in which direction kin discrimination changes the average level of cooperation in an evolving population. We find that kin discrimination may increase, decrease or leave unchanged the average level of cooperation, depending upon whether the optimal level of cooperation is a convex, concave or linear function of genetic relatedness. We develop an extension of the classic ‘tragedy of the commons’ model of cooperation in order to provide an illustration of these results. Our analysis provides a method to guide future research on the evolutionary consequences of kin discrimination.
Gardner A (2020) Price’s equation made clear. Philosophical Transactions of the Royal Society of London Series B — Biological Sciences 375, 20190361.Price’s equation provides a very simple—and very general—encapsulation of evolutionary change. It forms the mathematical foundations of several topics in evolutionary biology, and has also been applied outwith evolutionary biology to a wide range of other scientific disciplines. However, the equation’s combination of simplicity and generality has led to a number of misapprehensions as to what it is saying and how it is supposed to be used. Here, I give a simple account of what Price’s equation is, how it is derived, what it is saying and why this is useful. In particular, I suggest that Price’s equation is useful not primarily as a predictor of evolutionary change but because it provides a general theory of selection. As an illustration, I discuss some of the insights Price’s equation has brought to the study of social evolution.
Micheletti A, Ruxton GD & Gardner A (in press) The demography of human warfare can drive sex differences in altruism. Evolutionary Human Sciences.
Recent years have seen great interest in the suggestion that between-group aggression and within-group altruism have coevolved. However, these efforts have neglected the possibility that warfare – via its impact on demography – might influence human social behaviours more widely, not just those directly connected to success in war. Moreover, the potential for sex differences in the demography of warfare to translate into sex differences in social behaviour more generally has remained unexplored. Here, we develop a kin-selection model of altruism performed by men and women for the benefit of their groupmates in a population experiencing intergroup conflict. We find that warfare can promote altruistic, helping behaviours as the additional reproductive opportunities winners obtain in defeated groups decrease harmful competition between kin. Furthermore, we find that sex can be a crucial modulator of altruism, with there being a tendency for the sex that competes more intensely with relatives to behave more altruistically and for the sex that competes more intensely with non-relatives in defeated groups to receive more altruism. In addition, there is also a tendency for the less-dispersing sex to both give and receive more altruism. We discuss implications for our understanding of observed sex differences in cooperation in human societies.