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[New Paper] Intrafamily and intragenomic conflicts in human warfare

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Micheletti AJC, Ruxton GD & Gardner A (2017) Intrafamily and intragenomic conflicts in human warfare. Proceedings of the Royal Society of London Series B — Biological Sciences 20162699.

Recent years have seen an explosion of multidisciplinary interest in ancient human warfare. Theory has emphasized a key role for kin-selected cooperation, modulated by sex-specific demography, in explaining intergroup violence. However, conflicts of interest remain a relatively underexplored factor in the evolutionary-ecological study of warfare, with little consideration given to which parties influence the decision to go to war and how their motivations may differ. We develop a mathematical model to investigate the interplay between sex-specific demography and human warfare, showing that: the ecology of warfare drives the evolution of sex-biased dispersal; sex-biased dispersal modulates intrafamily and intragenomic conflicts in relation to warfare; intragenomic conflict drives parent-of-origin-specific patterns of gene expression—i.e. ‘genomic imprinting’—in relation to warfare phenotypes; and an ecological perspective of conflicts at the levels of the gene, individual, and social group yields novel predictions as to pathologies associated with mutations and epimutations at loci underpinning human violence.

[New Group Member] Petri Rautiala

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Petri Rautiala has joined us on a Newton International Fellowship, to develop theory on the epigenetical evolution of social behaviour. Welcome to the group, Petri!

[New Paper] Sexual selection modulates genetic conflicts and patterns of genomic imprinting

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Faria GS, Varela SAM & Gardner A (in press) Sexual selection modulates genetic conflicts and patterns of genomic imprinting. Evolution doi: 10.1111/evo.13153
gene_expression
Recent years have seen a surge of interest in linking the theories of kin selection and sexual selection. In particular, there is a growing appreciation that kin selection, arising through demographic factors such as sex–biased dispersal, may modulate sexual conflicts, including in the context of male-female arms races characterized by coevolutionary cycles. However, evolutionary conflicts of interest need not only occur between individuals, but may also occur within individuals, and sex-specific demography is known to foment such intragenomic conflict in relation to social behavior. Whether and how this logic holds in the context of sexual conflict – and, in particular, in relation to coevolutionary cycles – remains obscure. We develop a kin-selection model to investigate the interests of different genes involved in sexual and intragenomic conflict, and we show that consideration of these conflicting interests yields novel predictions concerning parent–of–origin-specific patterns of gene expression and the detrimental effects of different classes of mutation and epimutation at loci underpinning sexually–selected phenotypes.

[New Group Members] Bekah Best & Mauricio González Forero

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Two new people have joined our research group: Bekah Best will be doing her undergraduate project on genomic imprinting, and Mauricio González Forero has brought a Marie Skłodowska-Curie Fellowship to St Andrews to develop theory on brain evolution. Welcome to the group, Bekah and Mauricio!

[New Paper] The strategic revolution

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Gardner A (2016) The strategic revolution. Cell 166, 1345-1348.

selfishgene2

On the 40th anniversary of the publication of Richard Dawkins’s The Selfish Gene, we explore the origins of cynical, strategic thinking in evolutionary biology, investigate how this illuminated the sexual and social lives of animals, and assess Dawkins’s suggestion that evolution is best understood by taking the gene’s-eye view.

[New Paper] Ecology of sex explains patterns of helping in arthropod societies

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Davies NG, Ross L & Gardner A (2016) The ecology of sex explains patterns of helping in arthropod societies. Ecology Letters doi: 10.1111/ele.12621

ecologyofsex

Across arthropod societies, sib-rearing (e.g. nursing or nest defence) may be provided by females, by males or by both sexes. According to Hamilton’s ‘haplodiploidy hypothesis’, this diversity reflects the relatedness consequences of diploid vs. haplodiploid inheritance. However, an alternative ‘preadaptation hypothesis’ instead emphasises an interplay of ecology and the co-option of ancestral, sexually dimorphic traits for sib-rearing. The preadaptation hypothesis has recently received empirical support, but remains to be formalised. Here, we mathematically model the coevolution of sex-specific helping and sex allocation, contrasting these hypotheses. We find that ploidy per se has little effect. Rather, the ecology of sex shapes patterns of helping: sex-specific preadaptation strongly influences who helps; a freely adjustable sex ratio magnifies sex biases and promotes helping; and sib-mating, promiscuity, and reproductive autonomy also modulate the sex and abundance of helpers. An empirical survey reveals that patterns of sex-specific helping in arthropod taxa are consistent with the preadaptation hypothesis.

[New Paper] Misconceptions on the application of biological market theory to the mycorrhizal symbiosis

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Kiers ET, West SA, Wyatt GAK, Gardner A, Bücking H & Werner G (2016) Misconceptions on the application of biological market theory to the mycorrhizal symbiosis. Nature Plants 2, 16063.

mycorrhizae

The symbiosis between plants and arbuscular mycorrhizal fungi has been described as a biological market based on evidence that plants supply more carbohydrates to fungal partners that provide more soil nutrients, and vice versa. A recent paper by Walder and van der Heijden challenges this view. However, their challenge is based on misunderstandings of biological market theory, and evolutionary theory more generally.

[New Paper] Sex ratios, virginity & local resource enhancement in a quasisocial parasitoid

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Kapranas A, Hardy ICW, Tang X, Gardner A & Li B (2016) Sex ratios, virginity and local resource enhancement in a quasisocial parasitoid. Entomologia Experimentalis et Applicata 159, 243-251.

sclerodermus

Sclerodermus harmandi (Buysson) (Hymenoptera: Bethylidae) is an economically beneficial species of parasitoid wasp that has an unusual level of sociality: groups of female foundresses reproduce on a single host and exhibit cooperative post-ovipositional brood care. The beneficial effects females have on each other’s reproductive success provide, via the theory of local resource enhancement (LRE), an explanation for their female-biased progeny sex ratios, which is part of the same framework for understanding sex-ratio evolution as the more often invoked theory of local mate competition (LMC). Here, we show that S. harmandi sex ratios are overdispersed, with high variance largely attributable to the common occurrence (60%) of developmental mortality. Developmental mortality is also positively associated with the proportion of broods which contain only females at emergence (virgin broods). Virginity is more common when broods are produced by fewer foundresses. Virginity is expected to be disadvantageous under LRE, as it is under LMC, but theory for LRE is less extensively developed. We suggest approaches for the development of LRE theory, in particular using models of ‘population elasticity’ in which the intensity of kin competition is reduced because extra resources are available to local populations that are more cooperative. For S. harmandi, such extra resources may include large hosts that can only be successfully utilised if multiple foundresses cooperate.

[New Paper] Intragenomic conflict in polyembryonic parasitoid wasps

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Rautiala P & Gardner A (in press) Intragenomic conflict over soldier allocation in polyembryonic parasitoid wasps. American Naturalist. doi: 10.1086/685082

silvestri

Understanding the selection pressures that have driven the evolution of sterile insect castes has been the focus of decades of intense scientific debate. An amenable empirical test bed for theory on this topic is provided by the sterile-soldier caste of polyembryonic parasitoid wasps. The function of these soldiers has been a source of controversy, with two basic hypotheses emerging: the “brood-benefit” hypothesis that they provide an overall benefit for their siblings and the “sex-ratio-conflict” hypothesis that the soldiers mediate a conflict between brothers and sisters by killing their opposite-sex siblings. Here, we investigate the divergent sex-ratio optima of a female embryo’s maternal-origin and paternal-origin genes, to determine the potential for, and direction of, intragenomic conflict over soldiering. We then derive contrasting empirically testable predictions concerning the patterns of genomic imprinting that are expected to arise out of this intragenomic conflict, for the brood-benefit versus the sex-ratio-conflict hypothesis of soldier function.

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