[New Paper] Group selection versus group adaptation

Gardner A (2015) Group selection versus group adaptation. Nature 524, E3-E4.

Pruitt and Goodnight describe how the ratio of aggressive versus docile females varies among naturally occurring colonies of the social spider Anelosimus studiosus, with larger colonies exhibiting more aggression in high-resource environments and the reverse in low-resource environments. They experimentally manipulate this ratio to show that it influences a colony’s reproductive success. Pruitt and Goodnight conclude that this work demonstrates group-level adaptation and contradicts an earlier theoretical analysis. Here, I show that this conclusion is unfounded and arises from a conceptual misunderstanding.


[New Paper] Sex-biased dispersal, kin selection and the evolution of sexual conflict

Faria GS, Varela SAM & Gardner A (in press) Sex-biased dispersal, kin selection and the evolution of sexual conflict. Journal of Evolutionary Biology. doi: 10.1111/jeb.12697

There is growing interest in resolving the curious disconnect between the fields of kin selection and sexual selection. Rankin’s (2011, JEvolBiol. 24, 71–81) theoretical study of the impact of kin selection on the evolution of sexual conflict in viscous populations has been particularly valuable in stimulating empirical research in this area. An important goal of that study was to understand the impact of sex-specific rates of dispersal upon the coevolution of male-harm and female-resistance behaviours. But the fitness functions derived in Rankin’s study do not flow from his model’s assumptions and, in particular, are not consistent with sex-biased dispersal. Here, we develop new fitness functions that do logically flow from the model’s assumptions, to determine the impact of sex-specific patterns of dispersal on the evolution of sexual conflict. Although Rankin’s study suggested that increasing male dispersal always promotes the evolution of male harm and that increasing female dispersal always inhibits the evolution of male harm, we find that the opposite can also be true, depending upon parameter values.

[New Paper] More on the genetical theory of multilevel selection

Gardner A (in press) More on the genetical theory of multilevel selection. Journal of Evolutionary Biology. doi: 10.1111/jeb.12684

In my article The genetical theory of multilevel selection, I provided a synthesis of the theory of multilevel selection (MLS) and the theory of natural selection in class-structured populations. I framed this synthesis within Fisher’s genetical paradigm, taking a strictly genetical approach to traits and fitness. I showed that this resolves a number of long-standing conceptual problems that have plagued the MLS literature, including the issues of ‘aggregate’ vs. ‘emergent’ group traits, ‘collective fitness1’ vs. ‘collective fitness2’ and ‘MLS1’ vs. ‘MLS2 ‘. In his commentary, Goodnight suggests this theoretical and conceptual synthesis is flawed in several respects. Here, I show this is incorrect, by: reiterating the theoretical and conceptual goals of my synthesis; clarifying that my genetical approach to traits is necessary for a proper analysis of the action of MLS independently of non-Darwinian factors; emphasizing that the Price–Hamilton approach to MLS provides a consistent, useful and conceptually superior theoretical framework; and explaining the role of reproductive value in the study of natural selection in class-structured populations. I also show that Goodnight’s contextual analysis treatment of MLS in a class-structured population is mathematically, biologically and conceptually inadequate.


[New Paper] Hamilton’s rule

Gardner A (2015) Hamilton’s rule. American Naturalist 186, ii-iii.

(Part of The American Naturalist‘s “Countdown to 150” series)

The purpose of this series of commentaries is to celebrate long-forgotten or underappreciated articles from the archive. So it feels a little odd to be providing an appreciation of W. D. Hamilton’s 1963 work “The Evolution of Altruistic Behavior,” which the Web of Knowledge suggests has been cited more than 700 times. By Hamilton’s standards, however, that does constitute obscurity. And, in particular, these citations are dwarfed by those of his monumental article “The Genetical Evolution of Social Behaviour” (Journal of Theoretical Biology 7:1–52), published a year later, by nearly 20 to 1. Some of this imbalance is warranted, as the latter article covers much of the same ground in more detail and makes a number of additional contributions. But Hamilton’s “little-read first paper” (W. D. Hamilton, 1996, Narrow Roads of Gene Land, Volume 1: Evolution of Social Behaviour, Oxford University Press, Oxford, p. 5) manages, in barely more than two pages of text, to cover the core principles of inclusive fitness theory. So I believe it deserves a second look.

[New Paper] Intragenomic conflict over dispersal

Farrell EJ, Úbeda F & Gardner A (in press) Intragenomic conflict over dispersal. American Naturalist. doi: 10.1086/682275

Intragenomic conflict may arise when social partners are more related through one parent than the other—for example, owing to individuals or gametes of one sex dispersing further prior to fertilization. In particular, genes originating from the former parent are favored to promote selflessness, and those originating from the latter parent are favored to promote selfishness. While the impact of patterns of dispersal on the evolution of intragenomic conflict has received recent attention, the consequences of intragenomic conflict for the evolution of dispersal remain to be explored. We suggest that if the evolution of dispersal is driven at least in part by kin selection, differential relatedness of social partners via their mothers versus their fathers may lead to an intragenomic conflict, with maternal-origin genes and paternal-origin genes favoring different rates of dispersal. As an illustration, we extend a classic model of the evolution of dispersal to explore how intragenomic conflict may arise between an individual’s maternal-origin and paternal-origin genes over whether that individual should disperse in order to ease kin competition. Our analysis reveals extensive potential for intragenomic conflict over dispersal and predicts that genes underpinning dispersal phenotypes may exhibit parent-of-origin-specific expression, which may facilitate their discovery.


[New Paper] Simultaneous failure of two sex-allocation invariants

Rodrigues AMM & Gardner A (2015) Simultaneous failure of two sex-allocation invariants: implications for sex-ratio variation within and between populations. Proceedings of the Royal Society of London Series B — Biological Sciences 282, 20150570.

Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.