Modelling kin discrimination and demographic patterns to study sexual conflict

Kin discrimination and group dispersal can reduce harmful male behaviours at an individual level, but kin discrimination intensifies sexual conflict at the population level.

Kin selection has been successful in explaining a wide range of social behaviours in behavioural ecology, most notably the evolution of altruistic behaviours. There are three mechanisms that can promote the evolution of kin-selection effects: limited dispersal, whereby low dispersal means that social partners tend to be genetically-related; kin discrimination, whereby individuals discriminate kin from non-kin and act accordingly; and greenbeard effects, whereby individuals carry an allele that allows them to recognize and behave differently toward other carriers of the same allele.

A female whipping (Polypedates ssp.) frog scrambles through the vegetation surrounding a pong in Kuala Lumpur while bearing a courting male on its back (Malasia). Photo by Roberto García Roa (

Despite sexual behaviours being part of the repertoire of social behaviours of most organisms, kin selection concepts are largely absent in the sexual selection literature. I thus decided that the objective of my PhD would be to study the overlap between the two literatures by developing a theoretical framework including all of the three mechanisms that can generate kin-selection effects1-4.

For the last paper of my Phd, and through several productive discussions with Andy Gardner and Pau Carazo, I realized that theoretical and the empirical approaches to the study of kin selection and sexual conflict were disconnect. While theoretical studies focused on limited dispersal, empirical studies focused on kin discrimination (with one exception5). Moreover, in the kin-selection literature, it has long been known that the increase in relatedness through limited dispersal is counterbalanced by the scale of competition during the evolution of kin-selection effects. That is, when dispersal is low, competition is also necessarily more local, with relatives having to compete with other relatives for resources. Local competition may be strong enough to cancel the effect of relatedness in promoting kin-selection effects, but this has been largely ignored in the study of the effect of relatedness on sexual conflict.

Graphical representation of our kin selection model of sexual conflict.

The idea behind this paper was to plug these gaps in the literature and, at the same time, synthesize all the work – both theoretical and empirical – that has been done on kin selection and sexual conflict. We do this through the use of mathematical models. Broadly speaking, we addressed the role of two factors that can shape sexual conflict – relatedness and scale of competition. We found that kin discrimination and competition between groups for resources are two mechanisms that can disentangle the two, allowing both relatedness and the scale of competition to vary independently. Moreover, we also found that, when both kin discrimination and limited dispersal are present, limited dispersal does not generally work to reduce the male harm in the population. Instead, it tends to increase male harm due to the fact that limited dispersal also increases local competition. The drawback of kin discrimination is that, while it allows for a more direct measure of relatedness between an individual and its social partners, it seemingly increases the average harm in the population when compared to a scenario in which kin discrimination is absent.

Both the kin selection and sexual selection literatures are vast, given the contribution of brilliant scientists throughout decades of research. The study of the overlap between the two is still in its infancy, but seems like an exciting  novel avenue that continues to be the focus of my research, now as a research fellow at the Institute for Advanced Study in Toulouse.

The full study can be freely accessed here (

1. Faria, G. S., Varela, S. A. M. & Gardner, A. Sex-biased dispersal, kin selection and the evolution of sexual conflict. J. Evol. Biol. 28, 1901–1910 (2015). 

2. Faria, G. S., Varela, S. A. M. & Gardner, A. Sexual selection modulates genetic conflicts and patterns of genomic imprinting. Evolution 71, 526–540 (2017). 

3. Faria, G. S., Varela, S. A. M. & Gardner, A. The relation between R. A. Fisher's sexy‐son hypothesis and W. D. Hamilton's greenbeard effect. Evolution Letters 2, 190–200 (2018).

4. Faria, G. S., Varela, S. A. M. & Gardner, A. The social evolution of sleep: sex differences, intragenomic conflicts and clinical pathologies. Proc. R. Soc. B. 286:20182188 (2019). 

5. Łukasiewicz, A., Szubert-Kruszynska, A. & Radwan, J. Kin selection promotes female productivity and cooperation between the sexes. Sci. Adv. 3, e1602262 (2017).

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