Kin discrimination and demography modulate patterns of sexual conflict

Abstract

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.

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Fig. 1: Potential for harm to evolve as a function of relatedness and scale of competition.
Fig. 2: Kin selection model of sexual conflict.
Fig. 3: Optimal level of harm as a function of male dispersal (dm) and the average of harm in the population.

Data availability

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Code availability

Code used for the simulations is available at https://github.com/GSFaria-wasp/Sexual-conflict.git.

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Acknowledgements

G.S.F. acknowledges IAST funding from the French National Research Agency under the Investments for the Future (Investissements d’Avenir) programme (grant no. ANR-17-EURE-0010), and was supported by Portuguese National Funds through a Fundação para a Ciência e a Tecnologia PhD Scholarship (no. SFRH/BD/109726/2015). A.G. was supported by a Natural Environment Research Council Independent Research Fellowship (no. NE/K009524/1) and a European Research Council Consolidator grant (no. 771387). P.C. was supported by a Ramón y Cajal Research Fellowship (no. RYC-2013-12998) and by a Plan Nacional I+D+i Excelencia Research grant (no. CGL2017-89052-P). We thank D. Shuker, J. Kanwal, M. Ritchie, P. Rautiala and T. Hitchcock for helpful comments and discussion.

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Contributions

G.S.F., A.G. and P.C. conceived the study. G.S.F. led the theoretical analysis with input from A.G. G.S.F., A.G. and P.C. wrote the paper.

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Correspondence to Gonçalo S. Faria.

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Extended data

Extended Data Fig. 1 Optimal level of harm as a function of male dispersal (dm).

In the presence of kin discrimination and absence of budding dispersal (A), the optimal level of harm that males express decreases as male dispersal (dm) increases for discriminating males and increases as male dispersal (dm) increases for indiscriminating males. In the absence of kin discrimination and presence of budding dispersal (B), the optimal level of harm that males express increases as male dispersal (dm) increases. In the presence of kin discrimination and budding dispersal (C), the optimal level of harm for discriminating males decreases if males are interacting only with unfamiliar males and increases if males are interacting with familiar males as male dispersal (dm) increases. For indiscriminating males, the optimal level of harm that males express increases as male dispersal (dm) increases. Regardless of absence (A) or presence of budding dispersal (B), males interacting with unfamiliar males express higher level of harm, males interacting with one familiar male and one unfamiliar male express intermediate level of harm, and males interacting with two familiar males express lower level of harm. For all panels, the following parameters were used: marginal benefit of harm β = 0.5; female dispersal rate df = 1; number of females nf = 1; and number of males nm = 3. Additionally, in (B-C) budding dispersal rate dB = 1.

Extended Data Fig. 2 Optimal level of harm in the absence (A) and in the presence (B) of budding dispersal as a function of male dispersal (dm) for discriminating males.

In absence of budding dispersal (A), the optimal level of harm that males express decreases as male dispersal (dm) increases. In the presence of budding dispersal (B), as male dispersal (dm) increases, the optimal level of harm that males express decreases if males are interacting only with unfamiliar males and increases if males are interacting with familiar males. Regardless of absence (A) or presence of budding dispersal (B), males interacting unfamiliar males express higher level of harm, males interacting with one familiar male and one unfamiliar male express intermediate level of harm, and males interacting with two familiar males express lower level of harm. In both panels (A-B), the following parameters were used: marginal benefit of harm β = 0.5; female dispersal rate df = 1; number of females nf = 3; and number of males nm = 3. Additionally, in (B) budding dispersal rate dB = 1. Dots represent the simulations results, with the following additional parameters used: mutation rate of 0.01; population of 4000 patches; number of generations 5 ×104. Each dot is the average of the last 1 ×104 generations.

Extended Data Fig. 3 Level of harm as a function of relatedness between males.

In the absence of kin discrimination, the level of harm that males express changes convexly with relatedness. The following parameters were used: marginal benefit of harm β = 0.5; female dispersal rate df = 1; male dispersal rate dm = 0.5; and relatedness between females and males rfm = 0.

Extended Data Fig. 4 Comparison of different assumptions and how they differ from the main model.

When the level of harm that males express affect all the females in the patch (k = 0), the model is exactly the same as our main model. When harm that the females are subjected to comes half from the male that they mate with and half from the other males (k = 0.5), the model differs from our main model, with lower levels of harm. When harm that the females are subjected comes exclusively from the male that they mate with (k = 1), the model differs from our main model, with lower levels of harm. The following parameters were used: marginal benefit of harm β = 0.5; female dispersal rate df = 1; number of females nf = 3; number of males nm = 3; male dispersal rate dm = 0.5; and relatedness between females and males rfm = 0.

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Faria, G.S., Gardner, A. & Carazo, P. Kin discrimination and demography modulate patterns of sexual conflict. Nat Ecol Evol 4, 1141–1148 (2020). https://doi.org/10.1038/s41559-020-1214-6

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