The widespread presence of same-sex sexual behaviour (SSB) has long been thought to pose an evolutionary conundrum, as participants in SSB suffer the cost of failing to reproduce after expending the time and energy to find a mate. The potential for SSB to occur as part of an optimal strategy has received less attention, although indiscriminate sexual behaviour may be the ancestral mode of sexual reproduction. Here, we build a simple model of sexual reproduction and create a theoretical framework for the evolution of indiscriminate sexual behaviour. We provide strong support for the hypothesis that SSB can be maintained by selection for indiscriminate sexual behaviour, by showing that indiscriminate mating is the optimal strategy under a wide range of conditions. Further, our model suggests that the conditions that most strongly favour indiscriminate mating were probably present at the origin of sexual behaviour. These findings have implications not only for the evolutionary origins of SSB, but also for the evolution of discriminate sexual behaviour across the animal kingdom.
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This manuscript does not use data.
Code to replicate results can be found on Dryad at https://doi.org/10.5061/dryad.gxd2547jg.
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We thank M. Moore and M. Lambert for comments on early versions of the manuscript and A. Deconinck for suggesting the name ‘targeted’ sex. M.R.S. was supported by the National Science Foundation with award no. DEB-1939290.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Fig. 1, Methods and Appendices 1–4.
Video showing the fitness gradient as a function of attempted discrimination a changing with each parameter. The default setting for each parameter is c = 0.1, s = 1, σ = 0.5, d = 0.8, f = 1, p = 0 and r = 0. Each parameter is allowed to vary between 0 and 1, except for c, which is allowed to vary only between 0 and 0.2, and d, which is allowed to vary between 0 and 0.9. Evolutionary optima occur wherever the line crosses the x axis (and has a negative slope). If the line is always positive, the optimal strategy is to always discriminate. If the line is always negative, the optimal strategy is to never attempt sexual discrimination.
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Lerch, B.A., Servedio, M.R. Same-sex sexual behaviour and selection for indiscriminate mating. Nat Ecol Evol 5, 135–141 (2021). https://doi.org/10.1038/s41559-020-01331-w
Archives of Sexual Behavior (2021)