The official journal of the Behavioral Ecology ISBE International Society for Behavioral Ecology Behavioral Ecology (2018), 29(4), 798–803. Invited Commentaries be a powerful driver of speciation given the direct links between mate The research bias is unfortunate but preference, mate selection, and reproductive isolation. also unsurprising: a comment on By contrast, male–male competition is expected to be less effec - Tinghitella et al. tive in promoting speciation because additional processes are almost a, b certainly required to prevent homogenizing gene flow between Erin L. McCullough and Douglas J. Emlen diverging populations (van Doorn et al. 2009). Even if male–male Centre for Evolutionary Biology, University of Western Australia, competition contributes to the divergence of male phenotypes, Crawley, Western Australia 6009, Australia and Division of Biological unless females differ in their choice of breeding habitats, or unless Sciences, University of Montana, Missoula, MT 59812, USA they choose males on the basis of competitive phenotypes, then male–male competition may have little potential to strengthen assor- Sexual selection continues to be an active and exciting focus of tative mating and the likelihood of speciation. That is, speciation by research for behavioral ecologists and evolutionary biologists, but also male–male competition may not depend on differences in female continues to be heavily biased towards studies of female mate choice. preference for secondary sexual traits, but without reinforcement In particular, research on sexual selection as a driver of speciation has from female choice, speciation by male–male competition probably focused almost exclusively on the role of mate choice. Tinghitella et al. would require some other form of divergent ecological selection. (2018) offer a timely and insightful review that expands our under - Intriguingly, comparative studies find support for the hypothesis standing of how sexual selection can contribute to speciation. The that male–male competition has a weaker effect on speciation than authors summarize recent evidence that shows how male–male com- mate choice: speciation rate is positively correlated with dichroma- petition can facilitate divergence in sympatry, allopatry, and secondary tism, which is probably targeted by female choice, but negatively contact, and give specific recommendations for future research. correlated with sexual size dimorphism, which is probably favored Tinghitella et al. (2018) argue that our ability to describe how in the context of male–male competition (Kraaijeveld et al. 2011). sexual selection contributes to speciation has been hampered by the We doubt that male–male competition is ever a stronger or faster fact that the potential impact of male–male competition has been driver of speciation than female choice. However, we agree with largely overlooked. We believe that this oversight is due (at least in Tinghitella et al. that more empirical, theoretical, and comparative part) to imprecise terminology by sexual selection researchers—an studies are clearly needed to determine when male–male competi- issue that we argue has hampered our understanding of sexual selec- tion can and is most likely to contribute to species divergence. tion in general (McCullough et al. 2016). For example, Tinghitella et al. highlight that previous authors have erroneously defined specia - tion by sexual selection as occurring when “a parallel change in mate Address correspondence to E.L. McCullough. E-mail: mccullough.e@ preference and secondary sexual traits within a population leads to gmail.com. prezygotic isolation between populations” (Panhuis et al. 2001). This is a perfect example of the problem with conflating terms: when Received 28 November 2017; accepted 9 December 2017; editorial decision 4 December 2017; Advance Access publication 3 January 2018 “sexual selection” is used synonymously with “mate preference” or “mate choice”, research on the other components of sexual selection doi:10.1093/beheco/arx187 get ignored (McCullough et al. 2016). We hope that the review by Editor-in-Chief: Leigh Simmons Tinghitella et al. (2018) not only encourages more research on the role of male–male competition in driving speciation, but also, and more broadly, that it reminds researchers that male–male competi- REFERENCES tion and female choice are distinct mechanisms of sexual selection. van Doorn GS, Dieckmann U, Weissing FJ, Associate Editor: Sergey There is another reason why it is not surprising that research on Gavrilets. 2004. Sympatric speciation by sexual selection: a critical speciation by sexual selection has focused more on the role of mate reevaluation. Am Nat. 163:709–725. choice than male–male competition: the potential for mate choice to van Doorn GS, Edelaar P, Weissing FJ. 2009. On the origin of species by natural and sexual selection. Science. 326:1704–1707. lead to assortative mating is simply more direct. Because females often Kraaijeveld K, Kraaijeveld-Smit FJ, Maan ME. 2011. Sexual selection and select mates based on their preferences for secondary sexual traits, dif- speciation: the comparative evidence revisited. Biol Rev Camb Philos ferences in female mate choice can be a direct barrier to gene flow Soc. 86:367–377. between diverging populations. Although theoretical models suggest McCullough EL, Miller CW, Emlen DJ. 2016. Why sexually selected weap- ons are not ornaments. Trends Ecol Evol. 31:742–751. that mate choice is more likely to promote species divergence in con- Panhuis TM, Butlin R, Zuk M, Tregenza T. 2001. Sexual selection and spe- junction with other processes (e.g., divergent ecological selection and/ ciation. Trends Ecol Evol. 16:364–371. or divergent male–male competition), and probably rarely occurs on Tinghitella RM, Lackey ACR, Martin M, Dijkstra PD, Drury JP, Heathcote R, its own (van Doorn et al. 2004; van Doorn et al. 2009), there is still Keagy J, Scordato ESC, Tyers AM. 2018. On the role of male competition obvious intuitive appeal in the hypothesis that female preference can in speciation: a review and research agenda. Behav Ecol. 29:783–797. © The Author(s) 2018. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. Downloaded from https://academic.oup.com/beheco/article-abstract/29/4/798/4786636 All rights reserved. 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Behavioral Ecology – Oxford University Press
Published: Jan 3, 2018
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