Competition for limited resources is a major source of divergent selection, which fuels speciation processes. Tinghitella et al. (2018) focus on empirical and theoretical evidence that supports the role of competition among males in speciation. They observe that the research field has to date been dominated by speciation mechanisms in sympatry. Nonetheless, both empirical and theoretical findings suggest that competition for mates is most likely to contribute to speciation when it interacts with divergent ecological selection pressures (Tinghitella et al. 2018). Although Tinghitella et al. (2018) refer to “male competition” and “female mate choice,” to reflect how sex roles are most often represented in the literature, they also insightfully note that their conclusions should apply to “competitors” and “choosers,” regardless of sex. In parallel, many of the same processes may also be relevant for socially monogamous species in which both sexes in a pair together compete with other pairs for reproductive opportunities. To demonstrate this, I consider below each of the 3 major sources of compelling evidence, as singled out by Tinghitella et al. (2018), that male competition is a “potent evolutionary force capable of driving divergence.” First, Tinghitella et al. (2018) observe that in some mating systems, variance in reproductive success is tightly linked to competitive interactions among males. Similarly, in many socially monogamous species, the success of a pair in competition for limited reproductive resources defines reproductive success (Newton 1994; Pearce et al. 2011; Lehtonen et al. 2015). Here, species in which the sexes share discrete, competitively relevant phenotypes, such as the Gouldian finch, Erythrura gouldiae (Pearce et al. 2011), and cichlid fishes of the genus Amphilophus (Lehtonen 2014), are particularly interesting. Importantly, reproductive performance may peak when the mates in a pair have the same phenotype (Burtka and Grindstaff 2015). Individuals with the same/similar (competitive) phenotypes benefitting from pairing up with each other should result in a link between the (competitive) phenotype and mate choice. Such a link, in turn, is expected to increase the probability of speciation (Tinghitella et al. 2018). The second source of empirical evidence highlighted by Tinghitella et al. (2018) is the similarity between mate competition and competition for ecological resources, suggesting that the former can also be important in speciation. Similarly, as indicated above, the reproductive success of social pairs is commonly defined by their performance in competition with other pairs for limited (reproductive) resources (Newton 1994; Pearce et al. 2011; Lehtonen et al. 2015). For example, in many birds, nest cavities represent a critical, defendable, and limiting reproductive resource that is frequently under intense intra and interspecific competition (Newton 1994; Pearce et al. 2011). Such competition among pairs may also drive habitat choice, resulting in divergent ecological selection pressures. This is seen, for example, in a biparental Lake Tanganyika cichlid, Telmatochromis temporalis; albeit, in this species, the sexes pronouncedly differ in aggressiveness (Winkelmann et al. 2014). Third, Tinghitella et al. (2018) underscore recent theoretical and empirical results that also more directly support a role for male competition in speciation. Here, a particularly important group has been cichlid fishes (Tinghitella et al. 2018). Socially monogamous species have not been as commonly considered, although both sexes of, for example, Amphilophus sagittae, a color-assortatively mating biparental cichlid, bias aggression towards homotypic individuals (Lehtonen 2014). Interestingly, such a bias is arguably the most commonly considered mechanism that can promote phenotypic divergence in the context of aggression between males (Tinghitella et al. 2018). Moreover, evidence from socially monogamous cichlid fish (Lehtonen et al. 2015) and birds (Newton 1994), including those with assortatively mating color morphs (Pearce et al. 2011), suggests that selection from interspecific competition can influence the success of different (competitive) phenotypes. Indeed, Tinghitella et al. (2018) note how interspecific interactions drive habitat segregation between several bird species. Similar to the conceptual links between male competition and competition among pairs, the latter might be seen just as a specific case of intra and interspecific competition, or reproductive interference (sensu Grether et al. 2013). Avoiding getting caught up in semantics, however, can help move the field forward. This is exactly what Tinghitella et al. (2018) have done, especially by showing how the role of sexual selection in speciation is not only about mate choice, but that competition for mates is also important. REFERENCES Burtka JL, Grindstaff JL. 2015. Similar nest defence strategies within pairs increase reproductive success in the eastern bluebird, Sialia sialis. Anim Behav . 100: 174– 182. Google Scholar CrossRef Search ADS Grether GF, Anderson CN, Drury JP, Kirschel AN, Losin N, Okamoto K, Peiman KS. 2013. The evolutionary consequences of interspecific aggression. Ann N Y Acad Sci . 1289: 48– 68. Google Scholar CrossRef Search ADS PubMed Lehtonen TK. 2014. Colour biases in territorial aggression in a Neotropical cichlid fish. Oecologia . 175: 85– 93. Google Scholar CrossRef Search ADS PubMed Lehtonen TK, Sowersby W, Wong BBM. 2015. Heterospecific aggression bias towards a rarer colour morph. Proc R Soc B . 282: 20151551. Google Scholar CrossRef Search ADS PubMed Newton I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biol Conserv . 70: 265– 276. Google Scholar CrossRef Search ADS Pearce D, Pryke SR, Griffith SC. 2011. Interspecific aggression for nest sites: model experiments with long-tailed finches (Poephila acuticauda) and endangered Gouldian finches (Erythrura gouldiae). The Auk . 128: 497– 505. Google Scholar CrossRef Search ADS Tinghitella RMet al. 2018. On the role of male competition in speciation: A review and research agenda. Behav Ecol . Winkelmann K, Genner MJ, Takahashi T, Rüber L. 2014. Competition-driven speciation in cichlid fish. Nat Commun . 5: 3412. Google Scholar CrossRef Search ADS PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: firstname.lastname@example.org
Behavioral Ecology – Oxford University Press
Published: Jan 19, 2018
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