Interspecific competition, hybridization, and reproductive isolation in secondary contact: missing perspectives on males and females

Abstract

Research on sexual selection and hybridization has focused on female mate choice and male–male competition. While the evolutionary outcomes of interspecific female preference have been well explored, we are now gaining a better understanding of the processes by which male–male competition between species in secondary contact promotes reproductive isolation versus hybridization. What is relatively unexplored is the interaction between female choice and male competition, as they can oppose one another or align with similar outcomes for reproductive isolation. The role of female–female competition in hybridization is also not well understood, but could operate similarly to male–male competition in polyandrous and other systems where costs to heterospecific mating are low for females. Reproductive competition between either sex of sympatric species can cause the divergence and/or convergence of sexual signals and recognition, which in turn influences the likelihood for interspecific mating. Future work on species interactions in secondary contact should test the relative influences of both mate choice and competition for mates on hybridization outcomes, and should not ignore the possibilities that females can compete over mating resources, and males can exercise mate choice.

Differential introgression of a female competitive trait in a hybrid zone between sex‐role reversed species

“…A number of empirical studies suggest that asymmetry in competitive ability can facilitate differential introgression between lineages (reviewed in Lipshutz ; Tinghitella et al. 2018).…”

“…2018). However, little is known about the role female–female competition plays in the speciation process (Lipshutz ), despite evidence that female–female competition over mating resources is widespread (Rosvall ; Cain and Ketterson ; Cain and Rosvall ).…”

“…For instance, competition over mates can either impede or promote hybridization between species, depending on its interaction with mate choice and the extent to which both forces select for similar or divergent trait optima (Qvarnström et al. ; Lipshutz ; Tinghitella et al. 2018).…”

Genomic divergence in allopatric Northern Cardinals of the North American warm deserts is linked to behavioral differentiation

“…One key assumption is that males and females have similar responses to dialect differences such that songs that males recognize as conspecific rivals would be attractive to females (Hunt et al, 2009;Uy et al, 2018). This requires that both sexes have the same discriminatory abilities and use the same mechanisms, which is not always the case (Lipshutz, 2017b). Females of different populations may prefer the same group of males in spite of divergent phenotypes (Baldassarre & Webster, 2013;Ryan & Rand, 1993;Coyne & Orr, 2004;Price, 2008).…”

“…If males on either side of a barrier sing different songs, females may not recognize a novel song as a reproductive signal, reducing interactions between populations and preventing successful gene flow (Hunt, Breuker, Sadowski, & Moore, 2009;Lipshutz, 2017b;Searcy & Andersson, 1986). Populations would thus become isolated, and differentiation would be maintained by behavioral isolation.…”