American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“A general explanation for the persistence of reproductive interference”

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Jonathan P. Drury, Christopher N. Anderson, Maria B. Cabezas Castillo, Jewel Fisher, Shawn McEachin, and Gregory F. Grether (Aug 2019)

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Why is reproductive interference so common? A new study suggests animals may be caught in an evolutionary ‘catch-22’

A male <i>Hetaerina vulnerata</i> and an experimentally tethered female <i>H.&nbsp;cruentata</i> in tandem.<br />(Credit: Andrew Chao)
A male Hetaerina vulnerata and an experimentally tethered female H. cruentata in tandem.
(Credit: Andrew Chao)

Why do animals sometimes attempt to mate with members of other species, even though doing so is wasteful? A new study by Drury and colleagues offers an answer to this question. Investigators generally assume that wasteful interspecific matings—known as ‘reproductive interference’—will either be eliminated by natural selection or result in one species going locally extinct. Yet, examples of reproductive interference abound, even in species that seem to coexist over long periods of time. In this study, Drury and colleagues argue that such species might be caught in an ‘evolutionary catch-22’. That is, because females of different species often look similar, males are unable to distinguish between females of their own species and females of another species when they come into contact. As a result, natural selection cannot drive divergence in female phenotypes via reproductive character displacement, which requires that males can differentiate between species. Yet, males cannot evolve the ability to differentiate between females until female phenotypes diverge, meaning that reproductive interference persists indefinitely. The study then goes on to demonstrate that the catch-22 explanation is a viable explanation for ongoing reproductive interference in a clade of damselflies distributed throughout North and Central America in which species similarity in female phenotypes predicts levels of reproductive isolation. In particular, they find that in cases where reproductive isolation is high, this isolation cannot be explained by reproductive character displacement, and is better explained by divergence prior to secondary contact. The evolutionary ‘catch-22’ provides a previously undocumented reason why reproductive interference is widespread.


Abstract

Reproductive interference is widespread, despite the theoretical expectation that it should be eliminated by reproductive character displacement (RCD). A possible explanation is that females of sympatric species are too similar phenotypically for males to distinguish between them, resulting in a type of evolutionary dilemma or “catch-22” in which reproductive interference persists because male mate recognition (MR) cannot evolve until female phenotypes diverge further, and vice versa. Here we illustrate, and test, this hypothesis with data on rubyspot damselflies (Hetaerina spp.). First, reproductive isolation owing to male MR breaks down with increasing interspecific similarity in female phenotypes. Second, comparing allopatric and sympatric populations yielded no evidence for RCD, suggesting that parallel divergence in female coloration and male MR in allopatry determines the level of reproductive isolation upon secondary contact. Whenever reproductive isolation depends on male mate recognition and females of sympatric species are phenotypically similar, the evolutionary catch-22 hypothesis offers an explanation for the persistence of reproductive interference.

Una explicación general para la persistencia de la interferencia reproductiva

La interferencia reproductiva es común a pesar de la expectativa teórica de que esta debería ser eliminada por el desplazamiento del carácter reproductivo. Una posible explicación sugiere que cuando las hembras de especies simpátricas son muy similares fenotípicamente los machos no pueden distinguir entre ellas, causando así un tipo de dilema evolutivo o “catch-22”. En este caso la interferencia reproductiva persiste debido a que el reconocimiento de pareja por los machos no puede evolucionar hasta cuando se desarrolle una divergencia notoria en el fenotipo de las hembras, y viceversa. En este estudio ilustramos y probamos esta hipótesis con datos obtenidos en libélulas del género Hetaerina spp. Primero, el aislamiento reproductivo debido al reconocimiento de pareja por los machos disminuye con el aumento en la similitud fenotípica interespecífica de las hembras. Segundo, la comparación entre poblaciones alopátricas y simpátricas no mostró evidencia en el desplazamiento del carácter reproductivo. Esto sugiriere que la divergencia paralela en la coloración de las hembras y el reconocimiento de pareja por parte de los machos en alopatría determina el nivel de aislamiento reproductivo al contacto secundario. Cuando las hembras de especies simpátricas son fenotípicamente similares y el aislamiento reproductivo depende del reconocimiento por parte de los machos, la hipótesis evolutiva “catch-22” ofrece una explicación para la persistencia de la interferencia reproductiva.