ASN Address: “Nineteen years of consistently positive and strong female mate preferences despite individual variation”

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Michael J. Ryan, Karin A. Akre, Alexander T. Baugh, Ximena E. Bernal, Amanda M. Lea, Caitlin Leslie, Meghan B. Still, Dennis Wylie, and A. Stanley Rand (Aug 2019)

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Female Preferences: Fickle or Predictable?

The Túngara Frog, Physalaemus pustulosus.
(Credit: Ryan Taylor)

Female mate choice generates some of the most spectacular biological diversity in the animal kingdom. Or does it? Alfred Wallace was no supporter of Darwin’s sexual selection theory because he could not imagine females showing persistent preferences for the same details of sexual beauty over generations. Julian Huxley, another critic, voiced some similar concerns. For female choice to be an important driver of sexual beauty, it has been argued, it must be strong and it must be consistent—fickle preferences won’t cut it. Amazingly, there are very few studies of female mate choice across a substantial number of generations.

A group of researchers has been studying sexual selection in túngara frogs in Panama for several decades. Although the foci of this research program are varied, the hallmark has been the female’s preference for complex calls over simple calls. Simple calls are adequate to attract a mate but complex calls are preferred. But is this preference strong and consistent? Nineteen consecutive years of more than 5000 female mate choice tests have shown an average preference for the complex call of 0.86—more than a five-fold preference! Clearly it is strong, but is it consistent? Yes. There is very little variation in this strength of preference across years. Does this consistency across years mean there is similar consistency among females? No. Although most females have strong preferences for the complex call there is significant variation amongst females within years, much more so than the variation among years. Although other female preferences in this frog and female preferences in other species are known to be fickle, the preference for complex calls is strong and consistent just as Darwin suggested when he posited that females have a taste for the beautiful.


Abstract

Sexual selection driven by mate choice has generated some of the most astounding diversity in nature, suggesting population-level preferences should be strong and consistent over many generations. On the other hand, mating preferences are among the least repeatable components of an individual animal’s phenotype, suggesting low consistency across an animal’s lifetime. Despite decades of intensive study of sexual selection there is almost no information about the strength and consistency of preferences across many years. In this study we present the results of over 5000 mate choice tests with a species of wild frog conducted over 19 consecutive years. Results show that preferences are positive and strong and vary little across years. This consistency is despite the fact that there are substantial differences among females in their strength of preference. We also suggest mate preferences in populations that are primarily the result of sensory exploitation might be more stable over time compared to preferences that are primarily involved in assessing male quality.