Mate Preference Plasticity in a Critically Endangered Frog: Implications for Conservation Breeding

Variation in female mate preferences for male traits remains poorly understood (both among and within females), despite having important evolutionary and conservation implications, particularly for captive breeding. Here, we investigate female mate preferences for male advertisement call frequency, and determine whether preferences vary over repeated trials, in the critically endangered southern corroboree frog, Pseudophryne corroboree. We conducted a series of phonotaxis trials in a six-speaker arena where naïve, captive-bred, virgin females were offered a choice between low, average and high frequency male advertisement calls, with a subset of females tested repeatedly. In the first trial, we found no evidence for a population-level preference for call frequency, but females spent less time in the low call zone than expected by chance. However, our results showed that female mate preferences changed over sequential trials. Females spent significantly more time in the low frequency call zone in the third trial compared to the first trial, and, in the last trial, females exhibited a significant population-level preference for low frequency calls. Subsequently, repeatability estimates of female preferences were low and did not significantly deviate from zero. Our results indicate that female P. corroboree mate preferences can exhibit temporal variation, and suggest that females are more attracted to low call frequencies after repeated exposure. These findings imply that female P. corroboree may become choosier over time, and highlight the potential for mate preferences to exhibit phenotypic plasticity within a single reproductive cycle. Overall, these findings provide the first information on mate preferences in P. corroboree, and emphasize the importance of considering individual variation in mate choice studies. From a conservation perspective, knowledge of individual variation in female mate preferences may be used to conduct behavioral manipulations in captivity that facilitate the breeding of genetically valuable individuals, and improve the success of conservation breeding programs.

Domains of Female Choice in Human Evolution

The present article advances the view that women’s mate preferences can be grouped into at least two overarching domains: competitiveness and fatherhood. Theoretical and empirical considerations suggest that female mate preferences evolve in contexts of male competitiveness and often amplify the effects of male-male competition. Evidence for the importance of male-male competition and female choice for competitiveness in humans is reviewed. Evidence is likewise offered for the importance of human fatherhood as an additional domain of female choice outside of male competitiveness. Implications of more inclusive mate preferences for the evolution of cognitive architecture are discussed.

Mate choice for major histocompatibility complex (MHC) complementarity in the Yellow-rumped Flycatcher (Ficedula zanthopygia)

Background Genes of the major histocompatibility complex (MHC) are an important component of the vertebrate immune system and play a significant role in mate choice in animal populations. However, the MHC genetic targets of female mate choice have not been clearly identified, and whether female mate choice is based on neutral genetic characteristics remains an open question. Here, we focus on the effects of morphological traits and genetic similarity among individuals in MHC class IIB (MHC IIB) exon 2 on mating in a sexually dimorphic songbird that exhibits social monogamy with extra-pair paternity (EPP). Methods We sequenced 64 parent–offspring triads sampled over a 3-year period using two MHC class II loci to detect disassortative mating in the Yellow-rumped Flycatcher (Ficedula zanthopygia). Results We found that MHC similarity in social pairs was lower than that in random pairs. Extra-pair mate choice according to MHC IIB was observed, in which females’ extra-pair mates had fewer MHC alleles than their within-pair mates, but there was no significant band-sharing between extra-pair sires and potential extra-pair mates. However, the interaction between the MHC diversity of females and that of the social males affected the occurrence of EPP. Conclusions Our results support the “optimality hypothesis” of MHC-based social and extra-pair choice. Female choice probably maintains a certain level of MHC diversity in offspring in the Yellow-rumped Flycatcher.

Runaway evolution from male-male competition

Understanding why and how elaborated traits evolve remains a fascination and a challenge. Darwin proposed both male-male competition and female mate choice as explanations for elaboration because such traits are often mediators of social interactions that govern access to mates. Although we have robust evolutionary quantitative genetic models for how mate choice can lead to runaway evolution, we lack an equivalent framework for understanding how male-male competition can drive extreme elaboration of traits. Here, we integrate the logic of optimality models into the quantitative genetic framework of interacting phenotypes to fill this gap. We assume that males modulate their aggression based on the relative size of a trait that signals willingness and ability to fight and identify conditions where the signal undergoes rapid and exponential evolution. Males receive fitness benefits from winning contests, but they may accrue fitness costs due to threats imposed by their opponent. This cost leads to a force of social selection that accelerates as the signaling trait is elaborated, which may cause runaway evolution of the signal. Even when a runaway is checked by natural selection, we find that signaling traits evolving by male-male competition can be elaborated well beyond their naturally selected optimum. Our model identifies simple conditions generating feedback between the behavioral and morphological traits mediating male-male competition, providing clear testable predictions. We conclude that, like the well-characterized case of female mate choice, male-male competition can provide a coevolving source of selection that can drive a runaway process resulting in evolution of elaborate traits.

The Sexual Brain

Morphological and behavioural differences between the sexes are ubiquitous across the animal kingdom. There is also good evidence for differences in some brain regions between males and females, in humans, some rodents, and many songbirds. I look at the data for sex differences in cognition, of which there are some that show differences in spatial cognition and in hippocampal structure, at least some of which may be explained by variation in hormone levels. The thesis of The Mating Mind by Geoffrey Miller considerably increased interest in using sexual selection to explain variation in brain size. From female mate choice, male–male competition, sperm competition, mating strategy, to parental care, there are some data that appear to support selection acting on one species rather than the other in sexually a selected manner but I conclude that the data are not generally supportive of the Sexual Brain Hypothesis.