Multiple mating by females is difficult to explain in primarily socially monogamous taxa such as birds because mating outside the pair bond often provides no obvious benefit to females. Although indirect selection is often invoked to explain the evolution of polyandry, current evidence suggests that selection on indirect benefits of mating is weak. Here, I consider a direct benefit of remating in birds: increased fertilization success. I test whether increased hatching success of a female's eggs is related to rates of extra-pair paternity (EPP), a proxy of polyandry, across 113 bird species. I use two statistical approaches, control for phylogenetic uncertainty, and assess the fit of competing evolutionary models. Results show there is indeed a positive relationship between rates of EPP and hatching success in birds. I propose that by mating with many males, females may increase their fertility. I end by discussing the biological rationale for this explanation, alternative interpretations of the results, and how this study furthers our understanding of polyandry and mating system evolution.

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Why are asexual vertebrates so rare? One seldom explored avenue to understanding the evolutionary persistence of extant asexual species is their sensory ecology-how they perceive and respond to the environment. Asexual species formed by hybridization have been hypothesized to have an expanded sensory repertoire because they carry 1 allele from each of their parental species, including alleles that impact sensory function. The ability to detect odorants in the environment is a likely candidate for this expansion but has never been explored in this context. Here, we explore the olfactory abilities of the asexual Amazon molly, a gynogenetic fish formed by hybridization 100 000 years ago. We test whether Amazon mollies can use only olfactory cues to detect conspecifics, detect heterospecific males, and discriminate between males infected with a common parasite. We further explore whether a female's size, a proxy for age, explains any variation in her behavior. We find strong evidence that Amazon mollies use olfactory cues to detect conspecifics but surprisingly may avoid heterospecific males based on olfactory cues alone. We find no evidence that females use chemical cues to discriminate between infected and noninfected males. We also find that smaller Amazon mollies are more likely to use chemical cues. This study highlights the potential importance of sensory systems in asexual vertebrates.

Sexual selection, the suite of processes that lead to differential mating success among individuals, probably influences the evolutionary trajectory of populations. Because sexual selection often shifts traits away from their survival optima, strong sexual selection pressures are thought to increase potential for population extinction, especially during environmental change. Sexual selection pressures may also increase the opportunity for speciation by accelerating the generation of pre-zygotic isolation among populations. These relationships remain largely untested experimentally. Here, we allow populations of baker's yeast, Saccharomyces cerevisiae, to evolve for approximately 250 generations with altered sex ratios in order to test the effect of the strength of sexual selection on the fate of populations. We find that populations experiencing stronger sexual selection are less able to adapt to a novel environment compared with populations experiencing weaker sexual selection or no sex, and that strong sexual selection erases the benefits of sexual reproduction. This pattern persists when fitness is assayed in a closely related environment. We also identify a trend that may suggest the beginning of pre-zygotic isolation between populations experiencing stronger sexual selection, though this is not statistically significant. These results highlight the importance of sexual selection in shaping macroevolutionary patterns and biodiversity.

Choice of social group can affect the likelihood of survivorship and reproduction for social species. By joining larger social groups-shoalssmall freshwater fish like the mosquitofish Gambusia affinis can reduce predation risk and forage more efficiently. We tested shoal choice in mosquitofish to determine whether such choices are economically rational, i.e. consistent and optimal. Although many studies of decision-making assume rational choice, irrational decision-making is common and occurs across contexts. We tested rationality of shoaling decisions by testing the constant ratio rule, which states that the relative preference for two options should not change in the presence of a third option. Female mosquitofish upheld this rule when tested for shoal preference based on group size. Our results contrast with other studies showing violations of the constant ratio rule in foraging and mate choice decision-making contexts. These results suggest that decisions that immediately influence survivorship or decision-making along a single dimension may favour rational decision-making.