Baier F, Hoekstra HE.
The genetics of morphological and behavioral island traits in deer mice. Proceedings of the Royal Society B 2019;286:20191697.
AbstractAnimals on islands often exhibit dramatic differences in morphology and behavior compared to mainland individuals, a phenomenon known as the "island syndrome". These differences, such as changes in body size and aggression, are thought to be adaptations to island environments, where there are high resource levels, low predation, limited dispersal, and thus high population densities. However, the extent to which island traits have a genetic basis or instead represent plastic responses to environmental extremes is often unknown. Here, we revisit a classic case of island syndrome in deer mice (Peromyscus maniculatus) from British Columbia. Previous field studies suggested that Saturna Island mice evolved several island traits, including higher body weight and reduced aggression relative to mainland populations. Using historical collections, we show that Saturna Island mice and those from neighboring islands are approximately 35% (~5g) heavier than mainland mice. We then collected mice from two focal populations: Saturna Island and a nearby mainland population. First, using molecular data, we find that these populations are genetically distinct, having diverged approximately 10 thousand years ago. Second, we established laboratory colonies and find that Saturna Island mice are heavier both because they are longer and have disproportionately more lean mass. These trait differences are maintained in second-generation captive-born mice raised in a common environment, implying a strong heritable component. In addition, island-mainland hybrids are heavier when born to island mothers than to mainland mothers, revealing a maternal genetic effect on body weight. Next, using behavioral testing in the lab, we also find that wild-caught island mice are less aggressive than mainland mice. However, lab-raised mice born to these founders do not differ in aggression, regardless of whether they are tested in conditions that induce low or high aggression, suggesting the large behavioral difference observed between wild-caught island and mainland individuals is likely a plastic response. Together, our results reveal that these mice respond differently to environmental conditions on islands, evolving both heritable changes in a morphological trait and also expressing a plastic phenotypic response in a behavioral trait.
PDF Delaney EK, Hoekstra HE.
Diet-based assortative mating through sexual imprinting. Ecology & Evolution 2019;00:1-6.
AbstractSpeciation is facilitated by “magic traits,” where divergent natural selection on such traits also results in assortative mating. In animal populations, diet has the potential to act as a magic trait if populations diverge in consumed food that incidentally affects mating and therefore sexual isolation. While diet‐based assortative mating has been observed in the laboratory and in natural populations, the mechanisms causing positive diet‐based assortment remain largely unknown. Here, we experimentally created divergent diets in a sexually imprinting species of mouse, Peromyscus gossypinus (the cotton mouse), to test the hypothesis that sexual imprinting on diet could be a mechanism that generates rapid and significant sexual isolation. We provided breeding pairs with novel garlic‐ or orange‐flavored water and assessed whether their offspring, exposed to these flavors in utero and in the nest before weaning, later preferred mates that consumed the same flavored water as their parents. While males showed no preference, females preferred males of their parental diet, which is predicted to yield moderate sexual isolation. Thus, our experiment demonstrates the potential for sexual imprinting on dietary cues learned in utero and/or postnatally to facilitate reproductive isolation and potentially speciation.
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