Adaptive basis of geographic variation: genetic, phenotypic and environmental differences among beach mouse populations

Abstract

A major goal in evolutionary biology is to understand how and why populations differentiate, both genetically and phenotypically, as they invade a novel habitat. A classical example of adaptation is the pale colour of beach mice, relative to their dark mainland ancestors, which colonized the isolated sandy dunes and barrier islands on Florida's Gulf Coast. However, much less is known about differentiation among the Gulf Coast beach mice, which comprise five subspecies linearly arrayed on Florida's shoreline. Here, we test the role of selection in maintaining variation among these beach mouse subspecies at multiple levels-phenotype, genotype and the environments they inhabit. While all beach subspecies have light pelage, they differ significantly in colour pattern. These subspecies are also genetically distinct: pair-wise F ST -values range from 0.23 to 0.63 and levels of gene flow are low. However, we did not find a correlation between phenotypic and genetic distance. Instead, we find a significant association between the average 'lightness' of each subspecies and the brightness of the substrate it inhabits: the two most genetically divergent subspecies occupy the most similar habitats and have converged on phenotype, whereas the most genetically similar subspecies occupy the most different environments and have divergent phenotypes. Moreover, allelic variation at the pigmentation gene, Mc1r, is statistically correlated with these colour differences but not with variation at other genetic loci. Together, these results suggest that natural selection for camouflage-via changes in Mc1r allele frequency-contributes to pigment differentiation among beach mouse subspecies.

Adaptation of Pelage Color and Pigment Variations in Israeli Subterranean Blind Mole Rats, Spalax Ehrenbergi

“…This might suggest a functional effect of the MC1R haplotype on pheomelanin, in particular of the non-synonymous variant c.502A>G. However, only molecular biology experiments could prove that this variant is indeed the functional mutation that influences the pelage color. A similar example of MC1R effect was previously shown in a study of subspecies of the Gulf Coast beach mice where a strong association was found between MC1R genotypes, pigmentation and background sand brightness, consistent with local adaptation [43]. In pocket mice, four of nine MC1R non-synonymous variants were observed in the dark mice from the Pinacate locality.…”

Variation in founder groups promotes establishment success in the wild

“…The shifts in relative morph frequencies seen between individuals in founding groups and established populations are indicative of selection, but may also reflect differences among morphs in degree of parent-offspring resemblance. We consider selection for camouflage mediated by differential predation [19,23,31,32] to be one of the most important mechanisms behind the observed pattern. Their small size and locally high population densities render grasshoppers susceptible to visual predators such as birds [31,33] and lizards [34].…”

Detecting Natural Selection in Genomic Data

“…Moreover, it demonstrates the full realization of the modern synthesis: Darwinian concepts of selection have been rendered quantitative and measurable in real populations, thanks to methodological and technological advances (1). Through evolutionary genetics, many different traits became uncovered, from lactase persistence and skin pigmentation in humans (89,123), to coat color in field mice (80), to armored plates in stickleback fish (63). With ongoing advancements in genomic technology, we can now go further, from testing evidence for selection on specific traits hypothesized to be adaptive, to uncovering candidate regions through genome scans.…”