Communicated by Margaret G. Kidwell, College of Arizona, Tucson, AZ (obtained for evaluation December 17, 2002)


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Abstract

Identifying the genes underlying adaptation is a major challenge in evolutionary biology. Here, we describe the molecular changes underlying adaptive coat color variation in a herbal population of rock pocket mice, Chaetodipus intermedius. Rock pocket mice are mainly light-colored and also live on light-colored rocks. However, populaces of dark (melanic) mice are uncovered on dark lava, and also this concealing coloration provides defense from avian and mammalian predators. We performed association researches by using markers in candiday pigmentation genes and discovered 4 mutations in the melanocortin-1-receptor gene, Mc1r, that seem to be responsible for adaptive melanism in one populace of lava-dwelling pocket mice. Interestingly, another melanic populace of these mice on a different lava circulation mirrors no association with Mc1r mutations, indicating that adaptive dark shade has developed individually in this species through alters at various genes.

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A key problem in evolutionary biology is to affix genoform with phenoform for fitness-connected traits (1, 2). Finding the genes underlying adaptation has been challenging for a variety of factors. First, it calls for that we determine traits that are ecologically necessary and that we have actually some understanding of exactly how these traits influence fitness in various environments. 2nd, phenotypic variation of environmental relevance has actually frequently been stupassed away in species for which we have little hereditary information, making the genetic basis of the traits difficult to analyze. For example, one of the best recognized situations of adaptation requires shade morphs of the peppered moth, Biston betularia. Yet, after more than a half-century of research, the genes responsible for these color distinctions reprimary unwell-known (3). Finally, many type of fitness-associated traits are quantitative and are unlikely to have actually a straightforward genetic basis. Since of these difficulties, the molecular basis for adaptation is known in just a handful of cases. Most involve either biochemical polymorphisms (4–6) or response to humale disturbance, such as hefty metal tolerance in plants, insecticide resistance, warfarin resistance in rats, or antibiotic resistance (7), and also in many kind of instances, the specific nucleotide transforms have actually not been established.

The rock pocket computer mouse, Chaetodipus intermedius, gives a helpful mechanism for researching the genetics of adaptation. This species is discovered in rocky habitats in southern Arizona, New Mexico, and in surrounding locations in north Mexico. Standard studies (8, 9) in the 1930s revealed a strong correlation between the color of the dorsal pelage and also the shade of the substprice on which C. intermedius live. In many places, these mice have a sandy dorsal pelage and white underbelly, and they inhalittle bit light-colored rocks. In several various regions, but, these mice are found on lava flows. The mice from these lava sites are generally melanic, through dark-colored dorsal hairs and white underbellies. Most of the lava flows are surrounded by light-colored substprice and also are isolated from one another by numerous kilometers, increasing the opportunity that melanic mice have developed separately on various lava flows. The cshed enhance in between the shade of the mice and the shade of the substrate on which they live is thneed to be an adaptation against predation (8, 9). Owls are common predators of these mice, and also experiments by Dice (10) on deer mice proved that owls have the right to successfully discriminate between light and dark mice also at night. Hence, it is most likely that owls exert strong selection on coat color in C. intermedius, and also that differences in coat shade are an adaptation for crypsis. This check out is strengthened by the strong correlation in between substprice color and also coat color across 18 different populations in Arizona and also New Mexico, varying from extremely light to incredibly dark (9).

This system is amenable to hereditary analysis bereason the biochemisattempt, development, and genes of the pigmentation procedure have been intensively stupassed away in other mammals. Approximately 80 genes have been established that impact coat color in the laboratory mouse, and also more than one-quarter of these have been molecularly identified (11). A vital difference in melanogenesis is between the manufacturing of eumelanin (brvery own or babsence pigment) and also pheomelanin (yellow or red pigment). This distinction is managed in big component by the interaction of two proteins, the melanocortin-1-receptor (MC1R) and also the agouti-signaling protein (12–14). MC1R is a G protein-coupled receptor that is extremely expressed in melanocytes, the specialized cells that are the website of pigment manufacturing. A peptide hormone, α-melanocyte-stimulating hormone, frequently activates MC1R, leading to elevated levels of cAMP and boosted production of eumelanin. Agouti is an antagonist of MC1R; neighborhood expression of agouti results in decreased synthesis of eumelanin and also increased production of pheomelanin. Wild-type laboratory mice have actually banded hairs on their dorsum; these hairs have actually a babsence reminder, a middle yellow band also, and also a babsence base (the agouti hair). This banding is resulted in by a pulse of agouti expression throughout the middle phase of the hair cycle, causing deposition of pheomelanin throughout the middle of hair expansion and also deposition of eumelanin at the start and also finish of hair growth. Mutations at both agouti (14, 15) and also at Mc1r (16) have actually been determined that create unbanded dorsal hairs in the laboratory mouse. We observed banded dorsal hairs in all light C. intermedius, yet unbanded, uniformly melanic hairs in all dark C. intermedius, saying a feasible function for either agouti or Mc1r.

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We provided association studies via these candiday genes to investigate the hereditary basis of adaptive melanism in C. intermedius. Here, we report that mutations at Mc1r are perfectly linked via coat shade differences in one populace of these mice, however that an additional population of mice mirrors no association between Mc1r mutations and also coat color phenoform.