Hoekstra H E, Nachman M W
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
Mol Ecol. 2003 May;12(5):1185-94. doi: 10.1046/j.1365-294x.2003.01788.x.
Identifying the genes responsible for adaptation has been an elusive goal in evolutionary biology. Rock pocket mice (Chaetodipus intermedius) provide a useful system for studying the genetics of adaptation: most C. intermedius are light-coloured and live on light-coloured rocks, but in several different geographical regions, C. intermedius are melanic and live on dark-coloured basalt lava, presumably as an adaptation for crypsis. Previous work demonstrated that mutations at the melanocortin-1 receptor gene (Mc1r) are responsible for the dark/light difference in mice from one population in Arizona. Here, we investigate whether melanism has evolved independently in populations of dark C. intermedius from New Mexico, and whether the same or different genes underlie the dark phenotype in mice from these populations compared with the dark mice from Arizona. Seventy-six mice were collected from pairs of dark and light localities representing four different lava flows and adjacent light-coloured rocks; lava flows were separated by 70-750 km. Spectrophotometric analysis of mouse pelage and of rock samples revealed a strong positive association between coat colour and substrate colour. No significant differences were observed in the colour of rocks among the four lava flows, suggesting that mice in these separate populations have experienced similar selection for crypsis. Despite this similarity in environment, melanic mice from the three New Mexico populations were slightly, but significantly, darker than melanic mice from Arizona. The entire Mc1r gene was sequenced in all mice. The previously identified mutations responsible for the light/dark difference in mice from Arizona were absent in all melanic mice from three different populations in New Mexico. Five new Mc1r polymorphisms were observed among mice from New Mexico, but none showed any association with coat colour. These results indicate that adaptive melanism has arisen at least twice in C. intermedius and that these similar phenotypic changes have a different genetic basis.
确定导致适应性变化的基因一直是进化生物学中一个难以实现的目标。岩囊鼠（Chaetodipus intermedius）为研究适应性遗传学提供了一个有用的系统：大多数岩囊鼠毛色浅，生活在浅色岩石上，但在几个不同的地理区域，岩囊鼠毛色变黑，生活在深色玄武岩熔岩上，这可能是一种保护色适应。先前的研究表明，黑素皮质素-1受体基因（Mc1r）的突变导致了亚利桑那州一个种群的小鼠毛色黑/白差异。在这里，我们研究了新墨西哥州深色岩囊鼠种群中的黑化现象是否独立进化，以及与亚利桑那州的深色小鼠相比，这些种群的小鼠黑化表型是否由相同或不同的基因决定。从代表四种不同熔岩流和相邻浅色岩石的深色和浅色地点成对收集了76只小鼠；熔岩流相隔70 - 750公里。对小鼠皮毛和岩石样本的分光光度分析显示，毛色与底物颜色之间存在强烈的正相关。在四种熔岩流的岩石颜色上未观察到显著差异，这表明这些不同种群的小鼠经历了相似的保护色选择。尽管环境相似，但来自新墨西哥州三个种群的黑化小鼠比来自亚利桑那州的黑化小鼠略黑，但差异显著。对所有小鼠的整个Mc1r基因进行了测序。在新墨西哥州三个不同种群的所有黑化小鼠中，未发现先前确定的导致亚利桑那州小鼠毛色黑/白差异的突变。在新墨西哥州的小鼠中观察到五个新的Mc1r多态性，但没有一个与毛色相关。这些结果表明，适应性黑化现象在岩囊鼠中至少独立出现了两次，并且这些相似的表型变化具有不同的遗传基础。
