The Attractin Gene

I have spent much of this week further examining my data and reviewing my extensive research concerning the pigmentation pathway. One of the many interesting aspects of my research is how applicable the experimentation I am currently conducting is towards the further portrayal of evolution and natural selection. My work sequencing the Attractin gene in the Kenzin and Carrizozo populations of rock pocket mice is aiding immensely in the natural representation of convergent evolution.

Rock pocket mice serve as the first demonstration of the genetic basis of adaptive melanism (dark coloration) in mammals. Most rock pocket mice live on light rocks and have light, sandy-colored coats; however, when found on dark lava flows, these mice often have dark dorsal coats and white underbellies. The distinction between the phenotypes is identifiable by visually comparing mice. The lava flows from which the specimen were collected are geographically isolated by light rocks on which C. intermedius can reside or sand on which C. intermedius cannot reside. The sites range in area from a few km2 to 1500 km2. These sites further vary in age from under 1000 years old to almost two million years old. By camouflaging with its surroundings, a rock pocket mouse is less susceptible to attack by the owl predator, proving that coloration is essential to the mice’s fitness and is an adaptive tool against predation. For instance, Dice conducted an experiment in 1947, finding that Barn owls and Long-eared owls captured twice as many conspicuously colored mice as concealingly colored mice in the darkness. In 1937, Dice and Blossom noted variation in vertebrate coloration in the Tularosa Basin of New Mexico, where, within 25km, the substrate altered from nearly black basaltic lava to white gypsum (a nearly colorless mineral used to manufacture plaster and fertilizer) dunes. Specifically, the pocket mice from the genus Chaetodipus and Perognathus, range from nearly pure black to nearly pure white to match the substrate on which they live. The same findings have been noted on Florida’s Gulf and Atlantic coasts; however, these findings relate more to pattern differences of beach mice from the genus Peromyscus. Experimental studies of the adaptive importance of color variation show the strong effect of substrate matching on predation rates by visual avian hunters in many vertebrates (Hoekstra 2006). Additionally, while the Mc1r gene causes melanism in one mouse population, other genes, such as Agouti, have caused different pigmentations in other populations of both mice and other vertebrates; such melanic morphs, for instance, within Chaetodipus intermedius are present on geographically distant lava flows with little evidence of historical gene flow among them (Hoekstra 2006). Additionally, pocket gophers (Thomomys bottae) express variation in color to match its substrate that is not due to the mutation in Mc1r that is the source of pigmentation variation in the rock pocket mice of the Pinacate lava flow. Thus, the ongoing research concerning the coloration of Chaetodipus intermediusis clearly exemplifies convergent evolution, as multiple “genetic solutions” have led to the same result regarding coloration among species (Hoekstra and Nachman 2003, Kingsley et al. 2009; Nachman 2005, Wlasiuk and Nachman 2007).