Natural Selection of the Rhodopsin Gene During the Adaptive Radiation of East African Great Lakes Cichlid Fishes

摘要

The Great Lakes of the East African Rift Valley, Lakes Victoria, Malawi, and Tanganyika, harbor approximately 200, 400, and 170 endemic species of cichlid fishes, respectively (Fryer and Iles 1972, pp. 6-590, Greenwood 1991). These fishes have fascinated evolutionary biologists as spectacular examples of explosive adaptive radiation among living vertebrates because the fishes have adapted to a variety of niches in the lakes (Fryer and Iles 1972; Greenwood 1984). Accordingly, they are extremely diverse, both ecologically and morphologically, despite having evolved over a very short period (Meyer et al. 1990; Sturmbauer and Meyer 1992; Johnson et al. 1996; Takahashi et al. 2001). The visual systems of these fishes are of particular interest because they are important for feeding (Fryer and Iles 1972) as well as for mate choice (Seehausen, van Alphen, and Witte 1997; Seehausen and van Alphen 1998), and cichlids have adapted to different photic conditions that vary with depth and time of day (Fryer and Iles 1972; Coulter 1991). Furthermore, differences in visual capabilities among coexisting cichlid species may reduce the competition for resources (van der Meer and Bowmaker 1995). Therefore, it is reasonable to postulate that genes that are essential for visual acuity must have evolved adaptively during adaptive radiation of the cichlids in these African Great Lakes. We attempted to identify such genes by focusing on cichlid opsin genes.