Wednesday, May 16, 2007

Sexual dimorphism and adaptive radiation

Caribbean lizards have strong sexual dimorphism (that's a female Anolis lineatopus on the left, and male on the right in the above image). Their degree of sexual dimorphism has led them to use resources in different habitats that limit competition between the opposite sexes of the same species. Scientists from Harvard University, the University of Hawaii, and Washington University in St. Louis, studied the role of sexual dimorphism in evolutionary diversification among anole species during their well-known adaptive radiation.

Anolis lizards originating in the West Indies have evolved independently in Cuba, Hispaniola, Jamaica, and Puerto Rico. Each species on each island has evolved traits that have allowed them to fit specific habitats through adaptive radiation. Past studies on adaptive radiation has focused primarily on males but it is important to consider both sexes because the study of sexual dimorphism helps explain the importance of male and female contribution to the population’s survival.

Marguerite Butler, Stanley Sawyer, & Jonathan Losos studied 15 different species of Anolis lizards and found that only 14 percent of niches were occupied by both sexes of the same species. 45 niches were covered by females and 36 percent of niches were occupied by males. By occupying different niches, males and females can decrease competition. For example, the sexes in hummingbirds have different lengths in beak size. This allows them to obtain nectar from different flowers which eliminates competition for food. By reducing competition between males and females of the same species, individuals increase their chances of surviving which leads to a higher fitness level of the whole population

--contributed by Jemimah Corpuz



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