Over Evolutionary History, Many Groups of Organisms That Inhabit Caves

Essay

Over evolutionary history, many groups of organisms that inhabit caves have lost the organs of sight.For instance, although surface-dwelling crayfishes have functional eyes, several crayfish species that are restricted to underground habitats lack eyes.Opsins are a group of light-sensitive proteins known to have an important function in vision (see Chapter 45), and opsin genes are expressed in eye tissues.Opsin genes are present in the genomes of eyeless, cave-dwelling crayfishes.Two alternative hypotheses that might explain the presence of opsin genes in an eyeless organism are: (1) the genes are no longer experiencing purifying selection because there is no longer selection for function in vision; and (2) the genes are experiencing selection for a function other than vision.How would you investigate these two hypotheses, using the sequences of the opsin genes in various species of crayfishes?