THE MOLECULAR EVOLUTION OF VISUAL PIGMENTS OF FRESH-WATER CRAYFISHES (DECAPODA, CAMBARIDAE)

This study examines the diverse maximum wavelength absorption (lambda( max)) found in crayfishes (Decapoda: Cambaridae and Parastacidae) and the associated genetic variation in their opsin locus. We measured the wavelength absorption in the photoreceptors of six species that inhab it environments of different light intensities (i.e., burrows, streams , standing waters, and subterranean waters). Our results indicate that there is relatively Little variation in lambda(max) (522-530 nm) amon g species from different genera and families. The existing variation d id not correlate with the habitat differences of the crayfishes studie d. We simultaneously sequenced the rhodopsin gene to identify the amin o acid replacements that affect shifts in maximum wavelength absorptio n. We then related these to changes that correlated with shifts in lam bda(max) by reconstructing ancestral character states using a maximum- likelihood approach. Using amino acid sequences obtained from five spe cies (all were 301 amino acids in length), we identified a number of c andidates for producing shifts of 4 to 8 nm in lambda(max). These amin o acid replacements occurred in similar regions to those involved in s pectral shifts in vertebrates.