Sequence Divergence of Heat Shock Genes within and among 3 Oncorhynchids

Heat shock proteins (Hsps) are induced in response to high temperatures and other stressors, and sequence variation plays a role in regulation of expression of these genes. In this study, we investigated the sequence variation in the 3 major classes of Hsps (Hsp90, Hsp70, and low-molecular weight Hsp) within and among 3 cold-water fish species of Oncorhynchus (Oncorhynchus clarki, Oncorhynchus mykiss, and Oncorhynchus tshawytscha) with variable life history and thermal tolerance characteristics. Sequences collectively totaled 4556 bp across 9 gene fragments and 198 single nucleotide polymorphisms and 43 indel sites were observed among species. Within species, sequence variation was much lower for O. clarki than the other 2 species. Sequence variation within and among species was high in cis-regulatory regions that are potentially involved in transcription of Hsps under variable stressors. Our results indicate that Hsp genes may be locally adapted in O. clarki, whereas higher Hsp polymorphism is necessary for O. mykiss and O. tshawytscha and variation at the sequence level may have important evolutionary consequences for these species. Further studies are needed to determine the association of observed sequence variation with the regulation of Hsps and performance of fish under stress.