Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related speciesof Poeciliopsis demonstrated the existence of biochemical diversity in thehsp100, hsp70, hsp60, and hsp30 protein families among species. Eachspecies expressed five to seven hsp70-related isoforms. Constitutive 70-kDisoforms were identical among species, but four different patterns ofheat-inducible isoforms were seen in these six species. Members of thehsp70 family of molecular chaperones are included among the most highlyconserved proteins known, and the possibility of variation in hsp70 amongclosely related species has rarely been addressed. The hsp30 family isknown to be less conserved than the hsp70 family, and, as expected, thePoeciliopsis hsp30 patterns showed more variation. Most of the hsp30isoforms characteristic of a particular species were unique to thatspecies. Hsp100 and hsp60 were identical in five of the species, butalternate isoforms were found in P. monacha. The small size and limitedgeographical distribution of the P. monacha population have probablycontributed to the uniqueness of the monacha pattern. Two of the specieswere shown to acquire thermotolerance, the ability to withstand normallylethal temperatures when subjected to a gradual temperature increase.Rapid-heating protocols commonly used to establish critical thermal maximaof organisms do not include this inducible component of thermoresistanceand therefore do not adequately assess an organism's capacity to withstandthermal stress.