QUANTITATIVE EVIDENCE THAT BOTH HSC70 AND HSP70 CONTRIBUTE TO THERMALADAPTATION IN HYBRIDS OF THE LIVEBEARING FISHES POECILIOPSIS

The 70-kilodalton heat shock protein family is composed of both enviro nmentally inducible (Hsp) and constitutively expressed (Hsc) family me mbers. While the role of the constitutively expressed stress proteins in thermotolerance is largely unknown, de novo expression of stress pr oteins in response to elevated temperatures has been associated with i ncreased thermotolerance in many cell lines, developing embryos and ad ult organisms. Distinct, hemiclonal hybrids between the livebearing fi sh species Poeciliopsis monacha and P. lucida varied in their abilitie s to survive temperature stress, with survival being greatest when rat es of temperature increase to 40 degrees C were slowest and when P. mo nacha genomes were combined with a sympatric P. lucida genome. Quantif ication of Hsp70 under heat shock conditions and Hsc70 under normal ph ysiological conditions indicated that variation in survival among hemi clones was best explained by the combined effects of these two protein s. Similar complex interactions between maternal and paternal genomes and rate of temperature increase were found to underlie patterns of su rvival, Hsp70 accumulation and Hsc70 abundance. These data suggest tha t the relationship between Hsps and thermotolerance is more intricate than previously thought and that Hsps contribute to thermal adaptation in these fishes through genetic interactions specific to particular e nvironments.