Sympatric natural Saccharomyces cerevisiae and S-paradoxus populations have different thermal growth profiles

Saccharomyces cerevisiae and its close congener S. paradoxtis are typically indistinguishable by the phenotypic criteria of classical yeast taxonomy, but they are evolutionarily distinct as indicated by hybrid spore inviability and genomic sequence divergence. Previous work has shown that these two species coexist in oak-associated microhabitats at natural woodland sites in North America. Here, we show that sympatric populations of S. cerevisiae and S. paradoxtis from a single natural site are phenotypically differentiated in their growth rate responses to temperature. Our main finding is that the S. cerevisiae population exhibits a markedly higher growth rate at 37degreesC than the S. paradoxtis population; we also find possible differences in growth rate between these populations at two lower temperatures. We discuss the implications of our results for the coexistence of these yeasts in natural environments, and we suggest that thermal growth response may be an evolutionarily labile feature of these organisms that could be analyzed using genomic approaches. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.