Evidence for differences in the allozyme thermostability of deep-sea hydrothermal vent polychaetes (Alvinellidae):a possible selection by habitat

Abstract

Alv~nelhd polychaetes are, to date, restncted to deep-sea hydrothermal vents of the eastern and the western ndges of the Pacific Ocean These organisms live In vanous sulfide-rich habitats, Including the hottest part of the hydrothermal envlronment (l e chimneys) They expenence transient anoxia, h ~g h levels of heavy metals and H2S, natural radioactivity and temperatures ranging from 5 to 80C which vary greatly wlth tlme The Alvinellidae, as many vent organisms, have developed spec~fic adaptations to cope wlth this harsh and unstable envlronment Enzyme systems are good markers of the adaptation of ectotherms to temperature, which acts on both enzyme kinet~cs and proteln denaturation We est~mated g e n e t ~c distances between 11 alvlnellid species using a data set of allozymes and studied in vltro allozyme thermostabillties of aspartate-amino transferase (AAT), glucose-6-phosphate isomerase (GPI) and phosphoglucomutase (PGM) which may play a role In onentatlng aerobic versus anaerobic metabolism pathways, for 8 species using the most common homozygous genotypes Results show great genetlc d~vergences between species llving in distinct mlcrohabitats as well as stiong thermostability differences with~n and between specles which also rely on ddferent enzymatic strategies (phenotyp~c plasticity versus genetlc variab~lity) Allelic f~tness to temperature in a hlghly fluctuating environment may explain the high level of polymorphism found In alvinellids and may have also provided sufficient genetic divergence between i n d ~v ~d u a l s livlng in dist~nct thermal regimes to produce speciation KEY WORDS: Deep-sea hydrothermal vents