Hemocyanin genes as indicators of habitat shifts in Panpulmonata?

Abstract

Hemocyanin is the primary respiratory protein for the majority of the Mollusca and therefore directly interfaces with the physiological requirements of each species and the environments to which they are adapted. Hemocyanin is therefore likely to have been evolutionarily imprinted by significant habitat shifts. In the gastropod clade Panpulmonata (>30,000 species) major realm transitions have occurred multiple times independently and may have contributed to the diversification of this group. Yet, little is known about the adaptive changes linked to these habitat shifts. In order to gain deeper insight into the evolution of panpulmonate hemocyanins and to infer possible impacts associated with those scenarios, we have assembled and analysed hemocyanin isoforms from 4 panpulmonate species: (i) Helix pomatia, (ii) Cantareus aspersus (both Helicidae, Stylommatophora), (iii) Arion vulgaris (Arionidae, Stylommatophora) and (iv) Lymnaea stagnalis (Lymnaeidae, Hygrophila). Additionally, we describe a new hemocyanin isoform within the genome of the euopisthobranch Aplysia californica. Using these newly acquired hemocyanin data, we performed a phylogenetic analysis that reveals independent duplication events of hemocyanin within lineages that correlate with significant habitat shifts.