THE ESTUARY EFFECT: ENVIRONMENTAL AND PHYSIOLOGICAL CONTROLS ON MOLLUSCAN DIVERSIFICATION

A comprehensive survey of global diversity suggests that there is a large discrepancy in the diversity patterns of clades that solely inhabit the marine realm and those that have colonized freshwater and terrestrial environments. Diversification within many clades show marked differences in diversity. This study examines physiological and environmental parameters that possibly influence the terrestrialization of bivalves and gastropods, evaluating how diversity within these clades have changed through time before and after they invaded the continental realm. Data from the Paleobiology Database is enriched with data derived from the “Lake Faunas Through Time” database. This cross-referential, literature based dataset details paleoecological, lithostratigraphic and geographic information in primarily lacustrine and estuarine deposits.

Osmoregulatory capacity of bivalves and clams is a major physiological constraint on a clade’s ability to invade the continental realm. By mapping osmoregulatory characters onto environmental and phylogenetic analyses of Cenozoic gastropods and bivalves, this study demonstrates the correlation between osmoregulation, osmoconformation, environment and diversity.

The ability of an organism to control its internal body chemistry appears to be a major factor allowing for invasion of the continental realm and diversification of clades. While evolution of this important physiological novelty is essential for colonization of freshwater environments, it also appears to have a major role in contributing to the overall diversity of osmoregulators that remain in marine environments.