Synchronized evolution in lineages of land snails in oceanic islands

Abstract

Synchronous episodes of phenotypic change in five lineages of the endemic land snail genus Mandarina of the oceanic Bonin (Ogasawara) Islands through 40,000 years were documented by morphological analyses of radiocarbon-dated fossil specimens. Adult shell traits of these lineages show mostly synchronous patterns of change with longer intervals of stability and rapid shifts to other states of stability. Although there are intermediates between these different phenotypic states, the net interval of the phenotypic shift was relatively short, i.e., no longer than 7000 years. Extinction of a lineage and speciation occurred during the intervals of the rapid phenotypic shift. This period of abrupt change corresponds to the period of lowest sea level and end of the last glacial period. This implies that climatic change is one of the causes of these episodes of simultaneous rapid phenotypic shifts, speciation, and extinction in different lineages. These findings suggest that major phenotypic changes in phyletic evolution, separation of different species, and extinction of lineages may occur synchronously in many lineages during an extremely short interval.