The role of within-species differentiation in macroevolution of Chesapeake Group bivalves

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Abstract
Discriminant function analysis is used to examine the role of within-species differentiation in macroevolution of four Miocene bivalve genera. According to the punctuational model, macroevolution is decoupled from microevolution; within-species trends may be unrelated to between-species differences. The reductionist alternative suggests that intraspecific (primarily geographic) differentiation is the basis of macroevolution. If macroevolution depends on within-species differentiation, discriminant function analysis should separate interspecific and intraspecific populations of a genus using the same set of characters.Chesapecten macroevolution apparently involved within-species differentiation. Shell length, height, and posterior auricle length differentiate geographic populations within species as well as interspecific populations. Results for Astarte, Anadara, and Eucrassatella are more consistent with the punctuational model. Characters which readily separate species of a genus are much less successful at differentiating intraspecific populations. Rank correlation techniques indicate that, for all three genera, the order of importance of characters in interspecific discrimination is not significantly related to their order in intraspecific discrimination. Decoupling of macroevolution from microevolution is implied for these taxa.