Abstract

While concentration of morphologic change around the time of speciation is consistent with both known microevolutionary mechanisms and punctuated equilibria, punctuated equilibrium theory presupposes that most of the change occurs either before or during initial allopatry to produce morphologically static taxa. Considerable change in the initial phases of speciation could also result from known microevolutionary mechanisms, but if significant change occurs in the neosympatric phase, or at any time after the species have become differentiated, then that change is best explained by known microevolutionary mechanisms. Amount and rate of morphologic change during each phase of the allopatric speciation process were determined for two cognate species of the radiolarian genus Eucyrtidium. In this case, morphologic change accruing to these species during the neosympatric phase was 2-3 times as great as that which occurred during the initial allopatric phase. Morphologic trends in both these species during the allopatric phase differed significantly from a random walk. The size differential that characterized this speciation event was not the product of a single large step early in the process but of a disproportionate number of small steps in one direction during neosympatry. Therefore, the hypothesis of no statistically significant change following the "first stage" of speciation, which is a major tenet of punctuated equilibrium theory, is falsified for this case.

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