Speciation in pelagic Protista and its study in the planktonic microfossil record: a review

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Abstract
The punctuated equilibrium hypothesis, largely derivable from Mayr's peripheral isolate model of speciation, is but one of many possible paleontologic patterns of speciation which may be tested against the deep-sea fossil record of planktonic microfossils. The nature of reproduction and variation within a species has a profound effect on its expected tempo and mode of evolutionary change. Biologic data on pelagic plankton and on protistan genetics and reproduction suggest that speciation in pelagic holoplanktonic protists may also be parapatric, “equal” allopatric, or the result of hybridization. Each of these models is shown to make testable predictions of paleontologic pattern. Published records of speciation in planktonic deep-sea microfossil data are compatible with these alternative models. Existing data sets are not yet sufficiently complete to provide strong tests. Future work needs to integrate taxonomic, paleoecologic, biogeographic, and biometric data in studies of individual speciation events. Micropaleontologic studies of morphologic change through time may thereby contribute to our understanding of speciation mechanisms in the pelagic protistan plankton.