SPECIATION AND PHYLETIC EVOLUTION IN PTEROCANIUM (RADIOLARIA) (BIOMETRICS, OCEANOGRAPHY)

Taxonomic and biometric analysis of Pterocanium (Radiolaria) over the last 5 million years reveals 5 lineages: Pterocanium charybdeum, Pterocanium praetextum, Pterocanium korotnevi, Pterocanium prismatium, and Pterocanium audax. Several species are synonomized, and one new subspecies--Pterocanium charybdeum allium--is described. A variety of evolutionary patterns were seen, but none corresponding to the punctuated equilibrium model of Eldredge and Gould (1972).; Significant amounts of phyletic evolution are observed in all lineages studied. Phyletic evolution in P.praetextum results in gradual replacement of a cosmopolitan early Pliocene P.praetextum eucolpum population with a clinal Pleistocene population of P.p.eucolpum and P.praetextum praetextum. Gradual changes in mean thorax width and length measures for individual lineages over a 5 million year period amount to as much as 50% of the differences between co-existing sister species.; Geographically widespread cladogenic speciation of P.prismatium from P.charybdeum occurred gradually over a 0.5 million year interval in the early Pliocene. Divergence was observed in cores from both the equatorial Indian Ocean and equatorial Pacific Ocean. This pattern is consistent with sympatric or depth-parapatric models of speciation.; Reticulate evolution may be common in Pterocanium. The ancestry of the P.praetextum lineage can be traced to 2 different species in the earliest Pliocene: P.charybdeum in equatorial waters, and P.korotnevi in the North Pacific. Other reticulation events are inferred between P.audax and P.charybdeum in the latest Miocene/ early Pliocene, and between P.charybdeum and P.praetextum in the Pleistocene.; Ecophenotypic morphologic change cannot explain the above patterns. Multivariate morphologic analysis of glacial and interglacial populations of Pterocanium species in equatorial Pacific core V19-28 shows no significant environmentally related changes, and within species variation in sample means is only 0.25 the amount of the differences in means between species.; A three-dimensional digitizer developed to measure microfossil morphology is described. Accuracy is better than 1 micrometer horizontally and vertically and the digitizer can be programmed to measure distances, angles, areas, and shapes. Complete hardware and software listings are included.