Phenotypic covariance through geologic time: Micro- and macroevolution in the deep-sea ostracode genus Poseidonamicus

Biologists have long recognized variation as the raw material of evolution. On time scales of a few generations, the evolutionary influence of variation within and covariation among traits is accounted for by standard microevolutionary theory. In contrast, the role that patterns of variation play over thousands of generations is considerably less clear. In this dissertation, I use the rich fossil record of the ostracode genus Poseidonamicus to test if patterns of morphological variation have influenced long-term, macroevolutionary divergence.; There are three major parts to this thesis. First, I address the issue of estimating patterns of variation in fossil samples in the face of time-averaging, first from the standpoint of modeling. Expressions are derived that link time-averaging, evolutionary rates and phenotypic variation. The issue of time averaging and phenotypic variance is then addressed empirically using two literature-based approaches that compare the variance of samples that differ in temporal resolution. Both of these approaches find that time-averaging typically has only slight to moderate effects on phenotypic variance (median: 3–8% inflation).; The second part of this thesis investigates the ontogeny and phylogenetics of the deep-sea ostracode genus Poseidonamicus. Using 59 morphological characters defined on the basis of carapace morphology, the phylogenetic relationships among 72 populations of this genus are explored. The resulting phylogenetic hypothesis is generally consistent with the stratigraphic record of this genus, and provides an evolutionary framework for the final part of this dissertation.; The final part of this thesis addresses the question: have evolutionary changes in Poseidonamicus been disproportionately concentrated in morphological directions of high variance? Two sets of landmarks are used to quantify morphology, and evolutionary transitions are inferred at two scales of resolution: (1) evolutionary changes within lineages, as inferred by differences between ancestor-descendant populations, and (2) evolutionary changes between lineages, as inferred from a hypothesis of phylogenetic relationships. For both datasets and both types of transitions it is found that evolutionary changes were concentrated disproportionately in directions of high variance, suggesting that phenotypic variation and covariation can influence evolutionary divergence, even on macroevolutionary time-scales.