CHALLENGES IN INTEGRATING MORPHOLOGICAL AND MOLECULAR DATA IN STUDIES OF SPECIATION PATTERNS AND PROCESSES

Interest in empirical studies of evolutionary rates and processes of speciation has not waned in recent decades. The fossil record remains a unique source of information about patterns of morphologic changes through geologic time. Differences in select gene segments provide us with insights to phylogenetic relationships among closely related extant species and the timing of their evolutionary divergence (molecular clock).

By integrating morphologic (or taxonomic) data across multiple, ostensible ancestor-descendant, extant species pairs, insights can be inferred about general patterns of speciation events and evolutionary processes. Data for analyses include the First Occurrence Data (FAD) for both species’ ranges and the calculated date for their Most Recent Common Ancestor (MRCA). Values scaled as a percentage of the MRCA are placed in one of eight ranked bins that represent their relative likelihood for similar timing with the MRCA. Twenty-nine combinations of FADs and MRCA are possible, each carrying a likely inference for its micro-evolutionary process.

Applying this method to data from the Neogene of Panama with fossil bryozoan species pairs in Discoporella and Cupuladria, resulted in nine interpretable patterns: five branching from ancestral stasis, one as simultaneous split from an undocumented ancestor, and two with unlikely ancestor-descendant relationships. Exploration of additional published data with which to apply this method failed to provide suitable data for analysis. However, of the more than forty papers with published phylogenies and molecular estimates for MRCA, none provides corresponding fossil records or taxa represented in PBDB. None of the handful of papers with empirical Neogene fossil evolutionary patterns have associated molecular data. Is this discrepancy a factor of inherent deficiencies in the Neogene record? Cautions for interpreting all of the Phanerozoic? Or simply a call for improved communication between paleontologists and neontologists?