Avian Evolution During the Pleistocene in North America

Abstract

Late Pleistocene glacial cycles (Wisconsinian, Illinoian) in North America are thought to have caused speciation in many songbirds. If true, such species pairs should have diverged little in mitochondrial DNA (mtDNA) sequence owing to the short time span involved. We compared mitochondrial DNA sequences of the cytochrome b gene for 21 such pairs. Gamma-corrected Kimura two-parameter distances averaged 7.1%, which, across a range of potential calibrations, is much larger than expected on average for speciation events that occurred within the last 250,000 years. Hence, most species presumed by previous authors to be of very recent origins are in fact much older. To discover effects of Late Pleistocene glaciations, we examined the genetic architectures of present day species. Predictions from coalescence theory were examined in light of our expectation that most bird populations have undergone recent population expansions. We examined the few available continent-wide phylogeographic surveys, finding unstructured haplotype trees, geographic patterns of nucleotide diversity, mismatch distributions and plots of the number of lineages vs time, all consistent with recent population expansions as species recolonized deglaciated areas.