18
Avian Evolution During the
Pleistocene in North America
ROBERT M. ZINK AND JOHN KLICKA
J. F. Bell Museum of Natural History, University of Minnesota, St. Paul, Minnesota 55108,
USA
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.
1 Introduction
Historical patterns of speciation traditionally were inferred by associating events in
earth history with particular phylogenetic hypotheses derived from morphology.
Key words. mitochondrial DNA, glacial cycles, speciation, phylogeography, genetic distances, molecular clock, Late Pleistocene Origins model, songbirds, sequence saturation,
mismatch distribution, nucleotide diversity, likelifood ration tests, Song Sparrow, Timberline Sparrow, Red-winged Blackbird
275
Avian Evolution During the
Pleistocene in North America
ROBERT M. ZINK AND JOHN KLICKA
J. F. Bell Museum of Natural History, University of Minnesota, St. Paul, Minnesota 55108,
USA
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.
1 Introduction
Historical patterns of speciation traditionally were inferred by associating events in
earth history with particular phylogenetic hypotheses derived from morphology.
Key words. mitochondrial DNA, glacial cycles, speciation, phylogeography, genetic distances, molecular clock, Late Pleistocene Origins model, songbirds, sequence saturation,
mismatch distribution, nucleotide diversity, likelifood ration tests, Song Sparrow, Timberline Sparrow, Red-winged Blackbird
275