PHYLOGEOGRAPHY OF SPOTTED OWL (STRIX OCCIDENTALIS) POPULATIONS BASED ON MITOCHONDRIAL DNA SEQUENCES: GENE FLOW,GENETIC STRUCTURE,AND A NOVEL BIOGEOGRAPHIC PATTERN

Mitochondrial DNA control region sequences of spotted owls (Strix occidentalis) allowed us to investigate gene flow, genetic structure, and biogeographic relationships among these forest-dwelling birds of western North America Estimates of gene flow based on genetic partitioning and the phylogeography of haplotypes indicate substantial dispersal within three long-recognized subspecies. However, patterns of individual phyletic relationships indicate a historical absence of gene flow among the subspecies, which are essentially monophyletic. The pattern of haplotype coalescence enabled us to identify the approximate timing and direction of a recent episode of gene flow from the Sierra Nevada to the northern coastal ranges. The three subspecies comprise phylogenetic species, and the northern spotted owl (S. o. caurina) is sister to a clade of California (S. o. occidentalis) plus Mexican spotted owls (S o lucida); this represents a novel biogeographic pattern within birds. The California spotted owl had substantially lower nucleotide diversity than the other two subspecies; this result is inconsistent with present patterns of population density A causal explanation requires postulating a severe bottleneck or a selective sweep, either of which was confined to only one geographic region.