Introgression and dispersal among spotted owl (Strix occidentalis) subspecies

Abstract

Population genetics plays an increasingly important role in the conservation and management of declining species, particularly for defining taxonomic units. Subspecies are recognized by several conservation organizations and countries and receive legal protection under the US Endangered Species Act (ESA). Two subspecies of spotted owls, northern (Strix occidentalis caurina) and Mexican (S. o. lucida) spotted owls, are ESA-listed as threatened, but the California (S. o. occidentalis) spotted owl is not listed. Thus, determining the boundaries of these subspecies is critical for effective enforcement of the ESA. We tested the validity of previously recognized spotted owl subspecies by analysing 394 spotted owls at 10 microsatellite loci. We also tested whether northern and California spotted owls hybridize as suggested by previous mitochondrial DNA studies. Our results supported current recognition of three subspecies. We also found bi-directional hybridization and dispersal between northern and California spotted owls centered in southern Oregon and northern California. Surprisingly, we also detected introgression of Mexican spotted owls into the range of northern spotted owls, primarily in the northern part of the subspecies’ range in Washington, indicating long-distance dispersal of Mexican spotted owls. We conclude with a discussion of the conservation implications of our study.

Evidence for recent population bottlenecks in northern spotted owls (Strix occidentalis caurina)

“…Hybridization between northern spotted owls and the other two subspecies of spotted owls (California spotted owls, S. o. occidentalis, and Mexican spotted owls, S. o. lucida) and/or genetic drift in small populations are more likely explanations for LD in northern spotted owls. Funk et al (2008) demonstrated hybridization between northern spotted owls and the other two subspecies in some study areas, suggesting hybridization could contribute to LD. Additionally, evidence for bottlenecks presented above suggests that effective population sizes are decreasing which should in turn result in increased genetic drift and LD.…”

“…We did not observe consistent LD between the same pair of loci across populations, suggesting that LD was not due to physical linkage between loci. Moreover, previous analyses showed that there is little population structure within regions (Funk et al 2008), suggesting population structure is not the cause of LD. Hybridization between northern spotted owls and the other two subspecies of spotted owls (California spotted owls, S. o. occidentalis, and Mexican spotted owls, S. o. lucida) and/or genetic drift in small populations are more likely explanations for LD in northern spotted owls.…”

“…Ninety-four percent of these were collected from 1994 to 2006. We chose regions as an appropriate grouping for analysis because: (1) regions were genetically differentiated from each other (based on Funk et al 2008 and the current analysis); (2) N was large enough for each region to allow reasonable power to detect bottlenecks (mean = 59, range = 22-90; (Goodnight and Queller 1999), tended to be slightly larger than zero (mean = 0.044, SD = 0.032), as expected in a random sample from a randomly mating population.…”

Projecting Impacts of Fire Management on a Biodiversity Indicator in the Sierra Nevada and Cascades, USA: The Black-Backed Woodpecker

“…Further study is warranted to clarify the relationship of the population in California, which may also be disjunct to some degree with the eastern Oregon Cascades population, and is disjunct with other populations of the species. However, it appears that the population in the Sierra Nevada and Oregon Cascades is genetically distinct from other black-backed woodpecker populations, similar to the distinction between the northern spotted owl in the Pacific Northwest, a subspecies of Strix caurina that is listed as threatened [18,19], and the California subspecies, which is not listed. Therefore, in addition to the biodiversity for which it serves as an indicator or provides vital resources for reproduction, the black-back woodpecker is an important conservation concern in its own right in the Sierra Nevada and southern Cascades.…”

Range-wide phylogeographic analysis of the spotted frog complex (Rana luteiventris and Rana pretiosa) in northwestern North America

“…The effect of the Columbia River as a barrier appears to vary among species. In some, it corresponds with a genetic break (Monsen and Blouin, 2003), but in many it does not (Funk et al, 2008;Nielson et al, 2006;Recuero et al, 2006).…”