Abstract
The Californian Channel Islands are near–shore islands with high levels of endemism, but extensive habitat loss has contributed to the decline or extinction of several endemic taxa. A key parameter for understanding patterns of endemism and demography in island populations is the magnitude of inter–island dispersal. This paper estimates the extent of migration and genetic differentiation in three extant and two extinct populations of Channel Island song sparrows (Melospiza melodia graminea). Inter–island differentiation was substantial (G''ST: 0.14–0.37), with San Miguel Island having the highest genetic divergence and lowest migration rates. Santa Rosa and Santa Cruz Island populations were less diverged with higher migration rates. Genetic signals of past population declines were detected in all of the extant populations. The Channel Island populations were significantly diverged from mainland populations of M. m. heermanni (G''ST: 0.30–0.64). Ten mtDNA haplotypes were recovered across the extant and extinct Channel Island population samples. Two of the ten haplotypes were shared between the Northern and Southern Channel Islands, with one of these haplotypes being detected on the Californian mainland. Our results suggest that there is little contemporary migration between islands, consistent with early explanations of avian biogeography in the Channel Islands, and that song sparrow populations on the northern Channel Islands are demographically independent.
Highlights
Haplotype 3 was sampled from Santa Cruz song sparrows in a previous study [26], but no other previously published haplotypes were detected within our Channel Islands samples
Genetic divergence based on sequence differences revealed a closer relationship between the southern Channel Island populations on San Clemente and Santa Barbara, both to each other and to the mainland than to Santa Cruz and Santa Rosa populations (Table 1)
The sequences found on Santa Rosa, Santa Cruz and San Miguel had a closer affinity to those found on the southern Channel Islands and mainland populations, than to each other, which led to these islands being more divergent from each other than from San Clemente and mainland populations
Summary
Graminea (Santa Barbara Island); these subspecies were recognized on morphological characters [8] Based on this taxonomy, morphological differences and distribution, it was predicted that song sparrows colonized the Channel Islands in a single event from the mainland with inter-island colonization but limited subsequent dispersal [8]. Morphological differences and distribution, it was predicted that song sparrows colonized the Channel Islands in a single event from the mainland with inter-island colonization but limited subsequent dispersal [8] Throughout their range, song sparrows are highly polytypic with 25 diagnosable subspecies that range from c. We first use mitochondrial control region data to examine the patterns of genetic structure between extant (Santa Cruz, Santa Rosa and San Miguel Islands) and extirpated (Santa Barbara and San Clemente Islands) populations of the Channel Island song sparrow and several mainland sites. We use microsatellite data from the extant populations to: determine contemporary inter-island patterns of gene flow, test for evidence of historic population bottlenecks and to compare the genetic structuring found in other mainland song sparrow populations
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