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Northern Channel Islands (northern + channel_island)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Population structure of loggerhead shrikes in the California Channel Islands

MOLECULAR ECOLOGY, Issue 8 2004
LORI S. EGGERT
Abstract The loggerhead shrike (Lanius ludovicianus), a songbird that hunts like a small raptor, maintains breeding populations on seven of the eight California Channel Islands. One of the two subspecies, L. l. anthonyi, was described as having breeding populations on six of the islands while a second subspecies, L. l. mearnsi, was described as being endemic to San Clemente Island. Previous genetic studies have demonstrated that the San Clemente Island loggerhead shrike is well differentiated genetically from both L. l. anthonyi and mainland populations, despite the fact that birds from outside the population are regular visitors to the island. Those studies, however, did not include a comparison between San Clemente Island shrikes and the breeding population on Santa Catalina Island, the closest island to San Clemente. Here we use mitochondrial control region sequences and nuclear microsatellites to investigate the population structure of loggerhead shrikes in the Channel Islands. We confirm the genetic distinctiveness of the San Clemente Island loggerhead shrike and, using Bayesian clustering analysis, demonstrate the presence and infer the source of the nonbreeding visitors. Our results indicate that Channel Island loggerhead shrikes comprise three distinct genetic clusters that inhabit: (i) San Clemente Island, (ii) Santa Catalina Island and (iii) the Northern Channel Islands and nearby mainland; they do not support a recent suggestion that all Channel Island loggerhead shrikes should be managed as a single entity. [source]

Adaptive Units for Conservation: Population Distinction and Historic Extinctions in the Island Scrub-Jay

CONSERVATION BIOLOGY, Issue 2 2005
KATHLEEN S. DELANEY
Aphelocoma; diversidad genética especie; endémica; genética de conservación; Islas Channel Abstract:,The Island Scrub-Jay (Aphelocoma insularis) is found on Santa Cruz Island, California, and is the only insular bird species in the continental United States. We typed seven microsatellite loci and sequenced a portion of the mitochondrial DNA control region of Island Scrub-Jays and their closest mainland relative, the Western Scrub-Jay (Aphelocoma californica), to assess levels of variability and effective population size and to examine the evolutionary relationship between the two species. The estimated female effective population size, Nef, of the Island Scrub-Jay was 1603 (90% confidence interval: 1481,1738) and was about 7.5% of the size of the mainland species. Island and Western Scrub-Jays have highly divergent control-region sequences, and the value of 3.14 ± 0.09% sequence divergence between the two species suggests a divergence time of approximately 151,000 years ago. Because the four northern Channel Islands were joined as one large island as recently as 11,000 years ago, extinctions must have occurred on the three other northern Channel islands, Santa Rosa, San Miguel, and Anacapa, highlighting the vulnerability of the remaining population. We assessed the evolutionary significance of four island endemics, including the Island Scrub-Jay, based on both genetic and adaptive divergence. Our results show that the Island Scrub-Jay is a distinct species of high conservation value whose history and adaptive potential is not well predicted by study of other island vertebrates. Resumen:, Aphelocoma insularis se encuentra en la Isla Santa Cruz, California, y es la única especie de ave insular en Estados Unidos continental. Clasificamos siete locus microsatelitales y secuenciamos una porción de la región control del ADN mitocondrial de A. insularis y su pariente continental más cercano A. californica para evaluar niveles de variabilidad y tamaño poblacional efectivo y examinar las relaciones evolutivas entre las dos especies. El tamaño poblacional efectivo de hembras, Neh, de A. insularis fue estimado en 1603 (90% CI: 1481-1738) y fue aproximadamente 7.5% del tamaño de la especie continental. Aphelocoma insularis y A. californica tienen secuencias muy divergentes en la región control, y el valor de divergencia secuencial de 3.14 ± 0.09% entre las dos especies sugiere un tiempo de divergencia de aproximadamente 151,000 años. Debido a que las cuatro Islas Channel estuvieron unidas en una sola isla tan recientemente como hace 11,000 años, deben haber ocurrido extinciones en las otras tres islas Channel, Santa Rosa, San Miguel y Anacapa, acentuando la vulnerabilidad de la población remanente. Evaluamos el significado evolutivo de cuatro especies insulares endémicas incluyendo A. insularis con base en la divergencia genética y adaptativa. Nuestros resultados muestran que A. insularis es una especie distinta de alto valor de conservación, cuya historia y potencial adaptativo no es pronosticado correctamente por el estudio de otros vertebrados insulares. [source]

Brief communication: Additional cases of maxillary canine-first premolar transposition in several prehistoric skeletal assemblages from the Santa Barbara Channel Islands of California,

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010
Sabrina B. Sholts
Abstract This article identifies and discusses seven new cases of complete maxillary canine-premolar transposition in ancient populations from the Santa Barbara Channel region of California. A high frequency of this tooth transposition has been previously documented within a single prehistoric cemetery on one of the Channel Islands. A total of 966 crania representing 30 local sites and about 7,000 years of human occupation were examined, revealing an abnormally high prevalence of this transposition trait among islanders during the Early period of southern California prehistory (,5500,600 B.C.). One of the affected crania is from a cemetery more than 7,000-years-old and constitutes the earliest case of tooth transposition in humans so far reported. The results are consistent with findings by other studies that have indicated inbreeding among the early Channel Islands groups. Together with the normal transposition rates among mainland populations, the decreasing prevalence of maxillary canine-first premolar transposition among island populations across the Holocene suggests that inbreeding on the northern Channel Islands had all but ceased by the end of the first millennium B.C., most likely as a result of increased cross-channel migration and interaction. Am J Phys Anthropol 143:155,160, 2010. © 2010 Wiley-Liss, Inc. [source]