Phylogeography of California by Kristina A. Schierenbeck

Author:Kristina A. Schierenbeck
Language: eng
Format: epub
ISBN: 9780520278875
Publisher: University of California Press

CETACEA OR “CETARTIODACTYLA”

Although traditionally classified under the Linnean system as within Cetacea, molecular data firmly place cetaceans within Artiodactyla, the even-toed ungulates and sister to the Hippopotamus (Shimamura et al. 1997; Price et al. 2005). Recent emphasis has been placed on the use of “Cetartiodactyla” to include both groups and is proposed as the new clade name (Agnarsson and May-Collado 2008); regardless, within the Cetacea, there are two primary lineages, the Mysticeti (baleen whales) and the Odontoceti (toothed whales).

The Balaenopteridae is estimated to have diverged from other members of the Mysticeti during the middle Miocene (Gingerich 2004). Megaptera novaeangliae (humpback whales, Balaenopteridae) has been studied extensively using an array of genetic tools. Prior to the decline of M. novaeangliae due to hunting, their numbers exceeded 100,000; although protected since 1966 under a moritorium, their populations are now estimated to be 80,000. Megaptera novaeangliae individuals migrate each year from high-latitude summer feeding grounds to their low-latitude winter breeding grounds, a distance of more than 9,000 km (Mackintosh 1965). Those individuals that summer off the central coast of California are part of the eastern Pacific population and winter in Baja California and the Gulf of Mexico (Baker and Palumbi 1996). The retention of some genetic diversity despite severe population decline is likely attributed to the relatively short time of the genetic bottleneck and their long generation times. A number of cetaceans are matrifocal, and thus the genetic structure of their populations should contain a matrilineal signature (Avise 2008). Combined with a high fidelity of females to their breeding sites, M. novaeangliae shows mtDNA population subdivision among three ocean basins (Baker et al. 1993).

Phocoena phocoena (harbor porpoise, Phocoenidae) is a continuously distributed coastal resident with circumpolar distribution in the temperate Northern Hemisphere that shows genetic structures consistent with those found in Phoca vitulina and Eumetopias jubatus (Bickham et al. 1996; Westlake and O’Corry-Crowe 2002; Harlin-Cognato et al. 2006). An analysis of 358 bp of the mtDNA CR shows differentiation between the northern Pacific and the eastern/southern group from Baja California to Monterey, with higher levels of genetic diversity near the southern genetic boundary near Baja (Taguchi et al. 2010). Mantel tests and an NCA support a range expansion from the south to the north and northwest following bottlenecks in the Pleistocene about 400–300 ka and 50–40 ka, consistent with interglacial periods. Early to middle Pleistocene glacial cycles correspond with a break in genetic variation around British Columbia that is inferred to have resulted from reduced gene flow from south to north and east to west. The AMOVA values of 11.87 and a ΦST value of 0.14 among groups support a hypothesis of rapid expansion from multiple refugia following the Pleistocene reductions in gene flow (Taguchi et al. 2010). A similar study using 402 bp of the mtDNA CR (n = 249) and nine nuclear and mitochondrial microsatellites (n = 194) (Chivers et al. 2002) also reveals genetic subdivision from north to south, for example, FST values of 0.0193 (P = 0.012) between British Columbia and San Francisco but a difference between San Francisco and Monterey of 0.

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