Meeting Abstract
Planktonic marine copepods are abundant and ecologically important. Acartia spp. are common globally and in the San Francisco Estuary (SFE). The taxonomy and distribution of Acartia spp. in SFE are poorly described due to difficulty in reliable assessment of morphological characters. Genetic comparisons were made to evaluate the utility of common diagnostic characters including morphology of the fifth swimming leg (used in mating, hence often diagnostic of species) and caudal rami, and presence of a rostral filament. Maximum likelihood analysis of an approximately 400-bp segment of the 18s rDNA locus (n=60) revealed three well-supported genetic clades inferred to represent the 3 species recorded in SFE: Acartia californiensis, A. hudsonica and A. tonsa. Caudal rami and rostral filament characters provided the best prediction of genetic clade. Fifth swimming leg morphology can be variable and difficult to quantify. Genetic clades were compared with reference sequences for 9 other Acartia spp. Species-level genetic divergence ranged from 9-35%. SFE A. tonsa showed 30% genetic divergence from Atlantic coast USA A. tonsa. This result supports the designation of Pacific coast A. tonsa as a distinct species, as previously reported in the literature. Two SFE clades of morphological A. hudsonica were 9% divergent from each other, and 9-10% divergent from A. omorii, native to coastal Japan. This result suggests cryptic speciation or a new record of an Acartia sp. in SFE. This is the first genetic study of Acartia spp. in SFE, part of ongoing work to elucidate cryptic genetic diversity and distribution patterns of this genus.
