title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
Nucella emarginata vs. N. ostrina
Research study 1

photographs of Nucella ostrina and N. emarginata courtesy Rich Palmer, University of AlbertaConvincing evidence for the existence of 2 species in place of one species Nucella emarginata is provided in 4 lines of study on populations from 4 widely separated localities on the west coast: Torch Bay (Alaska), Bamfield (British Columbia), San Juan Island (Washington), and Santa Barbara (California).   The 4 lines of study include breeding compatibility, shell morphology, egg-capsule shape, and allozyme variation.  drawings of egg capsules showing differences between whelks Nucella ostrina and N. emarginata

First, breeding crosses between the 3 northern populations yield viable F1 and F2 offspring, while crosses of these same northern populations with the Santa Barbara population yield no viable offspring. 

Second, shell morphologies differ between the northern and southern populations, with the former being characterised by uniform spiral ribs and the latter by regularly spaced knobs along the spiral ribs (see photographs). 

Third, capsules are vase-shaped in the northern populations and rolling pin-shaped in the southern population (see drawings on Right). 

Finally, analyses of allozyme variations show clear separation between northern and southern populations.  The author provides several lines of genetic evidence for the existence of northern and southern populations of N. emarginata that actually belong to 2 reproductively isolated cryptic species.  Palmer et al. 1990 Veliger 33: 325.

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Research study 2

map showing distributions of whelks Nucella ostrina and N. emarginata in California Further investigation of allozyme variations in Nucella emarginata leads to the species being split into N. ostrina from Yakutat, Alaska to Point Conception, California, and N. emarginata from Fort Point near San Francisco, California to Punta Eugena, Baja California.  Although both species may be encountered in the overlap zone in central California, N. emarginata is apparently quite rare until just south of Point Conception.  Marko et al. 2003 Veliger 46: 77; see also Marko 1998 Evolution 52: 757.

NOTE based on frequencies of allozyme alleles