Hh. Ganz et Rs. Burton, GENETIC DIFFERENTIATION AND REPRODUCTIVE INCOMPATIBILITY AMONG BAJA-CALIFORNIA POPULATIONS OF THE COPEPOD TIGRIOPUS-CALIFORNICUS, Marine Biology, 123(4), 1995, pp. 821-827
Populations of the harpacticoid copepod Tigriopus californicus were sa
mpled from five sites from San Diego, California, to Playa Altamira, B
aja California, Mexico. Allozyme analyses revealed that all the study
populations are sharply differentiated genetically. At the extreme, tw
o populations, Punta Baja and Playa Altamira, have no alleles in commo
n at the seven allozyme loci studied. All pairwise interpopulation cro
sses successfully produced F-2 hybrids except those involving the Play
a Altamira population. All crosses using Playa Altamira females failed
to produce F-2 hybrids, while Playa Altamira males successfully produ
ced F-1 progeny with females from all other sites. These F offspring,
however, were completely sterile (with San Diego and Punta Banda femal
es) or only occasionally produced F-2 offspring (with Punta Morro and
Punta Baja females). These results suggest that allopatric differentia
tion among Baja populations has resulted in exceptionally high levels
of genetic divergence and nearly complete reproductive isolation of th
e Playa Altamira population, which should now be recognized at the sem
ispecies (or perhaps sibling species) level.