MAYER, MICHAEL S.*, JON P. REBMAN1, AND LAURA M. WILLIAMS. Department of Biology, University of San Diego, 5998 Alcala Park, San Diego, CA 92110-2492 and 1Department of Botany, San Diego Natural History Museum, Balboa Park, P.O. Box 121390, San Diego, CA 92112-1390. - Confirmation and characteristics of the hybrid origin of Opuntia prolifera through RAPD analyses.
Opuntia prolifera, the Coastal Cholla, is common to the coastal
sage scrub community extending from Ventura County, California to El
Rosario, Baja California. On the basis of morphological intermediacy,
O. prolifera is suspected to have originated through
hybridization between O. alcahes and O. cholla, both
species of coastal and inland deserts of Baja California and Baja
California Sur. For an independent test of this hypothesis, we
screened populations of O. prolifera and the putative parents
for RAPD banding patterns. In order to exclude other potential
parents and to distinguish species-specific RAPD bands we included
O. bigelovii, O. ganderi, O. tesajo, and O.
wolfii in the screening. The results provide abundant support for
the hybrization hypothesis as well as insight into various features of
the process. Twenty-nine primers revealed 44 bands shared only between
O. prolifera and just one of the two putative parents. Unique
bands are rare (=2) in O. prolifera compared with O.
alcahes (=19) or O. cholla (=23). Lack of marker asymmetry
within and among populations of O. prolifera, which is
triploid, is consistent with a single diploid-level hybridization
event. Trends in the degree of band sharing between O.
prolifera and its putative parents suggest a central Baja
California origin of the species.
Key words: cholla, hybridization, Opuntia prolifera, RAPD, speciation