MAYER, MICHAEL S.*, JON P. REBMAN1, MICHELLE DEASEY, AND DOUGLAS GILBERT. Department of Biology, University of San Diego, San Diego, CA 92110 and 1San Diego Natural History Museum, San Diego, CA 92112. - Hybrid speciation of Opuntia prolifera: morphological and molecular evidence.
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
in stem dimensions, tubercle size, spine width, and flower color,
O. prolifera is suspected to have originated through
hybridization between O. alcahes and O. cholla, species
of coastal and inland deserts of the region. Our chromosome counts
from these species do not rule out this possibility. For an
independent test of this hypothesis, we screened O. prolifera
and the putative parent species through PCR reactions involving 60
10-mer RAPD primers in separate reactions. Most primers did not
produce amplified products for one or more of the species, but for 15
of the primers, agarose gel electrophoresis revealed banding patterns
for O. prolifera that combines unique bands of the two putative
parents. Moreover, O. prolifera exhibited very few unique
bands. These findings constitute compelling support of the hybrid
origin hypothesis, but steps are now being taken to ensure that no
other species could have served as a parent of Opuntia
prolifera.
Key words: hybridization, Opuntia, RAPDs