Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California. II. Allozyme evidence

Morphological evidence has indicated that hybridization and introgression are occurring between Carpobrotus edulis L., a nonindigenous, invasive species in California (Bolus), and its putative native congener, C. chilensis. The identification of allozyme markers has enabled us to quantify hybridization and the extent of introgression between these species. Samples from 20 individuals of each of five morphological types (both parent species and three hybrid phenotypes) were collected from 39 populations along the coast of California from the Mexico to Oregon borders. Ten enzyme systems revealed a total of 17 resolvable loci, eight of which were polymorphic for the genus. Five of the polymorphic loci easily differentiate C. edulis and C. chilensis. Allele frequencies among the morphologically defined types are consistent with estimations of allele frequency changes due to first- and second-generation backcrossing. In comparison to long-lived, herbaceous perennials and widespread species, C. edulis and intermediate types have more variation in their populations (P = 41.73, Ap = 2.11, Ho = 0.246, and P = 38.13, Ap = 2.06, Ho = 0.216, respectively) than C. chilensis (P = 11.76, Ap = 2.00, Ho = 0.082). Indirect estimates of gene flow indicate four of the five morphological types are outcrossing. Gene flow between previously allopatric species may have broad implications if it results in an increase in fitness; further experimentation is needed to determine the ultimate ecological consequences of this phenomenon and its possible threat to limited, remaining natural habitat in California.