Fitness of invasive Carpobrotus (Aizoaceae) hybrids in coastal California

Natural hybridization between previously allopatric plant species can produce highly successful lineages. We test the low-fitness-hybrid hypothesis in Carpobrotus and its implications for hybrid invasion. We examine reproductive fitness components of hybrids between the invasive non-native succulent Carpobrotus edulis (L. Bolus) and the non-invasive putative native C. Chilensis (L.) from three populations in California coastal plant communities. Hybrids between the two species are very abundant and aggressive but it is not known if this is a transitory phenomenon. We find no support for the low-fitness-hybrid hypothesis in Carpobrotus. Fruit weight and seed set, mass and germination rate of hybrids were intermediate between or the same as a parental taxon. Survival, growth, and root to shoot ratio of hybrid seedlings did not differ from those of parental taxa. Although hybrid fitness is not superior to that of parental species, we believe that hybrids will continue to persist and invade California caostal communities because recruitment of seedlings did not differ from those of parental species. The highest survival probability of the introduced C. edulis may insure its successful invasion status compared to the putative native congener C. chilensis.