Fifty years of interspecific hybridization: genetics and morphometrics of a controlled experiment on the land snail Cerion in the Florida keys

Abstract

In 1915, 55 Bahamian Cerion casablancae were established on Bahia Honda Key, Florida. The introduced snails thrived, bred true to form, and the colony grey until about 1928 when it began to hybridize with C. incanum, the unrelated Florida species. In 1977, morphological hybrids occupied an area of c3.5 ha. Spatial and temporal aspects of the interaction were characterized morphologically and genetically. Comparison of 1933 with 1977 samples showed that the hybrids are gradually approaching C. incanum in phenotype. Regardless of phenotype, the snails on Bahia Honda Key were panmictic and outbreeding. There was no evidence for strong selection against hybrids, and by 1977 introduced alleles had spread over 5 ha. However, no pure C. casablancae remain; low but persistent gene flow has brought about a 30% diminution of the introduced genome. These observations are useful in interpreting Cerion's remarkable variability as colonization following hurricane dispersal has undoubtedly played a role in the group's complex evolution. -from Authors