Caribbean Island Zoogeography: A New Approach Using Mitochondrial DNA to Study Neotropical Bats

Genetic analysis of animal mitochondrial DNA is a new and valuable addition to the battery of techniques available to zoogeographers. This paper describes characteristics of mitochondrial DNA (mtDNA) that make it applicable for the study of island zoogeography. Some traditional zoogeographic questions are examined using mtDNA from the Neotropical fruit bat, Artibeus jamaicensis. The specific questions are: 1) To what extent are island populations isolated (that is, does interbreeding occur between the insular subspecies)? 2) Can a single founding female account for the mitochondrial genomes on specific islands in the Antilles? 3) Is there a correlation between the genomic diversity of an island population and the size of the island or the distance from the mainland? The mitochondrial genome in Artibeus jamaicensis is approximately 16,000-16,500 base pairs. Three major mtDNA groups (designated J, SV, and G), separated by 8 to 17.2 percent divergence in nucleotide sequence, were identified in Antillean Artibeus jamaicensis. The J and SV groups each includes two maternal lineages and the G group is represented by three lineages. The sequence divergence between the mtDNA groups is unusually high for conspecific mammals. Either the mtDNA in Artibeus jamaicensis can be traced to three relatively old origins or alternatively chiropteran mtDNA evolves at a faster rate than mtDNA in rodents and primates. Populations on five of eight islands were clearly derived from multiple maternal ancestors. The greatest genetic diversity (judged by numbers of lineages and sequence divergence) was found in A. j. trinitatus on Grenada, which probably is a reflection of the proximity of the island to the South American mainland. Genetic diversity did not correlate with island size. One particular mtDNA lineage, J-1, was the most widespread, being found from Jamaica to Barbados and Grenada. These bats trace their ancestry to a common female, underscoring the dispersal and colonization capabilities of A. jamaicensis. MtDNA data and paleontological evidence suggest these bats reached the Antilles recently, probably in conjunction with replacement of the xeric Pleistocene environment. The island distribution of mtDNA genotypes somewhat corresponds to the currently recognized subspecies: 77 percent of A . j . jamaicensis carry the J mtDNA genotypes; 93 percent of A. j. schwartzi carry the SV mtDNA genotype; and 60 percent of the A. j. trinitatus carry the G mtDNA genotypes. The geographic distribution of specific mtDNA genotypes on different islands documents gene flow between and among islands. For example, the data show that female bats with a common maternal ancestor have moved among the islands of St. Lucia, St. Vincent, Barbados, and Grenada even though they would be required to fly up to 150 km across open ocean. MtDNA and distributional data are used to postulate that the Grenadine islands, between Grenada and St. Vincent have been a partial barrier to gene flow, possibly because of their small size and xeric habitats