Unexpected evolutionary diversity in a recently extinct Caribbean mammal radiation

Abstract

Identifying general patterns of colonization and radiation in island faunas is often hindered by past human-caused extinctions. The insular Caribbean is one of the only complex oceanic-type island systems colonized by land mammals, but has witnessed the globally highest level of mammalian extinction during the Holocene. Using ancient DNA analysis, we reconstruct the evolutionary history of one of the Caribbean's now-extinct major mammal groups, the insular radiation of oryzomyine rice rats. Despite the significant problems of recovering DNA from prehistoric tropical archaeological material, it was possible to identify two discrete Late Miocene colonizations of the main Lesser Antillean island chain from mainland South America by oryzomyine lineages that were only distantly related. A high level of phylogenetic diversification was observed within oryzomyines across the Lesser Antilles, even between allopatric populations on the same island bank. The timing of oryzomyine colonization is closely similar to the age of several other Caribbean vertebrate taxa, suggesting that geomorphological conditions during the Late Miocene facilitated broadly simultaneous overwater waif dispersal of many South American lineages to the Lesser Antilles. These data provide an important baseline by which to further develop the Caribbean as a unique workshop for studying island evolution.

Keywords: Oryzomyini; ancient DNA; biogeography; extinct mammal; island evolution; phylogeny.

Figure 1.

Map showing the distribution of described species of extinct Lesser Antillean oryzomyine rice rats. Starred islands indicate those from which oryzomyine samples used in this study were collected.

Figure 2.

Oryzomyine phylogeny inferred from mtDNA (cyt b) and nuclear (IRBP and Adh1) sequence data, showing Bayesian posterior probabilities of nodes. Extinct Lesser Antillean oryzomyine taxa are highlighted in bold; outgroup (Peromyscus truei) removed for display purposes. Scale bar represents number of substitutions per site. (Online version in colour.)