NEW YORK (GenomeWeb News) – The Caribbean fruit bat species Artibeus schwartzi arose through the hybridization of three species, according to a paper scheduled to appear online this week in the Proceedings of the National Academy of Sciences.
Researchers from Texas Tech University examined hundreds of bats from a handful of species in the Artibeus genus in the Caribbean and South America. The team's nuclear and mitochondrial genotyping information, combined with bat morphological feature data, suggest A. schwartzi's nuclear genome is a melange of sequences from two other bat species — A. jamaicensis and A. planirostris. Its mitochondrial genome, meanwhile, resembles that of a third, yet unknown species that the researchers suspect may be extinct. Together, they say, the findings point to hybridization as an evolutionary factor within the region.
"Our genetic and morphometric analyses have identified a unique hybrid zone among species of fruit-eating bats," senior author Robert Baker, a biologist at TTU and director and curator of mammals and genetic resources at the TTU museum, and his colleagues wrote, "leading us to the hypothesis that natural hybridization has generated a distinct lineage that exists in these insular populations."
Despite the fact that A. schwartzi belongs to a fairly well characterized group of fruit-eating bats, the researchers explained, relatively little is known about its evolutionary history.
"Although Artibeus is one of the most extensively studied genera of Neotropical bats, the origin of A. schwartzi is unclear and has perplexed researchers for nearly [three] decades," they wrote.
In an effort to get a clearer picture of the A. schwartzi's evolution and relationship to other species, the team first assessed nuclear amplified fragment-length polymorphisms, mitochondrial DNA sequences, and morphological features for 73 Caribbean bats belonging to seven Artibeus species. They also sequenced cytochrome-b regions from another 164 bats to look for mtDNA haplotypes resembling A. schwartzi in South America.
From the 322 polymorphic regions they amplified, the researchers found seven clades, each coinciding with different species or sub-species. Even so, A. schwartzi did not form its own monophyletic clade and contained only three polymorphisms not found in other species.
Instead, many of the variable fragments that the team detected in A. schwartzi overlapped with those in A. jamaicensis or A. planirostris, causing it to cluster between these two species.
Nevertheless, comparisons of the bats' physical features — including head and jaw size and shape measurements — indicated that A. jamaicensis, A. planirostris, and A. schwartzi are physically distinct, though variation exists within each species.
And, the team noted, A. schwartzi does not share mitochondrial sequences with A. jamaicensis or A. planirostris. Rather, it appears to have nabbed its mitochondrial sequence from a third species that is either uncharacterized or has become extinct.
Overall, their nuclear, mitochondrial, and morphological data is consistent with the notion that a mitochondrial ancestor of A. schwartzi moved from South America to the Caribbean, where it hybridized with A. jamaicensis and A. planirostris, leading to the A. schwartzi species that became specialized to its Caribbean habitat and reproductively isolated.
"The most parsimonious explanation for the lack of structure in our [amplified fragment-length polymorphism] data and the existence of a distinct mitochondrial genome on southern Lesser Antillean populations is that the mtDNA genome was present in a now-extinct or uncharacterized lineage that hybridized in the Caribbean with A. jamaicensis and/or A. planirostris," the researchers wrote.