Sunday, 27 September 2009

Fruit bats going the wrong way

A couple of years back, Jeremy Pulvers and Don Colgan published an interesting paper on the intriguing fruit bat genus Melonycteris, that is restricted to the Solomon Islands and the Bismarck Archipelago. The fascinating thing about this bat is that it is believed to be placed right at the base of the Megachiroptera (flying foxes and their ilk). Why it is that this supposedly old lineage is restricted to these isolated island groups is still unknown, but it is not alone in this pattern. In the birds, a number of the more ancient groups are found in and around New Guinea and the Australasian region.

This however, is not the thrust of the Pulvers and Colgan paper. What they did is look at the genetic systematics and variation within the genus, particularly the Solomon Island species. To summarise, they found that the Solomon species are a group separate from the single Bismarck species. What was more interesting was the pattern of relationships within the Solomon Islands population. They found that the species on Makira (San Cristobal) was sister to the rest, followed by the Malaitan species, then the species found in the New Georgia group. Choiseul, Isabel and Guadalcanal populations composed a single group and were the most derived.

What is interesting about this pattern is that it is the opposite of what would be expected from a simple dispersal model originating in the Bismarcks. If that was the case, you would expect the sequence to be essentially the opposite---New Georgia; Choiseul, Isabel and Guadalcanal; Malaita, then Makira.

There has been increasing evidence from birds that the "Dispersal from New Guinea" model of the makeup of the Solomon Island fauna is not the only story, but as far as I'm aware, this is the first publication of evidence in vertebrates other than birds.

Pulvers JN, Colgan DJ. 2007. Molecular phylogeography of the fruit bat genus Melonycteris in northern Melanesia. Journal of Biogeography 34:713-723.

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