Sunday, September 9, 2012

The fangless homalopsid snakes of eastern Indonesia

Snakes in the family Homalopsidae have been long considered semiaquatic or aquatic forms with live birth and rear-fangs. In 2011, Brachyorrhos was confirmed as a member of the family (Murphy et al. 2011), but Brachyorrhos is terrestrial, feeds on worms, and has no rear fangs. The DNA evidence suggested Brachyorrhos was the most basal member of the family. Further investigation into the genus suggested it was restricted to Eastern Indonesia, the Moluccas, Aru, and the Raja Ampat Islands. However, the literature suggested it was also present in western New Guinea, frequently mentioning Brachyorrhos jobiensis, a species described from Yapen Island, known only from the type specimen which was destroyed in World War II.
For all of the 20th century, two species were thought to comprise the genus Brachyorrhos, B. albus  and B. jobiensis because G. A. Boulenger had synonomized several previously described species under the name Brachyorrhos albus. A review of museum specimens found four species of Brachyorrhos in the Moluccas, one species on Seram and nearby Ambon (B. albus), one species on Buru (B. gastrotaenius), one species on Ternate (B. raffrayi), and an undescribed species on Halmahera, that we named B. wallacei (Murphy et al. 2012).  Despite the fact that Ternate (a volcanic island) is only 14 km off the coast of Halmahera, the genetic difference between the snakes on the two islands was 7.2%, suggesting they had separated from their common ancestor quite some time ago.

Within the museum specimens examined were six specimens labeled Brachyorrhos jobiensis, all from extreme western New Guinea, in an area known as the Bird's Head. The Bird's Head is a biodiversity hot spot that has been poorly explored for squamate reptiles. Examination of the six specimens revealed three different undescribed species, based upon their body form. Two of the species had cylindrical bodies and stout tails (about 9 to 12 % of the body length) and appear to be cryptozoic/ fossorial/ aquatic species. The third species has a remarkable lateral compression of the body, an exceptionally abbreviated tail (about 3% of the body length) suggesting it is an aquatic form evolved from a fossorial ancestor (Murphy, 2012).
The differences between jobiensis-like snakes and the Brachyorrhos were striking, while they shared a considerable amount of morphology, the jobiensis -like snakes had rounded heads, a reduced number of scales at the back end of the body, a single internasal scale, and remarkably different looking tails. While the morphology they shared suggested they are related.
It seems likely that more Brachyorrhos species will be found, in eastern Indonesia. And, further investigation into these interesting snakes may provide insight into the evolution of fangs, as well as the shift from terrestrial to aquatic or aquatic to terrestrial life styles.
Literature Cited
Murphy, J. C., Mumpuni & K. L. Sanders, 2011. First molecular evidence for the phylogenetic placement of the enigmatic snake genus Brachyorrhos (Serpentes: Caenophidia). Molecular Phylogenetics and Evolution, 61: 953–957.

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