Thursday, February 7, 2013

Malagasy Leaf-nosed Snakes


Langaha madagascarensis male
Madagascar has been called the "eighth continent" as a result of its large size, unique habitats, and high faunal and floral (not to mention cultural and linguistic) endemism. Of the ninety-six species of snakes inhabiting the island, only two are found anywhere else: one is a sea snake (the widespread Pelamis platura) and the other is a ubiquitous introduced species (the parthenogenetic blindsnake Ramphotyphlops braminus). Most of the rest belong to the subfamily Pseudoxyrhophiinae, and each deserves its own article. But one has to start somewhere, and perhaps the best place to start is with one of the most unique Malagasy snakes, and one of my favorites: Langaha madagascarensis, the Malagasy Leaf-nosed Snake.

Langaha madagascarensis female
Langaha is so unique that it has been placed in its own genus ever since it was described, and was one of only eight1 genera recognized in Bonnaterre's 1790 Ophiologie, a book that covered 224 species of snake. That's right: at a time when snakes as different as wormsnakes, saw-scaled vipers, sea snakes, and blunt-headed tree snakes were being grouped together as "typical snakes" in the genus ColuberLangaha was considered unusual enough to justify its own genus! Today there are three recognized species of Langaha, but the most is known about L. madagascarensis.

Left: Captive juvenile Langaha madagascarensis exhibiting hanging behavior; photo from Krysko 2003
Right: Seed pods of the Ophiocolea floribunda, a Malagasy legume whose genus is Greek for 'hollow snake'
As their name implies, Leaf-nosed Snakes have bizarre nasal appendages. What's more, these structures are sexually dimorphic to a degree unusual among snakes. Female Leaf-nosed Snakes have a more elaborate, serrated nasal appendage, whereas males bear a longer, pointier one. These structures are present at birth, suggesting that they have some function beyond sexual signaling between rival males or potential mates. Often, these snakes are seen hanging from branches with their heads pointing towards the ground - perhaps the structures serve to drain water off the snake? Several Malagasy plants, including some legumes and bignonias, have long pointed seed pods that hang down from the plant, providing possible models that the snake may imitate with its posture and nasal appendage. No one knows for certain.

Male (right) and female
(left) L. madagascarensis 
This is a timely post in that it comes on the heels of newly published research on Malagasy Leaf-nosed Snakes. An article by recent Cornell University graduate Jessica Tingle has just appeared in the journal Herpetological Conservation and Biology documenting novel aspects of the behavioral ecology of this unusual snake. Everything known about the behavior of Langaha to date has been learned from observing captive individuals. Tingle's paper presents the first data collected on the behavior of Langaha in the wild. She observed several of these snakes foraging for and eating lizards, although one sentence in her paper stands out to me as typical of snake behavior studies: "The vast majority of their time (90%) was spent not moving at all." Although this sounds boring, it provides evidence that these snakes are primarily ambush predators, rather than active foragers (although Tingle did observe one Langaha chasing skinks on the ground). Spending months in Madagascar, Tingle was able to observe only a few snakes, and much remains to be learned about their natural history and ecology.

Plate showing a male Langaha madagascarensis from Bonnaterre's 1790 Ophiologie
From observations made on Langaha in captivity by Kenney Krysko of the Florida Museum of Natural Sciences, we know that Leaf-nosed Snakes lay eggs. When they hatch, the nasal appendages of juveniles are folded up so that their egg tooth can be used to break out of the egg. The appendage gains its normal shape after 36 hours. Juveniles exhibit the same vertical 'hanging' behavior as adults, which Krysko also suggests helps them mimic the seed pods of Malagasy plants (and perhaps deter predation, though by what predator is unclear).

Hatchling Langaha madagascarensis, from Krysko 2003
The other two species of Langaha are very poorly known. In Darren's TetZoo article, he states that only female Langaha alluaudi have nasal appendages, but I have been unable to find another source corroborating this fact, although I did find a photo on Flickr purported to be a male L. alluaudi (it looks similar to a male L. madagascarensis, also sometimes called L. nasuta, to me). Female L. alluaudi have longer, straighter nasal appendages than L. madagascarensis, and female L. pseudoalluaudi have shorter, more upturned ones (no word on what male L. pseudoalluaudi might look like). Why these differences? Perhaps differences in microhabitat or sexual preference are the cause. Who can say?

Female (left) and male(?, right) Langaha alluaudi

Female L. pseudoalluaudi

Although Madagascar is unique, it is similar to the rest of the world in at least one sad way: its natural places are disappearing quickly. Most of its forests have already been logged or converted to slash and burn agriculture, and what little remains is dwindling daily. If more effective conservation measures are not taken,  including supporting the human communities that depend on the rich natural resources of this hottest of biodiversity hotspots, we may never find out what Langaha's nose is for.

Male L. madagascarensis consuming Chalarodon madagascariensis
Photo from Herp. Con. Bio. gallery for Tingle 2012


1 Three of these eight genera turned out not to be snakes at all: the limbless lizards Anguis and Amphisbaena, and  the limbless amphibian Caecilia.

ACKNOWLEDGMENTS

Thanks to Dick Bartlett, Jessica Tingle, David d'OBernard DupontRussell Speight, and G.E. Schatz for use of their photos.

REFERENCES

Bonnaterre PJ (1790) Ophiologie, in Tableau encyclopédique et méthodique des trois règnes de la nature. Panconoke, Paris <link>

Krysko KL (2003) Reproduction in the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae). African Journal of Herpetology 52:61-68 <link>

Krysko KL (2005) Feeding behaviour of the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae), with an alternative hypothesis for its bizarre head structure. African Journal of Herpetology 54:195-200 <link>

Tingle JL (2012) Field observations on the behavioral ecology of the Madagascan Leaf-nosed Snake, Langaha madagascariensis. Herpetological Conservation and Biology 7:442-448 <link>

2 comments:

Russell Speight said...

Vences & Glaw (Field Guide to the Amphibians and Reptiles of Madagascar) have a picture of a Male L. pseudoalluaudi - body same colour and markings as female, but snout long and pointed as per (L.Madagascarensis).

That's my photo of the female by the way, proper link to:

http://www.flickr.com/photos/64231410@N00/7800989452/in/photolist-cTm7o9-e5UnEm-e5UnKL

Andrew Durso said...

Thanks Russell! I don't have a copy of the book but it's good to know it's out there. How lucky you are to have seen the female! Thanks for sharing your photograph.