Snakes are found in almost all
parts of the world, with the exception of New Zealand and Ireland, the polar
regions, the Atlantic Ocean, and some very urban areas. Many species are very
widespread. Pelagic
Sea Snakes (Pelamis platurus) are probably found
over the greatest percentage of the Earth's surface, although they are entirely
marine. On land, Ring-necked Snakes (Diadophis punctatus) and Racers (Coluber constrictor) are found throughout
North America, European Adders (Vipera berus) from Spain to Kamchatka and above the
Arctic Circle, Grass Snakes (Natrix
natrix) from Great Britian to Mongolia, and Gaboon Vipers (Bitis gabonica) from Africa's Gold Coast
to its Great Rift Valley. However, the title of "most widespread snake in
the world" goes to the tiny Brahminy Blindsnake (Ramphotyphlops
braminus), named after Hinduism's Brahmin
caste.
Brahminy
Blindsnakes are found on nearly every continent and on countless islands,
mostly in the tropics. They are so successful at least in part because they are
the only unisexual species of snake. There are
no male Brahminy Blindsnakes. There never have been and there never will be.
Instead, each female lays about 4 rice-grain-sized eggs a year, which hatch
into sewing-needle-sized daughters identical to each other and to their mother.
If that doesn't sound very fecund, it's because it isn't - it doesn't have to
be! In spite of their low reproductive output, Brahminy Blindsnakes have spread
over most of the world, because just a single individual is capable of founding
a new population. In fact, we don't even really know where the original native
range of the Brahminy Blindsnake was. It is most common in southern Asia, where it was first discovered in 1796, so it's
likely that it originated somewhere around there, but it's difficult to say for
sure. Usually, biologists can exploit differences in the genetics or morphology
of a widespread species to figure out where it came from. Attempts to uncover
the geographic origin of Brahminy Blindsnakes have been unsuccessful because
all Brahminy Blindsnakes are clones of one another, so there is almost no
variation to analyze!
How
did this species evolve? The leading theory for most unisexual species of
reptiles, amphibians, and fishes involves a hybrid origin, where two or more
"parent" species contribute genes. In most unisexual amphibians and
fishes, sperm from a male (often of one of the parent species, but sometimes
any sperm will do) is required to initiate development of the eggs but does not
contribute genetic material. This is not the case for lizards or for the
Brahminy Blindsnake, which are truly parthenogenetic. Which were the parent
species of the Brahminy Blindsnake? We don't know. Of the 400-odd blindsnake
species, the Brahminy Blindsnake is probably one of the best known due to its
wide distribution and peculiar reproductive habits. Some recent phylogenies
have shown that it is closely related to the South Indian Blindsnake (Typhlops
pammeces), and others to an undescribed species of Sri Lankan blindsnake,
both consistent with the hypothesis that south Asia
is the species' center of origin. One very recent analysis suggested
reclassifying all three species into a new genus, Indotyphlops. Because
up to a quarter of all blindsnake species are still undescribed, it's possible
that the parent species are as-yet unknown to science.
These
days Brahminy Blindsnakes mostly get around through the horticulture trade,
although in the past they may have hitchhiked along with Pacific Islanders.
Snakes are generally good dispersers, with the ability to go without food for
long periods of time and squeeze into tight spaces, which might help explain
why they have successfully colonized most of the world. Of all the fantastic
voyages Brahminy Blindsnakes must have undergone, one of the most amazing is
that documented by herpetologist
and TV personality Mark O'Shea in East Timor.
He and his team found a live Brahminy Blindsnake coming out of the back end of
a toad, demonstrating the snakes' resilience to even the most caustic of
environments.
Most
of the time, an introduced species has about a 50/50 chance of successfully
establishing itself in a new environment. Given how widespread Brahminy Blindsnakes
are and their infamy as invaders, you might ask whether an introduced
population of Brahminy Blindsnakes has ever failed to become
established? A comprehensive database of reptile introductions includes only
two such instances, one in southern Arizona
and one in New Zealand.
In Arizona, a population has subsequently
become established despite the arid climate, but New Zealand is probably too cold
for blindsnakes, and they take introduced species very seriously there.
Nevertheless, the Brahminy Blindsnake will probably continue to spread, at
least throughout the tropical regions of the world. The literature is full of
first reports of this species, so much so that at least one was reported twice!
Amazingly, both specimens were bicycle casualties collected in the same suburb
of Cairo,
leading the second author to title his article "How many times can a
flower-pot snake be run over for the first time?"
ACKNOWLEDGMENTS
Thanks
to Todd
Pierson for his photograph and to Phil Rosen, Jeff Servoss, Don
Swann, Michael Lau, and Skip Lazell for bringing me up to date on the latest in
blindsnake biology.
REFERENCES
Baha
el Din, S. M. 2001. On the first report of Ramphotyphlops braminus from Egypt: how many
times can a flower-pot snake be run over for the first time? Herpetological
Review 32:11.
Hedges,
S., A. Marion, K. Lipp, J. Marin, and N. Vidal. 2014. A taxonomic framework for
typhlopid snakes from the Caribbean and other
regions (Reptilia, Squamata). Caribbean
Herpetology 49:1-61 <link>
Kamosawa,
M. and H. Ota. 1996. Reproductive biology of the brahminy blind snake (Ramphotyphlops
braminus) from the Ryukyu archipelago, Japan. Journal of Herpetology
30:9-14.
Kraus,
F. 2009. Alien reptiles and amphibians: a scientific compendium and analysis
series. Springer, Dordrecht
<link>
Nussbaum,
R. A. 1980. The brahminy blind snake (Ramphotyphlops braminus) in the
Seychelles Archipelago: distribution, variation, and further evidence for
parthenogenesis. Herpetologica 36:215-221 <link>
O'Shea,
M., A. Kathriner, S. Mecke, C. Sanchez, and H. Kaiser. 2013. ‘Fantastic
Voyage’: a live blindsnake (Ramphotyphlops braminus) journeys through
the gastrointestinal system of a toad (Duttaphrynus melanostictus).
Herpetology Notes 6:467-470 <link>
Ota,
H., T. Hikida, M. Matsui, A. Mori, and A. H. Wynn. 1991. Morphological
variation, karyotype and reproduction of the parthenogenetic blind snake, Ramphotyphlops
braminus, from the insular region of East Asia and Saipan.
Amphibia-Reptilia 12:181-193.
Wynn,
A. H., C. J. Cole, and A. L. Gardner. 1987. Apparent triploidy in the unisexual
brahminy blind snake, Ramphotyphlops braminus. American Museum Novitates
2868:1-7 <link>
more strongly with one another than with distant relatives, because they occupy similar ecological niches. Most biologists long have accepted this to be true.
green algae failed to support Darwin's theory — at least in one case.
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