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HERPDIGEST
6) African Dwarf Crocodiles Split Into Three Species
Eureka Alert, 12/12/08
You'd think that if scientists were to discover a new species, it would
be in some remote, uncharted tropical forest, not a laboratory in New
York. But a team from the Sackler Institute for Comparative Genomics
at
the American Museum of Natural History
has done the unexpected. Looking at the genes of the African dwarf
crocodile, researchers found that the group—genetically
speaking—comprises three distinct
species rather than one. This not only ends a long debate about the
taxonomy of this group, previously thought to consist of two closely
related subspecies, but also defines a new, distinct species from
genetic
samples.
"In the past, the two morphologically distinct crocodile populations
were believed to be different genera, then later different species,
and
then finally different subspecies,"
explains first-author Mitchell Eaton. Eaton conducted the research at
the Sackler Institute and is finishing his doctoral degree at the
University of Colorado. "We collected samples in Africa to explore
this
taxonomic question, and we found a great deal of evolutionary
divergence
between populations in the Congo Basin and on the west coast of
Central
Africa. We also—quite unexpectedly—found a completely new species
from far West Africa; there may be even more species that we haven't
sampled yet!"
African dwarf crocodiles, genus Osteolaemus, live in the tropical
forests of Central and West Africa. Adults typically grow to no more
than 5
feet in length and are the smallest living members of the crocodilian
family. The three groups identified in this current research include a
species from the Congo Basin (O. osborni), another from Central
Africa's
Ogooué Basin (O. tetraspis), and the new, yet unnamed species from
West Africa.
All of these crocodiles look very similar, and all are widely hunted by
local people as a source of food. In fact, these animals provide up to
a quarter of the non-fish bush meat consumed in some areas of Central
Africa, but over-hunting to supply commercial 'bushmeat' markets may
threaten many populations with extinction. Dwarf crocodiles are listed
as
vulnerable on the International Union for Conservation of Nature's Red
List.
In the laboratory, the researchers sequenced more than 4,000 base pairs
of both mitochondrial and nuclear DNA from as many as 82 individuals
sampled across Central and West Africa. The results confirmed
species-level separations between three different groups of dwarf
crocodiles.
Crocodiles from the Congo Basin appear to be the oldest of the three
species, with some morphological characteristics placing them closer
to a
shared ancestor of the Nile crocodile. The dwarf crocodiles of the
Ogooué and West Africa, on the other hand, are more recently evolved
and
are more closely related to each other than either is to the Congo
Basin
species.
"These species have been on their own evolutionary trajectory for a
long time," says George Amato, Director of the Sackler Institute.
"They
are diagnostically distinct—every individual in one species has
characteristics that are not found in the other species, and the
number of
diagnostic characteristics is large."
The new taxonomic discovery has implications for the conservation
strategy of African dwarf crocodiles. "Without these genetic results,
the
level of biodiversity was cryptic, hidden," Amato continues. "Accurate
taxonomy is necessary for conservation management of each species, and
now we can calculate subsistence hunting levels that are manageable."
In addition to Amato and Eaton, coauthors include Andrew Martin of the
University of Colorado and John Thorbjarnarson of the Wildlife
Conservation Society (WCS). The research was funded in part by AMNH,
the
National Geographic Society, WCS, Lincoln Park Zoo, the Rufford
Foundation,
and the University of Colorado's Natural History Museum and Rozella
Smith Fellowship. It is published in the early online edition of
Molecular
Phylogenetics and Evolution.
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