The Chinese giant salamander, or Andrias
davidianus, is the one of the largest
amphibians in the world. Its' classification is as
follows:
Phylum: Chordata
Class: Amphibia
Order: Caudata
Family: Cryptobranchidae
The Cryptobranchid family encompasses three
species of giant salamander, all of which are among the largest in the
world. Andrias davidianus lives in the mountain streams of
China at elevations below 1,500 feet. More specifically, one may find a Chinese
giant salamander in the Yangtze,
Yellow,and Pearl Rivers and their tributaries. This species prefers cold, fast running
mountain streams and lives in muddy, dark rock crevices. It is also a nocturnal
species, preying on its food mostly at night. Due to
over exploitation and fragmentation of their environment, the Chinese giant
salamander is currently listed as critically
endangered by the IUCN
(International Union on Conservation of Nature). The Yangtze River basin alone is
home to 480 million people, or nearly one third of China’s total population.
The high density of humans in this basin puts added stress on the river
systems, which need to be protected in order to save the Chinese giant
salamander. Because of the growing population, the Chinese giant salamander
is loosing
valuable habitat, and the habitat it does
have left is becoming polluted. Overhunting also poses a major threat to this
species as it is considered a Chinese delicacy.
Another
recent possible factor contributing to the decline of this species is the iridovirus. During the summer months in 2010, researchers raising
populations of Andrias davidianus in China in mountain caves
and ditches for conservation reasons found a 95% mortality rate in one group.
More specifically, the most affected populations were those living in ditches.
Some effects of the iridovirus include swelling, emaciation, ulcers and
erythema on the dorsal and ventral body surfaces, toe necrosis, darkened
livers, and lesions on the kidney and spleen. Scientists were able to isolate
the iridovirus from the liver and spleen to better examine it. Researchers
attempted to intervene by giving antimicrobial drug treatments, but they proved
unsuccessful. They suggested that living in the cooler cave environments might
be a better alternative than the ditches because ambient temperatures are
cooler in the caves. One additional way to slow down the epidemic of
the iridovirus, especially in the summer months, is to limit the species
contact with other animals known to carry the disease to decrease the chances
of horizontal transmission. Other animals that have the ability to carry the
disease include the Chinese forest frog and gopher tortoises. By keeping these
populations of Andrias davidianus isolated from possible
carriers and in cooler environments, this iridovirus epidemic may be
controllable.
The
Chinese giant salamander is the largest species of salamander ranging in size
from 1 meter to 1.8 meters in length, although they seem to be getting smaller
in size due to over harvesting and exploitation of
their environment. No only are they long, they are also heavily built with
a dorso-ventrally flattened head as well as short and flattened legs. They
have small eyes and rely mostly on sensory organs to sense water and prey
movement. This species is unique in that it is fully aquatic with many
adaptations for this lifestyle. This salamander uses its skin
for respiration, which is specialized in
that it is rough, highly vascular, porous, and has folds to increase oxygen
absorption. The Chinese giant salamander can range in color from dark brown to black or green and further characterized
by having blotchy patches of color. They also have small, paired tubercles
arranged in rows parallel to the lower jaw, which contain neuromasts to detect
water and prey movement to aid in feeding. These neuromasts are mechanoreceptive organs which allow the organism to
sense mechanical changes in the water. The Chinese giant salamander uses these
mechanoreceptors to feed on smaller salamanders, worms, insects, crayfish, and
snails. It catches its pray by snatching them with a rapid sideways snap of the
mouth. Its only real predator is the human species as we over-harvest them for
the food trade.
The Chinese giant salamander has an interesting evolutionary
history seeing as there are only three species in
the Cryptobranchid family. The common ancestor of this family diverged from all
other amphibians more than 170 million years ago sometime during the Jurassic
Period. This is unique in that it is one of the longest unbroken lineages among
modern species such as the caecilians, salamanders, frogs, and toads. The
Cryptobranchids are thought to have evolved from primitive salamanders
primarily found in Asia. Because there is only three species within this
family, it is imperative that conservation efforts are put forth to preserve
the biodiversity in regions where these species live.
SOURCES:
1) Sparreboom, Max. (2000). Andrias davidianus. Retrieved from http://amphibiaweb.org/cgi/amphib_query?where-genus=Andrias&where-species=davidianus.
2) Browne, R., Li, J., & Wang, Z. (2012).
The Giant Salamanders: Paleontology, Phylogent, Genetics, and Morphology. Amphibian and Reptile
Conservation. (4), 17-29. Retrieved from https://ag.purdue.edu/fnr/discover/HerpetologyLab/Documents/Browne_GiantSalamanders.pdf.
3) Krebs, Jessi. (2008). Chinese giant
salamander. Retrieved from http://www.arkive.org/chinese-giant-salamander/andrias-davidianus/.
4) BBC. (2014). Chinese giant salamander.
Retrieved from http://www.bbc.co.uk/nature/life/Chinese_giant_ salamander.
5) Pender, Michael. (2006). Chinese Giant Salamander.
Retrieved from http://legacy.earlham.edu/~pendemi/giantsalamander.htm.
6) Encyclopedia of Life. (2014). Andrius davidianus; Chinese Giant
Salamander. Retrieved from http://eol.org/pages/1018725/hierarchy_entries/24916893/details.
7) Wild, G., Chen, S.,
Zhou, F., & Yan, F. (2006). Chinese giant salamander.
Retrieved from http://www.edgeofexistence.org/amphibians/species_info.phpid=547http://en.wwfchina.org/en/what_we_do/living_yangtze/.
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