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Berbagai pemetaan ular mengungkapkan pola evolusi yang tak terduga

Venom dari ular eastern diamondback rattlesnake  di Everglades berbeda dari  racun  oleh spesies yang sama di daerah  Florida panhandle area  , sekitar 500 mil jauhnya . Tapi tidak peduli di mana Anda pergi di tenggara Amerika Serikat  , racun ular eastern coral snake  selalu sama . Hasil ini , memberikan informasi penting bagi konservasi ular , dan akan membantu pengembangan  antivenom ular coral snake  ....read more

Mapping snake venom variety reveals
unexpected evolutionary pattern

Date:

January 8, 2015

Source:

Genetics Society of America

Summary:

Venom from an eastern diamondback
rattlesnake in the Everglades is distinct from the cocktail of toxins delivered
by the same species in the Florida panhandle area, some 500 miles away. But no
matter where you go in the Southeastern United States, the venom of the eastern
coral snake is always the same. The results challenge common assumptions in
venom evolution research, provide crucial information for rattlesnake
conservation, and will help coral snake antivenom development.

..............................

Venom from an eastern diamondback rattlesnake in the Everglades is distinct
from the cocktail of toxins delivered by the same species in the Florida
panhandle area, some 500 miles away. But no matter where you go in the
Southeastern United States, the venom of the eastern coral snake is always the
same. The results of a large-scale survey of venom variation in the two snake
species, published January 8, 2015 in the journal Genetics, challenge common assumptions in venom evolution research, provide crucial
information for rattlesnake conservation, and will help coral snake antivenom
development.

Each venomous snake species produces a unique venom, a mixture of around
50-200 toxic proteins and protein fragments that co-evolve with the typical
prey of the snake, such as the smaller reptiles eaten by the eastern coral
snake or the rodents preferred by rattlesnakes. In this cycle of evolutionary
attack and counterattack, any genetic variants that enhance venom resistance
tend to spread through the prey population, prompting tweaks to the snake venom
recipe that restore its effectiveness.

The result should be distinctive local co-adaptations between predator and
prey, as well as considerable regional diversity in the types and amounts of
the different venom proteins. But when Darin Rokyta (Florida State University)
and his colleagues collected and profiled venom from eastern coral snakes at
many sites within Florida, they found no variation at all. The mix of proteins
in coral snake venom from one part of the state was indistinguishable from that
collected anywhere else. In contrast, eastern diamondbacks, which live in the
same parts of the country as the coral snakes, produce venom with different
ratios of toxic proteins in nearly every sub-population across their range. For
example, two venom components, including one known to cause paralysis in prey,
are found at high levels in the northernmost populations, and were completely
absent in the snakes from Caladesi Island, near Tampa.

"We were shocked," Rokyta said. "This is the first time
anyone has looked at venom variation at this scale, and everybody has assumed
that the co-evolutionary arms race would cause local populations to diverge
quickly."

Rokyta says there could be several explanations for the lack of variation
in eastern coral snake venom. For example, a small population of the species
might have recently expanded and taken over the entire range, displacing other
populations and reducing genetic diversity. Or it could reflect a difference in
co-evolutionary dynamics between the species and its typically reptilian prey,
compared to the small mammals preferred by rattlesnakes. The team is now using
genetic clues to the population histories of each species to investigate
possible explanations.

The results of the study will be helpful to researchers developing eastern
coral snake antivenom. Making an antivenom requires samples of venom, but if
the mix varies substantially from place to place, this will affect the drug's
effectiveness and reliability. For this species, sampling from many populations
should not be necessary. "This tells us it doesn't matter where we catch
these relatively elusive snakes; we can stick to using those locations where
they're easy to find," Rokyta said.

The variation between eastern diamondback populations could provide crucial
information to authorities managing the conservation of this species, which is
in decline and under consideration for listing as threatened under the
Endangered Species Act. Eastern diamondback rattlesnake declines are thought to
have been caused by habitat loss compounded by hunting and persecution by
humans. The data from this study can be used for population management, to
ensure the full range of venom subtypes are conserved for the long-term
viability of the species.

"The received wisdom was that venoms are rapidly-evolving, but now we know
that's not necessarily the case." said Mark Johnston, Editor-in-Chief
of GENETICS. "Clearly, venom evolution in these two snake
species has been shaped by different forces. The next challenge is to
understand why."







Story Source:

The above story is based on materials provided
by Genetics Society of America. Note:
Materials may be edited for content and length.







Journal Reference:

1.   
M. J. Margres, J. J. McGivern, M. Seavy, K. P. Wray, J. Facente, D. R.
Rokyta. Contrasting Modes and Tempos of Venom Expression Evolution in
Two Snake Species. Genetics, 2014; DOI:10.1534/genetics.114.172437

http://www.sciencedaily.com/releases/2015/01/150108113703.htm

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