CALIFORNIA GROUND SQUIRREL (Spermophilus beecheyi)
DEFENSES AGAINST RATTLESNAKE VENOM DIGESTIVE
AND HEMOSTATIC TOXINS
JAMES E. BIARDI,
1,
*
DAVID C. CHIEN,
2
and RICHARD G. COSS
2
1
PROF Postdoctoral Program and Department of Chemistry, University of California,
1 Shields Avenue, Davis, CA 95616, USA
2
Department of Psychology, University of California, 1 Shields Avenue, Davis,
CA 95616, USA
( Received December 12, 2004; revised August 2, 2005; accepted October 3, 2005)
Abstract—Previous studies have shown that some mammals are able to
neutralize venom from snake predators. California ground squirrels (Spermo-
philus beecheyi) show variation among populations in their ability to bind
venom and minimize damage from northern Pacific rattlesnakes (Crotalus
oreganus), but the venom toxins targeted by resistance have not been
investigated. Four California ground squirrel populations, selected for differ-
ences in local density or type of rattlesnake predators, were assayed for their
ability to neutralize digestive and hemostatic effects of venom from three
rattlesnake species. In Douglas ground squirrels (S. b. douglasii), we found
that animals from a location where snakes are common showed greater in-
hibition of venom metalloprotease and hemolytic activity than animals from a
location where snakes are rare. Effects on general proteolysis were not
different. Douglas ground squirrels also reduced the metalloprotease activity
of venom from sympatric northern Pacific rattlesnakes (C. o. oreganus) more
than the activity of venom from allopatric western diamondback rattlesnakes
(C. atrox), but enhanced the fibrinolysis of sympatric venom almost 1.8 times
above baseline levels. Two Beechey ground squirrel (S. b. beecheyi) pop-
ulations had similar inhibition of venoms from northern and southern Pacific
rattlesnakes (C. o. helleri), despite differences between the populations in the
locally prevalent predator. However, the venom toxins inhibited by Beechey
squirrels varied among venom from Pacific rattlesnake subspecies, and
between these venoms and venom from allopatric western diamondback
rattlesnakes. Blood plasma from Beechey squirrels showed highest inhibition
of metalloprotease activity of northern Pacific rattlesnake venom, general
proteolytic activity and hemolysis of southern Pacific rattlesnake venom, and
0098-0331/06/0100-0137/0
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2006 Springer Science + Business Media, Inc.
137
Journal of Chemical Ecology, Vol. 32, No. 1, January 2006 (
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2006)
DOI: 10.1007/s10886-006-9357-8
* To whom correspondence should be addressed. E-mail: jebiardi@ucdavis.edu