Do thermal cues influence the defensive strike of cottonmouths (Agkistrodon piscivorus)?
Xavier Glaudas, J. Whitfield Gibbons
Crotaline snakes (family Viperidae, subfamily Crotalinae) are unique among
snakes in the possession of facial pits situated on each side of the head
between the nostril and the eye (Klauber, 1972). These organs are depressions
with highly innervated membranes at their bases that have a heat-sensing
function and that transmit information to the part of the brain that receives
visual data (Desmoulins, 1824; Bullock and Diecke, 1956; Barrett, 1970;
Hartline et al., 1978). Thus, pitvipers can detect temperatures through
the radiant heat energy emitted by objects and/or organisms relative to
the background temperature. This thermoreceptive sense is not specific
to crotalines: some booids also have the capacity to detect temperature
variation but the thermal receptors are situated on the labial scales,
and hence are called labial pits.
The significance of this thermoreceptive organ on the predatory strike ofbooid and viperid snakes has been established (De Cock Buning, 1983; Kardong and Mackessy, 1991; Shine and Sun, 2003). However, no evidence has been provided on alternative functional roles played by thermal pits (Greene, 1992), specifically on defense. It has been suggested that thermal pits might help snakes in detecting predators (De Cock Buning, 1983), in finding optimal basking sites for thermoregulation (Goris and Nomoto, 1967; Herbert and Hayes, 1992), and in locating winter dens (Sexton et al., 1992).
Because
we lack empirical studies on the role of these pits in a non-predatory
context, this study provides further understanding on the function of
thermal pits. We conducted a simple experiment to test the influence of
warm thermal cues on the defensive strike of a pitviper species, the cottonmouth
(Agkistrodon piscivorus). Visual cues are of paramount importance
in releasing a defensive strike (Scudder and Chiszar, 1977). In addition,
cottonmouths are preyed upon by predators with different thermal profiles
(e.g., ectotherms, endotherms). Thus, we predicted that there would be
no difference in the striking response of cottonmouths tested with a warmed
versus a non-warmed artificial arm.
We
collected 21 cottonmouths, 14 females and 7 males (–± SVL
= 74.25±3.33 cm), on the Savannah River Site, South Carolina, USA,
during spring 2003. After capture, we fasted each snake for 7 days to
eliminate the effect of recent feeding on defensive behavior (Herzog and
Bailey, 1987). The snakes were individually housed in identical polyethylene
containers (RubbermaidTM [58 x 42 x 14-cm high]) within an environmental
chamber (12L: 12D, 26°C) with water dish (provided adlibitum) and
bark mulch as a substrate. We did not disturb snakes prior to the experiment.
Snout-vent length of the specimens was within a range of 60 to 100 cm
SVL, and all were mature individ- uals (Blem, 1997).
SREL Reprint #2873
Glaudas, X. and J. W. Gibbons. 2005. Do thermal cues influence the defensive strike of cottonmouths (Agkistrodon piscivorus)? Amphibia-Reptilia 26:264-267.
