Biology Reference
In-Depth Information
been discussed elsewhere (Kardong, 1996; Weinstein et al., 2010), it is unfortunate
that oral secretions from squamate reptiles are most often defined in a medically/
pharmacologically biased context. Biological function—how the secretion is used—
must contribute to the accurate and robust application of the term, “venom.” It is nec-
essary to again emphasize that the marked differences of venom delivery systems
of elapids, viperids, and atractaspidids (high-pressure systems associated with cana-
liculate dentition) with the Duvernoy's gland system of non-front-fanged colubroids
(low-pressure systems associated with noncanaliculate dentition) must be considered
when assigning biological and clinical use of the term, “venom gland.” Of course,
the evolutionary development and derivation of venom delivery systems must be
evaluated in their totality. However, critical analysis/synthesis of available evidence
suggests that it is essential to avoid premature assignment of a broad, encompass-
ing term (e.g., “venom,” “venom gland”). This terminology inherently implies a
dynamic process (evolution of oral glands of various functions, associated dentition,
and recruitment/derivation of biologically active components of oral secretions) and
should not be assigned to ophidian oral glands of unverified function (Duvernoy's
gland) that undoubtedly are also the result of multiple evolutionary experiments, and
preadaptation of multifunctional proteins, as well as many morphological modifica-
tions per selective needs. Therefore, these terms should be used with caution until
biological function is verified/confirmed for a given species. For example, the pre-
mature use of the term “venom” for Duvernoy's secretions of taxa such as garter
snakes (
Thamnophis
spp.) implies active use of their oral secretions in prey cap-
ture and, due to the frequently applied and popular interpretation of the term, also
suggests medical importance. These impressions are misleading and unproven. As
has been demonstrated here, these snakes have no significant medical importance,
and active use of their secretions in prey capture/subjugation has not been verified.
Therefore, it is likely that a more accurate term, such as “prey-specific venom,” may
be used as biological function becomes verified for additional species of non-front-
fanged colubroids [e.g., as essentially verified for venom of
A.
(
Borikenophis
)
por-
toricensis
]. This could improve the accuracy of the term by including notation of use
in prey capture and/or subjugation and simultaneously obviate the need to qualify the
term by emphasizing a lack of medical importance.
Ophidian oral secretions may be defined as true venoms and promote rapid prey
death, but many have additional roles such as producing quiescence/immobiliza-
tion of prey (Rodriguez-Robles, 1992; Rodriguez-Robles and Leal, 1993), lubrica-
tion, digestion, poststrike trailing, defense, and others (Kardong, 2002). To date, a
relatively small number of non-front-fanged colubroid genera have been found
to produce Duvernoy's secretions of varying toxicity. This is largely due to lim-
ited investigation of the immobilization or subjugation qualities of these secretions
(e.g., few studies have used potential prey items for testing) in addition to lethal
potency studies. The relatively minimal attention to these secretions, in comparison
to the many studies of front-fanged ophidian venoms, is not a result of disinterest
on the part of venom researchers. Rather, this is due to technical difficulties (tedious
collection of secretion, even with parasympathomimetic stimulation facilitating
