Biology Reference
In-Depth Information
Plate 2.8
King cobra, or hamadryad; taw-gyi mwe haut, yanjing wang she, ular tedong selar;
others (
Ophiophagus hannah
), Trang, Thailand.
Native to Southeast Asia (India, Burma/Myanmar,
Nepal, Bangladesh, Malaysia, Indo-China, Thailand, Indonesia, and the Philippines),
O. hannah
is
the largest of venomous snakes, and has been documented to reach a length of 5.7 m long. The venom
contains long-chain postsynaptic neurotoxins, a multitude of enzymes, is known for a species-specific
hemorrhagin, hannahtoxin, but is moderately toxic (murine i.p. LD
50
is approximately 1.5-1.7 mg/
kg). However, clinically a bite may result in severe envenomation due to the potentially large venom
yield (average
420 mg dry wt., but may well exceed 1 g). The natural diet of this impressive serpent
is typically restricted to other snakes (thus the genus name), especially Indian rat snakes, or dhaman
(
Ptyas mucosus
), and, opportunistically, varanid lizards. Although currently considered monotypic,
ongoing research suggests that there may be several species or clades of these elapids.
Photo copyright to David A. Warrell.
and biochemistry of the evolution of venom and venom-delivery systems (Bogert,
1943; Fry et al., 2003, 2006, 2008, 2009a; Jackson, 2002, 2003; Jackson and Fritts,
1995; Kardong, 1979, 1980a; Kardong and Luchtel, 1986; Kochva, 1965, 1978, 1987;
Kochva et al., 1980; Kuch et al., 2006; Mackessy and Baxter, 2006; Mebs, 1978, 2002;
Minton and Minton, 1980; Vonk et al., 2008; Weinstein et al., 2010). Current theories
advance a single evolutionary appearance of the primordial venom-delivery system
with subsequent radiation and taxon-specific modification of the venom-delivery
system [Fry et al., 2006, 2008; also advocated in the mid-twentieth century by Bogert
(1943) and others through dentitional/osteological studies]. Other researchers have
used phylogenetic and/or functional morphological studies or analyses in order to
support appearance of Duvernoy's glands early in colubroid evolution, and independent
evolution of high-pressure venom glands multiple times in viperids, elapids, and
atractaspidids (Cadle, 1988; Jackson, 2002, 2003; Kardong, 1982; Kraus and Brown,
1998; Weinstein et al., 2010, and others). The reader is referred to the cited studies for
details regarding these interesting but still unresolved hypotheses.
Anatomical studies of venom glands from viperids, elapids, and atractaspidids,
as well as Duvernoy's glands from other colubroids, have demonstrated a likely com-
mon origin from dental glands (Kochva, 1978). Some authors have considered a venom
gland origin from the rictal gland, rather than a precursor Duvernoy's gland (McDowell,
