CONTENT - International Society of Zoological Sciences

S14 ICZ2008 - Abstracts
Evolutionary and ecological relationships of the venoms of
the related coral snakes Micrurus dissoleucus and Micrurus
mipartitus
Camila Renjifo 1 , Alain Riveros 2 , Armando Sanchez 2 , Juan Manuel
Renjifo 3 , Henry Aceros 2 , Darío Riascos 2 , Jairo Maldonado and
Gabriel Pascual
1 Pontificia Universidad Javeriana, Bogotá-Colombia Facultad de
Ciencias Básicas, Departamento de Biología, Colombia
2 Pontificia Universidad Javeriana, Bogotá-Colombia, Facultad de
Medicina, Departamento de ciencias fisiológicas, Colombia
3 Universidad del Magdalena, Santa Marta-Colombia, Facultad de
Ciencias, Departamento de Biología, Colombia
The venoms of coral snakes (genus Micrurus) clinically produce
flaccid paralysis; the high-rate of mortality results from respiratory
failure. While studies have investigated potential human effects,
the neurotoxic effects have been poorly investigated in terms of
venom evolutionary relationships. The purpose of this study was to
investigate the physiological effects on neuromuscular junction of
the venom of the closely related species Micrurus dissoleucus and
Micrurus mipartitus to be able to compare their venoms in terms of
ecology. While both species are likely to be specialist-feeders on
reptiles, they occupy very different habitats. M. dissoleucus lives
mainly in xeric to semiarid or seasonal dry regions while M.
mipartitus is found in a wide range of habitats including lower
montane wet forest and cloud forest. We examined the
neurotoxicity of M. dissoleucus and M. mipartitus venoms in chick
biventer cervicis muscle preparations and the venoms were also
compared by mass spectrometry. M. dissoleucus and M. mipartitus
venom produced a progressive decrease in the amplitude of
miniature end-plate potentials, with the indirect stimuli, until these
were abolished, both venoms significantly inhibited contractile
responses to the exogenous nicotinic agonists (i.e. ACh and CCh)
but not KCl, showing mainly a post synaptic effect with different
doses and times of blocking. These results allow for a relation of
toxicity to ecology and shed additional light on the forces driving
venom evolution.
Evolution of venomous reptiles
Nicolas Vidal
UMR 7138, Systématique, Evolution, Adaptation, Département
Systématique et Evolution, C.P. 26, Muséum National d’Histoire
Naturelle, 43 Rue Cuvier, Paris 75005, France
The evolution of the venomous function is considered to be a key
innovation driving ecological diversification in advanced snakes.
Recent phylogenetic, toxicological, and histological results
demonstrate a single early origin of venom in squamate reptiles in
the Jurassic that may also have been a key factor in the adaptive
radiation and subsequent ecological success of several lizard
lineages. The well-supported anguimorph/iguanian/snake clade,
named Toxicofera, represent ~4600 out of ~7900 extant squamate
species, or 58 % of the total squamate species diversity. These
results provide new insights into the evolution of the venom system
in squamate reptiles and open additional new avenues for
biomedical research and drug design using hitherto unexplored
venom proteins. Among snakes, the caenophidian venom
apparatus has experienced extensive evolutionary tinkering
throughout its history. All traits, ranging from biochemical
(specialization of the venoms) to dentition and glandular
morphology, have changed independently, resulting in many kinds
of toxins and diverse delivery systems. Rear-fanged—or more
correctly defined, non front-fanged—caenophidians possess
complex venoms containing multiple toxin types, while the frontfanged
venom system appeared three times independently: once
early in caenophidian evolution with viperids, once within
atractaspidines, and once with elapids. Further a reduction of the
venom system is observed in species in which constriction has
been secondarily evolved as the preferred method of prey capture
or dietary preference has switched from live prey to eggs or to
slugs and snails.
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Variation in snake venom composition; evidence for natural
selection and adaptation to diet
Wolfgang Wüster, Axel Barlow, Catharine E. Pook and Nicholas R.
Casewell
Bangor University, School of Biological Sciences, Bangor LL57
2UW, UK
Variation in venom composition in snakes is a ubiquitous
phenomenon at all taxonomic levels. The causes of this variation
have been subject to considerable debates, especially at low
taxonomic levels (within species and between closely related
species). Some authors have argued for the importance of natural
selection for different prey items, whereas others suggest that the
high lethal potential of most snakes makes natural selection for
different prey types unlikely.
This lecture will summarise the available evidence on causes of
venom variation in snakes. There is ample evidence for the likely
role of natural selection from correlation between variation in
venom composition and diet, examples of high levels of resistance
to venom in some prey animals, the reduction in venomous
function in snakes feeding on undefended prey, and apparent
specific action of venom against the main prey of the snakes.
This information is complemented with novel data on variation in
venom composition, gene expression and diet in saw-scaled vipers
(Echis): the four main species groups in the genus differ
profoundly in the proportion of arthropods in the diet. Venom
toxicity to scorpions reflects the importance of arthropods in the
diet of the species groups, and gene expression patterns reflect
adaptation of venom composition to physiologically highly
divergent prey types.