Snakes have the
ability to adapt their body size relatively quickly to their environments. This
has been demonstrated with Australian Tiger Snakes, and is also suggested by
island dwelling pit vipers in China and Brazil.
The Western
Terrestrial Garter Snake (Thamnophis
elegans) has two ecomorphs, one is long-lived, and the other is
short-lived. The long-lived ecotype inhabits grassy meadows at 1.6 to 2.1 km in
elevation, is exposed to summer day time temperatures of 15-30ºC, and prefers
28ºC, it is preyed upon by medium sized raptors, feeds on frogs and leeches,
has a mean adult body size of 538 mm, females sexually mature in 5 to 7 years
at a length of 400 mm, litter sizes average 4.3, and it has a median life span
of 8 years. The short-lived ecomorph inhabits rocky shorelines at 1.5 km in
elevation, is exposed to summer day time temperatures of 20-35ºC, and prefers
28ºC, it is preyed upon by large sized raptors, feeds on fish and leeches, has
a mean adult body size of 660mm, females sexually mature in 3 years at a length
of 450 mm, litter sizes average 48.8, it has a median life span of 4 years. The
ecomorphs also have different coloration and patterns.
Now, Anne
Bronikowski and David Vleck (2010) at Iowa State University show that the
adult, short-lived ecotype of the garter snake has a higher mass-specific
resting metabolic rates at any given body mass at normal activity temperatures
(15–32.8C). The short-lived snakes reaches a larger body size, and has life-history
traits that essentially cause the snake to live fast and die young, but they
find that this is a continuum (fast growth, early maturation, high reproductive
output) relative to individuals of the small-bodied, long-lived ecotype. The
authors suggest the difference between ecotypes in metabolic intensity, even
after acclimation to identical conditions in the laboratory, may reflect
evolutionary divergence and genetic differences between ecotypes. The
difference in metabolic intensity is not present at birth, so an alternative
hypothesis is that the developmental environment may permanently influence
metabolic rate and life history. And, that the developmental path leads to
altered gene expression via environmental influences on the epigenome and
results in altered metabolic trajectories in the snakes’ natural habitats.
Full Citation: Bronikowski,
A. and D. Vleck. 2010. Metabolism, Body
Size and Life Span: A Case Study in Evolutionarily Divergent Populations of the
Garter Snake (Thamnophis elegans) Integrative and Comparative Biology
doi:10.1093/icb/icq132