San Francisco Garter Snake, dead end species
San Francisco Garter Snake Thamnophis sirtalis tetrataenia eats a California Toad, Bufo boreas halophilus
San Bruno California Toad was a common sight on the San Francisco peninsula into the 1960s but the populations crashed in the middle 1970s. This event was not confined to only Bufo boreas halophilus. Experts blamed this extinction on a toad Virus-Infected planet. The Cane toad was not infected. Is this to be a species specific world wide extinction?
The San Francisco Garter Snake (Thamnophis Sirtalis Tetrataenia) are known to eat poisones Toads and Newts, that in equal doses of toxin can kill approximately 25,000 white mice (Brodie et al 1974). Physiological studies have shown that they have resistance1000 times stronger then that of any other member of the genus (Thamnophis). The strongest resistance of any other snake or animal to TTX toxins.
To the San Francisco Garter this coevolution is predicated on the existence of variable selection across an interaction between species. A range of ecological factors, from differences in resource availability to differences in community composition, can generate such a mosaic of selection among pop- ulations, and thereby differences in the strength of coevolution. The result is a mixture of hotspots, where reciprocal selection is strong, and coldspots, where reciprocal selection is weak or absent, throughout the ranges of species. Population subdivision further provides the opportunity for nonadaptive forces, including gene ﬂow, drift, and meta- population dynamics, to inﬂuence the coevolutionary interaction between species. Some predicted results of this geographic mosaic of coevolution include maladapted or mismatched phenotypes, maintenance of high levels of polymorphism, and prevention of stable equilibrium trait combinations.
To evaluate the potential for the geographic inﬂuence predator-prey coevolution, the geographic pattern of genetically determined TTX resistance in the garter snake Thamnophis sirtalis over much of the range of its ecological interaction with toxic newts of genus Taricha. Then assayed TTX resistance in over 2900 garter snakes representing 333 families from 40 populations throughout western North America.
This dramatic evidence that geographic structure is an important component in coevolutionary interactions between predators and prey. Resistance levels vary substantially (over three orders of magnitude) among populations and over short distances. The spatial array of variation is consistent with two areas of intense evolutionary response by predators surrounded by clines of decreasing resistance. Some general predictions of the geographic mosaic process are supported, including clinal variation in phenotypes, polymorphism in some populations, and divergent outcomes of the interaction between predator and prey. Conversely, TTX resistance have evolved independently. Second, in the one region that TTX levels in prey have been quantiﬁed, resistance and toxicity levels match almost perfectly over a wide phenotypic and geographic range. However, these results do not preclude the role the nonadaptive forces in generating the overall geographic mosaic of TTX resistance. Much work remains to ﬁll in the geographic pattern of variation among prey populations and, just as importantly, to explore the variation in the ecology of the interaction that occurs within populations.
By out gunning competition for for thousand of years on poison prey the SFGS created a dead end for its species. A species the San Francisco Garter snakes food source rapidly disappeared. Will it successfully survive competitions for local tree frogs as a alternate main food source? Conversely can the SFGS find its way into habitats full of TTX poison Cane toads to reclaim its place as the top predator of poison amphibians on the planet.