Rather than a longish comment on Rachael's latest post, I thought I'd write up a brief entry on Ensatina.
First, the picture:
Ensatina eschscholtzii eschscholtzii, or Monterey subspecies of E. escscholtzii. The "Monterey Salamander", found near Monterey, CA.
Ensatina are an interesting species of salamander in that they are a "ring species", or, they have a sequence of morphotypes that gradually change regionally, and these morphotypes overlap but do not interbreed. There are two terminal morphotypes that are too distantly related to be capable of interbreeding (see Wikipedia's discussion of the subject). The beauty of ring species is that they provide a living sample of speciation and evolution.
In particular, Ensatina in the Bay Area differ from the Monterey morphotype in that they are very morphologically similar to the non-terrestrial stage of Taricha torosa, which are highly toxic to ingest. The tetrodotoxin they produce is a neurotoxin that is potent enough to kill most vertebrates (though some Thamnophis (Garter snakes) have evolved modified sodium channels to enable consumption of them as prey items; see this paper and others for more) (DOI: 10.1007/s10886-005-1345-x). Thus, Ensatina in the Bay Area mimic Taricha presumably to avoid predation.
For those of you curious about the diagnostic differences, an Ensatina is generally smoother than a Taricha, with more prominent costal grooves (the grooves along the side), has nasolabial grooves, and has a constricted base at its tail. The Monterey specimen here lacks the yellow eyes of Taricha, though the Bay Area ecomorph has eyes that are quiet similar to those of Taricha.
Suggested Thamnophis/Taricha studies:
- Brodie and Brodie. Tetrodotoxin Resistance in Garter Snakes: An Evolutionary Response of Predators to Dangerous Prey. Evolution, Vol. 44 No. 3 (May 1990).
- Brodie and Brodie. The Evolutionary Response of Predators to Dangerous Prey: Hotspots and Coldspots in the Geographic Mosaic of Coevolution between Garter Snakes and Newts. Evolution, Vol. 56, No. 10 (October 2002).
- Brodie et al. Parallel Arms Races between Garter Snakes and Newts Involving Tetrodotoxin as the Phenotypic Interface of Coevolution. Journal of Chemical Ecology, 2005. DOI: 10.1007/s10886-005-1345-x
- Geffeney et al. Mechanisms of Adaptation in a Predator-Prey Arms Race: TTX-Resistant Sodium Channels. Science 2002. DOI: 10.1126/science.1074310.
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