Morphological variation in the clouded salamander, Aneides ferreus (Cope) (Amphibia: Caudata: Plethodontidae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dz010v34g

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  • Multivariate morphometric analyses performed on ten populations of Aneides ferreus indicate that phenotypic expression in this species is exceedingly similar, but that on a fine scale there is considerable significant heterogeneity between most populations as well as between regional groups of populations. in terms of variation between California, Oregon, and Vancouver Island specimens. California is differentiated from Vancouver Island at of 2.13; Oregon-California D² of 2.13; Oregon-California D² = 1.35, and Oregon-Vancouver Island exhibited D² of 1.38. These values represent significant F-ratio comparisons at p <<.01. These slight but significant differences in phenotypic expression are not unexpected for a species which ranges over such a wide and varied geographic area, and can be correlated with major topographic features of the Pacific Northwest. Prior to Pleistocene glaciation, populations of A. ferreus were probably continuous throughout northwestern California, western Oregon and Washington, as well as Vancouver Island and British Columbia. As Cordilleran ice advanced and inundated most of British Columbia, and Vancouver Island, populations became isolated in refugia on Vancouver Island, and were probably extirpated from British Columbia proper. The slight, but significant levels of heterogeneity produced from comparisons of Vancouver Island specimens with California and Oregon specimens indicate that the observed disjunction between Vancouver Island populations and those inhabiting coterminous U.S. is probably a relatively recent occurrence, correlating well with events produced by the Fraser Glaciation approximately 15,000 yr BP. Since other plethodontids inhabit Vancouver Island and Washington it is impossible to utilize Pleistocene glaciation as a direct causal mechanism which produced the disjunction, accounting for the absence of A. ferreus in Washington. On a finer scale, significant phenotypic dissimilarity was found to exist between a majority of the pairwise comparisons between populations within each of the three regions. Patterns of heterogeneity within California populations are consistent with predictions derived by utilizing a model based upon a gradual latitudinal environmental dine. No apparent pattern can be seen when pairwise comparisons are made between Oregon populations, although all populations exhibit slight but significant levels of heterogeneity. The effects of Pleistocene climatic events upon California and Oregon populations were probably slight since the maximum southern incursion of Cordilleran ice reached latitudes just south of Olympia, Washington. Montaine glaciers in the Klamath-Siskiyou Mountains provided potential barriers to gene flow between California and Oregon populations until about 10,000 yr BP. The equable redwood forest ecosystem in northwestern California must be considered to be the ancestral habitat for Aneides in general and A. ferreus in particular. Specimens from this region exhibit high tooth counts, a character that has been considered to be primitive by Wake (1963; 1966). Also, all three western Aneides occur in sympatry in northwestern California redwood associations, and the earliest known fossil Aneides were associated with redwood forests during Eocene times in Montana. Comparison of morphological relationships with electrophoretic and chromosomal data for each region and population indicates that there is little agreement between morphological and electrophoretic relationships, but that karyotypic variation is present which allows classification of a collection of individuals to one of the three regions with a high degree of certainty.
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