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Shaping intraspecific variation: Development,ecology and the evolution of morphology and life history variation in tiger salamanders
Authors:James P. Collins  Kim E. Zerba  Michael J. Sredl
Affiliation:(1) Department of Zoology, Arizona State University, 85287-1501 Tempe, AZ, USA;(2) Department of Human Genetics, University of Michigan, 48109 Ann Arbor, MI, USA;(3) Nongame Branch, Arizona Game and Fish Department, 221 West Greenway Road, 85023-4312 Phoenix, AZ, USA
Abstract:The tiger salamander,Ambystoma tigrinum, is a geographically widespread, morphologically variable, polytipic species. It is among the most variable species of salamanders in morphology and life history with two larval morphs (typical and cannibal) and three adult morphs (metamorphosed, typical branchiate, cannibal branchiate) that vary in frequency between subspecies and between populations within subspecies. We report morphometric evidence suggesting that branchiate cannibals arose through intraspecific change in the onset or timing of development resulting in the wider head and hypertrophied tooth-bearing skull bones characteristic of this phenotype. We also quantified bilateral symmetry of gill raker counts and abnormalities, then evaluated fluctuating asymmetry as a measure of the developmental stability of each morph. There was a significant interaction between fluctuating asymmetry of developmental abnormalities in cannibals and typicals and the locality where they were collected, suggesting that relative stability of each phenotype could vary among populations. While altered timing of developmental events appears to have a role in the evolution and maintenance of morphs, novel phenotypes persist only under favorable ecological conditions. Predictability of the aquatic habitat, genetic variation, kinship, body size, intraspecific competition and predation all affect expression and survival of the morphs inA. tigrinum. This taxon provides an excellent model for understanding the diversity and complexity of developmental and ecological variables controlling the evolution and maintenance of novel phenotypes.
Keywords:fluctuating asymmetry  heterochrony  intraspecific  morphology  polymorphism
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