An Analysis of Tiger Salamander (Ambystoma tigrinum nebulosum) Survival Based on BodySize and Other Covariates

Polyphenisms occur when populations exhibit alternative, discrete phenotypes in response to environmental variation, and are examples of phenotypic plasticity. This phenomenon is thought to be adaptive because it allows quicker response to environmental shifts than those that are genetically fixed. However, few studies have quantified the fitness consequences of polyphenisms. Ambystoma tigrinum nebulosum (Arizona Tiger salamander) inhabits montane ecosystems throughout Colorado, Utah, Arizona, and New Mexico. This species is polyphenic, in that genotypic variation coupled with environmental stimuli trigger two distinguishable adult forms (metamorphic and paedomorphic), which is termed facultative paedomorphosis. Using a capture-recapture database started in 1988, we analyzed survivorship of the Mexican Cut population to test hypotheses about how survival, one component of fitness, varies within this population. MARK was used to estimate survivorship of the salamanders based on parameters such as sex, morph, and size. To incorporate size, we used the ratio of mass to snout-vent length defined as body condition, which was categorized into four size classes. We found that the medium size class had lower survival than other size classes, irrespective of morph, and that neither morph nor sex appears to have a major impact on survival.