Life Histories and Natural Selection in Populations of the Salamander Desmognathus Ochrophaeus

Abstract

Populations of Desmognathus ochrophaeus Cope in the vicinity of Mt. Mitchell, Yancey County, North Carolina, differ from one another with respect to age at first reproduction, a trait in which variation can strongly affect individual fitness. Maturity is delayed in high elevation populations relative to low elevation populations, and in low elevation woodland populations relative to low elevation rockface populations. Juvenile growth rate appears to vary but slightly between populations, so that delay maturity results in individuals being larger at maturity. This may be responsible for the altitudinal size clines noted in D. ochrophaeus by other authors. Body size is positively correlated with clutch size, so that delay reproduction enhances subsequent age—specific fecundity. When populations are compared, indications of delayed maturity are usually accompanied by adult male age structures indicative of higher survivorship. In woodland populations such indications occur in samples from habitats where higher survivorship would be expected. High elevation woodland populations also exhibit higher adult growth rates, which in turn enhance female age—specific fecundities. The degree to which interpopulational differences in life history patterns are genetically based is unknown. The differences which occur are however, compatible with predictions drawn from current theory on the adaptive nature of life history patterns. Specifically, theory predicts that delayed maturity should be adaptive in relative stable environments and where it is accompanied by increased survivorship and fertility. The evolutionary ecology of Desmognathus ochrophaeus is such that these conditions may be met in high elevation woodland environments in southern Appalachians. Evidence for earlier maturity on low elevation rockfaces created by man's activities during 1938—39 suggest that, if these differences are genetically based, natural selection affects are at maturity with great effectiveness. Whether interpopulational differences in age at maturity prove to be genetic or not, interdemic variation in a trait to which fitness is potentially so sensitive is of theoretical interest.