Life-History Contributions to Miniaturization in the Salamander Genus Desmognathus (Urodela: Plethodontidae)
I investigated the contributions of several life-history traits to small body size in the two smallest species of the genus Desmognathus, D. aeneus and D. wrighti. The research was conducted in the southern Nantahala Mountains of western North Carolina, where the two species co-occur and are similar in body size and life history. Desmognathus ocoee, the next-smallest species in the local Desmognathus assemblage of six species, served as a reference species. All three species have similar juvenile growth rates. Desmognathus aeneus and D. wrighti have smaller propagule sizes (i.e., egg and hatching sizes) and higher developmental rates to sexual maturation than D. ocoee. These two factors, especially the latter, appear to explain much of the difference in adult size between D. ocoee and both D. aeneus and D. wrighti. Thus, miniaturization in D. aeneus and D. wrighti may be mainly a product of acceleration in developmental rate. I suggest that body size itself, rather than other, correlated life-history traits, has been the target of selection in these two species, in response to ecological opportunities for small salamanders in the mesic forests of the southern Appalachian Mountains.Abstract
Distributions of standard lengths of the 1998 samples of Desmognathus aeneus (n = 101) and D. wrighti (n = 124), based on the data in Hining and Bruce (2005:fig. 1). The curves were fitted by MIXDIST, under the hypothesis that each distribution consists of three normal distributions, representing first-year, second-year, and third-year and older individuals. The red triangles on the x-axis are the estimated means of the successive cohorts.
Distribution of standard lengths of 106 Desmognathus ocoee from Coweeta Hydrologic Laboratory, December 1994–July 1995 (Bruce et al., 2002). Upper histogram shows total sample; lower histograms show winter and late spring–early summer samples of juveniles. Symbols in this and later histograms: white squares = juveniles, black squares = mature males, gray squares = mature females.
Plot of standard length versus age of Desmognathus ocoee in the 1994–95 collections from the Coweeta Creek watershed (Bruce et al., 2002). The solid curve is a Gompertz function fitted to the entire sample. The dashed line is a linear function fitted to the younger (≤ 3 yr), juvenile component of the sample.
Distributions of standard lengths of Desmognathus ocoee from the upper Nantahala River watershed. (A) 8 September 2006 (n = 31), (B) 21–22 April 2007 (n = 68), (C) 6 July 2007 (n = 29), (D) 20 August 2007 (n = 30).
Distributions of standard lengths of juvenile Desmognathus ocoee from the upper Nantahala River watershed on 12 October 2007 (n = 25) and 28 March 2008 (n = 30).
Contributor Notes
Associate Editor: M. J. Lannoo.