Size and Cycle in Dusky Salamanders
The equal fitness paradigm (EFP) is a life-history model in which the currency of fitness is usable energy rather than individuals, and the principal trade-off is between survival, evaluated as generation time, and productivity, evaluated as growth and reproductive rates. In the current study I examined variation in generation time, age at first reproduction, productivity, and mortality in salamanders of the genus Desmognathus within the framework of the EFP. Desmognathus salamanders are restricted to eastern North America, with a center of distribution in the southern Appalachian Mountains. The data sources of the present report are published studies of life histories and demographics of five species of Desmognathus that include the smallest and largest members of the genus. The analysis showed that Desmognathus salamanders have greater ages at first reproduction, lengthier generation times, lower productivities, and lower mortality rates than are predicted by the scaling functions of the EFP for vertebrates of equivalent sizes. The differences among species in these parameters are correlated with variation in adult body size and the association between body size and habitat utilization in the genus, wherein the largest species are aquatic in mountain streams and the smallest are terrestrial in mesic forests. Streamside species of intermediate size exploit a broader range of habitats and are more widely distributed than the stream- and forest-dwelling forms. It is likely that the streamside mode of life in Desmognathus represents an adaptation promoting dispersal. Adaptive radiation in the genus is expressed in extreme life-history and body-size diversification mediated through variation in age at first reproduction and generation time.ABSTRACT
The study areas in southwestern North Carolina. (1) Wolf Creek, Cowee Mountains, Jackson County. (2) Coweeta Creek and upper Nantahala River, Nantahala Mountains, Macon and Clay Counties. Coordinates are given in degrees north latitude and degrees west longitude (WGS 84).
Representative Desmognathus from Wolf Creek and Coweeta/Nantahala. Body sizes, when given, are estimates based on field measurements. (A) The three species of Wolf Creek Desmognathus photographed against the substrate of a tributary stream. Subadults of D. amphileucus (left) and D. monticola (below right); adult of D. ocoee (above right). (B–F) Coweeta-Nantahala Desmognathus. (B) Adult D. monticola. (C) Adult D. ocoee. (D) First-year larvae of D. monticola (15 mm SL) (above) and D. ocoee (12 mm SL). (E) Adult D. amphileucus. (F) Third-year larva of D. amphileucus (32 mm SL).
(A) Tributary of the upper Nantahala River. Six species of Desmognathus and four other species of plethodontid salamanders co-occur within the field of view of this photograph. (B) Adults of the miniaturized Coweeta/Nantahala species, D. wrighti (left) and D. aeneus (each about 25 mm SL). (C) Terrestrial egg clutch of D. aeneus attended by the female parent.
Blue regression lines and symbols: ordinary least-squares regressions of log10 transforms of the scaling functions of generation time (G) and productivity (B) on dry body mass (M), from Table 1. Black regression lines represent the log10 transforms of the consensus scaling functions G = 3.0M0.25 and B = 2.54M−0.25 from Brown et al. (2018). (A) G = generation time. (B, C, D) B = productivities for several values of F, where F = fraction of productivities allocated to surviving offspring.
Ordinary least-squares regressions of log10 transforms of the scaling functions of age at first reproduction (x*) and productivity (B) on dry body mass (M), from Table 2. LCL, UCL: lower, upper confidence limits. LPL, UPL: lower, upper prediction limits.
(A) Solid black line: least-square consensus regression of loge mortality rate (ln Z) on loge body mass of the fish data set of McCoy and Gillooly (2008). Dashed black line: approximate lower limit of the point scatter of the fish data. See Fig. 2b in McCoy and Gillooly (2008). Blue line and symbols: least-squares regression of loge mortality rate on loge body mass of Wolf Creek and Coweeta Desmognathus, from life tables. Z values for Desmognathus calculated as mortality rate over average life span; that is, age = generation time (G). (B) Details of the Desmognathus regression. LCL, UCL: lower, upper confidence limits. LPL, UPL: lower, upper prediction limits.
Contributor Notes
Present address: 50 Wagon Trail, Black Mountain, North Carolina, 28711, USA
