SREL Reprint #2766

Amphibian Conservation Genetics

Christine M. Bridges, Christopher L. Rowe, William A. Hopkins

Introduction: Growing concern over worldwide reports of declining amphibian populations has focused attention on potential environmental factors thathave changed in some magnitude over recent years to generate these declines (e.g., increased ultraviolet [UV] radiation from ozone depletion, increased pollutants, acid rain). Such environmental changes can act upon individuals by natural selection and can drive the genetic structure of populations. The amount of genetic variation in a population can determine the response to selection. Further, the long-term maintenance of genetic variation is critical to understanding long-term adaptation as environmental conditions change. Mechanisms for the maintenance or generation of genetic variability (i.e., additive genetic variation) must be evaluated to understand the evolutionary potential of populations (Lande and Shannon 1996), because this variance ultimately fuels evolutionary change through differential selection and dictates population persistence.
Genetic diversity is one of the most important yet most understudied aspects of amphibian population biology, especially as it relates to environmental stress. As amphibian populations decline, population genetic theory predicts that rare alleles will be lost, and more common ones will be driven to fixation (Galbraith 1997). However, breeding amphibian population sizes and reproductive success can fluctuate dramatically from year to year (e.g., Semlitsch et al. 1996), possibly rendering traditional, more simple models of small populations less applicable. Stochastic factors (e.g., early pond drying, a pulse of contaminant) in combination with life history characteristics of many pond-breeding amphibians (e.g., explosive breeding, large egg masses, dependence on seasonal habitat) can lead to highly variable juvenile recruitment and individual reproductive success. So even in undisturbed populations, gene frequencies may change erratically and demographic bottlenecks, as defined by a significant but temporary reduction in the effective population size, can frequently occur. Such processes can be exacerbated in stressful or changing environments (e.g., those where amphibian declines have been reported), where natural selection can further reduce population numbers...

SREL Reprint #2766

Bridges, C. M., C. L. Rowe, and W. A. Hopkins. 2003. Amphibian conservation genetics. p. 59-71. In: G. Linder, S. Krest and D. Sparling (Eds.). Amphibian Decline: An Integrated Analysis of Multiple Stressor Effects. Society of Environmental Toxicology and Chemistry.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).