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 magBitude 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 (see Figure
2A-l, p 10). 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 man1tenance 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 Call 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 Amphibian Decline: An Integrated Analysis of Multiple Stressor Effects, edited by G. Linder, S. Krest and D. Sparling. Society of Environmental Toxicology and Chemistry.
