Hybridization Between Declining Native and Invasive Exotic Tiger Salamande (Ambystoma californiense and A. tigrinum)

EPA Grant Number: U915724
Title: Hybridization Between Declining Native and Invasive Exotic Tiger Salamande (Ambystoma californiense and A. tigrinum)
Investigators: Fitzpatrick, Benjamin
Institution: University of California - Davis
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2000 through August 1, 2003
Project Amount: $80,613
RFA: STAR Graduate Fellowships (2000) RFA Text |  Recipients Lists
Research Category: Fellowship - Zoology , Academic Fellowships , Biology/Life Sciences


The objectives of this research project are to: (1) document the mechanisms of reproductive isolation between the tiger salamanders Ambystoma tigrinum and A. californiense; (2) discover what causes the breakdown of reproductive isolation in some unnatural habitats; (3) describe ecological interactions between the species; and (4) create a model to predict the eventual outcome of these genetic and ecological interactions.


To distinguish the importance of natural selection against hybrids from environmental influences on mating patterns, existing genetic tools are being used to test for nonrandom patterns in the production of hybrid eggs and the survival of hybrid offspring. If the cohort analysis identifies assortative mating as a primary cause of the deficiency of hybrids in natural ponds, a series of experiments will be conducted that are aimed at discovering why assortative mating breaks down in cattle ponds. If selection against hybrid larvae proves more important, experiments to test factors influencing relative fitness will be used. There are several potentially important differences between pond types. For example, the shallow water of vernal pools tracks ambient air temperature while cattle ponds, being deeper, are thought to be more buffered against extreme temperature fluctuations. Heat stress has been shown to affect relative fitness of hybrid Drosophila and Tribolium. Differences in vegetation structure suggest that small salamander larvae would be more vulnerable to invertebrate predators in natural vs. artificial ponds, making natural ponds fundamentally more dangerous. Vegetation also may influence the frequency and intensity of sexual competition among adult males. These observations suggest some straightforward experiments that will help identify the mechanism of environment-dependent reproductive isolation. Simple experiments complementary to those aimed at mechanisms of isolation will be used to describe the effects of competition on relative fitness of pure and hybrid larvae. In addition to fundamental competitive ability, differences in breeding time, age at first reproduction, fecundity, and individual growth rates will influence the rate of spread of nonnative genes.

Expected Results:

Mechanistic understanding and good quantitative estimates of important parameters will allow for the construction of a dynamic mathematical model of the hybrid zone. This model is intended to estimate the current rate of spread of the invasion and to quantitatively describe the influence of vernal pool vs. cattle pond abundance on the ultimate outcome.

Supplemental Keywords:

hybrid zone, reproductive isolation, habitat-dependent isolation, vernal pools, invasion biology., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Ecology and Ecosystems, adaptive genetic variation, habitat dynamics, habitat species co-occurrence, biodiversity, genetic consequences, habitat patch dynamics, salamanders, conservation biology, invasive species, breeding habitat

Progress and Final Reports:

  • 2001
  • 2002
  • Final