1. ¹Department of Environmental and Evolutionary Biology, University of St Andrews, St Andrews, Fife, UK
2. ²Departamento de Ecologia Evolutiva, Instituto de Ecologia, Universidad Nacional Autónoma de México, Coyoacán, Mexico DF, México

Correspondence: Dr C Macías Garcia, Departamento de Ecologia Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, A. P. 70-275. c. p. 07510, Coyoacán, Mexico DF, México. E-mail: maciasg@servidor.unam.mx

³Current address: NW Bailey, Department of Biology, University of California, Riverside, CA 92521, USA.

Received 28 February 2006; Revised 25 January 2007; Accepted 26 January 2007; Published online 28 February 2007.

Abstract

The relative importance of genetic and non-genetic factors in extinction liability has been extensively debated. Here, we examine the levels of genetic variability at 13 (seven informative) loci in wild and captive populations of two endangered species of Mexican Goodeid fish, Ameca splendens and Zoogoneticus tequila. Allelic diversity was higher in the wild populations, and F_IS lower. Values of (=4Ne) were estimated using a coalescent approach. These implied that the effective population size of all captive populations of A. splendens were smaller than that of the wild population; qualitatively similar results were obtained using an analytical method based on within-population gene identity disequilibrium. However, the wild population of Z. tequila did not show a significantly greater estimate of . We used the Beaumont approach to infer population declines, and found that both species showed clear evidence of a decline in effective population size, although this was stronger and probably occurred over a longer period of time in Z. tequila than in A. splendens. The decline in Z. tequila probably occurred before captive populations were established. We discuss implications for the conservation of critically endangered populations.