Population cage experiments with a vertebrate: The temporal demography and cytonuclear genetics of hybridization on Gambusia fishes

Evolution
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Abstract

The dynamics of mitochondrial and multilocus nuclear genotypic frequencies were monitored for 2 yr in experimental populations established with equal numbers of two poeciliid fishes (Gambusia affinis and Gambusia holbrooki) that hybridize naturally in the southeastern United States. In replicated "small-pool" populations (experiment I), 1018 sampled individuals at six time periods revealed an initial flush of hybridization, followed by a rapid decline in frequencies of G. affinis nuclear and mitochondrial alleles over 64 wk. Decay of gametic and cytonuclear disequilibria differed from expectations under random mating as well as under a model of assortative mating involving empirically estimated mating propensities. In two replicate "large-pond" populations (experiment II), 841 sampled individuals across four reproductive cohorts revealed lower initial frequencies of F1 hybrids than in experiment I, but again G. holbrooki alleles achieved high frequencies over four generations (72 wk). Thus, evolution within experimental Gambusia hybrid populations can be extremely rapid, resulting in consistent loss of G. affinis nuclear and cytoplasmic alleles. Concordance in results between experiments and across genetic markers suggests strong directional selection favoring G. holbrooki genotypes. Results are interpreted in light of previous reports of genotype-specific differences in life-history traits, reproductive ecology, patterns of recruitment, and size-specific mortality, and in the context of patterns of introgression previously studied indirectly from spatial observations on cytonuclear genotypes in natural Gambusia populations.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Population cage experiments with a vertebrate: The temporal demography and cytonuclear genetics of hybridization on Gambusia fishes
Series title Evolution
DOI 10.2307/2410011
Volume 48
Issue 1
Year Published 1994
Language English
Publisher Society for the Study of Evolution
Contributing office(s) Alaska Science Center
Description 17 p.
First page 155
Last page 171
Country United States
State South Carolina