SREL Reprint #2386

Empirical evaluation of cytonuclear models incorporating genetic drift and tests for neutrality of mtDNA variants: data from experimental Gambusia hybrid zones

Kim T. Scribner1,2, Susmita Datta3,4, Jonathan Arnold5, and John C. Avise5

1Department of Zoology, University of Georgia, Athens, GA 30602, USA
2Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824-1222, USA
3Department of Statistics, University of Georgia, Athens, GA 30602, USA
4Department of Mathematics and Computer Science, Georgia State University,
University Plaza, Atlanta, GA 30303,USA
5Department of Genetics, University of Georgia, Athens, GA 30602, USA

Abstract: Statistical tests of genetic drift and of the neutrality of mtDNA are presented using empirical time-series data on multi-generational changes in cytonuclear disequilibria within replicated experimental hybrid populations of two species of live-bearing Poeciliid fishes (Gambusia holbrooki and G. affinis) which were monitored over a period of two years (three generations). Cytonuclear disequilibria D1 and D2 (which measure departures from random associations of cytoplasmic and nuclear genotypes) over the three generations of the experiment were non-zero for all replicate populations. For each of five nuclear loci, the observed measures of D1 and D2 were highly concordant between replicates during each generation. Significant departures from expectations were observed after one and two generations. A statistical measure of goodness of fit of observed changes in cytonuclear disequilibria (and implicitly of the neutrality of the mtDNA markers) was calculated for each nuclear locus. When the results for the replicates were combined into an overall test of neutrality, the fit to the random union of zygotes (RUZ) model was rejected for four of the five nuclear loci (P < 0.05). A simple genetic drift model does not explain the temporal changes in composite cytonuclear genotypic frequencies. Frequencies of parental G. holbrooki mitochondrial alleles and nuclear genotypes exceeded expected values during most time periods, implying some selective advantage of offspring produced by G. holbrooki females. Expansion of cytonuclear models to explicitly address questions of genetic drift and neutrality have general relevance to studies of natural populations.

Keywords: disequilibrium, Gambusia, genetic drift, mtDNA, neutrality

SREL Reprint #2386

Scribner, K.T., S. Datta, J. Arnold, and J.C. Avise. 1999. Empirical evaluation of cytonuclear models incorporating genetic drift and tests for neutrality of mtDNA variants: data from experimental Gambusia hybrid zones. Genetica 105:101-108.

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