Evol Ecol Res 1: 277-283 (1999)     Full PDF if your library subscribes.

Rapid evolution towards equal sex ratios in a system with heterogamety

Mark W. Blows,1 David Berrigan2,3 and George W. Gilchrist3

1Department of Zoology, James Cook University, Townsville, Queensland 4811, Australia, 2Department of Genetics and Human Variation, La Trobe University, Bundoora, Victoria 3083, Australia and 3Department of Zoology, University of Washington, Seattle, WA 98195, USA

Address all correspondence to Mark W. Blows, Department of Zoology, University of Queensland, Brisbane, Queensland 4072, Australia.
e-mail: mblows@zoology.uq.edu.au


The equal sex ratios found in many species with heterogametic sex determination may be a consequence of selection for equality or the result of the Mendelian segregation of the two sex chromosomes. A lack of genetic variation in sex ratio in species with heterogamety has been the major obstacle in distinguishing between these two hypotheses. We overcome this obstacle by generating hybrids between two species of Drosophila. The resulting hybrid lines had biased sex ratios, allowing us to observe the evolution of sex ratio in replicate populations. Sex ratio converged towards 1 : 1 after 16 generations of natural selection. These changes in sex ratio were not due to differences in viability between the sexes and the loci underlying the variation in sex ratio were not sex-linked. Equal sex ratios may therefore be the result of natural selection as Fisher predicted.

Keywords: heterogamety, interspecific hybrids, natural selection, sex ratios.

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