Nonrandom mate choice by females of Drosophila pseudoobscura: a case of outbreeding avoidance?

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Abstract
Relative mating success of genetically different males of Drosophila pseudoobscura was measured with five female strains using an experimental set-up consisting of a mating chamber containing 20 females of one strain and a total of 20 males of two different strains. No evidence was found indicating negative assortative mating, neither of the direct type, nor of the "rare male" type. Some strains, however, displayed strong positive assortative mating, as males of the same strain as the females were significantly more successful in obtaining copulations than were males of another strain present in the mating chambers. Deviations from random mating can be interpreted as the result of some males possessing higher levels of "vigour," but an alternative explanation is favoured, one involving female choice. Experimental results do indicate that the orange-eyed mutant flies, used as one of the male strains in all experiments, did have a relatively low level of courtship vigour, but not low enough to account for more than a small fraction of the differential mating success observed in some of the experiments.
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