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EVOLUTION IN MIXED POPULATIONS OF TRIBOLIUM

Comparative performance of pure and mixed stands of plants has received a great deal of experimental attention. More recently, dramatic improvement in mixtures of two strains of Drosophila melanogaster was reported by Seaton and Antonovics (1967). They found that a mutant and a wild type strain, which initially produced fewer progeny in mixtures than expected from their performance in pure cultures, changed dramatically in only three generations, after which the mixtures were consistently superior. It was shown that both the mutant and wild type strains improved in their ability to avoid interference by the other genotype. Sokal et al. (1970) were unable to repeat these results with either flour beetles or houseflies. Here I report two separate sets of experiments designed to explore this phenomenon in flour beetles, Tribolium castaneum and T. confusum, which have in recent years become an increasingly valuable tool to experimental population biologists (King and Dawson, 1972).