GENETIC ANALYSIS OF A POPULATION OF TRIBOLIUM. VI. POLYMORPHISM AND DEMOGRAPHIC EQUILIBRIUM

A. M. Moffa ¹ and R. F. Costantino ¹

¹ Department of Zoology, University of Rhode Island, Kingston, Rhode Island 02881

Demographic and genetic data of continuously growing populations of Tribolium castaneum initiated with identical age structures but with different frequencies of the unsaturated fatty acid-sensitive allele were collected for 68 weeks.—The life history data provided the following insights: Genotypic differences for total number of offspring were due primarily to larval viability. The total lifetime offspring production of the genotypes predicted a stable polymorphic genetic equilibrium. The genotypic reproductive functions forecast that a stable age structure was not a prerequisite for genetic equilibrium.—Those cultures initially segregating for the unsaturated fatty acid-sensitive allele converged to an equilibrium allele frequency of 0.25 and a genotypic array composed of equal numbers of +/+ and +/cos individuals.—The numbers of larvae, pupae and adults during the first six weeks were quadratic functions of the initial frequency of the sensitive allele. Qualitative age structure changes that followed were similar in all cultures and demographic equilibrium was realized at week 50. The overall demographic pattern during the 68-week study was interpreted in terms of the interactions among the numbers of small larvae, large larvae plus pupae, and adults.

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