DEVELOPMENTAL AND GENETIC HOMEOSTASIS IN TWO SPECIES OF FLOUR BEETLES.

Abstract

Flour beetles of the genus Tribolium have served as a useful tool for ecological studies for many years (e.g., Park, 1962) and have recently begun to attract the attention of other population biologists. The two species Tribolium castaneum and T. confusum are closely related but completely reproductively isolated both in nature and in the laboratory. Based on a comparative cytological study, Smith (1952) suggested that T. confusum, which has nine pairs of chromosomes, was derived from an ancestral form similar cytologically to T. castaneum (ten pairs) by a translocation involving a pair of autosomes and the sex chromosomes. Genetic studies have revealed a number of presumed gene-homologies between the two species (Sokoloff, 1964). Geographic distribution data for these two, species indicate that they are both cosmopolitan, being easily transported from place to place in grain sacks, etc. (Good, 1936; Hinton, 1948). Temperature does seem to have quite an effect on distribution however. T. castaneum is essentially a subtropical species, whereas T. confusum is more frequently found in temperate, more northerly regions. It should be noted that both species are found throughout the range of conditions because they can live in heated granaries, food stores, etc. In general, however, natural populations of T. confusumn probably have to withstand more severe cold conditions and in particular, greater fluctuations in temperature and humidity. This is corroborated by laboratory studies on survival, productivity and developmental rate measured under different temperature and humidity regimens (Gray, 1948; Howe, 1956, 1960; Dawson, 1965b). T. confusum is found to be more tolerant of extremes, particularly of cold, than T. castaneum. On the other hand, T. castaneum is generally found to survive better and develop faster at higher temperatures and humidities. Optimum temperatures for development are about 2'/2C higher for this species. Competition experiments utilizing these two species have shown that T. castaneum is favored under warm, wet conditions and T. confusum under cool, dry ones (Park, 1954). This is also in accord with the data on distribution of natural populations of the two species. Tantawy and Mallah (1961) concluded from studies on Drosophila siiiiulans and D. melanogaster that populations from a temperate region were more homeostatic than populations collected near the Equator in terms of response to various laboratory temperatures. They suggested that