NUCLEUS-CYTOPLASM INTERACTIONS CAUSING REPRODUCTIVE INCOMPATIBILITY BETWEEN 2 POPULATIONS OF TETRANYCHUS-QUERCIVORUS EHARA-ET-GOTOH (ACARI, TETRANYCHIDAE)

Partial reproductive incompatibility between two local populations of Tetranychus quercivorus Ehara et Gotoh derived from Sapporo (43 degrees N) and Tsukuba (36 degrees N), Japan, was found. The incompatibility was unidirectional: the Sapporo female was incompatible with the Tsukuba males, which resulted in a low egg hatchability and strongly male-biased sex ratio, whereas the reciprocal cross was compatible and produced normal progeny with a female-biased sex ratio. To determine the genetic mechanism responsible for the incompatibility, crosses were made between the two populations over five to six filial generations as well as backcrosses. The results suggested that the incompatibility could be caused by an interaction between the cytoplasm from the Sapporo population and a single nuclear gene from the Tsukuba population. Compatibility was not restored when individuals of the Sapporo population were treated with antibiotics or high temperature, indicating a possibility that the cytoplasmic factors are cytoplasmically inherited elements such as mitochondria rather than microorganisms.