ON THE EVOLUTIONARY IMPORTANCE OF CYTOPLASMIC STERILITY IN MOSQUITOES

Abstract

~ rl' ~ rl' b b a a 2' 2' 2' 2' (a + b = 1) and assume random mating and equal selective values, except that ~ Og X rl' Ha is sterile. In the next generation the proportions of the four types will be: Og Ha In mosquitoes, it has been repeatedly described that crosses between local races or subspecies may be fertile if the cross is carried out in one direction, completely sterile if it is carried out in the opposite direction. This phenomenon has been thoroughly investigated by Laven (1957) using local populations of Culex pipiens. He particularly investigated two strains from Ham-burg (Ha) and Oggelshausen (Og) in which the cross ~ Ha X rl' Og is fertile, while in the cross ~ Og X rl' Ha the offspring die as embryos. He transferred the Og genome by 52 successive generations of outcrosses of (~Ha X rl' Og) hybrids to Ogmales into Ha cytoplasm, and found that the resulting animals as males do not produce viable offspring when crossed to Og females. Though other interpretations are not rigidly excluded , Laven suggests as the most likely explanation a cytoplasmic difference between strains Ha and Og which results in incompatability between the cytoplasm of an Og ovum and a cytoplasmic component of Ha sperm, leading to death of the embryos.