Different hybrid effects in reciprocal crosses between Chironomus thummi thummi and Ch. th. piger including spontaneous chromsome aberrations and sterility

Hybrids from reciprocal erosses between two Chironomus thummi thummi and Ch. th. piger laboratory stocks show four abnormalities in comparison to the parental stocks. One cross direction (Ch. th. thummi ♂ x Ch. th. piger ♀) is characterized by chromosome aberrations, reduced hatchability and malformations, whereas in reciprocal hybrids both sexes are sterile. Sterility is the consequence of rudimentary or non developed gonads. In Ch. th. thummi ♂ x Ch. th. piger ♀ crosses chromosome aberrations were analysed in salivary gland nuclei. These aberrations are all somatic in origin, and they are induced during the first 40 h of embryonic development, prior to the onset of polytenization. The chromosomes of both subspecies are equally affected. In all four chromosomes breaks occur preferentially at specific regions. Reduced hatchability and malformations are presumably caused by chromosome mutations because within egg-masses a correlation exists between the rate of salivary gland chromosome aberrations and the rates of hatchability and malformations. © 1984 Dr W. Junk Publishers.