The genetics of hybrid sterility between subspecies of the complex ofGlossina morsitansWestwood (Diptera: Glossinidae)

Abstract

Crosses were made between the three subspecies of the complex of Glossina morsitans Westwood and the hybrid females backcrossed. Hybrid female fecundity was highly 'reactive' to foreign male genes when the mother was G. morsitans centralis Machado compared with the reciprocal crosses and backcrosses. Hybrid Fj males were unable to inseminate females successfully, and although in nearly a quarter of the dissections sperm was transferred to the uterus, it did not migrate to the spermathecae. Heterozygosity between the X-and Y-chromosomes and most of the autosomes led to high frequencies of sterile males, but homozygosity between the X-and Ychromosomes could still yield 30-50% sterility. Successive backcrosses of hybrid females between G. m. morsitans and G. m. centralis to the latter subspecies continued to increase the frequency of fertile males. Interactions between X-chromosome and autosomal gene seemed to be responsible for hybrid male sterility, and the number of sterility genes involved appeared to be very few. Crosses involving G. morsitans submorsitans Newstead generally agreed with those between the other two subspecies, but the distortion in the sex ratio of emergent adults limited the application of the data to this subspecies. Competition experiments using sterile hybrid males and fertile males in population cages (30 cm cube) showed that suppression was possible, especially when the ratio of sterile:fertile males was 2:1. The value of sterile hybrid males in tsetse control programmes and the evolution of reproductive isolation in the complex is discussed.

Genetic basis of sterility in hybrids from crosses of Glossina morsitans submorsitans and Glossina morsitans morsitans (Diptera: Glossinidae)

“…Similar, but not identical, results were obtained by Rawlings (1985) using G. m. submorsitans, from colonies of Nigerian origin, and G. m. morsitans from colonies that came from Zimbabwe. The temperature at which females were maintained influenced fertility of hybridized females: at least one G. m. morsitans mated to G. m. submorsitans became pregnant when maintained at 2g°C, but none became pregnant at 25 "C (Rawlings 1985).…”

“…The results are presented and analyzed only as a first approximation to an understanding of the genetic basis of hybrid sterility in crosses of G. m. submorsitans and G. m. morsitans. Nonetheless, .the results represent an advance over previous work, in which either no genetic markers were used (Curtis 1972;Gooding 1982Gooding , 1985 or a single X chromosome marker was used (Rawlings 1985).…”

“…The temperature at which females were maintained influenced fertility of hybridized females: at least one G. m. morsitans mated to G. m. submorsitans became pregnant when maintained at 2g°C, but none became pregnant at 25 "C (Rawlings 1985). One of 33 (G. m. submorsitans x G. m. morsitans) F1 hybrid males was able to inseminate his mates (Rawlings 1985), but these females were not maintained long enough to determine whether they would have become pregnant. Rawlings (1985) one X chromosome marker gene (but no autosomal marker Results genes), fertilized by G. m. submorsitans and others fertilized by G. m. morsitans.…”

“…One of 33 (G. m. submorsitans x G. m. morsitans) F1 hybrid males was able to inseminate his mates (Rawlings 1985), but these females were not maintained long enough to determine whether they would have become pregnant. Rawlings (1985) one X chromosome marker gene (but no autosomal marker Results genes), fertilized by G. m. submorsitans and others fertilized by G. m. morsitans. One of two backcross males that had X and Y chromosomes and an estimated 75% of the autosomes from G. m. morsitans was fertile, but two backcross males with X from G. m. submorsitans and Y and an estimated 75 % of the autosomes from G. m. morsitans were sterile.…”

“…Four backcross males with X from G. m. morsitans and the Y and an estimated 75 % of the autosomes from G. m. submorsitans were sterile. Rawlings (1985) interpreted these results as indicating that hybrid male sterility involves "an interaction between genes on the autosomes and X chromosomes. "…”