Inbreeding depression by recessive deleterious genes affecting female fecundity of a haplo-diploid mite

The effect of inbreeding on haplo-diploid organisms has been regarded as ve ry low, because deleterious recessive genes on hemizygous (haploid) males w ere immediately purged generation by generation. However, we determined suc h recessive genes to decrease female fecundity in a population of Schizotet ranychus miscanthi Saito which is known in the Acari as a subsocial species with haplo-diploidy. In mother-son inbreeding experiments, there was no de pression in egg hatchability nor in the larval survival of progeny over fou r generations. There was, on the other hand, significant inbreeding depress ion in the fecundity with increasing f-value. Crosses between two lineages, one having deleterious effects on the fecundity and the other having no su ch effects, established during the inbreeding, revealed heterosis, and back crosses showed that the depression was caused by deleterious recessive(s). These results strongly suggest the existence of some deleterious genes gove rning only the traits of adult females in wild populations of haplo-diploid organisms.