Abstract
Cytological aspects of gametogenesis were investigated in populations of Gyrinicola batrachiensis (Oxyuroidea; Nematoda) from various anuran hosts. Populations parasitizing Rana clamitans reproduced by haplodiploidy. Females had eight chromosomes and oocytes underwent normal meiosis. Fertilized eggs containing eight chromosomes and unfertilized eggs containing four chromosomes were observed in the uterus of females. Males had four chromosomes and spermatozoa were produced mitotically. This is the first report of haplodiploidy in a nematode. Populations of G. batrachiensis parasitizing tadpoles in ponds where R. clamitans was absent reproduced by apomictic thelytoky. Females had six, seven, or eight chromosomes depending on the strain. There was no chromosome pairing nor bivalent formation. A diploid number of univalents divided to form a single polar body and a pronucleus. Apomictic strains of G. batrachiensis probably arose when mutations supressed the first meiotic division in haplodiploid strains. Apomictic females do not need to locate a mate and can begin to reproduce as soon as they are mature. Gyrinicola batrachiensis occurs only in the tadpole stage and apomictic strains are most successful in anurans in which the tadpole stage is brief.
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