Incipient Reproductive Isolation between Geographic Populations of Ophryotrocha labronica (Polychaeta, Dorvilleidae)

Åkesson, B. (Department of Zoology, University of Gothenburg, Göteborg, Sweden.) Incipient reproductive isolation between geographic populations of Ophryotrocha labronica (Polychaeta, Dorvilleidae). Zocl. Scripta 1 (5): 207–210, 1972.–The mechanism of sex determination and the incipient reproductive isolation between geographic populations of Ophryotrocha labronica are studied in intra- and interpopulation crosses. Two populations from the Naples area and one from Leghorn are employed in the crosses. The considerable genetic difference between the Leghorn population and any of the Naples populations is reflected in some crossing combinations by changes in sex ratios, by occurrence of individuals with a reduced viability in the progeny, by a decreased mating propensity, and by discrimination of mates from alien populations. It is stated that the changes in sex ratios, the decreased mating propensity, the dwarfed individuals in the progeny, and the preferential mating all reflect the incompatibility of gene complexes. The differences between reciprocal crosses are not fully explained. The occurrence of extranuclear DNA, as well as the existence of a maternal heredity in intrapopulation crosses, indicate that cytoplasmic inheritance may be one of the factors behind these reciprocal differences.