Multiple mating in a natural population of the isopod Sphaeroma rugicauda; evidence from distorted ratios in offspring

Fertilised females of the isopod Sphaeroma rugicauda were collected from a natural population. Offspring ratios at a diallelic phosphoglucose isomerase locus were determined for individual broods. Out of 211 broods 37 showed significant departures from Mendelian expectations. The pattern of distortion in broods segregating for two genotypes was consistent with a hypothesis of multiple mating under which two males contribute equally to the brood. The pattern of distortion in broods segregating for three genotypes was also compatible with multiple mating. However in this case the ratios deviate from those expected on the basis of the two male genotypes contributing equally to each brood.