Inheritance of colour polymorphism and the pattern of sperm competition in the apple snail Pomacea canaliculata (Gastropoda: Ampullariidae)

The mode of inheritance of body colour polymorphism (yellow or brown) was studied in the apple snail Pomacea canaliculata. Analyses of snail body colour over three generations showed that the yellow colour follows simple Mendelian inheritance, being recessive to brown. There were no deleterious effects of the yellow colour gene on the number of eggs per egg mass, egg weight, hatchability, daily egg mass production, or survival of the snails carrying it. By using the yellow colour as a genetic marker, the pattern of sperm competition was investigated. When two males (yellow and brown) were mated successively to a yellow female, sperm of the first male were displaced by the second male in all 10 cases studied. However, the duration needed for complete displacement varied among females, from just after the male exchange (within 4 days) up to 38 days. Yellow males had a comparable reproductive success to that of brown males.