STUDIES ON CROSS-FERTILIZATION AND SELF-FERTILIZATION IN LYMNAEA STAGNALIS APPRESSA SAY

Abstract

Pigmentation in Lymnaea stagnalis appressa is inherited as a simple Mendelian recessive. This fact was used as a tool in determining the relative percentage of cross-fertilization as compared with self-fertilization. Eighteen albino snails mated with homozygous pigmented snails and later maintained in isolation culture clearly showed in their progeny that cross-fertilization was the predominating process. During the first 50 days following isolation from the pigmented mates, the albino snails collectively produced over 80% pigmented progeny. After this period there was a gradual drop in the percentage of pigmented progeny until about the 100th day, when this percentage dropped very close to 0%. Pigmented sperm received by 1 albino snail was effective in fertilizing the eggs up to 116 days. Removal of intromittent organs and portions of the vas deferens did not prevent self-fertilization, suggesting that self-copulation was not necessary for self-fertilization. Ten albino snails, previously mated with pigmented snails and later crossed with other albino snails, did not transfer their pigmented sperm to the albinos. These results suggest that fertilization does not occur in the hermaphroditic duct as was suggested by another worker.