The effect of isolation on the life-history traits of Pseodosuccinea columella (Pulmonata : Lymnaeidae)

A population of Pseudosuccinea columella was raised under laboratory condit ions and its life tables were determined in isolated and paired snails. Iso lated snails were significantly larger in shell size than paired snails fro m five weeks of age onward. Also, statistically significant differences wer e found for the number of eggs per mass per individual from week 5 to 9, is olated snails exhibiting the highest values. The intrinsic and finite rates of increase were greater in isolated than in paired snails. Either an inhi bition of the reproductive output between individuals or the advantage of s elling may be the cause of the differences in this species, acting as a pos sible mechanism that increase the fitness of isolated snails.