Social facilitation affects longevity and lifetime reproductive success ina self-fertilizing land snail

Factors that reduce the reproductive output of self-fertilizing hermaphrodi tes are receiving increasing attention. The combined effects of reduced Fec undity of selfing parents and inbreeding depression of the progeny have bee n referred to as self-fertilization depression. In isolated freshwater snai ls the reproductive output of selfing individuals also decreases due to the lack of social facilitation (absence of a conspecific). We examined the ef fect of social facilitation on lifetime reproductive success (number of you ng produced and longevity) over two generations in the simultaneously herma phroditic land snail Balea perversa. In a parallel study we showed that B. perversa kept singly and in pairs reproduced exclusively by self-fertilizat ion. In the parent generation, snails kept singly produced less offspring t han snails kept in pairs. The difference in lifetime number of young was ma inly due to differences in adult life span. Snails of the two groups did no t differ in reproductive rate (number of young produced per 100 d of reprod uctive life) and hatchling size. In the offspring generation, snails kept s ingly did not differ from individuals kept in pairs in the lifetime number of young and hatchling survival. As in the parent generation, snails kept s ingly reproduced during a shorter period than snails kept in pairs. However . the shorter reproductive life span of snails kept singly was compensated for by a slightly (but not significantly) higher reproductive rate which re sulted in a similar number of offspring produced for both groups. In both g enerations, snails of the two groups did not differ in size at first reprod uction, adult growth rate and size at death. These findings suggest that so cial facilitation may affect longevity in selfing B. perversa.