Estimates of natural allosperm storage capacity and self-fertilization rate in the hermaphroditic freshwater pulmonate snail, Physa acuta

Abstract

Summary Previous estimates of allosperm storage capacities and self-fertilization rates in pulmonate snails have been derived almost exclusively from laboratory mating experiments. Here we report observations on a single adult albino Physa acuta collected from a natural pond in Charleston, South Carolina. Cultured in isolation from August 2002 until its death in February, this individual laid an average of 78.3 eggs per week (s.e.m. = 6.2), with a hatching success of 35.1% and an overall frequency of albino (putatively selfed) offspring of 6.4%. We found no evidence of reduced fecundity, reduced offspring viability, or increased self-fertilization over 20 weeks of observation, suggesting that stores of allosperm at no time approached exhaustion. We suggest that self-fertilization in primarily outcrossing populations of pulmonate snails may not be an adaptation, but rather may be a consequence of inefficiency in the mechanism sorting autosperm from allosperm.