The influence of self-fertilization and pairing on life-history traits in the freshwater snail Bulinus forskalii (Gastropoda, Planorbidae)

This study analyses the basic reproductive biology of the schistosonie-vect or snail Bulinus forskalli. This hermaphroditic species can self-fertilize. Variation of the mating system was analysed in two populations from Camero on in a three-step experiment. (i) The fecundity (number of eggs and of egg capsules) of isolated virgin individuals from both populations was followe d over a month, as well as the survival of offspring from these individuals . Estimates of these parameters were intermediate. Our results also indicat e that inbreeding depression has a maximum value of about one-half in both populations. No difference was observed between populations for both the ov erall fecundity of adults and survival of offspring. (ii) Individuals were then paired either within, or between populations over three successive day s, and the number of copulations recorded. Copulations were observed in all situations, including between-population pairs. No significant dlifference in the number of copulations per pair was detected. However, this value de creased with time, and reciprocal copulations were significantly less numer ous between than within populations. (iii) Individuals that successfully co pulated as female in (ii) were isolated, and their fecundity was followed o ver 3 weeks. The fecundity of individuals that had been maintained isolated over the whole experiment served as a control. No significant difference w as on the whole detected. Our results collectively suggest that the individ uals from the two populations studied are rather selfers, confirming that B . forskalii is a preferentially selfing species. There is also some pre-zyg otic isolation against crosses between populations. (C) 2000 Elsevier Scien ce B.V. All rights reserved.