F. Njiokou et al., The influence of self-fertilization and pairing on life-history traits in the freshwater snail Bulinus forskalii (Gastropoda, Planorbidae), ACT TROP, 76(2), 2000, pp. 159-167
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.