The following hypotheses were tested for groups of simultaneous
hermaphrodites Biomphalaria tenagophila: (a) snails that have low
reproductive success during the process of self-fertilization do not
increase their reproductive success after the end of grouping; (b) the
copulation behaviour and the presence of one snail whose eggs have a low
viability rate influence the partner's reproductive success by
cross-fertilization. Groups were constituted by a homozygous pigmented
snail and two albinos: one with a viability rate higher than 70% ("good
reproducers") and the other less than 10% ("bad reproducers"). All
pigmented snails had viability rates higher than 70%. The "good" and "bad"
reproducer albino snails had similar copulation behaviour. However, after
the end of grouping, the "bad reproducers" continued to have viability
rates less than 10% over 30 days. In 100% of the cases that pigmented
snails copulated (performing either a male role or simultaneously male and
female roles) exclusively with "good" reproducer albinos, they presented
high reproductive success (producing, on average of 8.4 pigmented
embryos/egg-mass). However, in 100% of the cases that pigmented snails
copulated with both partners, the "good" reproducer albino snails produced
none or very few embryos (the highest average was 2.2 pigmented
embryos/egg-mass). Therefore, the production of viable embryos by
cross-fertilization was more influenced by self-fertilization performance
than by copulation behaviour. The presence of a snail whose eggs have a low
viability rate could decrease their partners reproductive success.
