The influence of self-fertilization performance and copulation behaviour in reproduction by cross-fertilization in groups of Biomphalaria tenagophila (Mollusca, Planorbidae)

RESUMO

The following hypothesis were tested for groups of simultaneous hermaphrodites Biompharia tenagophila (a) snails that have 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 per cent ("good reproducers") and the other less than 10 per cent ("bad reproducers"). All pigmented snails had viability rates higher than 70 per cent. The "good" and "bad" reproducer albine snails had similar copulation behaviour. However, after the end of grouping, the "bad reproducers" continued to have viability rates less than 10 per cent over 30 days. In 100 per cent 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/eggs-mass). However, in 100 per cent of cases that pigmented snails copulated with both partners, the "good" reproducer albine snails produced none or very few embryos (the highest average was 2.2 pigmented embryos/eggs-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 partner reproductive success.