Size-assortative mating and non-reciprocal copulation in a hermaphroditic intertidal limpet: test of the mate availability hypothesis |
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Authors: | Purba Pal Johan Erlandsson Martin Sköld |
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Institution: | 1. Department of Zoology and Entomology, Rhodes University, 6140, Grahamstown, South Africa 3. Department of Animal Ecology, Ecology Building, University of Lund, 223 62, Lund, Sweden 4. Tj?rn? Marine Biological Laboratory, 452 96, Str?mstad, Sweden 2. Centre for Mathematical Sciences, University of Lund, Lund, Sweden
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Abstract: | Mating behaviour and mating patterns are affected to a large extent by body size in both hermaphrodites and gonochorists.
Detailed research on mating patterns, mate choice, pre- and post-copulatory sexual selection in marine pulmonates is wanting,
thus warranting more attention as a study system in the future. The simultaneous hermaphroditic limpet Siphonaria capensis (Pulmonata: Basommatophora) shows size-dependent fecundity, and acts as a suitable organism to test the effects of body size
on mating patterns, mating success, gender expression and reciprocity in hermaphroditic marine gastropods. We mainly used
bootstrap resampling techniques to estimate the effects of different factors on mating patterns. In the populations studied,
a strong size-assortative mating pattern was observed, where small-scale spatial distribution of potential mating partners
(the mate availability hypothesis) could explain 65% of this pattern, while mate choice and mating constraints explaining
the rest. No significant difference in mating success between limpets with different body size was found, even though in one
population, the sperm recipients were larger than the non-copulating limpets. Interestingly, we found that intromission was
non-reciprocal during copulations. This may mean that this species does not conform to the common rule of reciprocity predicted
for hermaphrodites, unless there is sex-role alternation between individuals in a mating pair. The mating partners consisted
of similar sized, acting males and females, thus without any indication of the body size determining the gender expression.
The matings took place in early mornings only at spring tides and the animals were observed laying egg masses only during
neap tides. Since siphonariid limpets possess both a spermatheca and a seminal vesicle, which may have either a sperm storing
and/or digestive function, post-copulatory sexual selection (e.g., sperm competition) cannot be dismissed. |
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