Sexual selection, sperm competition and reproductive strategies in simultaneous hermaphrodites

Bruno Baur , Ellen Reinartz

The study of sexual selection attempts to explain the evolution of structures and behaviour associated with reproduction. Thus far, theories on sexual selection have been developed and tested almost exclusively in species of separate sexes (gonochorists), such as insects, birds and mammals. We investigate different aspects of sexual selection in simultaneous hermaphrodites. Since simultaneous hermaphrodites combine a female and a male function, conflicts arise within and between individuals that do not exist in gonochorists. Land snails with different reproductive systems (both facultative and obligate selfing and outcrossing) have been chosen as study objects because experimental manipulations and laboratory breeding can be performed with relative ease.
It has been proposed that the sexual conflict between the two genders in simultaneous hermaphrodites could be resolved by gamete trading. Theory predicts that sperm trading should occur in hermaphrodites in which the female role controls fertilization, e.g. in gastropods with a gametolytic gland and/or sperm storage such as the land snail Arianta arbustorum. We examined whether individuals of A. arbustorum adjust the number of sperm they release to the number they receive from their mating partner (i.e. whether sperm trading occurs). There was a high degree of reciprocity in spermatophore transfer: in 45 of the 46 investigated mating pairs both partners delivered a spermatophore which contained spermatozoa. The number of sperm transferred ranged from 0.8 Mio. to 4.0 Mio (mean = 2.2 Mio; N = 91). However, the numbers of sperm transferred by the two mating partners were not correlated. This indicates that sperm trading does not occur in this simultaneously hermaphroditic land snail. We also examined whether individuals of A. arbustorum differentially release sperm to virgin or non-virgin partners with respect to the potential risk of sperm competition in a given mating. The results indicate that individuals of A. arbustorum are not able to adjust sperm expenditure to the mating history of the partner.

Keywords: sex allocation - gastropods - snail - sperm size - reproductive conflict

Selected publications

Baur B & Baur A (2017) — Reproductive strategies in stylommatophoran gastropods — In: Physiology of Molluscs: a Collection of Selected Reviews, Volume 2 (Saleuddin,S  & Mukai S, eds). Apple Academic Press, Waretown, New Jersey: 311–377

Schmera D, Pizá J, Reinartz E, Ursenbacher S & Baur B (2016) — Breeding system, shell size and age at sexual maturity affect sperm length in stylommatophoran gastropods — BMC Evolutionary Biology 16: 89

Janssen R & Baur B (2015) — Seasonal effects on egg production and level of paternity in a natural population of a simultaneous hermaphrodite snail — Ecology and Evolution 5: 2916–2928

Häussler EM, Schmera D, Baur A & Baur B (2014) — Random mating with respect to mating status in the simultaneously hermaphroditic land snail Arianta arbustorum — Invertebrate Reproduction and Development: 58: 115–123

Häussler EM, Schmera D & Baur B (2014) — Parasitic mites influence intra- and interpopulational variation in sperm length in a simultaneous hermaphrodite land snail (Gastropoda: Helicidae) — Biological Journal of the Linnean Society 113: 1036–1046

Minoretti N, Stoll P & Baur B (2013) — Heritability of sperm length and shell size in the land snail Arianta arbustorum — Journal of Molluscan Studies 79: 218–224

Kupfernagel S, Beier K, Janssen R, Rusterholz H-P, Baur A & Baur B (2013) — An immunolabelling technique to track sperm from different mates in the female reproductive organs of terrestrial gastropods — Malacologia 56: 253–266

Häussler EM, Piza J, Schmera D & Baur B (2012) — Intensity of parasitic mite infection decreases with hibernation duration of the host snail — Parasitology 139: 1038–1044

Kupfernagel S & Baur B (2011) — Partial precopulatory isolation between two geographically distant populations of the land snail Arianta arbustorum (L.) — Journal of Molluscan Studies 77: 87–94

Minoretti N, Schmera D, Kupfernagel S, Zschokke S, Armbruster GFJ, Beese K, Baur A & Baur B (2011) — Determinants of female and male reproductive success in a simultaneous hermaphrodite land snail — Animal Behaviour 82: 707–715

Kupfernagel S, Rusterholz H-P & Baur B (2010) — Variation in multiple paternity and sperm utilization patterns in natural populations of a simultaneous hermaphrodite land snail — Biological Journal of the Linnean Society 99: 350–361

Schüpbach HU & Baur B (2010) — Contact-based transmission models in terrestrial gastropod populations infected with parasitic mites — International Journal for Parasitology 40: 1045–1050

Schüpbach HU & Baur B (2010) — Within- and among-family variation in parasite load and parasite-induced mortality in the land snail Arianta arbustorum, a host of parasitic mites — Journal of Parasitology 96: 830–832


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