Abstract
BackgroundSperm size and quality are key factors for fertilization success. There is increasing empirical evidence demonstrating that sperm form and function are influenced by selective pressures. Theoretical models predict that sperm competition could favour the evolution of longer sperm. In hermaphrodites, self-fertilizing species are expected to have shorter sperm than cross-fertilizing species, which use sperm stored from several mating partners for the fertilization of their eggs and thus are exposed to intense sperm competition. We tested this hypothesis by comparing original data on sperm length in 57 species of simultaneously hermaphroditic stylommatophoran gastropods from Europe and South America with respect to the species’ breeding system. We used 28S rRNA nuclear and COI mitochondrial sequence data to construct a molecular phylogeny. Phylogenetic generalized linear models were applied to examine the potential influence of morphological and life-history characters.ResultsThe best-fit model revealed that the breeding system and age at sexual maturity influence sperm length in gastropods. In general, species with predominant cross-fertilization had longer sperm than species with predominant self-fertilization or a mixed breeding system. Across species with shells (snails), sperm length also increased with shell size.ConclusionsOur study provides evidence that sperm length in stylommatophoran gastropods is influenced by the risk of sperm competition, as well as by age at sexual maturity and shell size. This finding extends present knowledge of sperm evolution to a group of so far poorly studied simultaneous hermaphrodites.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0661-9) contains supplementary material, which is available to authorized users.
Highlights
Sperm size and quality are key factors for fertilization success
Positive relationships between sperm length and sperm competition risk have been found across nematodes [12], butterflies [13], moths [14], and frogs [15], but not in Scathophagidae [16], while the results from studies of birds vary among taxa [17]
Interspecific variation in sperm traits The gastropod species examined differed significantly in total sperm length with mean values ranging from 101.4 μm to 1340.9 μm (Table 1; F56,94 = 3093.3, p < 0.001)
Summary
Sperm size and quality are key factors for fertilization success. There is increasing empirical evidence demonstrating that sperm form and function are influenced by selective pressures. Self-fertilizing species are expected to have shorter sperm than cross-fertilizing species, which use sperm stored from several mating partners for the fertilization of their eggs and are exposed to intense sperm competition. We tested this hypothesis by comparing original data on sperm length in 57 species of simultaneously hermaphroditic stylommatophoran gastropods from Europe and South America with respect to the species’ breeding system. Theory predicts that sperm size can increase with sperm competition risk when longer sperm achieve a higher fertilization success than shorter sperm [10, 11]. Our understanding of how sperm competition influences sperm size and Schmera et al BMC Evolutionary Biology (2016) 16:89 structure is hampered by lack of understanding of sperm function [4, 19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
