Sperm competition and maternal effects differentially influence testis and sperm size in Callosobruchus maculatus

<p>The evolutionary factors affecting testis size are well documented, with spermcompetition being of major importance. However, the factors affecting spermlength are not well understood; there are no clear theoretical predictions andthe empirical evidence is inconsistent. Recently, maternal effects have beenimplicated in sperm length variation, a finding that may offer insights into itsevolution. We investigated potential proximate and microevolutionary factorsinfluencing testis and sperm size in the bruchid beetle Callosobruchus maculatususing a combined approach of an artificial evolution experiment over 90generations and an environmental effects study. We found that whilepolyandry seems to select for larger testes, it had no detectable effect onsperm length. Furthermore, population density, a proximate indicator ofsperm competition risk, was not significantly associated with sperm length ortestis size variation. However, there were strong maternal effects influencing sperm length.</p>