Testes mass and reproductive mode of minnows

Most comparative analyses of relative testes: mass find that testes are larger in species in which more sperm competition is predicted (multiple males mate with individual females). I tested for differences in adjusted testes mass (for body mass) by spawning mode and by sexual size dimorphism in a comparative analysis of 37 minnow species. No significant differences were found for testes mass by spawning mode or sexual size dimorphism. These results imply a lack of response to selection on testes size from sperm competition in minnow species. Possible explanations for the lack of the expected relationship between testes mass and mating systems in minnows are presented.