Testes mass and reproductive mode of minnows

Most comparative analyses of relative testes: mass find that testes are lar ger 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 c omparative analysis of 37 minnow species. No significant differences were f ound for testes mass by spawning mode or sexual size dimorphism. These resu lts imply a lack of response to selection on testes size from sperm competi tion in minnow species. Possible explanations for the lack of the expected relationship between testes mass and mating systems in minnows are presente d.