Sexual selection favours investment in traits that improve the likelihood of fertilization given limited access to opposite-sex gametes due to competition with members of the same sex and is generally considered to be a significant component of natural selection. Sexual selection is the component of natural selection associated with variation in mating success. We compare these findings with examples of sperm and pollen competition and show that many similarities between these systems and nuclear competition in mushrooms exist. We did not find trade-offs between male reproductive success and other fitness components. The one line with net reduced competitive fitness had increased spore production, but reduced fertilisation efficiency. In two lines, fitness change was also accompanied by increased spore production.
Even though only two of those five remained significant after correcting for multiple comparisons, for all five lines we found a correlation between the efficiency with which the female mycelium is accessed and fitness, providing additional circumstantial evidence for fitness change in those five lines. From the twelve tested evolved lines, four had increased and one had decreased fitness relative to an unevolved competitor. In our setup, an evolving population of nuclei was serially mated with a non-evolving female mycelium for 20 sexual generations. These fertilizing ‘male’ nuclei migrate through the receiving ‘female’ mycelium. Mating in mushroom fungi occurs by donation of nuclei to a mycelium. We test the hypothesis that sexual selection can increase competitive fitness during mating, using experimental evolution in the mushroom-forming fungus Schizophyllum commune (Basidiomycota). In fungi, similar processes have not been shown directly yet. In animals and plants, sperm and pollen competition have yielded many interesting adaptations for improved mating success. When many gametes compete to fertilize a limited number of compatible gametes, sexual selection will favour traits that increase competitive success during mating.
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