S6.3c Adaptive dynamics in experimental populations of Aspergillus nidulans

S6.3 FUNGAL ADAPTATION AND EVOLUTION, SEPTEMBER 22, 2022, 4:45 PM - 6:15 PM: : A total of 12 replicate populations initiated with a laboratory strain of the ascomycete fungus Aspergillus nidulans evolved on synthetic minimal glucose agar medium for 1 year, using weekly transfers of 1% of the produced asexual spores to fresh medium. This Aspergillus short-term evolution experiment (ASEX) was designed to understand how filamentous fungi adapt to growth on limited carbon in a spatially structured environment. We observed no systematic improvement in the fitness components tested and neither in the competitive fitness relative to the ancestor. Instead, we observed the repeated evolution of at least two morphotypes, with a fluffy-like (FL) or an ancestor-like (AL) colony morphology, leading to non-transitive fitness interactions among isolates in two selected populations. The genomic analyses of clones from all 12 populations at an early (week 10) and the final time point (week 52), show a clear role of natural selection during ASEX. We also observed a shared genetic basis and different timing of adaptation of AL and FL types. In addition, in most populations, both morphotypes do not form monophyletic groups, but they frequently disappear and re-evolve from ancestral forms of both types. Reduction in asexual spore yield, the most evident parallel phenotypic change found in all our evolved populations, is not due to the direct selection of genes involved in asexual reproduction. Instead, we argue that reduced spore yield is a pleiotropic effect of adaptive changes in metabolism.