Parental effects in a filamentous fungus: phenotype, fitness, and mechanism

Adaptation to changing environments often requires meaningful phenotypic modifications to match the current conditions. However, obtaining information about the surroundings during an organism’s own lifetime may only permit accommodating relatively late developmental modifications. Therefore, it may be advantageous to rely on inter-generational or trans-generational cues that provide information about the environment as early as possible to allow development along an optimal trajectory. Transfer of information or resources across generations, known as parental effects, is well documented in animals and plants but not in other eukaryotes, such as fungi. Understanding parental effects and their evolutionary consequences in fungi is of vital importance as they perform crucial ecosystem functions. In this study, we investigated whether parental effects are present in the filamentous fungus Neurospora crassa, how long do they last, are the effects adaptive, and what is their mechanism. We performed a fully factorial match / mismatch experiment for a good and poor quality environment, in which we measured mycelium size of strains that experienced either a matched or mismatched environment in their previous generation. We found a strong silver spoon effect in initial mycelium growth, which lasted for one generation, and increased fitness during competition experiments. By using deletion mutants that lacked key genes in epigenetic processes, we show that epigenetic mechanisms are not involved in this effect. Instead, we show that spore glycogen content, glucose availability and a radical transcription shift in spores are the main mechanisms behind this parental effect.