Origin and evolution of carnivorism in the Ascomycota (fungi).

Carnivorism is one of the basic life strategies of fungi. Carnivorous fungi possess the ability to trap and digest their preys by sophisticated trapping devices. However, the origin and development of fungal carnivorism remains a gap in evolution biology. In this study, five protein-encoding genes were used to construct the phylogeny of the carnivorous fungi in the phylum Ascomycota; these fungi prey on nematodes by means of specialized trapping structures such as constricting rings and adhesive traps. Our analysis revealed a definitive pattern of evolutionary development for these trapping structures. Molecular clock calibration based on two fossil records revealed that fungal carnivorism diverged from saprophytism about 419 Mya, which was after the origin of nematodes about 550-600 Mya. Active carnivorism (fungi with constricting rings) and passive carnivorism (fungi with adhesive traps) diverged from each other around 246 Mya, shortly after the occurrence of the Permian-Triassic extinction event about 251.4 Mya. The major adhesive traps evolved around 198-208 Mya, which was within the time frame of the Triassic-Jurassic extinction event about 201.4 Mya. However, no major carnivorous ascomycetes divergence was correlated to the Cretaceous-Tertiary extinction event, which occurred more recently (about 65.5 Mya). Therefore, a causal relationship between mass extinction events and fungal carnivorism evolution is not validated in this study. More evidence including additional fossil records is needed to establish if fungal carnivorism evolution was a response to mass extinction events.