Niche and phenotypic differentiation in fern hybrid speciation, a case study of Pteris fauriei (Pteridaceae).

Abstract

Niche differentiation is a critical issue in speciation. Although it has a well-known role in adaptive processes of hybrid angiosperms, it is less understood in hybrid ferns. Here we investigate whether an intermediate ecological niche of a fern hybrid is a novel adaptation that provides insights into fern hybrid speciation. Pteris fauriei (Pteridaceae) is a natural hybrid fern, occurring environments between its parent species. The maternal P. minor is found in sunny areas, but the habitat of the paternal P. latipinna is shady. We combined data from morphology, leaf anatomy, and photosynthetic traits to explore adaptation and differentiation, along with measuring the environmental features of their niches. We also performed experiments in a common garden to understand ecological plasticity. The hybrid P. fauriei is intermediate between the parent species in stomatal density, leaf anatomical features, and photosynthetic characteristics in both natural habitats and a common garden. Interestingly, the maternal P. minor showed significant environmental plasticity and was more similar to the hybrid P. fauriei in the common garden, suggesting that the maternal species experiences stress in its natural habitats but thrives in the environments similar to the hybrid's. Based on the similar niche preferences of the hybrid and parents, we propose hybrid superiority. Our results indicate that the hybrid P. fauriei exhibits greater fitness and can compete with and occupy the initial niches of the maternal P. minor. Consequently, we suggest that the maternal P. minor has experienced a niche shift, elucidating the pattern of niche differentiation in this hybrid group. These findings offer a potential explanation for the frequent occurrence of hybridization in ferns and provide novel insights into fern hybrid speciation, enhancing our understanding of fern diversity.