LAUSR

PREMISE OF THE STUDY The successful establishment of polyploid species is hypothesized to be promoted by niche differentiation from the parental species, or by range shifts during climate oscillations. However, few studies have considered both causes simultaneously. Here we resolve the origin of a tetraploid fern, Lepisorus yamaokae, and explore a pattern of niche differentiation among the allotetraploid and parental species in past and current climates. METHODS We reconstructed phylogenetic trees based on plastid marker and single-copy nuclear genes to resolve the allopolyploid origin of L. yamaokae. We also evaluated climatic niche differentiation among L. yamaokae and its two parental species using species distribution models in geographic space, and principal component analysis. KEY RESULTS We infer that Lepisorus yamaokae had a single allotetraploid origin from L. annuifrons and L. uchiyamae. Climatic niche analyses show that the parental species currently occupy different niche spaces. The predicted distribution of the parental species at the Last Glacial Maximum (LGM) suggests more opportunities for hybridization during the LGM or during other recent temporary range shifts. Lepisorus yamaokae has a narrower niche than the additive niche of the parental species. We also observed niche conservatism in L. yamaokae. CONCLUSION Range shifts of the parental species during climatic oscillations in the Quaternary likely facilitated the formation and establishment of L. yamaokae. Further, the genetic intermediacy of L. yamaokae may have enabled a niche shift in its microenvironment, resulting in its successful establishment without a macroclimatic niche shift in L. yamaokae. This article is protected by copyright. All rights reserved.