Manchester, S. R. | Search bioRxiv

bioRxiv2023

Spatial phylogenetics of Fagales: Investigating the history of temperate forests

AimQuantifying the phylogenetic diversity of temperate trees is essential for understanding what processes are implicated in shaping the modern distribution of temperate broadleaf forest and other major forest biomes. Here we focus on Fagales, an iconic member of forests worldwide, to uncover global diversity and endemism patterns and investigate potential drivers responsible for the spatial distribution of fagalean forest communities. LocationGlobal. TaxonFagales. MethodsWe combined phylogenetic data covering 60.2% of living species, fine-scale distribution models covering 90% of species, and nodulation data covering all species to investigate the distribution of species richness at fine spatial scales and compare this to relative phylogenetic diversity (RPD) and phylogenetic endemism. Further, we quantify phylogenetic betadiversity and bioregionalization of Fagales and determine hotspots of Fagales species engaging in root nodule symbiosis (RNS) with nitrogen-fixing actinomycetes. ResultsWe find the highest richness in temperate east Asia, eastern North America, and equatorial montane regions of Asia and Central America. By contrast, RPD is highest at higher latitudes, where RNS also predominates. We found a strong spatial structuring of regionalizations of Fagales floras as defined by phylogeny and traits related to RNS, reflecting distinct Northern and Southern Hemisphere floras (with the exception of a unique Afro-Boreal region) and highly distinct tropical montane communities. Main conclusionsSpecies richness and phylogenetic regionalization accord well with traditional biogeographic concepts for temperate forests, but RPD does not. This may reflect ecological filtering specific to Fagales, as RNS strategies are almost universal in the highest RPD regions. Our results highlight the importance of global-scale, clade-specific spatial phylogenetics and its utility for understanding the history behind temperate forest diversity.

evolutionary biology↗

bioRxiv2023

Fagalean phylogeny in a nutshell: Chronicling the diversification history of Fagales

Reconstructing the biogeographical history and timing of the diversification of temperate forests is essential for understanding their history and resolving uncertainties about how flowering plants emerged from their deep tropical origins to dominate in todays freezing terrestrial environments. The angiosperm order Fagales, comprising iconic components of temperate forests worldwide with an extensive fossil record, are an excellent plant system in which to apply a fossil-aware paradigm, such as the fossilized birth-death (FBD) process, for investigating the macroevolution of temperate forest biomes. Here, we improve upon previous efforts to resolve phylogeny and incorporate fossils in Fagales using low-copy nuclear loci and an expanded morphological matrix to reevaluate the Fagales fossil record and: (1) infer the phylogenetic relationships and the time of origin of the clade using the FBD model as implemented in RevBayes, (2) provide a framework for evaluating the climatic and biogeographic history of Fagales, and (3) investigate how the inclusion of fossils via the FBD method influences ancestral reconstruction and diversification estimation. The phylogenetic relationships we recovered are conventional except for the position of Nothofagaceae, while our inferred ages support older timelines than previously proposed, with a mid-Cretaceous date for the most recent common ancestor (MRCA) of the order. Biogeographical analysis shows an origin of Fagales consistent with an ancestral circumboreal temperate distribution corroborated by ancestral niche reconstructions. While distributions today largely reflect the general conservatism of temperate forests, we identified two episodes of high diversification, one at the mid-Cretaceous origin of the clade and the other continuing from the Miocene to the present. Removing fossil taxa from the tree reveals a different story, shifting the origin of extant families from North America to East Asia, reflecting refugial distributions in this biodiversity "museum" and implying a general bias towards low extinction areas in biogeographic reconstruction. Likewise, without fossil data, diversification estimates were higher and unable to detect an early diversification burst. Based on our analyses, we close with recommendations regarding the interpretation of estimates of diversification and ancestral state reconstruction using phylogenetic trees with only extant species as tips.

plant biology↗