Historical reconstruction of climatic and elevation preferences and the evolution of cloud forest-adapted tree ferns in Mesoamerica

Abstract

BackgroundCloud forests, characterized by a persistent, frequent or seasonal low-level cloud cover and fragmented distribution, are one of the most threatened habitats, especially in the Neotropics. Tree ferns are among the most conspicuous elements in these forests, and ferns are restricted to regions in which minimum temperatures rarely drop below freezing and rainfall is high and evenly distributed around the year. Current phylogeographic data suggest that some of the cloud forest-adapted species remained in situ or expanded to the lowlands during glacial cycles and contracted allopatrically during the interglacials. Although the observed genetic signals of population size changes of cloud forest-adapted species including tree ferns correspond to predicted changes by Pleistocene climate change dynamics, the observed patterns of intraspecific lineage divergence showed temporal incongruence.MethodsHere we combined phylogenetic analyses, ancestral area reconstruction, and divergence time estimates with climatic and altitudinal data (environmental space) for phenotypic traits of tree fern species to make inferences about evolutionary processes in deep time. We used phylogenetic Bayesian inference and geographic and altitudinal distribution of tree ferns to investigate ancestral area and elevation and environmental preferences of Mesoamerican tree ferns. The phylogeny was then used to estimate divergence times and ask whether the ancestral area and elevation and environmental shifts were linked to climatic events and historical climatic preferences.ResultsBayesian trees retrieved Cyathea, Alsophyla, Gymnosphaera and Sphaeropteris in monophyletic clades. Splits for species in these genera found in Mesoamerican cloud forests are recent, from the Neogene to the Quaternary, Australia was identified as the ancestral area for the clades of these genera, except for Gymnosphaera that was Mesoamerica. Climate tolerance was not divergent from hypothesized ancestors for the most significant variables or elevation. For elevational shifts, we found repeated change from low to high elevations.ConclusionsOur data suggest that representatives of Cyatheaceae main lineages migrated from Australia to Mesoamerican cloud forests in different times and have persisted in these environmentally unstable areas but extant species diverged recentrly from their ancestors.

Rates of molecular evolution in tree ferns are associated with body size, environmental temperature, and biological productivity

“…, ; Ramírez‐Barahona and Luna‐Vega ; Sosa et al. ). To reduce statistical bias, we removed duplicate occurrence records identified using a 0.1 × 0.1 decimal degree grid.…”

“…; Sosa et al. ): (1) altitude; (2) mean annual temperature; (3) temperature seasonality; (4) annual precipitation; (5) precipitation seasonality; and (6) soil water balance. We also estimated the mean normalized difference vegetation index (NDVI) for each species, which was used as a proxy of biological productivity within the geographic region inhabited by each species (Running ).…”

“…These data were updated, verified, and complemented using information from monographic studies (see Methods S1 for references). The distribution data have been previously used in biogeographic studies (Ramírez-Barahona et al 2011Ramírez-Barahona and Luna-Vega 2015;Sosa et al 2016). To reduce statistical bias, we removed duplicate occurrence records identified using a 0.1 × 0.1 decimal degree grid.…”

“…For each species, we estimated mean values for six environmental variables that are ecologically relevant for plants in general and for tree ferns in particular (Page 2002;Ramírez-Barahona et al 2016;Sosa et al 2016): (1) altitude; (2) mean annual temperature; (3) temperature seasonality; (4) annual precipitation; (5) precipitation seasonality; and (6) soil water balance. We also estimated the mean normalized difference vegetation index (NDVI) for each species, which was used as a proxy of biological productivity within the geographic region inhabited by each species (Running 1990).…”

“…Several lineages exhibit a large variation in body size among species, from small ferns less than 1 m in height to massive tree-like ferns up to 20 m high Noben and Lehnert 2013). In addition, although core tree ferns have maintained a broadly stable climatic niche throughout geological time-particularly in terms of humidity and temperature-there is evidence for multiple colonization events into "new" ecological niches in unrelated groups Bystriakova et al 2011;Ramírez-Barahona et al 2016;Sosa et al 2016).…”