Morphological innovation, ecological opportunity, and the radiation of a major vascular epiphyte lineage

Abstract

The emergence of angiosperm-dominated tropical forests in the Cretaceous led to major shifts in the composition of biodiversity on Earth. Among these was the rise to prominence of epiphytic plant lineages, which today comprise an estimated one-quarter of tropical vascular plant diversity. Among the most successful epiphytic groups is the Polypodiaceae, which comprises an estimated 1500 species and displays a remarkable breadth of morphological and ecological diversity. Using a time-calibrated phylogeny for 417 species, we characterized macroevolutionary patterns in the family, identified shifts in diversification rate, and identified traits that are potential drivers of diversification. We find high diversification rates throughout the family, evidence for a radiation in a large clade of Paleotropical species, and support for increased rates of diversification associated with traits including chlorophyllous spores and noncordiform gametophytes. Contrary to previous hypotheses, our results indicate epiphytic species and groups with humus-collecting leaves diversify at lower rates than the family as a whole. We find that diversification rates in the Polypodiaceae are positively correlated with changes in elevation. Repeated successful exploration of novel habitat types, rather than morphological innovation, appears to be the primary driver of diversification in this group.

A review of symbiotic fungal endophytes in lycophytes and ferns – a global phylogenetic and ecological perspective

“…They are interpreted as being primordially epiphytic (Schuettpelz and Pryer 2009;Sundue et al 2015) and concordantly have a below-average mycorrhization rate (45 %) and an even lower occurrence of confirmed AMF (16 %; Table 2). The Polypodiaeae show many anatomical features that can be interpreted as adaptations that compensate for the loss of the symbiotic partner: The root hairs are well developed and longlived; most species have thick, long-lasting rhizomes that store carbohydrates; species can be very drought resistant, with thick fronds, strong cuticles and dense indument of scales on the laminae; niche-forming leaves that act as leaf litter collectors have developed several times independently (Aglaomorpha, Drynaria, Platycerium) (Watkins and Cardelús 2012); domatia for ants, which not only defend their host plant but also fertilize it with their faeces, occur among pteridophytes only in this family (Lecanopteris, Solanopteris) (Kramer et al 1995;Dubuisson et al 2009).…”

“…; Zotz 2013). Several phylogenetic studies have focused on the evolution of epiphytism in pteridophytes in connection with the advent of angiospermdominated forests (Hennequin et al 2008;Schuettpelz and Pryer 2009;Sundue et al 2015), but have not included mycorrhizae as modulating factor in the evolution of ferns within this stressful ecological niche. Comparative studies between terrestrial and epiphytic orchids (Martos et al 2012) have shown that epiphytes are more conservative in their mycorrhizal partner, which indicates a more pronounced parallel evolution between plant and fungus than in the terrestrial species.…”

Rates of ecological divergence and body size evolution are correlated with species diversification in scaly tree ferns

“…Although the primary advantage of using rates of evolution is that these are time-independent [17,50], assuming constant rates of diversification within clades is probably a gross oversimplification [3,17,22]. The exploration of more complex models of trait evolution in scaly tree ferns, ideally with a complete time-calibrated phylogeny, might identify specific branches within clades where rate shifts have occurred [21,59], which would allow us to ascertain the direction of causality between ecological divergence, morphological change and species diversification.…”

“…Thus, adaptive models make a direct link between rates of species diversification and the rates of eco-morphological evolution among species. Alternatively, there are many instances where species diversification would not be correlated with phenotypic or ecological evolution [20,21]. In this case, species richness would be largely determined by other factors such as the age and distribution of lineages or environmental heterogeneity [10,22 -25].…”

Cyanobacteria in Terrestrial Symbiotic Systems

“…Rhizosphere associations between fungi and bacteria must have promoted the evolution of mycorrhizal symbioses and the subsequent diversification of seed plants. The radiation of modern ferns, bryophytes, fungal endophytes, and lichens was in turn facilitated by the diversification of seed plants (Schneider et al 2004;Schuettpelz and Pryer 2009;Feldberg et al 2014;Li et al 2014;Lóriga et al 2014;Sundue et al 2016).…”