Abstract Detail


Testo, Weston [1], Sundue, Michael A. [2].

Are rates of species diversification and body size evolution coupled in the ferns?

Evolutionary biologists have long sought to understand the relationship between species diversification and morphological evolution. Theory predicts that rates of morphological evolution and diversification should often be correlated, particularly in cases where morphological innovation promotes ecological divergence, leading to speciation. Previous research found this was the case in tree ferns (Cyatheaceae), but not so in the primarily epiphytic Polyodiaceae. Here, we use a comparative phylogenetic approach to test the hypothesis that rates of body size evolution and lineage diversification are positively correlated across the fern phylogeny. We used a large time-calibrated phylogeny that including nearly 40% of extant fern diversity, calibrated with 26 fossil taxa. We used mean leaf area as a body size proxy. Rates of diversification (speciation, extinction, and net diversification) and body size evolution were independently estimated using the program BAMM v.2.5.0. We performed PICs of log-transformed body size evolution rates against log-transformed diversification rates to test our hypotheses. We find that rates of body size evolution and lineage diversification are decoupled across the fern phylogeny; thus, we reject our hypothesis that these rates would be positively correlated. Support for a correlation between body size evolution and diversification rates was not significant for either epiphytic or terrestrial taxa, and we conclude that the primary mode(s) of speciation in ferns is unrelated to divergence in leaf area. Unlike groups where morphological evolution and lineage proliferation have been shown to correlate, speciation in ferns appears to be driven primarily by a combination of geographic isolation, hybridization, and ecophysiological specialization. None of these processes are intrinsically linked to changes in body size. Under several evolutionary scenarios, morphological evolution and lineage diversification should not be correlated. Non-adaptive radiations, for example, are characterized by periods of elevated diversification without appreciable corresponding functional divergence. Among plants, such radiations are generally considered to be associated with highly dynamic climate and habitat conditions and this appears to hold true for ferns, with montane forests playing a particularly important role. Our study highlights the importance of using a densely and broadly sampled phylogeny as a framework for investigating macroevolutionary patterns across a variety of clades, rather than attempting to generalize findings based on the study of the radiation of a single group. It also provides a context for appreciating and understanding the exceptional diversity of leaf sizes in the ferns: as a marker of their collectively broad ecological amplitude, not a correlate of their rapid diversification.

1 - University Of Florida, 313 NW 2nd St, Gainesville, FL, 32601, United States
2 - University of Vermont, The Pringle Herbarium, Department of Plant Biology, Burlington, VT, 05405, USA

adaptive radiation
Leaf size.

Presentation Type: Oral Paper
Abstract ID:481
Candidate for Awards:None

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