RT Journal Article SR Electronic T1 Inferring the Evolutionary Reduction of Corm Lobation in Isoëtes using Bayesian Model-Averaged Ancestral State Reconstruction JF bioRxiv FD Cold Spring Harbor Laboratory SP 212316 DO 10.1101/212316 A1 Forrest D. Freund A1 William A. Freyman A1 Carl J. Rothfels YR 2017 UL http://biorxiv.org/content/early/2017/11/01/212316.abstract AB Inferring the evolution of characters in Isoëtes has been problematic, as these plants are morphologically conservative and yet highly variable and homoplasious within that conserved base morphology. However, molecular phylogenies have given us a valuable tool to test hypothesis of character evolution within the genus. One such hypothesis is that extant Isoëtes have undergone a morphological reduction from larger arborescent lycophyte ancestors. In this work we examine the reduction in lobe numbers on the underground trunk, or corm, over evolutionary time. Using reversible-jump MCMC and Bayesian inference, our results support the hypothesis of a directional reduction in lobe number in Isoëtes, with the best-supported model of character evolution being one of irreversible reduction. Furthermore, the most probable ancestral corm lobe number of extant Isoëtes is three, and a reduction to two lobes has occurred at least six times. From our results, we can infer that corm lobation, like many other traits in Isoëtes, shows a degree of homoplasy, yet also shows ongoing evolutionary reduction.