Quantification and analysis of variation in leaf shape: Climate signals in dicot leaves and evolution of leaf form in Pleopeltis (Polypodiaceae).

摘要

Charles Darwin described the study of morphology as "the most interesting department of natural history." Geometric morphometrics endeavors to advance that field through the development of quantitative metrics of shape.; I undertook two studies to better understand the ecological and evolutionary patterns of leaf shape variation. First, I assessed the degree to which dicotyledonous leaf shape relates to climate. Second, I examined the evolution of fern leaves with divergent morphologies. Studies in both of these fields have been limited by the tools available to quantify morphology.; Using leaves from a diverse range of climates, I tested eigenshape analysis as a means to decompose shape variation into meaningful shape variables. I found that dicotyledonous leaf form can be described using twenty quantitative shape characters, of which eight had an association with climate.; The fern genus Pleopeltis (Polypodiaceae) is characterized by multiple origins of simple leaves within clades of dissected leaves (the archetypal fern frond). I developed a novel analytic approach to compare simple and dissected leaves and demonstrated that controlling for curvature was crucial to extraction of meaningful shape measures. To better understand the resulting shape variables, I developed an asymmetry metric able to give both the type and strength of asymmetry in individual characters extracted by eigenshape analysis.; Dimorphy between fertile and sterile leaves was shown to be widespread in Pleopeltis, and fundamentally different between simple- and dissected-leaf species, supporting laminar reduction as the cause. Further work demonstrated considerable covariation among tip, base, and overall shape. This work demonstrated that patterns of shape variation and covariation are comparable between simple and dissected leaves, and provided evidence for a different developmental program in the murorum-lanceolatum clade.; This work has produced new tools and methods for the study of leaf form, as well as the open-source platform Morph-tools.net to deliver these tools to a broad audience. The results of the leaf-climate study indicated that eigenshape-generated measures of leaf shape merit further exploration for models estimating paleoclimate parameters. The Pleopeltis study has yielded insights into the degree and manner in which shared developmental machinery impacts shape variation between divergent leaf forms in ferns.