Morphometric analysis of Passiflora leaves: the relationship between landmarks of the vasculature and elliptical Fourier descriptors of the blade

Abstract

Background: Leaf shape among Passiflora species is spectacularly diverse. Underlying this diversity in leaf shape are profound changes in the patterning of the primary vasculature and laminar outgrowth. Each of these aspects of leaf morphology—vasculature and blade—provides different insights into leaf patterning. Results: Here, we morphometrically analyze >3300 leaves from 40 different Passiflora species collected sequentially across the vine. Each leaf is measured in two different ways: using 1) 15 homologous Procrustes-adjusted landmarks of the vasculature, sinuses, and lobes; and 2) Elliptical Fourier Descriptors (EFDs), which quantify the outline of the leaf. The ability of landmarks, EFDs, and both datasets together are compared to determine their relative ability to predict species and node position within the vine. Pairwise correlation of x and y landmark coordinates and EFD harmonic coefficients reveals close associations between traits and insights into the relationship between vasculature and blade patterning. Conclusions: Landmarks, more reflective of the vasculature, and EFDs, more reflective of the blade contour, describe both similar and distinct features of leaf morphology. Landmarks and EFDs vary in ability to predict species identity and node position in the vine and exhibit a correlational structure (both within landmark or EFD traits and between the two data types) revealing constraints between vascular and blade patterning underlying natural variation in leaf morphology among Passiflora species.

Drivers of bromeliad leaf and floral bract variation across a latitudinal gradient in the Atlantic Forest

“…We discriminate landmarks into anatomical, when located at homologous points with biological meaning; mathematical, when located at extreme points with some geometrical property; and pseudo-landmarks, when located between other landmarks (Dryden & Mardia, 2016). We used these set of landmarks to better describe the shape of structures without making use of numerous equidistant pseudo-landmarks along the contour itself (Bensmihen et al, 2008) or the Elliptical Fourier Descriptors (Chitwood & Otoni, 2017), alternatives when homologous points are lacking. Such landmarks at the greatest and least width of bract margins reflect greater or lesser cell activity, and their dorsal opposites are needed to minimize the distance among base and tip describing the protuberance they can present ( Figure S1a, Appendix S2).…”

Morphological Analysis of Size and Shape (MASS): An integrative software program for morphometric analyses of leaves

“…From the leaves of A. saccharum , the landmarks provided greater variation among the samples, albeit only by a little. Chitwood and Otoni () observed a similar result when examining species of Passiflora L., using both landmarks and outlines. Whereas the landmarks provided greater total variation among the leaves, the outline analyses did allow for separation and identification of morphological variation among the samples (Fig.…”

“…In doing so, geometric morphometrics takes advantage of a larger number of characteristics than may be available (and easily discernable) in traditional morphometric approaches and also allows for variation in organ size and shape, which may be challenging to include in analyses that use only traditional morphometrics. Geometric morphometrics has increased in popularity during the past decade in multiple fields (Adams et al, 2013;Manacorda and Asurmendi, 2018), and, as with traditional morphometrics, has allowed for an understanding of patterns of species diversity (Chitwood and Otoni, 2017;Klein et al, 2017). Indeed, given the number of digitized herbarium specimens currently publicly available (e.g., JSTOR's Global Plants database [https ://plants.jstor.org] and the SEINet specimen database [http://swbio diver sity.org/seine t/colle ction s/ index.php]), it is possible to take advantage of scanned specimens for geometric morphometrics.…”

The arms race between heliconiine butterflies and Passiflora plants – new insights on an ancient subject

“…Passiflora tryphotemmatoides ). Additionally, leaf shape may vary in the same individual according to its developmental stage (Chitwood & Otoni, ). Hence, why did closely related species evolve to have such diverse leaf patterns?…”