3D revelation of phenotypic variation, evolutionary allometry, and ancestral states of corolla shape: a case study of clade Corytholoma (subtribe Ligeriinae, family Gesneriaceae).

Hao-Chun Hsu,Yan-Fu Kuo,Wen-Chieh Chou

doi:10.1093/gigascience/giz155

Abstract

BackgroundQuantification of corolla shape variations helps biologists to investigate plant diversity and evolution. 3D images capture the genuine structure and provide comprehensive spatial information.ResultsThis study applied X-ray micro-computed tomography (µCT) to acquire 3D structures of the corollas of clade Corytholoma and extracted a set of 415 3D landmarks from each specimen. By applying the geometric morphometrics (GM) to the landmarks, the first 4 principal components (PCs) in the 3D shape and 3D form analyses, respectively, accounted for 87.86% and 96.34% of the total variance. The centroid sizes of the corollas only accounted for 5.46% of the corolla shape variation, suggesting that the evolutionary allometry was weak. The 4 morphological traits corresponding to the 4 shape PCs were defined as tube curvature, lobe area, tube dilation, and lobe recurvation. Tube curvature and tube dilation were strongly associated with the pollination type and contained phylogenetic signals in clade Corytholoma. The landmarks were further used to reconstruct corolla shapes at the ancestral states.ConclusionsWith the integration of µCT imaging into GM, the proposed approach boosted the precision in quantifying corolla traits and improved the understanding of the morphological traits corresponding to the pollination type, impact of size on shape variation, and evolution of corolla shape in clade Corytholoma.

Highlights

Quantification of corolla shape variations helps biologists to investigate plant diversity and evolution. 3D images capture the genuine structure and provide comprehensive spatial information
With the integration of micro-computed tomography (μCT) imaging into geometric morphometrics (GM), the proposed approach boosted the precision in quantifying corolla traits and improved the understanding of the morphological traits corresponding to the pollination type, impact of size on shape variation, and evolution of corolla shape in clade Corytholoma
We first revealed that the evolutionary allometry of corolla shapes was weak in Corytholoma species

Summary

Background

The variation in corolla shapes and forms (i.e., shape and size together [1]) in angiosperms has received considerable research attention [2, 3]. Scheffe ’s multiple comparison test results suggested that tube curvature and tube dilation formed 3 clusters corresponding to the 3 pollination types (P < 3.09 × 10−4 and P < 3.42 × 10−4, respectively; Fig. 9; Table 2). The permutation test for logarithm of the odds (LOD) scores indicated that the centroid size and the tube curvature was significantly associated with the 3 pollination types (LOD = 21.71 and LOD = 45.52, P = 1.32 × 10−14 and P = 1.19 × 10−22, respectively). The pollinator types of the 3D corolla shapes and forms at the ancestral states were estimated using sPC1–sPC4 and fPC1–fPC4, respectively, and the k-nearest neighbor algorithm with a k value of 5. By contrast to the shape analysis, the corolla forms at nodes 10 and 12 were estimated to be moth-pollinated and hummingbird-pollinated, respectively (Fig. 11B). Both morphospaces were sparse in the neighborhoods of S. barbata and S. tubiflora compared with those of other species

Discussion

Findings

Methods