Adapting spherical-harmonics-based geometric morphometrics (SPHARM) for 3D images containing large cavity openings using ambient occlusion: a study with hermit crab claw shape variability

One of the advantages of mesh-based geometric morphometrics (GM) over landmark-based approaches, is that it affords the possibility of the precise examination of highly irregular shapes and complex topographic surfaces. In the case of spherical-harmonic-based GM, the main prerequisite is a completel...

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Bibliographic Details
Published in:Zoomorphology 2020-09, Vol.139 (3), p.421-432
Main Authors: Ege, Yannic C., Foth, Christian, Baum, Daniel, Wirkner, Christian S., Richter, Stefan
Format: Article
Language:English
Subjects:
Algorithms
Animal Anatomy
Animal Systematics/Taxonomy/Biogeography
Aquatic crustaceans
Biomedical and Life Sciences
Crustaceans
Developmental Biology
Evolutionary Biology
Histology
Life Sciences
Marine crustaceans
Methods
Methods Paper
Morphology
Morphometry
Occlusion
Segmentation
Separation
Shape
Statistical analysis
Variance analysis
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Summary:One of the advantages of mesh-based geometric morphometrics (GM) over landmark-based approaches, is that it affords the possibility of the precise examination of highly irregular shapes and complex topographic surfaces. In the case of spherical-harmonic-based GM, the main prerequisite is a completely closed mesh surface, which is often lacking, particularly when dealing with natural objects. Here we present a methodology to prepare 3D segmentations with large cavity openings for spherical-harmonics-based GM analysis. This will be exemplified by a case study of hermit crab (Paguroidea, Decapoda, and Crustacea) claws. The joint openings of the claws—between manus and ‘movable finger’ (dactylus)—typify the problem of the large cavity opening. We described a methodology, including an ambient-occlusion-based segmentation algorithm, which leads to precise results and thereby enables the study of inter- and intraspecific differences in the shape of hermit crab claws. Analysis showed a statistically significant separation between all examined diogenid and pagurid claws, whereas separation observed between all left and right claws was not significant. Additionally, the procedure offers other benefits: it is easy to reproduce and causes little variance in the data, closures integrate smoothly into the overall structures and the algorithm saves a significant amount of time.
ISSN:0720-213X
1432-234X
DOI:10.1007/s00435-020-00488-z