Using pictographs as traits to explore morphological diversity in sharks

Area of Science:

• Ichthyology
• Morphometrics
• Computational Biology

Background:

• Body shape is crucial for species differentiation but traditional measurements face challenges like distortion and collection difficulties.
• Scientific illustrations (pictographs) are underutilized despite offering rich morphological data.
• This study explores the utility of pictographs for analyzing shark body shape.

Purpose of the Study:

• To validate the use of pictographs as a reliable data source for morphological measurements in sharks.
• To construct a multivariate morphospace for shark body shape using pictograph data.
• To assess the influence of habitat, endemism, and illustrator on body shape variability.
• To demonstrate the application of pictographs in ancestral trait reconstruction and phylogenetic modeling.

Main Methods:

• Collected and landmarked 473 pictographs from 67 shark species.
• Employed Elliptical Fourier Analysis and principal components analysis to create a morphospace.
• Evaluated variability using habitat association, endemism, and illustrator data.
• Applied pictograph data to ancestral trait reconstruction and phylogenetic generalized linear mixed models (PGLMM).

Main Results:

• Measurements from pictographs showed minimal deviation from specimen-derived data.
• Habitat preference significantly impacted pictograph discovery rates and within-species similarity.
• Limited illustrators exhibited systematic variability; habitat was a stronger influence.
• Pictographs provided greater explanatory power than traditional measurements in PGLMM.
• Observed Lamnid divergence ~100 MYA and linked endemism to specific body shape features in Carcharhinidae + Sphyrnidae.

Conclusions:

• Pictographs are a reliable, easily digitizable, and undervalued data source for species' body shape analysis.
• Pictograph data enhances accuracy in ancestral trait reconstruction and phylogenetic modeling.
• Further research can leverage established methods for comparing pictographs and assessing variability in biodiversity studies.