Sample Size and Geometric Morphometrics Methodology Impact the Evaluation of Morphological Variation

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Morphological evolution

Background:

• Two-dimensional geometric morphometrics (2DGM) is crucial for studying morphological evolution.
• 2DGM outcomes can be influenced by sample size, selected views, and elements, often due to practical constraints.
• Understanding these influences is vital for reliable evolutionary and taxonomic studies.

Purpose of the Study:

• To evaluate the impact of sample size on 2DGM analyses of bat skull shape.
• To assess the concordance of different skull views and elements in 2DGM.
• To determine if 2DGM can differentiate morphologically cryptic bat species.

Main Methods:

• Utilized large intraspecific sample sizes (>70) for two bat species: Lasiurus borealis and Nycticeius humeralis.
• Performed 2DGM analyses on multiple skull views and elements.
• Assessed shape variation, variance, and centroid size, and compared results across different sample sizes and views.

Main Results:

• Reduced sample size altered mean shape and increased shape variance.
• Shape differences were inconsistent across skull views and elements.
• 2DGM successfully differentiated the cryptic species Lasiurus borealis and Lasiurus seminolus across all views and elements.

Conclusions:

• Sample size and the choice of 2D views/elements critically affect 2DGM results.
• No single sample size or view is universally optimal; selection must align with research questions.
• Preliminary analyses with varied parameters are recommended for robust 2DGM conclusions.