Testing repeatability, measurement error and species differentiation when using geometric morphometrics on complex shapes: a case study of Patagonian lizards of the genus Liolaemus (Squamata: Liolaemini)

Abstract

The repeatability of findings is the key factor behind scientific reliability, and the failure to reproduce scientificfindings has been termed the "replication crisis". Geometric morphometrics is an established tool in evolutionarybiology. However, different operators (and/or different methods) could act as large sources of variation in the dataobtained. Here, we investigated inter-operator error in geometric morphometric protocols on complex shapes ofLiolaemus lizards, as well as measurement error in three taxa varying in their difficulty of digitalization. We alsoexamined the potential for these protocols to discriminate among complex shapes in closely related species. Wefound a wide range of inter-operator error, contributing between 19.5% and 60% to the total variation. Moreover,measurement error increased with the complexity of the quantified shape. All protocols were able to discriminatebetween species, but the use of more landmarks did not imply better performance. We present evidence that complexshapes reduce repeatability, highlighting the need to explore different sources of variation that could lead to suchlow repeatability. Lastly, we suggest some recommendations to improve the repeatability and reliability of geometricmorphometrics results.