Camel spider trait evolution demonstrates repeated patterns of convergence (Arachnida: Solifugae: Eremobatidae)

Abstract

Morphology has long been used to classify and identify living organisms. However, taxonomic descriptions are often limited to qualitative descriptions of size and shape, making identification difficult due to the subjective language used to describe complex shapes. Additionally, for some taxa, there are few reliable qualitative characters available for delimitation that have yet to be tested objectively in a phylogenetic context. Solifugae is one such example. The order, Solifugae, is recognized from the other arachnid orders by the possession of large, powerful jaws or chelicerae. Male cheliceral morphology is the leading diagnostic character system in solifuge systematics and is the basis for much of solifuge current taxonomy. Female chelicerae, on the other hand, are reportedly deeply conserved and much of the species identification is based on female operculum morphology. To elucidate patterns of chelicerae and opercula trait evolution within the solifuge family, Eremobatidae, we used a 2-dimenstional morphological analysis using an Elliptical Fourier approach for closed outlines, in addition to an analysis of traditionally used measures in a phylogenetic context. Using ancestral state reconstruction and ultra-conserved elements, we assessed the taxonomic utility of female cheliceral and opercular morphology, and we evaluated which male morphological characters reflect shared, derived ancestry. Investigation into ubiquitously used character sets, in addition to newly proposed characters herein, illustrates the complex evolution of traits with high levels of convergence. Our results provide taxonomic insight into future, higher level taxonomic revisions of Eremobatidae.