Geometric morphometrics reveal sister species in sympatry and a cline in genital morphology in a ghost spider genus

Abstract

Morphological boundaries between species of the maculatipes-group in the ghost spider genus Sanogasta Mello-Leitão are ambiguous, and the most widespread species, S. maculatipes, is unusually variable and may represent multiple cryptic species. To resolve these issues, we perform a geometric morphometric analysis on the female genitalia of the group, visualizing and testing for differences in shape between described species, and between putative cryptic species within S. maculatipes. We complement this with a multi-locus phylogenetic analysis of the group, to place the morphological results in a phylogenetic context. Our study reveals that two species in the group, S. alticola and S. mandibularis, are morphologically and molecularly distinct lineages that can be objectively distinguished. However, we reveal that S. maculatipes actually consists of two widespread sister species which occur in sympatry throughout the grasslands of northern Argentina. We further discover a geographical cline in the shape of the female genitalia of one of these sister species, such that specimens from the east and west of the range display morphological differences comparable to those between species, despite being virtually identical at the COI locus. Our study demonstrates the strength of a geometric morphometric approach for delimiting species in species-complexes where morphological differences are subtle and confounding factors such as overlapping ranges, allometry and high levels of intraspecific variation are present.