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.

Genetic and morphometric differentiation between two morphs of Haematobosca sanguinolenta (Diptera: Muscidae) from Thailand

“…Geometric morphometrics (GM) provides a valuable complementary technique by revealing unique differences in shape between species. This technique has facilitated the discovery of new species of various insects, such as the ghost spider ( Wilson et al, 2021 ) and caddisfly ( Vilarino et al, 2024 ).…”

Morphometric Analysis of a Trapdoor Spider (Araneae, Idiopidae) across Different Brazilian Biomes Reveals the Geographic Variation of Spiders from the Caatinga Biome

“…In spiders, few studies have explored morphometric variation throughout the range of a species [22][23][24][25][26][27][28]. The majority of the existing morphometric studies are focused on species delimitation and on the investigation of sexual dimorphism [22][23][24][28][29][30][31][32][33][34]. There are also some studies that focus on habitat preference and foraging ecology [35,36], and others that investigate the morphological variation of specific structures in a phylogenetic context [36][37][38][39].…”

The Vitruvian spider: Segmenting and integrating over different body parts to describe ecophenotypic variation

“…However, despite the statistical strength of GM in characterizing the shape of morphological structures, few studies have applied this morphometric technique in spiders. Previously, LM‐based analyses have been limited to characterizing genitalic variation across species (Crews, 2009 ) and intraspecific allometry in sexual dimorphism (Fernández‐Montraveta & Marugán‐Lobón, 2017 ; Kallal et al, 2019 ), and delimiting and identifying species overlooked with traditional methods (Wilson et al, 2021 ). Thus, although morphological studies on spiders have been extensive, we lack fine‐tuned protocols for shape data acquisition and a detailed knowledge of the variation of different body parts and how these are integrated with each other.…”