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

Abstract

Widespread species are exposed to different environmental drivers and can consequently present variations in body shape and/or size. Trapdoor spiders of the genus Idiops are generally associated with a sedentary lifestyle and limited dispersion. However, the species Idiops pirassununguensis has a wide distribution, occurring in a diverse range of distinct environmental conditions, with their presence recorded in the Amazon, Caatinga, and Cerrado Brazilian biomes. We investigated how their morphological variation is structured regarding the biomes in which they occur through a morphometric analysis of the linear measurements and morphogeometric shapes of 64 specimens. Combining different methods proved to be a valuable approach to understanding how the spider’s morphology varies in different environments. The results were congruent and complementary, indicating intraspecific geographic variation, with the Caatinga specimens being distinct from their biome conspecifics. In Caatinga, a biome with periods of severe drought and warm climate, I. pirassununguensis specimens were found to be smaller, in addition to having narrower and elongated sternums and shorter legs. The morphological structuring herein is consistent with the results found comparing animals from Caatinga and other Brazilian biomes. Despite differences in their non-sexual structures, the specimens share a set of diagnostic sexual characteristics for the species, allowing all individuals to be classified as belonging to the same species.