Morphological variation in populations of Pinelema elinae Brescovit, Gallão & Cizauskas, 2023 (Araneae, Telemidae): a morphometric analysis with natural history notes

Abstract Pinelema elinae spiders, described from seven caves located in the Serra do Ramalho and Chapada Diamantina regions, in the state of Bahia, represent a troglobitic and relict species in the Neotropical context. Its wide geographic distribution, contrasted with low dispersal ability, high levels of endemism, and the punctual records of other species of the genus Pinelema , constitutes a biogeographical dilemma and raises the hypothesis that this taxon may represent a complex of cryptic species. In this context, the present study employed linear and geometric morphometric analyses to compare different populations from the karst area of Serra do Ramalho, aiming to assess the existence of morphological differentiation among them. Natural history observations indicate that individuals are restricted to the aphotic zone of the caves, lack visual structures, and exhibit a female-biased sex ratio (3.33:1) that varies among populations, together with clear ontogenetic differences in pigmentation, body size, and microhabitat use between juveniles and adults. Morphometric analyses reveal morphological differences among P. elinae populations from Serra do Ramalho associated with body size and with the shape of the sternum and pedipalp bulb, whereas carapace shape did not differ significantly among populations. These heterogeneous, structure-specific patterns of differentiation are consistent with the hypothesis that this taxon represents a cryptic species complex, possibly resulting from geographic isolation and local selective pressures.