A new species of the mygalomorph spider genus Euagrus Ausserer (Araneae: Euagridae) from central Mexico and new records of E. gus Coyle from Tlaxcala

Posted by
  A new species of the mygalomorph spider genus Euagrus Ausserer (Araneae: Euagridae) from central Mexico and new records of E. gus Coyle from Tlaxcala Abstract  A new species of the spider genus Euagrus Ausserer, 1875 from temperate pine-oak forests in the states of Tlaxcala and Hidalgo, Mexico is described: E. pulque sp. nov. The description of the new species is based on male and female adult specimens. Additionally, Euagrus gus Coyle, 1988 is recorded for the very first time in the state of Tlaxcala. These species have sympatric distributions in La Malinche National Park, Tlaxcala. With this description, the diversity of the genus increases to 23 species, with Mexico harboring the highest diversity with 17 described species.  Valdez-Mondragón, A., Salinas-Velasco, H. V. & Bueno-Villegas, J. (2026). A new species of the mygalomorph spider genus Euagrus Ausserer (Araneae: Euagridae) from central Mexico and new records of E. gus Coyle from Tlaxcala. Zootaxa 5810 (...

Copulatory mechanics in ghost spiders (Amaurobioidinae, Anyphaenidae) reveals an independent regressive evolution of a key genital trait through functional replacement

Posted by

 


Copulatory mechanics in ghost spiders (Amaurobioidinae, Anyphaenidae) reveals an independent regressive evolution of a key genital trait through functional replacement

Abstract

During evolution, the morphology of animal organs can vary drastically, such as the reduction or loss of structures. This phenomenon is recurrent in the male copulatory organs of many spiders, where structures that are usually well-developed, are missing or vestigial in some taxa. One example is the retrolateral tibial apophysis (RTA) of the male pedipalp of the most diverse lineage of spiders, the RTA clade. It frequently performs a key function during genital coupling, which is the first and main mechanical engagement during genital coupling (i.e., primary locking). However, in several lineages the RTA is either lost or reduced, raising questions on how genital coupling is achieved in these taxa, and what are the potential drivers for the regression of the RTA. To address these questions, we used the subfamily Amaurobioidinae (Anyphaenidae) as a model and studied the genital mechanics of nine species with different degrees of RTA size. Genital coupling was reconstructed using microcomputed tomography (micro-CT) data of cryofixed mating pairs, revealing that, except for a species with a prominent RTA, primary locking is solely achieved by inserting the conductor (a male genital sclerite) into one of the female copulatory openings. Our phylogenetic analyses indicate that the RTA has been independently lost or reduced six times in Amaurobioidinae, and that at least one functional replacement of the RTA by the conductor has occurred within the subfamily. We hypothesize that the use of the conductor for primary locking replaced the primary function of the RTA, allowing its repeated regressions.
Poy, D., Piacentini, L. N., Michalik, P., Lin, S., Martínez, L. A., & Ramírez, M. J. (2025). Copulatory mechanics in ghost spiders (Amaurobioidinae, Anyphaenidae) reveals an independent regressive evolution of a key genital trait through functional replacement. Arthropod Structure & Development, 86, 101442. https://doi.org/10.1016/j.asd.2025.101442