The issue of continuous characters in the copulatory bulb of Neodiplothele spiders: a morpho-geometric approach

Abstract

The definition of species boundaries in mygalomorph spiders is historically based on morphological characters, which can be problematic due to the homogeneous morphology and continuous variation across species. The male copulatory bulb of Neodiplothele, as of many mygalomorphs, is phenotypically diverse and the differences are displayed mostly by subtle shape variations. The purpose of this research was to evaluate the traditional morphology-based delimitation of species informal groups and assess the significance of morphological characters in the systematics of the highly variable and widespread mygalomorph spiders of the barychelid genus Neodiplothele. We conducted a geometric morphometric analysis on the bulb of specimens of Neodiplothele using Fourier descriptors. The results show that the bulb is rather difficult to apply as a discrete character in a taxonomic context and show the proximity of a group of undescribed species of Neodiplothele to both groups proposed in a previous revision, indicating a continuous variation. As a taxonomic character, the use of the copulatory bulb shape as a discrete character may be uninformative in the case of species that present one or more intermediate states, when the incorrect treatment of the character can result in a misrepresentation of shape diversity and equivocate inference of evolutionary relationships.https://zoobank.org/urn:lsid:zoobank.org:author:471C6BE5-D24C-4805-B2DE-EB89B6D1D8FAhttps://zoobank.org/urn:lsid:zoobank.org:author:D4955FF5-FE7F-4E68-AB2F-4A89593F9850.