The overrated use of the morphological cryptic species concept: An example with Nyctelia darkbeetles (Coleoptera: Tenebrionidae) using geometric morphometrics

Abstract

The cryptic concept refers to two or more species that have been classified as a single nominal species due to the fact that they are apparently morphologically indistinguishable. In recent years, the development of advanced morphometric tools has allowed researchers to differentiate subtle variations that cannot be distinguished by mere “eyeballing” as was carried out in in traditional cladistics. These robust statistical techniques alongside with molecular analyzes have enabled the distinction of formerly “cryptic” species, thus highlighting the associated problems and overuse of this concept. In this article we used geometric morphometric (GM) methods to test if it was possible to distinguish two species of tenebrionid beetles (Nyctelia multicristata and Nyctelia confusa) that has been traditionally classified as cryptic. The goal of this study was twofold: on one hand it was expected to draw the attention of taxonomy researchers to be careful when using the concept of cryptic species. On the other hand, it was tested if the GM toolkit allows the differentiation of a species usually categorized as cryptic. Our results allowed the distinction between N. multicristata and N. confusa, hence rejecting the “cryptic” denomination. Based on our results it is possible to suggest that possibly many times species are classified as cryptic due inappropriate methodological designs and comparisons.