Sperm package morphology in scorpions and its relation to phylogeny

Abstract

Sperm packages are widespread in the order Scorpiones, but absent in the family Buthidae. The morphology of sperm packages is diverse and apparently has phylogenetic information. The objectives of this work were to show diversity of sperm packages and to provide a quantitative basis for using sperm packages' morphology as a taxonomic character. For this, we conducted a morphological analysis and comparison of the different sperm packages of species of the family Bothriuridae. The seminal content from males of species of Bothriuridae was studied. Specimens from Iuridae, Buthidae, Euscorpiidae, Liochelidae, Scorpionidae, Vaejovidae, Chaerilidae, and Chactidae were used for comparison. Digital images of sperm packages were measured and statistically analysed based on the following variables: total length, head width, head-body angle, total area, and head length. Pairs of variables were also contrasted, and all the variables were correlated with the current phylogenetic hypothesis for Bothriuridae. High morphological diversity and variability in measures was observed. In general, measurements were similar within each genus, but differed amongst genera. Cane-like sperm packages are very common in species of the family Bothriuridae. Species from Bothriurus show a wide range of sperm package shapes, some of them shared with Timogenes and Vachonia species, supporting the idea of nonmonophyly of the genus. Many species showed sperm package dimorphism inside a single male. Some of the analysed features fit well with the phylogenetic hypothesis in Bothriuridae, and the general package shape shows high correlation with scorpion phylogeny in other families. Bent and round packages are the most common amongst the different families. Sperm packages are not developed in Chaerilidae, as in Buthidae. This is the first morphological and comparative analysis of sperm packages in scorpions, and reveals much greater diversity in this trait than previously known. Our results reinforce the idea that the study of morphology of sperm packages would contribute characters for scorpion phylogeny at different levels.