# Trechus from Ethiopia with Aedeagus Right Side Superior in Repose, an Unusual Character State in Trechine Beetles (Coleoptera: Carabidae)

## TL;DR

This paper describes eight new species and three subspecies of Trechus beetles from Ethiopia, highlighting a unique genital inversion trait in some species.

## Contribution

The study documents the first known case of species-specific male genital inversion in Trechine beetles.

## Key findings

- Eight new Trechus species and three subspecies endemic to Mt. Choke in Ethiopia are described.
- Male genital inversion is a diagnostic feature in some species of the T. lobeliae and T. basilewskianus subgroups.
- An identification key for Trechus species from Mt. Choke is provided.

## Abstract

The Ethiopian highlands are a hotspot of taxonomic and morphological diversity for the ground beetle genus Trechus. The subgenus Abyssinotus is particularly noteworthy in this respect. This article describes eight new species and three new subspecies endemic to the Miocene volcano Mt. Choke in northern Ethiopia. These species belong to two subgroups, referred to as the T. lobeliae and the T. basilewskianus subgroups. The peculiarity is that most of the species in these subgroups are characterised by male genitalia rotated 180° in the abdomen in the resting position compared with the normal position. This means that the original ventral side is dorsal in these species. The inversion of the genitalia is, therefore, a diagnostic feature of the species. This is the first documented case of such a species-specific character state in the subfamily Trechinae. An overview of ground beetle groups in which such an inversion of the male genitalia has been documented is provided. Finally, an identification key for all Trechus species from Mt. Choke is presented.

The Miocene volcano Mt. Choke in northern Ethiopia is known for its very species-rich Trechus fauna. In addition, the enormous morphological diversity that is expressed within a single subgenus, Abyssinotus, which is endemic to northern Ethiopia, is unique within the global Trechus fauna. In this paper, we describe eight additional new species and three subspecies of the Trechus subgenus Abyssinotus, all of which are endemic to Mt. Choke. These species belong to two different lineages within Abyssinotus, each differing from other lineages of the subgenus by certain morphological character states described in this paper and alternatively named the T. lobeliae and the T. basilewskianus subgroups. Several species of these subgroups are characterised by an apomorphical inverse male genital, with the right side up in repose. The T. lobeliae subgroup comprises two species and is monomorphic with respect to this character. The T. basilewskianus subgroup comprises eight species, including six species with monomorphically inverse male genitalia and two species with male genitalia monomorphically in the ‘normal’ position. These are the first examples within Trechinae in which inverse male genitalia are a species- or even group-specific characteristic. A brief summary of the distribution of this trait within the Carabidae is provided. We also present a new identification key for the Trechus species known so far from Mt. Choke.