The trechine beetle fauna (Coleoptera, Carabidae) of the Ethiopian Highlands is known to be highly diverse in species, and many species groups were recognized to be characterized by unusual character states of external and genital morphology. Earlier authors described several genera and subgenera of Ethiopian Trechina endemic to certain high mountains of the country. However, the relationships of these species groups and their evolutionary history are unknown so far. Here, we present the first molecular phylogenetic analysis of Ethiopian Trechina, detect several synonymic names under Trechus sensu lato, and introduce two new species groups to the country’s fauna: the monotypic genus Baehria Schmidt & Faille, gen. nov., with the type species B. separatasp. nov. from Mt. Choke in northern Ethiopia, and the Trechus subgenus Abunetrechus Schmidt & Faille, subgen. nov., with the type species T. bipartitus Raffray, 1885; this subgenus includes three species of northern Ethiopia. We show that the composition of the Ethiopian fauna is based on multiple events of immigration, which started simultaneously with or some million years after the Oligocene-Early Miocene orogenic events north and south of the Rift Valley. Our results support the habitat island hypothesis for the evolution of the Ethiopian highland fauna. We found no evidence for an alternative hypothesis assuming a close connection of the Trechina immigration to Ethiopia and Pleistocene cooling. We, thus, conclude that the geomorphological development rather than the climatic changes are the main drivers of the diversification of the high-altitude Trechina fauna in Ethiopia.

A provisional checklist and a synopsis of published records and localities (occurrence data) in Ethiopia for ground and tiger beetles are presented. The checklist comprises 878 species, of which 313 (ca. 36%) are endemic or potentially endemic (i.e., so far not recorded from elsewhere) to Ethiopia. In addition, 36 Ethiopian endemic subspecies are listed. The known distribution of each species and subspecies is shown in grid cell-based distributional maps. An annotated gazetteer of included collection localities is provided with the respective synonymic names and variant spellings used in the literature.

The Holarctic ground beetle genus Trechus Clairville, 1806, is highly diverse in the Ethiopian highlands, both in terms of species numbers and morphology. Particularly noteworthy are the extraordinarily large species of the subgenus Abyssinotus Quéinnec and Ollivier, 2021, with a body length up to 8.5 mm, that occur on Mt. Choke in northern Ethiopia. Recent, intensive field work on Mt. Choke resulted in a significantly large number of specimens that are the basis for our taxonomic revision of the species related to the giant species, T. dimorphicus Pawłowski, 2001 and T. gigas Pawłowski, 2001. We describe three new species and one new subspecies and discuss a likely interspecific hybrid that combines morphological character states of representatives of the dimorphicus and gigas subgroups of Abyssinotus. An iconography of males and females as well as photographs of the aedeagi of all the considered species are presented. The distributions of the species are detailed and knowledge of the species-specific habitat preferences is summarized. Based on the distributions and habitat specificity, a threat assessment based on the current land use pattern at Mt. Choke is provided.

Trechus (Abyssinotus) hauthi Schmidt & Faille, sp. n. wird vom Mt. Choke in Nord-Äthiopien beschrieben. Aufgrund mehrerer morphologischer Merkmale, die einmalig innerhalb der afrikanischen Fauna der Gattung Trechus Clairville sind, ist die neue Art besonders bemerkenswert: 1) basale Protarsomere des Männchen wie beim Weibchen ausgebildet, nicht verbreitert und gezähnt; 2) Körper gänzlich unpigmentiert, 3) Komplexaugen stark verkleinert; 4) Einlenkungsstelle der subapikalen Sinnesborste der dorsalen Borstenreihe auf den Flügeldecken nach laterad zur Spitze des vierten Streifens verschoben. Die neue Art ist wahrscheinlich nahe verwandt mit T. abyssinicus Quéinnec & Ollivier, 2021, der im selben Gebirge vorkommt, diesem in äußeren Merkmalen jedoch nicht ähnlich sieht.

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.

Flight loss, through its effect on the resulting dispersal capacity and gene flow, has been proposed as a driver of diversification. Ground beetles of the genus Calosoma are unique among the predominantly flightless Carabinae, as nearly half of the species retain flight-capability. Most flightless Calosoma occur in extreme, often isolated habitats such as montane ecosystems. Species in this genus provide an ideal system to investigate the impact of flight loss on diversification across geographical scales. Here, we focus on the flightless species Calosoma (Carabophanus) gestroi, which occurs at high elevations in the southern mountains surrounding the Great Rift Valley of Ethiopia. We investigate genetic differentiation among populations and the biogeographical history of this species across its geographical range using HyRAD-X data. Our results indicate that populations from different mountains form distinct clades, exhibiting both deep genetic differentiation and signatures of recent admixture. The combination of warmer Pliocene climatic conditions and the ongoing orogeny of the Ethiopian highlands promoted an ideal setup for complex cycles of population isolation and admixture. Warm periods drove genetic fixation on either side of the Great Rift Valley, whereas glacial oscillations across emerging sky islands in the Eastern Mountains facilitated genetic homogenization through cycles of allopatric isolation and secondary contact.