Explosive radiation versus old relicts: The complex history of Ethiopian Trechina, with description of a new genus and a new subgenus (Coleoptera, Carabidae, Trechini)

Abstract

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.

Trechus (Coleoptera: Carabidae) of Appalachia: A Phylogenetic Insight into the History of High Elevation Leaf Litter Communities

“…from other genera, with an offset of 15 and reverse log normal distribution. This was consistent with the dates obtained in the recent trechine literature [50,51]. The six genes were partitioned with unique rates and a single tree.…”

“…Outgroups were limited in this analysis because of their variable genetic coverage. A dated phylogeny was created in BEAST2 with a standard carabid mutation rate for COI [49,50] of 0.0145 mutations per site per million years. A fossil parameter was included, creating a mean of 25 MYA for the separation of Trechus s.l.…”

Taxonomy, Distribution and Habitat of the Giant Trechus Beetles Endemic to Mt. Choke, Ethiopia (Coleoptera: Carabidae)

“…Within the beetle fauna of the Ethiopian highlands, the genus Trechus Clairville, 1806 is particularly noteworthy in several respects. Although the genus is of Holartic origin, it is by far the most species-diverse ground beetle genus in Ethiopia, with 77 species described to date [1]. All of the species are wingless and endemic to single volcanos, with the exception of T. patrizzii Jeannel, 1960 that occurs on some immediately adjacent mountains in southern Ethiopia [1,2].…”

“…Although the genus is of Holartic origin, it is by far the most species-diverse ground beetle genus in Ethiopia, with 77 species described to date [1]. All of the species are wingless and endemic to single volcanos, with the exception of T. patrizzii Jeannel, 1960 that occurs on some immediately adjacent mountains in southern Ethiopia [1,2]. The elevational distribution of Trechus reflects the adaptation of this group to colder temperatures, and species are restricted to the Afromontane and Afroalpine belts, with observed occurrences between 1800 and 4300 m above sea level [3,4].…”

“…Most surprising are the results of a recent molecular phylogenetic study showing that morphologically highly divergent Trechus species, syntopically occurring, e.g., on Mt. Choke in northern Ethiopia, belong to one and the same lineage (subgenus Abyssinotus Quéinnec and Ollivier, 2021) [1]). The same pattern was found for the Bale and Arsi Mountains in southern Ethiopia (subgenus Minitrechus Magrini, Quéinnec and Vigna Taglianti, 2009) [1].…”