Diversity and evolution of African Grass Rats (Muridae:Arvicanthis)—From radiation in East Africa to repeated colonization of northwestern and southeastern savannas

Abstract

African Grass Rats of the genus Arvicanthis Lesson, 1842, are one of the most important groups of rodents in sub‐Saharan Africa. They are abundant in a variety of open habitats, they are major agricultural pests, and they became a popular model in physiological research because of their diurnal activity. Despite this importance, information about their taxonomy and distribution is unsatisfactory, especially in eastern Africa. In this study, we collected the most comprehensive multilocus DNA dataset to date across the geographic and taxonomic range of the genus (229 genotyped specimens from 130 localities in 16 countries belonging to all currently recognized species). We reconstructed phylogenetic relationships, mapped the distribution of major genetic clades, and used the combination of cytogenetic, nuclear, and mitochondrial markers for species delimitations and taxonomic suggestions. The genus is composed of two major evolutionary groups, called here the ANSORGEI and NILOTICUS groups. The former contains four presumed species, while the latter is more diverse and we recognized nine species. Most relationships among species are not resolved, which suggests a rapid radiation (dated to early–middle Pleistocene). Further, there is an indication of reticulate evolution in Ethiopia, that is, the region of the highest Arvicanthis diversity. The distribution of genetic diversity suggests diversification in eastern Africa, followed by repeated dispersals to the west (Sudano‐Guinean savannas) and to the south (Masai steppe). We propose nomenclatural changes for Ethiopian taxa and provide suggestions for future steps toward solving remaining taxonomic questions in the genus.

Annotated checklist, taxonomy and distribution of rodents in Ethiopia

“…This genus includes primarily diurnal rodents, often very abundant in various types of open grassland habitats (from arid lowland savanna to Afroalpine grasslands). The taxonomy of this genus is still far from resolved, but a recent multilocus genetic study (Bryja et al 2019) has shed light on the evolutionary history of this important group and described diversity patterns. There are eight genetic clades in Ethiopia, occupying different regions and habitats of the country and they are considered here as separate species.…”

“…There are eight genetic clades in Ethiopia, occupying different regions and habitats of the country and they are considered here as separate species. Bryja et al (2019) proposed names for particular Ethiopian taxa based on the analysis of original species descriptions and we follow this work here. However, these names need to be confirmed by comparison with the type material, which is unfortunately impossible for some of them as they have been destroyed (see Bryja et al 2019).…”

“…Bryja et al (2019) proposed names for particular Ethiopian taxa based on the analysis of original species descriptions and we follow this work here. However, these names need to be confirmed by comparison with the type material, which is unfortunately impossible for some of them as they have been destroyed (see Bryja et al 2019). Three species are endemic to the Ethiopian Highlands (A. abyssinicus, A. blicki, A. saturatus), and two to lowland savanna mainly in the Ethiopian Rift Valley (A. mearnsi, A. raffertyi).…”

“…Three species are endemic to the Ethiopian Highlands (A. abyssinicus, A. blicki, A. saturatus), and two to lowland savanna mainly in the Ethiopian Rift Valley (A. mearnsi, A. raffertyi). The remaining three species (A. somalicus, A. niloticus, A. niloticus "C2-C4" sensu Bryja et al 2019) have wide distributions extending to other parts of Africa.…”

“…This is in contradiction to the original description of A. abyssinicus, because the type locality lies at the elevation of 3250 m a.s.l. (Bryja et al 2019; but incorrect in Yalden et al 1976). Yalden et al (1976Yalden et al ( , 1996 reported A. abyssinicus as a very common species over a wide elevational range 1300-3400 m a.s.l., which is not confirmed by genetic data.…”