The effect of the last glacial age on speciation and population genetic structure of the endangered Ethiopian wolf (Canis simensis)

Abstract

During the last glacial age, Afro-alpine habitats were widespread across the highlands of Ethiopia. A wolf-like canid ancestor is thought to have colonized this expanding habitat and given rise to a new species that was remarkably well adapted to the high altitude environment: the Ethiopian wolf Canis simensis. Here, we address the timing of genetic divergence and examine population genetic history and structure by investigating the distribution of mitochondrial DNA (mtDNA) sequence variation. The pattern of mtDNA variation and geographical distribution indicate an initial population expansion, probably immediately after divergence from the wolf-like ancestor, around 100,000 years ago. The partition of mtDNA haplotypes that followed was most likely the result of habitat reduction and fragmentation at the onset of deglaciation approximately 15,000 years ago. Phylogenetic and geographical associations suggest that the most likely genetic partitioning corresponds to three mountain areas, Arsi/Bale, Wollo/Shoa and Simien/Mt. Guna. Although there is a degree of clustering of haplotypes from both sides of the Rift Valley, the lack of reciprocal monophyly does not support the taxonomic classification of two subspecies. This study highlights the importance of populations north of the Rift Valley for the maintenance of genetic variability within the species and has consequent implications for conservation.

Pleistocene colonization of afro-alpine ‘sky islands’ by the arctic-alpine Arabis alpina

“…The importance of the Great Rift Valley as a phylogeographic barrier has been repeatedly documented for animals, notably the Ethiopian wolf (Gottelli et al, 2004), the ostrich (Freitag and Robinson, 1993) and the wildebeest (Arctander et al, 1999). Also, phytogeographic studies have previously documented a stronger link of the Simen Mountains to the Arabian Peninsula than to the Bale Mountains (Gillett, 1955;Puff and Nemomissa, 2001), confirming the strong barrier effect of the Rift.…”

“…Also, phytogeographic studies have previously documented a stronger link of the Simen Mountains to the Arabian Peninsula than to the Bale Mountains (Gillett, 1955;Puff and Nemomissa, 2001), confirming the strong barrier effect of the Rift. However, for example for the Ethiopian wolf, the barrier effect was not absolute, and some dispersal across the Rift has been inferred from genetic data (Gottelli et al, 2004). The understanding of the Great Rift Valley as a significant, but permeable, barrier to dispersal may be applicable to afro-alpine plants as well.…”

“…The mountains bordering the Red Sea may have formed stepping stones for alpine plants, connecting Eastern Europe and the Caucasus through the Middle East to northeast Africa (Kingdon, 1990). Gottelli et al (2004) suggested that the Ethiopian wolf evolved from a Eurasian grey wolf-like ancestor which followed this route during the late Pleistocene, probably as late as during the last glacial period (B100 000 years ago).…”

“…During glaciations in the northern Hemisphere, the African tropics were cooler and drier (Bonnefille et al, 1990;deMenocal, 1995). While the top of many mountains was covered by glaciers, both the afroalpine and the ericaceous zone extended about 1000-1500 m lower than today and thus occupied considerably larger areas (Flenley, 1979;Gottelli et al, 2004). Thus, during the last glaciation, the Ethiopian highlands on both sides of the Great Rift Valley ( Figure 1) were covered by afro-alpine heaths and grassland (Messerli et al, 1977), and provided habitat for a large population of the endemic Ethiopian wolf, a specialized predator of the afro-alpine zone (Gottelli et al, 2004).…”

“…While the top of many mountains was covered by glaciers, both the afroalpine and the ericaceous zone extended about 1000-1500 m lower than today and thus occupied considerably larger areas (Flenley, 1979;Gottelli et al, 2004). Thus, during the last glaciation, the Ethiopian highlands on both sides of the Great Rift Valley ( Figure 1) were covered by afro-alpine heaths and grassland (Messerli et al, 1977), and provided habitat for a large population of the endemic Ethiopian wolf, a specialized predator of the afro-alpine zone (Gottelli et al, 2004). Also in the mountain massifs of tropical East Africa, of which some are more isolated (for example, Mt Kilimanjaro and Mt Meru), afro-alpine populations may have been larger and distances among habitat patches smaller during the cool periods of the Pleistocene, facilitating dispersal from one mountain to another (Moreau, 1963;Hedberg, 1986;Livingstone, 1993).…”