Dendrohyrax interfluvialis lives in the wet and dry forests that lie between the two rivers in coastal regions of southeastern Ghana, southern Togo and Benin, and southwestern Nigeria.
Dendrohyrax interfluvialis. Image credit: Oates et al., doi: 10.1093/zoolinnean/zlab029.
Tree hyraxes (genus Dendrohyrax) are one of only three genera currently recognized in Procaviidae, the only extant family in the mammalian order Hyracoidea.
Also known as tree dassie, these medium-sized mammals are native to Africa.
They are sometimes active by day, but, for the main part, they are nocturnal, especially in areas where they are hunted.
They are believed to be solitary, and to rely on acoustic communication for advertising their position relative to one another during the night.
“Tree hyraxes are closely related to elephants and manatees,” said Yale University’s Professor Eric Sargis and his colleagues.
“They are usually regarded as nocturnal and tree dwelling, but their behavior has proved difficult to study, in part because, unlike most nocturnal mammals in Africa, their eyes don’t shine at night, making them more difficult to spot.”
In the new research, the scientists studied 418 recordings of tree hyrax calls made between 1968 and 2020 at 42 sites in 12 countries.
They produced sonograms from a sample of the 96 clearest and most complete recordings, including 34 from the population between the Niger and Volta and 62 from tree hyrax populations across West, Central, and East Africa.
The analysis revealed that nearly all the calls recorded between the rivers were ‘rattle-barks’ that differed from the shrieking calls recorded on the western side of the Volta and the eastern side of the Niger.
The authors also studied the skulls of 69 adult tree hyrax specimens from six museum collections in Europe and North America.
They found subtle but clear differences in the shape and size of skulls from specimens collected between the rivers and those gathered elsewhere.
The skulls of the new species, Dendrohyrax interfluvialis, were shorter and broader than those of their counterparts from outside the interfluvial zone.
The further analysis of museum skins, carcasses of hyraxes killed by hunters, and camera-trap imagery obtained in Ghana revealed differences in fur color between Dendrohyrax interfluvialis and other populations, with the flanks and limbs of the former being brindled dark brown and lighter yellow-brown while the latter are dark brown to nearly black.
Finally, genetic analyses of 21 samples of hyrax tissue from across the African rainforest found that the interfluvial populations were genetically distinct from other hyrax lineages.
“There is increasing evidence that the Niger and Volta Rivers are significant biogeographic barriers to a range of mammals,” said Professor John Oates, a researcher at Hunter College in New York City.
“Hyraxes, for instance, don’t cross water easily, so it makes sense that, through millions of years of changing climate, as African forests have expanded and contracted, new species would have differentiated in isolated forest fragments known as refugia, and then have been limited in their subsequent dispersal by large rivers.”
The team’s paper was published in the Zoological Journal of the Linnean Society.
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John F. Oates et al. A new species of tree hyrax (Procaviidae: Dendrohyrax) from West Africa and the significance of the Niger-Volta interfluvium in mammalian biogeography. Zoological Journal of the Linnean Society, published online June 15, 2021; doi: 10.1093/zoolinnean/zlab029
