What makes the common impala (Aepyceros melampus) tick? Some initial thoughts...

The common impala (Aepyceros melampus) is unusual in its oral allogrooming (mutual grooming of the pelage, by different individuals).

It is well-equipped to self-groom most of its pelage by means of specialised, comb-like front teeth, plus an additional tooth-like bulge of the gums. The difficulty of reaching its own head and neck helps to explain the allogrooming.

Several other extremes in the nature of the common impala may be relevant here.

Firstly, the common impala is unusually gregarious for a 'cover-dependent' species with camouflage-like colouration.

This helps to explain why the common impala is seldom kept in zoos, which are too cramped for a large group.

Likewise, it has long been known that the common impala cannot be reintroduced to game ranches as a few founders in the normal way. Instead, a group-size at least in the dozens is needed, right from the start.

Secondly, the common impala is the smallest species of host attractive to oxpeckers (Buphagus). These birds comb through the pelage in search of ticks and other parasites, as well as - on far larger hosts such as giraffes (Giraffa spp.) and the African savanna buffalo (Syncerus caffer) - blood and pus oozing from wounds.

These three extremes, in allogrooming, gregariousness, and complementary grooming by birds, may fit together.

We may never fully distinguish cause and effect in the full context of the predator- and parasite-rich habitat of the common impala. However, let me start to put together the pieces of the puzzle by pointing out a fourth extreme, in the form of the pelage itself.

Some African ungulates have hairs which are simply circular or oval in cross-section.

However, many have hairs which are kidney-shaped in cross-section, which may alter the colouration by means of complex sheen-like effects. For example, wildebeests (Connochaetes) are brown close-up. However, they can seem black, bluish or car-bonnet silver at a distance, because of how the light plays on the micro-texture of the pelage.

Oddly, the hairs of the common impala have a triangular cross-section, resembling that of a cricket bat.

Possibly its odd pelage helps the common impala to achieve its peculiar combination of 'gregarious camouflage' and a system of flags and semets.

However, a downside of its hair-shape may be that ticks find it particularly easy to cling to the fur, requiring the extreme compensation by various forms of grooming that we see in the common impala.

If so, the various oddities might begin to add up to a coherent adaptive strategy.

Posted on April 26, 2021 11:06 AM by milewski milewski


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