An easily overlooked but extreme adaptation in the grey rhebok

The grey rhebok (Pelea capreolus) has long been recognised as unrelated to other living antelopes despite a superficial resemblance to reedbucks. However, up to now an obvious aspect of this peculiarity has been 'hiding in plain sight'.

The colouration of the grey rhebok is a prime example of crypsis, i.e. plainness designed to blend into the surroundings. Few African antelopes have such uncomplicated markings, so that even a group of six can be overlooked as they stand among the low shrubs of the fynbos.

However, when alarmed the grey rhebok does something not done to the same degree by any other antelope or, indeed, any other bovid. It transforms itself in the simplest but most effective possible way by curling its tail over its rump, producing an unnaturally luminescent, handkerchief-sized patch of white which can be spotted by the naturalist at ranges up to several hundred metres.

Although many field guidebooks state or imply that reedbucks similarly display themselves when fleeing, such is not the case. And any displays of the white underside of the tail by bushbucks, kudus and their relatives are less noteworthy than that of the grey rhebok because the tails are not consistently raised and do not flash much white, and these antelopes have complicated rather than plain colouration in the first place.

The springbok (Antidorcas marsupialis) has an equally spectacular but far more complicated display of white on its hindquarters, produced by unfolding a fur-lined fold of skin on the rump. But this is categorically different from the case of the grey rhebok, because the overall colouration of the springbok (as in gazelles generally) is designed to be conspicuous, not cryptic or camouflaged. So, the springbok when fleeing transforms a flag on its already flag-like body, but does not emulate the grey rhebok in transforming itself from effective invisibility into a white flag.

In this ability to transform its appearance, no bovid and perhaps not any deer rivals the grey rhebok. And this extreme adaptation has been configured in a deceptively simple way, by deploying a tail, in itself similar in its white underside to that of reedbucks and bushbucks, on the plainnest of bodies. All that is needed is for the tail to be raised and held raised in flight.

פורסם על-ידי milewski milewski, אוגוסט 31, 2020 02:24 לפנה"צ

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