How does infantile colouration inform subspecies in the dama gazelle?

Any given species of ungulate usually consists of subspecies, living in different parts of the geographical distribution. Subspecies usually differ somewhat in adult colouration, but many naturalists would be surprised to find that the colouration of infants varies accordingly. Newborns can hardly be expected to be subspecifically distinct in colouration given that they rely mainly on lying so low that they are out of sight of both conspecifics and potential predators. Furthermore, there is a notion that 'ontogeny recapitulates phylogeny', suggesting that infants would tend to retain an ancestral pattern of colouration.

Variation within the dama gazelle (Nanger dama) was clinal over a vast, contiguous distribution, any boundaries between subspecies being blurred. This has led to a recommendation in iNaturalist that no attempt be made to identify photos below species-level. Who, then, would have predicted that the infants of the westernmost and easternmost forms of the dama gazelle are easily distinguished by their colouration?

Owing to captive breeding, we now have clear photos of several individual infants of each form, and these show that the western and eastern dama gazelle differ in colouration already at birth. This is all the more surprising because the infantile colouration of the western dama gazelle is so different from the adult colouration that, viewed in isolation, it would not be identified as the same species, let alone subspecies.

In the western dama gazelle, the conspicuous white markings of the adult are absent in the infant, developing only after the horn-tips erupt (see https://www.alamyimages.fr/photo-image-bebe-gazelle-dama-dama-mhorr-nanger-92733857.html and https://www.zooborns.com/zooborns/2017/03/endangered-dama-gazelles-arrive-with-the-spring.html and https://www.biolib.cz/en/image/id304238/) . By contrast, in the eastern dama gazelle the hornless infant is already relatively pale overall with white emerging on the face and lower flanks (see https://www.zooborns.com/zooborns/2008/11/baby-gazelle-at-the-national-zoo.html and https://www.washingtonian.com/2017/09/21/prepare-to-fall-in-love-with-the-new-baby-gazelles-at-the-national-zoo/ and https://www.smithsonianmag.com/smithsonian-institution/dama-gazelle-calf-born-smithsonian-national-zoo-180970587/).

While these surprising differences need not, in themselves, validate the subspecies of the dama gazelle, they show the cline to be more profoundly differentiated than previously assumed. Should our scientific names not reflect this differentiation? Given that the populations are now artificially separated (partly because the species is virtually extinct in the wild), my recommendation is to resume the use of the subspecies names mhorr (western), dama (central) and ruficollis (eastern), while acknowledging that these subspecies originally graded into each other.

פורסם על-ידי milewski milewski, יוני 07, 2021 07:39 לפנה"צ

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