Unexplained tropical hues in giraffes

In a previous Post (https://www.inaturalist.org/journal/milewski/58139-the-bambis-part-7-why-do-certain-genera-show-tropical-hues#), I pointed out that tropical - and particularly equatorial - species and subspecies of small ruminants in Africa tend to differ from their extratropical relatives in a particular aspect of colouration.

Whereas extratropical forms tend to be plain brownish, related tropical forms tend to be differentiated into bright hues (particularly reddish or yellowish) vs dull hues (greyish). There is individual variation within a given population, but the trend is noticeable overall.

As a reminder for readers, this difference is exemplified by the following carefully-chosen photos within a single species of klipspringers (Oreotragus):

TROPICAL
https://www.alamy.com/klipspringer-antelope-oreotragus-oreotragus-manyara-national-park-tanzania-africa-image342083213.html

EXTRATROPICAL
https://www.gettyimages.com.au/detail/photo/view-of-deer-standing-on-land-royalty-free-image/1288047662?adppopup=true

Giraffes are extremely large ruminants, but they show a similar pattern of differentiation. Again, this is individually variable but noticeable overall. The most illustrative comparison is that between Giraffa tippelskirchi (tropical) and Giraffa giraffa (extratropical) - which are so closely related that they may be subspecies of a single species.

Giraffa tippelskirchi tippelskirchi

https://www.inaturalist.org/observations/19512687

https://www.istockphoto.com/photo/giraffe-in-kennya-on-safari-africa-gm1354465322-429280918

https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=16&search_type=pagination&get_facets=0&asset_id=99535779

https://stock.adobe.com/sk/search/images?k=%22masai+giraffe%22&asset_id=471740668

https://www.dreamstime.com/stock-photo-masai-giraffe-head-portrait-aka-maasai-kilimanjaro-kenyan-its-dark-face-shows-image83751633

https://pixels.com/featured/masai-giraffe-portrait-morris-finkelstein.html

https://www.alamy.com/close-up-head-portrait-of-masai-giraffe-giraffa-camelopardalis-tippelskirchii-in-the-masai-mara-game-reserve-in-kenya-image357170029.html

https://www.robertharding.com/preview/764-1534/head-female-masai-giraffe-giraffa-camelopardalis-tippelskirchi-masai/

https://www.alamy.com/close-up-portrait-of-a-female-masai-giraffe-giraffa-camelopardalis-tippelskirchii-sinya-wildlife-management-area-tanzania-image336274916.html

https://www.posterazzi.com/close-up-of-masai-giraffe-giraffa-camelopardalis-tippelskirchii-head-in-savannah-serengeti-national-park-tanzania-poster-print-by-nick-dale-design-pics-item-vardpi12554249/

https://www.robertharding.com/preview/764-1534/head-female-masai-giraffe-giraffa-camelopardalis-tippelskirchi-masai/

https://www.alamy.com/close-up-portrait-of-a-female-masai-giraffe-giraffa-camelopardalis-tippelskirchii-sinya-wildlife-management-area-tanzania-image339794315.html

https://www.offset.com/photos/maasai-giraffe-walking-through-trees-feeding-themselves-in-the-maasai-55419

https://stock.adobe.com/sk/search/images?k=%22masai+giraffe%22&asset_id=223202428

https://stock.adobe.com/sk/search/images?k=%22masai+giraffe%22&asset_id=227628900

https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=6&search_type=pagination&get_facets=0&asset_id=419027336

https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=8&search_type=pagination&get_facets=0&asset_id=408407008

Giraffa giraffa giraffa

https://stock.adobe.com/au/images/south-african-giraffe-or-cape-giraffe-giraffa-camelopardalis-giraffa-portrait-kwazulu-natal-south-africa/250782571

https://www.alamy.com/portrait-of-a-giraffe-photograph-taken-at-pilanesberg-national-park-south-africa-image219089461.html

https://www.alamy.com/stock-photo-giraffe-face-ears-big-eyes-south-africa-green-plants-36581539.html

https://www.istockphoto.com/photo/giraffe-face-gm472236694-63251233

https://www.canstockphoto.com/male-giraffe-with-red-billed-oxpeckers-67648944.html

https://www.istockphoto.com/photo/portrait-of-a-giraffe-in-blue-background-in-kruger-park-south-africa-gm838185980-136417567

https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=21&search_type=pagination&get_facets=0&asset_id=182142069

In this species/superspecies of giraffe (i.e. tippelskirchi/giraffa), the upper lip tends to feature a fawn-coloured longitudinal strip, while the cheeks tend to be grey. But it is in the tropical form that the differentiation on the basis of hue is most likely to be distinct.

The tropical differentiation of hues in giraffes is most obvious on the face. However, it can also be seen on the neck and legs in some individuals, e.g. https://www.offset.com/photos/masai-giraffe-family-on-the-serengeti-national-park-tanzania-136257 and https://stock.adobe.com/sk/search/images?k=%22masai+giraffe%22&asset_id=408407109 and https://stock.adobe.com/sk/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=%22masai+giraffe%22&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=22&search_type=pagination&get_facets=0&asset_id=140125064 and https://www.inaturalist.org/observations/62028200 and https://www.alamy.com/stock-photo-rhodesian-giraffes-giraffa-camelopardalis-thornicrofti-mating-south-79329988.html.

It remains possible that, in the eyes of the animals as opposed to the human observer, the tropical forms are as plain as the extratropical forms. Since ruminants and the carnivores that prey on them do not see hues in the same way as humans, we cannot assume that the patterns shown here have adaptive value.

However, are the differences not food for thought in the context of differences in the quantities and qualities of sunlight at tropical vs extratropical latitudes?

Publicado por milewski milewski, 17 de diciembre de 2021

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