A first theory on the adaptive colouration of giraffes, part 1

Giraffes are familiar in a larger-than-life way, and recognised by their colouration second only to their peculiar shape.

So iNaturalists might reasonably suppose that the adaptive colouration of giraffes has long since been solved by zoologists.

However, such is not the case. Instead this question continues, after centuries, to lie on the table, free to be picked up by any enquiring mind.

As far as I know, no scientist has even attempted to explain the colouration of giraffes coherently. I attribute this lapse to:

  • a view that colouration, because it defies statistics, is beyond rigorous science,
  • preoccupation with social behaviour and genetics,
  • discouragement by the contradictions and inconsistencies that appear as soon as the subject is tackled, and
  • a deep ambivalence between faith in adaptation (by natural selection) and assumption that many features are accidental.

So, on the downside, this topic is unfashionable in our current scientific scene. But, on the upside, anyone can tackle it without special funding, access to a laboratory, or even leaving home.

I studied giraffes in the wild for years (mainly on the Athi-Kapiti plain in Kenya, 1985-1988), so intimately that I actually developed an allergy to some substance in their fur. I have also collected what is perhaps the biggest archive of hard-copy photographs of giraffes in the world, starting with pamphlets and postcards when I was a schoolboy more than half a century ago.

So here is an attempt at a theory of adaptive colouration of giraffes.

First, some principles applying to ungulates and carnivores:

  • these mammals fail to see most hues because of their dichromatic (https://en.wikipedia.org/wiki/Dichromacy), motion-sensitive visual systems,
  • darkness and paleness, and particularly the contrasts between them, are much of what adaptive colouration is about in ungulates (including giraffes) and their non-human predators,
  • human eyes tend to mislead because we are too sensitive to hues (other than ultraviolet) and not sensitive enough to motion - particularly in dim light,
  • we should therefore view colour photos and videos as if converted to black, white, and shades of grey, while at the same time
  • we should remember that even slight/partial motion can annul the most elaborate camouflage.

In summary so far, the most important features of adaptive colouration are dark/pale contrasts at various scales - which are as visible to humans as to the ungulates and carnivores.

Additional principles include the following:

  • colouration functions differently depending on scale/distance and night vs day,
  • most animals combine conspicuous and inconspicuous features, striking a compromise between the need to hide from predators and the need to communicate with their own kind,
  • adaptive pressures for inconspicuousness are likely to be strongest for infants, and weakest for mature males of sexually dimorphic species,
  • dark/pale effects can result from not only pigmentation/depigmentation but also antisheen/sheen, and
  • conspicuously pale or dark features can be expected to be located on particularly mobile body-parts, e.g. the ear pinnae, tail-tassel and feet.

to be continued...

Publicado por milewski milewski, 07 de diciembre de 2021

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