Dedomestication series Pt.III: In which way feral cattle might evolve

Immunological adaptions would not be visible. Adaptions to climate would show in the structure of the fur – cold winters, no matter if dry or wet, require dense fur that isolates the animal to reduce heat loss. The overgrown long hair of Highland cattle, on the other hand, is known to be disadvantageous even in Central European summers, not to speak of Southern European summers. Usually, cattle winter fur is bilayered.

For part I, go here. For part II go here.

Body proportions and conformation probably would change dramatically. We know that the proportions and the body shape of domestic cattle are very different from the aurochs and other wild cattle. The trunk of cattle got longer and limbs and head shorter. This is not merely an aesthetic flaw but also a functional, because there is a reason why wild cattle have the proportions they have. The shorter the trunk and the longer the legs, the more manoeuvrable is the body. No need to say that longer limbs enable a higher running pace than shorter limbs. The trunk of domestic cattle in general is heavy and the “hump” is usually very reduced, so the centre of gravity is probably somewhere in the middle of the trunk or even a little bit posterior. In any (quadrupedal) mammal, the forelimbs are most important for changes in direction during running, so a more anterior centre of gravity makes the animal more agile. The so-called “hump” (actually we are talking about a shoulder area with high processi spinosi that attach well-developed dorsal and neck muscles) is also, or even more so, advantageous for intra- and interspecific fight. That’s exactly the function of this trait, and all wild bovines – including the aurochs – have it. Stronger back- and neck muscles are a direct advantage when pulling the opponent away, pushing or stabbing a conspecific or a predator.

Without question, cattle with those morphological traits should have a way higher evolutionary fitness than those who are proportionated and shaped like domestic cattle.

The size, shape and orientation of the horns likely also has a direct influence on evolutionary fitness. Horns and antlers evolved as a tool for intraspecific competition for dominance and breeding rights. In my view, the shape of the horns in cattle has a primarily mechanic function. Cattle fight by pulling and pushing the opponent in a head-to-head and horn-to-horn fight. Not only bulls but also cows fight this way. It is clear that horns need to have a certain shape and size for that. It is most advantageous when the horns curve outwards at first and then inwards and a little bit upwards, instead of being curled outwards or pointing directly outwards. Also it is probably advantageous when they do not have an either very high or very low orientation relative to the skull. And it might also make sense that larger horns are more useful than smaller horns in such a competition until a certain size. So it seems logical that intraspecific fights would affect horn shape, orientation and size. Other large bovines that do not have the same kind of horns also have different fighting modes, take bison for example. Horns are of course defensive weapons as well, but selection by predation probably tolerates more kinds of horn shapes than intraspecific competition does.

Large body size is favoured by predation and intraspecific fights. The larger and stronger the animal, the better the chances of succeeding.

Physical competition would likely require behavioural changes as well, as outlined above. Natural selection would definitely favour the alleles responsible for an energetic temper and the will to take risks. This might cause a kind of reversal of the hormonal, and therefore developmental, changes that took place during domestication. Perhaps the level of corticosteroids, responsible for the fight/flight reaction, and thyroid hormones (low levels of these cause shorter limbs and snouts, floppy ears and reduced body size in laboratory rats), would rise – the opposite apparently happens during domestication by selection for tameness (see Pt. I). Maybe it is not a coincidence that Lidia, bred for aggression, is one of the very few breeds that retained a very aurochs-like body conformation with a well-pronounced hump, tight muscles and an athletic posture. However, Lidia are small, but humans actively select them for that. Regardless of whether the Lidia example is correct, I consider it likely that natural selection for genes that regulate both behavioural traits and developmental traits might reduce or eradicate paedomorphism and other developmental changes that occurred during domestication.

Sexual selection certainly would increase sexual dimorphism, which had been drastically reduced during cattle domestication. Bulls with high levels of testosterone are more likely to win combats, and the larger the bull the higher the chance to win. The coat colour in wild-type coloured cattle is influenced by testosterone level: the higher, the stronger the melanisation of the fur, and therefore the darker the colour. Therefore sexual selection would probably favour larger, stronger and more hot-tempered bulls with a darker colour. Cows do fight as well, but these combats cannot be nowhere nearly as important for reproductive success as those of bulls in my opinion.

Large, black bulls might also be more attractive to cows than smaller, less melanised ones. And yes, cows do have a choice to a certain degree – in all harem-systems there are the so-called “sneakers” that cover cows in moments unwatched by the dominant bull, and cows do have a choice which one is allowed to mate with them.

Needless to say that environment also directly affects how the cattle are going to evolve. Apart from climatic factors, nutrition and the size of the area are important. As outlined in the first part of the Dedomestication series, the morphology of animals is plastic. Quality and quantity of the food supply affect overall body size and horn size. Theoretically, intraspecific competition would always prefer larger over smaller individuals, but on a restricted area with limited food supply it is harder for larger animals to find enough food than for smaller ones, and an ill-nourished bull might defeat against a smaller but well-nourished bull. To put it in a nutshell, the so-called island effect would take place, especially in the absence of predators.

Colouration

Colour probably has the weakest effect on the evolutionary fitness of large herbivores. If white spots are indeed correlated with neuronal deficiencies, then pleiotropy might work against the piebald pattern, but probably only on a very long-term sight. However, in a reserve with predators, solid-coloured calves are definitely better camouflaged than piebald ones when hiding in a shelter. As I wrote in the first post, a lack of melanisation in cattle skin increases the risk of developing eye lid cancer. Perhaps dilutions that also de-melanise the skin, f.e. the allele e “red” which causes lightly-coloured mucous membranes and eyelids are evolutionary disadvantageous. But the influence likely would be small, because cancer often develops after reaching reproductive age and it is not immediately fatal. The “black” mutation E^d results in a solid, uniform black coat colour. I do not see much disadvantages in this colour, except perhaps signal function. The dorsal stripe as much as the muzzle ring very likely evolved for that purpose (a white mouth area is actually widespread among bovids, and wild horses have it too). On the other hand, the frequency and intensity of muzzle rings in banteng and gaur are very variable too. In fact I have been speculating that “black” might have evolved in the aurochs already (just as an idea). Apart from that, we should not forget that female choice has a far weaker effect on reproductive success for bulls than combats with other males have, so we have to consider a very long time span if sexual selection would indeed disadvantage “black”.

So “red” and “black” will probably remain in the population for a pretty long time, and without predators white spots would probably too.

How about brindle, and all those dilution factors causing tan, beige and grey colours? I don’t know. Again, we can only speculate how large the effect of sexual selection on the reproductive success of bulls would be. If there is, it would probably be small, and take very long to wheedle them out of the population. I am talking of centuries or more. One factor might be predators again. Although the calves probably wouldn’t be affected since these dilutions show their affect only when growing their adult coats, single individuals with a lighter colour might be disadvantaged because they stand out for predators. Brindle probably would be less problematic.

If a cattle population living in the wild is exposed to predation to a sufficient extent, piebald patterns probably would disappear first. Perhaps sufficiently strong predative pressure would also affect greyish, tan or beige individuals. Sexual selection probably would take a very long time to affect colouration.

Nevertheless, sooner or later dedomesticated cattle would be more or less homogeneous in colour. But not necessarily in the most advantageous way, even if all wild-type colour traits are present in the founding population. I think so because colour seemingly is the least important trait for fitness in cattle (except for certain colours under strong predation pressure, as outlined above). Horns, morphology, weather tolerance, behaviour, immunology, seasonal mating and other traits are simply more important. And so it might happen that, coincidentally, some wild-type colour features get lost while some domestic variants become fixated. Genetic bottlenecks can have the same effect. So it might – note, might – happen that a dedomesticed cattle population that is otherwise well-adapted to its environment has a “red” or diluted coat colour instead of a fully wild-type colour. Also, it might turn out that selective pressure for a strongly marked sexual dichromatism is not that strong at all and both sexes would show a uniform colour. 

All in all, I think that wild, dedomesticated cattle would develop proportions, body shape and horns resembling the aurochs because they are functionally advantageous. Pleiotropic effects and developmental cascades would eradicate paedomorphic traits. Size would not only be dependent on intraspecific competition and predative pressure, but also on what the resources of the  environment allows. Sexual dimorphism would be increased, by developmental changes as much as sexual selection. Natural selection would affect colour the least. Pleiotropy might or might not affect white spots, but predation very likely would. If strong enough, predation might speed up the homogenization of the coat colour. Sexual selection might play a role, but much more important is pure coincidence because the other traits listened before are more effective and genetic bottlenecks might also be important. In the end, the dedomesticated population would be homogeneously coloured, but only after a very long time.

The behaviour would change as well. Their reproductive circle would adapt to the season.

All in all I think that “Does evolution take the same road twice?” is a bad question. Animals evolve according to what abiotic and biotic factors currently require and to what their possibilities are, and to a certain degree also coincidence. But traits that were advantageous in the wild type of a species might also be advantageous in feral domestic members of the same species because it was (mostly) not a coincidence that the wild type was the way it was. Especially when the domestic descendants live under the same or very similar conditions as the wild type did, which is the case in aurochs and domestic cattle. How fast these phenotypic changes will occur is dependent on how variable the starting population is (see Fisher’s fundamental theorem). Behavioural and developmental changes, as much as the transformation of traits like overall morphology would probably work without “original alleles” (if there are such) having to be present. Colour, being regulated by only a few loci, are another thing – the wild-type colour alleles have to be present in the population if you want that the cattle will show this type of colouration – it won’t evolve from new. I don’t know if it is necessary, but it would certainly be helpful and quicker if there were some cattle in the founding population already that have functionally advantageous (and therefore aurochs-like) horn traits for such a horn shape to evolve.

The next post will take a look at existing feral populations and see how far they confirm the predictions in this post.