Tuesday, 17 September 2013

Heck cattle at Oostvaardersplassen - A special population

In 1983, 32 Heck cattle were released in the Dutch reserve Oostvaardersplassen, an area of 5600 hectares. Oostvaardersplassen is the only place where Heck cattle live under natural conditions without much influence of man, such as no supplementary food during the first decades and no artificial selection. The cattle grew to 350 individuals in 2011 and evolved into a very heterogeneous population, making it a very interesting dedomestication experiment. It is cool to see some individuals with broken horn tips, split ears or even scars; that shows that they have a rough life and those which do best pass on their genes.
Keep in mind though that Heck cattle in Oostvaardersplassen are by far not the only free-ranging cattle population in Europe. Chillingham cattle and Betizu cattle have been living freely since centuries, and especially the last one is way more dedomesticated than the Oostvaardersplassen cattle. Sadly though, feral cattle (or feral domestic animals in general) are an ashamedly understudied field. Their social behaviour, reproduction cycle, habitat choice, food selection, species interaction and so on could tell us so much about their ancestral wild type, the aurochs. And if it is a very variable population (what makes the Oostvaardersplassen cattle so interesting here), a statistic evaluation of the changing frequency of certain phenotypic features over the time would provide a lucid example of evolution at work

Most of the Heck cattle at Oostvaardersplassen do barely resemble the aurochs. When people in the Netherlands started to buy Heck cattle from other countries in the 1980s, the breeders mostly sold their less good cattle (this is understandable, I would have done the same), and some individuals were bought as calves, so that their quality was not yet discernable. Therefore, most Dutch Heck herds, and the Oostvaardersplassen herd in particular because no artificial selection takes place, are less aurochs-like than many German herds, but there are also some good animals among them (more on other Dutch herds in a future post).

Nevertheless, the population at Oostvaardersplassen is very valuable because it has been exposed to intense natural selection over the past 30 years. Predators are still absent in the reserve, so the selective pressure mainly concerns the ability to survive harsh winters, resistance against injuries and competition for food, social dominance and breeding rights. I am not aware of any diseases in this population.
The ability to survive harsh winters and to live on poor forage is dependent on saving as much energy as possible. This requires a thick and insulating winter coat (Heck cattle, like other cold-resistant cattle breeds, have such a winter coat), but also a small, hairy udder, short dewlap and short scrotum in order to reduce the heath loss. Those individuals which loose too much energy during winter cannot keep up sufficient strength or fall ill and die, what favours the cattle that are more effective in saving energy and resist diseases. Storing fat during autumn is another factor that is important for cattle to survive strong winters. Also, seasonal adaption of the reproduction cycle is important for the cow and calf’s survival, because cows having calves during the cold season have difficulties in subsisting themselves and their offspring. Therefore, cattle should mate during August/September and give birth during spring, like it seemingly was the case in the aurochs [3], and is the case in Highland cattle under natural conditions [3][2]. Heck cattle usually give birth all the year round like most domestic cattle, unfortunately there is no information on the reproductive cycle of the Oostvaardersplassen population that I am aware of.
The competition for social dominance (which has advantages such as better feeding places and less stress) and breeding rights is directly connected to the animal’s superiority in intraspecific fights, which is dependent on the weight/size, horns and also the psyche of the individual [1][2]. Long-legged and agile animals also have a higher chance in succeeding in a fight. Intraspecific fights occur in both sexes, but especially the mating competition of bulls has a direct influence on the evolution within the population. High shoulder spines that allow large neck and shoulder muscles to develop provide another important advantage in combat; that’s the kind of “hump” that’s present in all wild bovines, aurochs included. Also the horns of the aurochs were shaped for a purpose: their curvature had a functional advantage in competitions, because large, forwards and inwards-facing horns made it possible for the animal to pull and push the opponent more effectively than other horn shapes would do. This is the reason why bovine species fighting in a similar manner also have very similar horns (Kouprey, Yak) and why the aurochs’ horns were relatively uniform, no matter which respective time and region.

© treverius on flickr
Having tried to make predictions on how the functional phenotype (among other aspects) of a released cattle population might change under such conditions, now lets have a look at how the present Oostvaardersplassen Heck cattle look like.
The body shape of many cows is still domestic in having a bulky rear, visible pelvic bones and no hump (thus, comparable to usual Heck cattle). However, single cows seem to develop a slight hump and a slender waist. This trend is even more apparent in bulls, some of which do really have an athletic body shape with a clear hump and a slender waist, resembling Spanish fighting bulls and wild bovines. Also, many bulls and cows have long legs as in the aurochs. Therefore, the prediction that body shape and proportions in a feral variable cattle population re-develops to an athletic, aurochs-like body seems to be confirmed, because such a body conformation is found in no other Heck cattle population. Down below you see screenshots of an Oostvaardersplassen bull (sadly with the wrong colour and horns) that has perfectly aurochs-like body shape and proportions. However, there are still some quite bulky and dachshund-proportioned Hecks in this reserve.

Slender, long-legged bulls
Perfectly "wild" proportions and body shape (Screenshot from youtube)
The horns within this population are mostly steppe cattle-like and thin, the length is varying and they are oriented very upright both in bulls and cows. However, I was surprised to discover cows with horns facing more forwards and inwards than in any other Heck cows. This is a strong hint that this horn shape developed in Oostvaardersplassen and therefore is a product of natural selection instead of artificial selection. In essence, the curvature of the horns in these two individuals is nearly perfect, except that they are oriented to vertical. I see the same tendency several in other cows and also bulls in Oostvaardersplassen.

(© evoergo on flickr)
(© Frits van Hout) Cows with aurochs-like inwards-facing horns, 
very likely a product of natural selection
The skull of the Oostvaardersplassen Heck cattle is short and paedomorphic like in most other representatives of the breed. However, surprisingly some cows show an elongated skull, similar to Sayaguesa. I wonder what causes this development and if a longer snout perhaps provides an advantage for grazing, or if it is influenced by environmental factors.
The colour of those cattle is extremely variable. Dark brown bulls with a kind of saddle and either dark or reddish-beige cows are most common, but black cows and black bulls, as much as reddish brown or beige bulls do appear. Gray individuals exist in both sexes and are a relatively common sight. The portion of spotted animals seems to be higher than in usual Heck herds, unfortunately. These spots either are limited to the forehead or cover the whole body.
Spotted bull calf (©Jaap Rouwenhorst)
There is no size data for the Heck cattle at Oostvaardersplassen, and also no useful photos from which the size of the animals could be extracted, so we can only speculate how large they are. Do the conditions in the reserve favour a size increase or decrease against the 140 cm shoulder height in bulls and 130 cm in cows? As discussed above, the natural selection created by the physical competition of the animals likely favours larger animals. But considering the small size of the reserve, the high density of herbivores and the limited amount of food, as much as the absence of predators, makes Oostvaardersplassen a kind of island. These island conditions favour a size decrease in larger animals, as numerous examples of insular tetrapod evolution have shown. After all, the aurochs itself “dwarfed” slightly on Sicily after it became isolated from the mainland. It makes sense that a smaller animal needs less energy than a larger one, and a healthy and strong small bull might succeed over a larger but emaciated one in a competition. Therefore, we have to assume that the Heck cattle at Oostvaardersplassen are as large/small as the average of the breed given above, or even slightly smaller.

If the conditions like they are now remain unchanged, how will the population in Oostvaardersplassen develop in future decades? I think that on a middle- and long-term sight, the portion of animals with an athletic body and aurochs-like proportions and horns will increase, while the bulky and domestic looking ones will get constantly fewer because these factors have a considerable impact on the fitness of the animals. Also, if the food situation does not change (f.e. by increasing the supplementary food that already is provided during winter), those with the smalles udders and shortest dewlaps and scrota, and most effective winter coat and resistance to diseases will become more common.  The island situation of the reserve will favour a size decrease more than a size increase. The colour of the animals has, as far as we know and in the absence of predators, no direct influence on the fitness of the cattle, so it will remain heterogeneous for a very, very long time. Perhaps sexual selection favours dark bulls and lightly coloured cows, but only on a very long term.
In essence, future Heck cattle in Oostvaardersplassen will be more adapted to their habitat and living as a wild animal than they are now. They probably will evolve into a population with aurochs-like horns and proportions/body shape, but varying colours and a small size. Probably it would also take a considerable time span until these alleles are fixed, and I am speaking perhaps of centuries. But what if man would “help” natural selection to speed up the process? Individuals with undesired features, such as grayish coat colour and steppe cattle-like horns, or many of the spotted individuals, could be culled, and a wild type colour with the right sexual dimorphism could be fixated. To compensate the loss of individuals, cows of herds that add what is lacking in the population can be added, such as from the Wörth herd (for the horn dimensions and curvature) and the Taurus cattle at Lippeaue (for the size, proportions/body shape and horn curvature). Later culling should focus on the bulls in order not to decrease the population too much, and because single bulls have a greater influence on the evolution within the population than single cows.
This plan could lead to a dedomesticated, wild cattle population that is adapted to their habitat and resembles the aurochs very well. However, it is up to the responsible people if this is turning into reality or not.

It seems that the next step in Oostvaardersplassen will be expanding the reserve. The plan of Oostvaardersland, a new 150 square kilometres large nature area that would be formed by the connection of Oostvaardersplassen to the reserve Hosterwold by a corridor named Oostvaarderswold, ran into political trouble. This is a shame, as Oostvaardersland would be one of the most precious nature areas in western Europe. Not only because of its rich avifauna and the wet zones which are very important for the amphibian fauna, but also because it is the only place in western Europe where large populations of cattle, deer and horses live side by side. Also, the cattle would have the chance to chose between forests and open grassland, what would tell us more about the habitat preference of this species. However, let’s stay tuned and see if Oostvaardersland is going to happen.


[1] Frisch, Walter: Der Auerochs – das europäische Rind. 2010.
[2] Julia Poettinger: Vergleichende Studie zur Haltung und zum Verhalten des Wisents und des Heckrinds. 2011.
[3] van Vuure, Cis: Retracing the Aurochs - History, Morphology and Ecology of an extinct wild Ox.

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