Wednesday, 9 August 2017

How good is the sexual dichromatism in the Lippeaue?

One of last week's posts was on sexual dichromatism in "breeding-back". Today's post will be on the same topic. I start with two pictures: 
The upper photo is from Hortobagy (© Istvan Sandor) and shows the breeding bull Rimu with a cow. The lower photo shows two Taurus individuals from the Lippeaue. As you see the colour difference between bull and cow is very strong on these photos, but do not fall into the pitt concluding that these photos automatically show good sexual dichromatism - it is not said that both individuals are closely related and inherit the sexual dichromatism that we want in these cattle. Their genotype is very heterogeneous and we cannot know for sure. That is why we should always look at the tendency in the total population, and I did this for the Lippeaue anno 2015. 

In my post on the genetic and developmental background of morphological traits, I outlined that it might be very difficult to impossible to achieve an authentic aurochs-like sexual dimorphism, in particular sexual dichromatism (the colour difference between the sexes), based on conventional phenotypic selection:

Always simply choosing red cows and dark bulls, or small cows and large bulls, or whatever sexually dimorphic trait, probably will work not here. You would actually have to choose individuals where the sexual dimorphism is laid down in the genome. A phenotypically red cow might either have a more or less strong sexual dichromatism (s. dimorphism in colour), or simply be red and have no sexual dichromatism at all, depending on the bulls that she would produce. The same is the case with dark bulls. How to know that? Well, at first the genetic background of the dimorphic trait has to be resolved, and then the individuals would have to be tested.

So not only would the auto- and gonosomal genes and alleles involved in sexual dichromatism have to be identified, each individual would have to be genetically tested. This would be very expensive and requires research. Therefore I concluded:

I think there are only two possibilities regarding breeding a good sexual dimorphism: either relying heavily on a breed where a well-marked sexual dimorphism is still retained […], or putting up with the fact that there will always be a certain number of cow-coloured bulls and bull-coloured cows

Nevertheless, this does not have to mean that the extent of sexual dichromatism cannot reach a satisfying level. I am going to have a brief look at some cases of breeding-back populations with a satisfying level of sexual dichromatism, and go deeper into my usual case-study herd of Taurus cattle at the Lippeaue in Germany.

As a brief reminder: standard “aurochs bull colour” is to be considered black with the exception of a dorsal stripe and a muzzle ring, the area on the back can also have a slight brownish tint but it is unlikely that European aurochs bulls possessed a so-called colour saddle. The full colour spectrum of the forelocks is unknown. “Cow colour” probably includes all shades of reddish brown to darker until black with a colour saddle or completely “bull coloured”. But those black cows were, according to written sources, very rare. For details, have a look at my previous post.

Sexual dichromatism in existing breeding-back populations

For the case of the Tauros and Auerrind Project, the time is surely to early now to judge sexual dichromatism yet – the gene pool is not mixed enough yet in the case of the Tauros Project, and the Auerrind Project is just getting started. For Taurus cattle, I pick the Lippeaue as an example but serve that for later. So what is left is Heck cattle for now.
Heck cattle are very heterogeneous in regards to sexual dichromatism, as they are in regards to all traits. In some herds, one has to conclude that there is little to no dichromatism at all (many bull-coloured cows, many bulls with a colour saddle). In many herds, there is a tendency of the cows being coloured lighter than the bulls but still contain many variations. In some Heck herds and lineages, however, a quite satisfying level of sexual dichromatism has been achieved. One good example is the herd at Hellabrunn zoo, Munich, at least when I visited it in 2011.
The Hellabrunn Zoo Heck herd has a really good colour and dimorphism
The Neandertal lineage has a satisfying level of sexual dichromatism as well. Many cows show the reddish-brown colour I we see in cave paintings. There are black ones too, of course. Both the Hellabrunn herd and the Neandertal lineage have a very good colour, very intense and seemingly cleared of dilution alleles (there have been no diluted individuals from these lineages for quite some time). Another herd with a good amount of sexual dichromatism that I know of is the one at the Lainzer Tiergarten at Vienna. But in a different way: there are no cows that can be considered “of a reddish-brown colour”, but the type with the dark base colour and the light colour saddle/back is prevalent instead. There were almost no black cows in the herd and no bulls with saddles when I last had a look at the herd in 2014.  Another Heck herd that I visited that also had a quite good colour is the herd at Tierpark Haag, Lower Austria, but the number of the individuals was so small that the gene pool cannot really be judged properly with only a handful of individuals.
The dimorphism in the Lainzer Tiergarten herd is good as well
So where did those Heck herds get their good dichromatism from? Of the founding breeds of Heck cattle, Corsican cattle is best in regards to colour in general and sexual dichromatism. The breed left a strong mark in Heck cattle’s phenotype, which is also not surprising since Heinz Heck relied heavily on crossed individuals with a high portion of Corsican cattle. And the comparably careful selection in both the Munich zoo and the Wildgehege Neandertal probably kept the genes responsible for good dichromatism abundant in those lineages compared to other Heck herds (which often turned into a bit of a “phenotypical mess”).

The sexual dichromatism in the Lippeaue

Taurus cattle is, just like Heck cattle, a mosaic population that is heterogeneous in appearance and instable in inheritance yet. This is not surprising as there are still some first-generation crosses in the herd, the youngest individuals are of the 7th generation already. Taurus cattle is heterogeneous, but one could still determine whether there is a tendency to sexes having different colours or whether the inheritance of colours is independent from sex. In order to determine that tendency, I decided to count the individuals and note their colour, and distribution among the sexes. I made two categories for the sexes respectively: for bulls, “bull colour” as defined above and anything that is less eumelanisized than that (so either a prominent colour saddle or reddish brown colour overall) and for cows either “bull colour” (or black, if you will; except for the light markings of course) and anything lighter coloured than that (so either black with a saddle, or the various shades of reddish brown). Some individuals show diluted colours where the red pigment is reduced. However, the amount of sexual dichromatism is determined by black pigment, so I counted those diluted animals with reduced red pigment but not the half-Chianina individuals (neither bulls nor cows) which have a semi-dominant dilution that reduces black pigment, what makes them not comparable. I counted the individuals in their summer coat, as the winter coat is often darker than the summer coat and a saddle might disappear that is otherwise present.
I used a photo archive I was provided by Matthias Scharf that showed all individuals present in the herd in the year 2015 on several clear photos. I counted only individuals that already had their adult colour, so no calves. Usually it would be problematic that only the breeding bulls are kept till full age, but luckily they kept a lot of young bulls with their adult colour until fall 2015 when they were either sold or slaughtered.
These are the results:

Total number: 71

Bulls total : 25
Bulls black: 22 (88%)
Bulls with a saddle*: 3 (12%)

* There where no reddish-brown bulls, and from what I know usually such bulls do not appear in the Lippeaue, except for half-Chianina individuals.

Cows total: 46
Cows “cow coloured”: 39 (85%)
Cows black: 7 (15%)

We should expect those numbers to fluctuate slightly with each year, and are of course dependent on the "selection policy" in the Lippeaue. But this should be a number that can be worked with. In my opinion, this is a quite satisfying degree of sexual dichromatism. In the past, I have been wondering what would be the minimum point from which on the sexual dichromatism can be considered satisfying, and I concluded that no bulls with saddles and only 5-10% black cows would be satisfying to me. The amount of dichromatism in the Lippeaue comes comparably close. The question is if phenotypic selection could increase it any further in this case. I think it would be difficult. But to me, the level of dichromatism in the Lippeaue is satisfying. It would be interesting to do the same evaluation for other herds, such as Heck herds with good dimorphism (f.e. Neandertal or Hellabrunn) and such with very low dimorphism. Perhaps this level of sexual dichromatism would also be found in a lot of other herds of Taurus and Heck cattle. It will be very interesting to compare it with future herds of the Tauros Project and Auerrind project that work with different breeds.

Where did the Lippeaue population get its good dichromatism from? Sayaguesa has almost no sexual dichromatism, so probably not that breed. Most likely it is thanks to the Heck cattle from the Neandertal lineage that were the base of the herd in the 1990s. It is also plausible that Chianina inherits some degree of sexual dichromatism masked beneath their colour dilutions, as Sayaguesa x Chianina cows tend to be of a much lighter colour than bulls of the same combination.

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