Looking at other bovine species, it becomes obvious that the primigenius spiral is found also in species other than Bos primigenius. Wild yaks have horns identical to that of the aurochs in both dimensions and curvature (see here or here). It is also found in male koupreys (see here). Occasionally, the primigenius spiral also appears in wisent (see here).
Now the question is: did the primigenius spiral evolve independently in these species, or was it already found in their common ancestor?
In order to resolve that question, we have to look at the phylogeny of the Bos-Bison clade.
+--- Bos primigenius (aurochs, including taurine and zebuine cattle)
`-+---+--- Bos sauveli (kouprey)
| `+--- Bos javanicus (banteng)
| `--- Bos gaurus (gaur)
`+--- Poephagus mutus (yak)
`---- Bison
This phylogeny is based on mitochondrial data from three studies [1,2,3]. The wisent, as it is a special case, is not included in my cladogram.
If the primigenius spiral evolved independently in the three species aurochs, yak and kouprey, it must have evolved three times according to the cladogram. If it goes back to a common ancestor, which would be the common ancestor of the Bos-Bison clade, it must have been lost two times again, once in the bison clade and once in the banteng-gaur clade which possess more crescent-shaped horns. But did banteng and gaur really lose the primigenius spiral? It depends on the angle you are looking at the horns. When looking from above, it becomes obvious that even banteng still have the primigenius spiral (see the horns of this cow), the horns are just more upright. And considering that this shape still can occur in wisent, it might indeed be possible that the primigenius spiral is basal for all members of the Bos-Bison clade.
The primigenius spiral is even found in Leptobos, a possible ancestor of the Bos-Bison clade, at least in the species Leptobos stenometopon (see here).
Putting everything together it is not unlikely that the basic horn shape of the aurochs, the primigenius spiral, was basal to all members of the Bos-Bison clade.
[1] Hassanin et al.: Has the kouprey (Bos sauveli Urbain, 1937) been domesticated in Cambodia? 2006.
[2] Verkaar et al.: Maternal and Paternal lineages in cross-breeding bovine species. Has the wisent a hybrid origin? 2004.
[3] Wang et al.: Incomplete lineage sorting rather than hybridization explains the inconsistent phylogeny of the wisent. 2018.
I wandered for long time about horns shape and functions. Looking at african buffaloes we can see how they turns their head to one side or the other and then upwords in order to lift or hurt lions usually attacking from the back side,whose weight can exceed 200 kg.By this movement they can reach their backs.In case of frontal attack,more often occurring from other buffaloes,they can also rely on the cap at the base of the horns.
ReplyDeleteWe can see this backwords horns in other asiatic bovines,each with its own variant,where tigers lives,but not high on the mountains among the yaks, where the biggest predator is the snow leopard,much lighter.
Modern bison have upwords and relatively short horns,and aurochs had forword spiral,but both had dealings with lions in the past.This makes me think that perhaps they don't needed to reach their backs alone.Maybe they had some social defens behavior more effective than those seen today in other species,or simply their intraspecific fights were greater selective pressure.In turn,this lead me to ask why;maybe predation were less common due to lower predator density in northern environment (or at list big feline).
Or maybe they often uses horns as tools against shrubs and bushes in a habitat inclined towords thorny plants and forest,and this were a more pressing need than self defense.
If this phylogeny is correct, and kouprey/banteng/gaur are closer to bison than cattle, wouldn't it make the genus Bos paraphyletic? To make it monophyletic you'd need either need to resurrect Bibos for the tropical Asian clade, or group yaks and bison under Bos (which would be my preference). Even if you did retain separate genera for these groups, it probably makes more sense to have yaks under Bison than to give them their own genus.
ReplyDeleteYes, Bos turns out to be paraphyletic in all mitochondrial phylogenies that I have seen so far. The question is indeed either to lump or to split. I am unsure what to choose. That's why I wrote the "Bos-Bison-clade", because Bos alone would not be a clade.
DeleteI've seen some autosomal phylogenus as well, and the only difference is that wisents group with bison rather than with cattle. In these studies koupreys are usually left out due to lack of data. The paraphyly problem exists regardless.
ReplyDeleteDo you have a link to those autosomal phylogenies maybe?
Deletehttps://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/age.12974?casa_token=l-Vbs7NmnPQAAAAA:9FYjSy22ML7JXkWrtLpywpyOlmQZm9Lqh9Jhw0GckCWqsB2HYPaaG_a_EO5uabHqR7LrbVLHMh-oyfPfDQ
DeletePage 641, turns out Kouprey were included. It says in this one that cattle are slightly closer to bison/yak, but that it's a weak correlation and unclear.
DeleteThis one's a bit old now, but it uses Y-chromosomes, which actually creates a closer relationship between the Banteng/Gaur and Cattle clades. https://www.researchgate.net/publication/227791929_Phylogeny_of_Y_chromosomes_from_bovine_species
DeleteSome nuclear studies produce even stranger relationships, ultimately more information is needed to resolve I think. Interbreeding seems to have had a big impact. https://www.sciencedirect.com/science/article/pii/S1055790318304354?casa_token=MR258sMCgDoAAAAA:J0InVp6zr7_X5LC8bj3TNzIx76wVdS1cRNkaq1dzb23ft2oNeamg_J4cMeUj-AvGzV5IU-g38mPn
DeleteMany thanks!
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