New study finds exchange of crucial genes between several cow species.
Humans are good at two things: telling stories and domesticating animals. A recent paper in Nature Ecology & Evolution explores both talents by studying the domestication of cows. Dong-Dong Wu and colleagues sequenced the genomes of several cow species (genus Bos) and uncovered a history heavily influenced by hybridization. The interbreeding of several cow species led to the exchange of particular genes, each with its own story to tell.
A quick word of caution. Genome-wide analyses often uncover interesting genes and it is very tempting to tell a story about these genes. We should be careful not to make up just-so-stories, no matter how plausible they might sound. Every gene story should be the starting point for further analyses. This is nicely illustrated by the first example.
High Altitude Cows
Hybridization between yak and Tibetan cattle resulted in the introgression of genes involved in adaptation to high altitude (EGLN2 and HIF3α). Yaks have probably lived on the Tibetan plateaus for millions of years and have numerous adaptations to cope with the high altitude, such as enlarged lungs and hearts. Introgression of high-altitude-genes to Tibetan cattle helped these animals to survive on the Tibetan plateau.
Sounds plausible, right? The authors provide some extra evidence for this gene story. They compared the blood parameters in Tibetan cattle with and without the yak-like genes. Cattle with the introgressed genes showed higher lower haemoglobin levels and red blood cell counts, indicating adaptation to high altitude.
Interestingly, similar patterns have been documented in humans and dogs: Tibetans acquired genes from Denisovans, while the Tibetan mastiff received genes from Tibetan wolfs. In all cases, the beneficial genes came from related species that were already adapted to living at high altitudes.
Comparing the genomes of zebu cattle and gayal pointed to introgression of the gene SYN3. Doesn’t ring a (cow) bell? Knocking out this gene in mice results in animals that display less fear. This makes the gene particularly relevant for domestication, as domesticated animals show reduced fear towards humans.
Hybridization between zebu cattle and bali cattle resulted in the exchange of similar ‘domestication genes’ (SEPT5 and GP1BB). Again, knocking out SEPT5 in mice leads to reduced anxiety.
The zebu has been domesticated for much longer than gayal and bali cattle. The authors speculate that introgression of these genes facilitated successful domestication of the latter two species.
The Changing View of Species
These examples show that hybridization can be an important player in adaptation and domestication. The authors conclude:
The changing view of the basic properties of species has profound implications for animal breeders and conservation biologists alike. Introgression and admixture has previously been considered a detrimental process to avoid. We now know that it is an important natural process of significant importance for adaptation.
Wu, D.-D., Ding, X.-D., Wang, S., Wojcik, J.M., Zhang, Y., Tokarska, M., Li, Y., Wang, M.-S., Faruque, O., Nielsen, R., Zhang, Q. & Zhang, Y.P. (2018) Pervasive introgression facilitated domestication and adaptation in the Bos species complex. Nature Ecology & Evolution.