The role of hybridization in the domestication of geese

Gene flow patterns between wild and domestic geese changed during the domestication process.

Geese probably saved the Roman empire. The Gauls were secretly climbing the Capitoline Hill when they woke up a flock of geese. The noise of the honking geese alarmed the Romans that managed to fend off the Gaul attack. This story indicates that geese were already domesticated in Roman times. The earliest reliable reference to domestic geese can be traced back even further, to the 8th century BCE in Homer’s Odyssey. But when did humans domesticate geese?

This question is difficult to answer because different domestic goose breeds are derived from two species: the Greylag Goose (Anser anser) and the Swan Goose (Anser cygnoides). In addition, some breeds are probably the outcome of hybridization between these species, and several breeds are known to hybridize with their wild relatives. Marja Heikkinen and her colleagues tried to solve this complex puzzle of hybridization and domestication with genetic data. Their results recently appeared in the journal G3: Genes | Genomes | Genetics.

Gene Flow

The researchers collected samples from wild and domestic geese across Eurasia. Genomic data revealed a clear separation between wild Greylag Geese, European domestic breeds and Chinese domestic breeds. Demographic analyses suggested that the wild and domestic lineages diverged around 14,000 years BCE (although the authors indicate that this divergence time has wide confidence intervals and will need to be confirmed with more detailed analyses). This divergence was followed by several episodes of hybridization and consequent gene flow.

At the onset of domestication, gene flow was primarily from domestic into wild geese. Probably, geese were not intensively managed at that time, allowing domestic geese to interbreed with their wild relatives. Moreover, goose farmers might occasionally restock their flock by collecting eggs from the wild and raising them in captivity. By Medieval times, goose-keeping was a common phenomenon and the escaped birds would regularly mix with wild flocks. This resulted in gene flow in the opposite direction, from the wild into the domestic population. A patterns that is still visible in present-day goose populations.

A principal component analysis indicates a clear separation between wild Greylag Geese (blue), European domestic breeds (green) and Chinese domestic breeds (red). Some locations, such as Turkey, show admixture from different lineages.

Turkish Hybrids?

Interestingly, the amount of gene flow from wild into domestic goose populations differs between countries. In Finland and Norway – where goose rearing is not so popular – the genetic influence of wild birds is relatively low. In the Netherlands, however, the genetic signs of hybridization is more pronounced. This can be explained by the popularity of waterfowl collections in this country and the fact that many Greylag Geese winter in the Dutch fields (and a large proportion is even present year-round). There is thus ample opportunity for domestic geese to interbreed with wild ones.

Turkish goose populations showed genetic signatures from both European and Chinese domestic breeds. They might thus be a hybrid population between these independently domesticated breeds. Alternatively, the Turkish geese might represent the ancestral genetic variation of Greylag Geese, supplemented with some gene flow from Chinese breeds. More research is needed to solve this mystery and determine whether the domestication of geese started in Turkey.

References

Heikkinen, M. E., et al. (2020). Long-term reciprocal gene flow in wild and domestic geese reveals complex domestication history. G3: Genes, Genomes, Genetics, 10(9), 3061-3070.

Featured image: Domestic geese © Hippopx

This paper has been added to the Anseriformes page.

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