Ancient DNA helps to place two extinct duck species on the Tree of Life

Mitochondrial DNA from Chendytes lawi and the Labrador Duck reveals some interesting evolutionary patterns.

The fossil record of birds is not great (to start with an understatement), but occasionally some wonderful fossils pop up. Some even contain traces of ancient DNA which can be used to pinpoint the phylogenetic position of these extinct species. On this blog, I have written about studies on ancient DNA from the Creighton’s Caracara (Caracara creightoni) and the Poūwa (an extinct Black Swan from New Zealand). Another recent paper in the journal Molecular Phylogenetics and Evolution took a closer look at two extinct waterfowl species: Chendytes lawi and the Labrador Duck (Camptorhynchus labradorius).

The extinct Labrador Duck © James St. John | Wikimedia Commons

Sea ducks or not?

The genus Chendytes was erected in 1925 to classify Holocene fossils from the California coast and nearby Channel Islands and holds two species. One species (C. lawi) is the size of a goose and shows degeneration of the wings. The second species (C. milleri) is smaller with larger wings. It might represent an intermediate form between a flying ancestor and the flightless C. lawi (similar to Tachyeres ducks, see this blog post). Based on several morphological traits, these extinct species were considered sea ducks (tribe Mergini).

In 2018, Janet Buckner and her colleagues managed to extract mitochondrial DNA from a C. lawi fossil. Comparing these DNA sequences with extant species revealed that Chendytes ducks are not sea ducks, but basal dabbling ducks (tribe Anatini). Hence, this lineage represents an independent evolution towards a diving lifestyle. The traits shared with sea ducks are thus the outcome of convergent evolution.

The phylogenetic positions of two extinct species inferred from mtDNA. From: Buckner et al. (2018) Molecular Phylogenetics and Evolution

What about the Labrador Duck? In contrast to the Chendytes ducks, this species does belong to the sea ducks. Indeed, the Labrador Duck is closely related to the Steller’s Eider (Polysticta stelleri). This finding refutes the morphological work by Bradley Livezey, who considered the Labrador Duck a scoter in the genus Melanitta.

However, one should always be careful with mitochondrial phylogenies and ducks because of hybridization. Waterfowl are known for their high levels of hybridization and mtDNA can easily be transferred between species (i.e. mitochondrial capture, see for example Jacamars). The Labrador Duck might be closely related to the Steller’s Eider, but you never know whether hybridization mixed things up a bit.

References

Buckner, J. C., Ellingson, R., Gold, D. A., Jones, T. L., & Jacobs, D. K. (2018). Mitogenomics supports an unexpected taxonomic relationship for the extinct diving duck Chendytes lawi and definitively places the extinct Labrador Duck. Molecular phylogenetics and evolution, 122, 102-109.