The Mottled duck (Anas fulvigula) is a North-American dabbling duck species. There are two main populations: one in Florida and one in Louisiana, Texas and Northern Mexico (known as the Western Gulf Coast population). In addition, a third population originated in 1976 and 1982 when about 1200 Western Gulf Coast and 26 Florida ducks were introduced in South Carolina.
Whether the two main populations (Florida and Western Gulf Coast) can be considered discrete populations is unclear. If so, they should be recognized as separate conservation units. Although there is some genetic evidence that these populations are isolated, it remains to be determined if the genetic differences between these populations are simply a consequence of geographic distance (a pattern known as isolation-by-distance or IBD). To settle this issue, Peters et al. (2016) sequenced over 3000 genetic loci for 100 Mottled ducks from the three populations.
The multilocus data clearly separated the two main populations. In addition, kinship coefficients showed a sharp transition that coincides with the range gap between the populations. If these populations were still connected by gene flow, the transition would have been smoother. Finally, modelling of the demographic history of these populations indicated low levels of gene flow (about 1-3 individuals per generation).
These genetic results are backed up by ringing data: Mottled ducks ringed in Florida have never been recovered in Texas or Louisiana (2075 recoveries), and vice versa (8111 recoveries).
The authors conclude that ‘collectively, these results suggest that Florida and Western Gulf Coast Mottled ducks are on independent evolutionary trajectories and may be in the early stages of speciation. Therefore, they should be considered as distinct units for conservation and management.’
Apart from the 100 Mottled ducks, 17 Mallards (Anas platyrhynchos) were included in the analyses. Feral mallards are interbreeding with Mottled ducks and this genetic study confirms high levels of gene flow between these species. Hybridization with the Mallard, in combination with habitat loss, is a major conservation threat for the Mottled duck. Therefore, it is important for managers to confidently discriminate between Mottled ducks, Mallards, and their hybrids. For this purpose, Bielefeld et al. (2016) developed a genetically cross-validated phenotypic key.
Bielefeld, R. R., Engilis, A., Feddersen, J. C., Eadie, J. M., Tringali, M. D. & Benedict, R. J. (2016). Is it a mottled duck? The key is in the feathers. Wildlife Society Bulletin 40, 446-455.
Peters, J. L., Lavretsky, P., DaCosta, J. M., Bielefeld, R. R., Feddersen, J. C. & Sorenson, M. D. (2016). Population genomic data delineate conservation units in mottled ducks (Anas fulvigula). Biological Conservation 203, 272-281.
These two papers have been added to the Anseriformes page.