It's all about MC1R!

Fig. 1 Melanic arctic skua

In a recent paper, Janssen and Mundy put forth the genetic mechanism controlling melanic polymorphism in pomarine skuas (Stercorarius). A previous study demonstrated that a mutation on MC1R is responsible for the melanic plumage coloration observed in Arctic skuas (Figure 1), a related species. However, the plumage of the Arctic skuas and pomarine skua shows plumage polymorphism, and until now the genetic mechanism behind this polymorphism has been unknown.

The authors sequenced a segment from Mc1R and introns from four different nuclear genes. Similarly to arctic skuas, the authors found that the MC1R allele M is associated with melanic plumage in pomarie skuas in a wild population as well as in museum samples from various locations (Figure 2). This allele is closely related to MC1R allles in three other species of great skuas. Moreover, variation within the nuclear loci points to relatedness between the pomarine skuas and great skuas; thus, the authors suggest that plumage polymorphism was present in a common ancestor but only retained in pomarine skuas, or that it was introduced via introgression. The main take-away though is that evolution at the same locus, is due partially to the same mutation - a classic case of convergent evolution.

Fig. 2 MC1R allele M is associated with melanic birds in Lena Delta (n = 10) and museum specimens at multiple sites (n = 7). Source: Janssen and Mundy, 2017.

- Elizabeth (Liz) Tapanes
3rd non-potluck