Mitochondrial Genomes of the Sakhalin Calidris alpina actites and Kamchatka C. a. kistchinski Subspecies of Dunlin (Charadriiformes, Scolopacidae) and New Insights into Intraspecific Relationships of Calidris alpina sensu lato

For the first time, complete mitochondrial genomes have been sequenced for two subspecies of dunlin: the range-restricted and protected Sakhalin subspecies Calidris alpina actites and the Kamchatka subspecies C. a. kistchinski (Charadriiformes, Scolopacidae). For C. a. actites, a low level of genetic diversity was confirmed, which may reflect the critical condition of the declining Sakhalin population. We analyzed the available genetic material from all currently recognized dunlin subspecies, which allowed a more accurate reconstruction of their phylogenetic relationships. Contrary to previously published data, a closer relationship between C. a. actites and C. a. kistchinski (0.3–1%) was revealed, suggesting that the former may have originated relatively recently from a C. a. kistchinski-like ancestral population. A parallel is drawn with C. a. schinzii, another endangered western European Baltic subspecies. The absence of morphological and genetic differentiation among the western European subspecies C. a. alpina, C. a. arctica, and C. a. schinzii, except for the smaller body size of the latter, suggests that the origins of C. a. arctica and C. a. schinzii, as in the previous case, are relatively recent and associated with the southwestward range expansion of the nominate subspecies C. a. alpina. The small body size of the southernmost dunlin forms, C. a. actites and C. a. schinzii, is likely an example of Bergmann’s rule. Unexpectedly, Alaskan C. a. pacifica/C. a. arcticola showed a closer relationship to the Central Siberian subspecies C. a. centralis (1.1%) than to the geographically nearer eastern subspecies C. a. kistchinski/C. a. sakhalina (2%). The isolated eastern North American subspecies C. a. hudsonia, possessing a deeply differentiated mitochondrial haplotype, occupied an intermediate position between the western European and Central Siberian subspecies in the phylogenetic reconstruction, which does not support the antiquity of its mitochondrial haplotype but rather may indicate its origin from one of these forms. Inclusion of all C. alpina subspecies in a comprehensive analysis enabled a new reconstruction of intraspecific relationships and a reassessment of the demographic history of dunlin subspecies, as well as an evaluation of the genetic status of endangered taxa, which may provide additional justification for prioritizing conservation measures.