Application of Genealogical-Concordance Principles to the Taxonomy and Evolutionary History of the Sharp-Tailed Sparrow (Ammodramus caudacutus)

We examined geographic differentiation in mitochondrial (mt) DNA and in morphometric characters among 12 populations of the Sharp-tailed Sparrow (Ammodramus caudacutus) representing all recognized subspecies and geographic regions. Both data sets reveal the existence of two distinct groups of populations, a northern group from the Canadian maritime provinces and Maine, the St. Lawrence Valley, Hudson Bay lowlands, and interior prairies, and a southern group from along the Atlantic coast north to southern Maine. In one sample from southern Maine, both forms co-occur, and about 40% of the individuals there appear to be of hybrid ancestry. Recently, principles of genealogical concordance have been proposed as a conceptual basis for recognition of biological taxa. Here we provide an empirical application of these principles in the context of observed concordance between the mtDNA phylogenetic partition and the subdivisions evidenced by morphological (and behavioral) attributes in the Sharp-tailed Sparrow complex. We recommend that two subspecies of A. caudacutus be recognized: one (A. c. nelsoni) to encompass the northern populations (formerly A. c. nelsoni, A. c. alterus, and A. c. subvirgatus); and the other (A. c. caudacutus) to encompass the southern populations (formerly A. c. caudacutus and A. c. diversus). By taxonomically formalizing what appears to be a fundamental phylogenetic partition among Sharp-tailed Sparrow populations, study of the biogeographic history, reproductive relationships, and management of the forms will be facilitated.