New World nine-primaried oscine relationships : constructing a molecular framework

—Historically, a paucity of comparative morphological characters has led to much debate regarding relationships within and among the major lineages of New World nine-primaried oscines. More recently, DNA-DNA hybridization studies have provided novel and testable hypotheses of relationships, although no consensus has been reached. For 40 songbird taxa, we obtained 1,929 base pairs (bp) of DNA sequence from the mitochondrial cytochrome-b (894 bp) and NADH dehydrogenase subunit 2 (1,035 bp) genes. Phylogenetic analyses confirm the monophyly of this assemblage as traditionally defined. The lineages delineated historically on morphological grounds are retained; finches (Fringillinae) are sister to a well-supported clade (Emberizinae) containing blackbirds (Icterini), sparrows (Emberizini), wood-warblers (Parulini), tanagers (Thraupini), and cardinal-grosbeaks (Cardinalini). However, each tribe individually is either paraphyletic or polyphyletic with respect to most recent songbird classifications. Our results suggest that Euphonia is not a tanager but perhaps represents a derived form of cardueline finch. Piranga, traditionally considered a typical tanager, is a cardinaline in all of our analyses. Calcarius falls outside the sparrow lineage in all of our analyses, but its true affinities remain unclear. Elements of four different AOU families are represented in our clade Thraupini. The inclusion of several ‘‘tanagerfinches’’ (Haplospiza, Diglossa, Tiaris, Volatinia, Sporophila) and a nectarivore (Coereba) in this clade is consistent with findings from other molecular phylogenies in suggesting that convergence in feeding specializations among some lineages has confounded traditional morphological classifications. We obtained a novel arrangement of relationships among tribes in our ‘‘best’’ topology; Cardinalini is sister to the rest of the Emberizinae assemblage (as defined by Sibley and Ahlquist [1990]), and Thraupini is sister to a clade containing Icterini, Emberizini, and Parulini. Despite nearly 2,000 bp of sequence for each taxon, and a high degree of stability across most weighting schemes and analytical methods, most nodes lack strong bootstrap support. The ND2 gene provided higher resolution than did cytochrome b, but combining genes provided the most highly supported and resolved topology. We consider the phylogeny a working hypothesis to be used as a guide for further studies within the nine-primaried oscine assemblage. Received 6 November 1998, accepted 4 August 1999. THE NEW WORLD nine-primaried oscines, with about 1,000 species, represent roughly 10% of all living species of birds. This group is ‘‘by almost unanimous agreement, an assemblage of families of close relationship and common ancestry’’ (Tordoff 1954a:274). Although this statement still rings true, the systematic relationships within and between the major groups (i.e. families of AOU [1998], tribes of Sibley and Monroe [1990]; unless otherwise specified we use the nomenclature of the latter throughout this paper) of nine-primaried oscines continue to be among the most problematic systematic questions within an avian order. 1 E-mail: klicka@biosci.cbs. umn.edu 2 Present address: Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA. A long history of attempts to clarify relationships among members of this assemblage has included comparative studies of external morphology (Ridgway 1901, 1902), jaw musculature (Beecher 1953), pelvic musculature and serology (Stallcup 1954), cranial and palatal characters (Tordoff 1954b), and appendicular myology (Raikow 1978). Such works have led to a general agreement regarding the taxonomic boundaries of this passerine assemblage, but they have yielded only a handful of useful characters with which to define the relationships among the component groups (Mayr and Amadon 1951, Sibley 1970, Feduccia 1996). Of these characters, many are often inconsistent with one another (Bledsoe 1988). This result has led to a series of linear classifications (see Sibley and Ahlquist [1990] for a comprehensive re322 [Auk, Vol. 117 KLICKA, JOHNSON, AND LANYON view) that differ only slightly from one another. The traditional view of nine-primaried oscine evolution held that ‘‘the major groups are products of adaptive radiations into discrete adaptive zones defined mainly in terms of feeding specializations’’ (Raikow 1978:34). Early classifications based on this perspective had in common the following six ‘‘core’’ groups: the cardueline finches (Sushkin 1925), wood-warblers, blackbirds, sparrows, cardinal-grosbeaks, and tanagers. However, overlapping bill morphologies between the latter three have led to relatively arbitrary boundary distinctions (e.g. Sclater 1886, Ridgway 1902, Tordoff 1954b). As a consequence, genera with ‘‘finch type’’ bills have been shuffled about taxonomically as have a few other genera (e.g. Cyanerpes, Spiza, Icteria) that failed to conform to one of the general adaptive (trophic) types. Because of the extreme morphological uniformity (i.e. paucity of phylogenetically informative characters), earlier oscine classifications lacked insight into among-group relationships, and with the exception of Raikow’s (1978) cladistic analysis, few offer much in the way of testable phylogenetic hypotheses. Classifications based on a new source of data, DNA-DNA hybridization comparisons (Bledsoe 1988, Sibley and Ahlquist 1990), have provided a fresh perspective that has challenged traditional views by demonstrating that the adaptive radiation of New World nine-primaried oscines is characterized by convergence at many levels. These molecular phylogenies have provided novel insights concerning the phylogenetic placement of difficult (anomalous) genera and also furnished testable hypotheses of relationships among groups. More recently, the direct sequencing of mitochondrial DNA (mtDNA) has provided an abundance of characters for the construction of phylogenetic hypotheses (e.g. see Mindell 1997). Despite much prior debate, it is now generally accepted (i.e. the prevailing phylogenetic hypotheses suggest) that the New World nineprimaried oscines (the Fringillidae of Sibley and Ahlquist [1990]) are comprised of two main sister clades, one containing the fringilline and cardueline finches along with the Hawaiian honeycreepers (subfamily Fringillinae), and the other (subfamily Emberizinae) consisting of the tribes Emberizini (true buntings and New World sparrows), Parulini (wood-warblers), Thraupini (tanagers and tanager-finches), Cardinalini (cardinal-grosbeaks), and Icterini (blackbirds and allies). Because Fringillinae is considered primarily an Old World group, and most members of the Emberizinae are thought to be of New World origin, the latter is the more narrowly defined ‘‘New World nine-primaried oscines’’ of some authors (e.g. Sibley and Ahlquist 1990). Because neither subfamily is strictly Old or New World in distribution, we favor the traditional and more inclusive definition of this term. The monotypic genus Peucedramus, long considered a member of Parulini, has been excluded from that group on both morphological (George 1962) and biochemical grounds (Sibley and Ahlquist 1990) and is tentatively considered the sister taxon (subfamily Peucedraminae) to all other members of the nine-primaried oscine clade. Perhaps the most important component of any systematic study is defining a monophyletic group within which systematic relationships are to be addressed. If the monophyly of the group of interest is not certain, then a systematic study can be compromised (Lanyon 1994). The goal of this study was to test hypotheses of monophyly within the nine-primaried oscine assemblage using mtDNA sequences. We focus in particular on the five tribes that constitute the subfamily Emberizinae. To this end, we sampled representatives of each of the three outlined subfamilies, including several typically problematic taxa, and sequenced 1,929 base pairs of the mitochondrial genome. We analyzed these data with a series of phylogenetic reconstruction methods. From these analyses, we attempt to unravel the problematic relationships within the nine-primaried oscines and present a phylogenetic hypothesis as a framework for future systematic studies of the nine-primaried oscines.