Demography and linked selection interact to shape the genomic landscape of codistributed woodpeckers during the Ice Age.

The influence of genetic drift on population dynamics during Pleistocene glacial cycles is well understood, but the role of selection in shaping patterns of genomic variation during these events is less explored. We resequenced whole genomes to investigate how demography and natural selection interact to generate the genomic landscapes of Downy and Hairy Woodpecker, species codistributed in previously glaciated North America. First, we explored the spatial and temporal patterns of genomic diversity produced by neutral evolution. Next, we tested (i) whether levels of nucleotide diversity along the genome are correlated with intrinsic genomic properties, such as recombination rate and gene density, and (ii) whether different demographic trajectories impacted the efficacy of selection. Our results revealed cycles of bottleneck and expansion, and genetic structure associated with glacial refugia. Nucleotide diversity varied widely along the genome, but this variation was highly correlated between the species, suggesting the presence of conserved genomic features. In both taxa, nucleotide diversity was positively correlated with recombination rate and negatively correlated with gene density, suggesting that linked selection played a role in reducing diversity. Despite strong fluctuations in effective population size, the maintenance of relatively large populations during glaciations may have facilitated selection. Under these conditions, we found evidence that the individual demographic trajectory of populations modulated linked selection, with purifying selection being more efficient in removing deleterious alleles in large populations. These results highlight that while genome-wide variation reflects the expected signature of demographic change during climatic perturbations, the interaction of multiple processes produces a predictable and highly heterogeneous genomic landscape.

The Genomic Signature of Allopatric Speciation in a Songbird Is Shaped by Genome Architecture (Aves: Certhia americana).

The genomic signature of speciation with gene flow is often attributed to the strength of divergent selection and recombination rate in regions harboring targets for selection. In contrast, allopatric speciation provides a different geographic context and evolutionary scenario, whereby introgression is limited by isolation rather than selection against gene flow. Lacking shared divergent selection or selection against hybridization, we would predict the genomic signature of allopatric speciation would largely be shaped by genomic architecture-the nonrandom distribution of functional elements and chromosomal characteristics-through its role in affecting the processes of selection and drift. Here, we built and annotated a chromosome-scale genome assembly for a songbird (Passeriformes: Certhia americana). We show that the genomic signature of allopatric speciation between its two primary lineages is largely shaped by genomic architecture. Regionally, gene density and recombination rate variation explain a large proportion of variance in genomic diversity, differentiation, and divergence. We identified a heterogeneous landscape of selection and neutrality, with a large portion of the genome under the effects of indirect selection. We found higher proportions of small chromosomes under the effects of indirect selection, likely because they have relatively higher gene density. At the chromosome scale, differential genomic architecture of macro- and microchromosomes shapes the genomic signatures of speciation: chromosome size has: 1) a positive relationship with genetic differentiation, genetic divergence, rate of lineage sorting in the contact zone, and proportion neutral evolution and 2) a negative relationship with genetic diversity and recombination rate.

Cryptic diversity across the Trans-Mexican Volcanic Belt of Mexico in the montane bunchgrass lizard Sceloporus subniger/ (Squamata: Phrynosomatidae).

Sceloporus subniger Poglaygen Smith is a montane bunchgrass lizard distributed across pine-oak forests of central Mexico. Prompted by the discovery of a new population of this lizard in far western Mexico, and by recent studies suggesting S. subniger may be a composite of several distinct species, we examined in more detail the genetic structure of S. subniger. We generated a mitochondrial DNA (mtDNA) dataset from 81 specimens and an ultraconserved elements (UCE) dataset representing thousands of genomic regions from 12 specimens to specifically evaluate the genetic distinctiveness of populations from western Michoacán and adjacent Jalisco along with the newly discovered population in the Sierra de Mascota in western Jalisco. We also recorded morphological data from 47 museum specimens to compare to our genetic data. Results from our analyses of the genetic data, augmented by specimen measurements and scale counts, support the notion that S. subniger is indeed a composite of distinct species. Montane bunchgrass lizards from western Michoacán and adjacent Jalisco, and from the Sierra de Mascota in western Jalisco, each represent distinct new species, which we describe and name here.

Cryptic and extensive hybridization between ancient lineages of American crows.

Most species and therefore most hybrid zones have historically been defined using phenotypic characters. However, both speciation and hybridization can occur with negligible morphological differentiation. Recently developed genomic tools provide the means to better understand cryptic speciation and hybridization. The Northwestern Crow (Corvus caurinus) and American Crow (Corvus brachyrhynchos) are continuously distributed sister taxa that lack reliable traditional characters for identification. In this first population genomic study of Northwestern and American crows, we use genomic SNPs (nuDNA) and mtDNA to investigate the degree of genetic differentiation between these crows and the extent to which they may hybridize. Our results indicate that American and Northwestern crows have distinct evolutionary histories, supported by two nuDNA ancestry clusters and two 1.1%-divergent mtDNA clades dating to the late Pleistocene, when glacial advances may have isolated crow populations in separate refugia. We document extensive hybridization, with geographic overlap of mtDNA clades and admixture of nuDNA across >900 km of western Washington and western British Columbia. This broad hybrid zone consists of late-generation hybrids and backcrosses, but not recent (e.g., F1) hybrids. Nuclear DNA and mtDNA clines had concordant widths and were both centred in southwestern British Columbia, farther north than previously postulated. Overall, our results suggest a history of reticulate evolution in American and Northwestern crows, perhaps due to recurring neutral expansion(s) from Pleistocene glacial refugia followed by lineage fusion(s). However, we do not rule out a contributing role for more recent potential drivers of hybridization, such as expansion into human-modified habitats.

Dense Geographic and Genomic Sampling Reveals Paraphyly and a Cryptic Lineage in a Classic Sibling Species Complex.

Incomplete or geographically biased sampling poses significant problems for research in phylogeography, population genetics, phylogenetics, and species delimitation. Despite the power of using genome-wide genetic markers in systematics and related fields, approaches such as the multispecies coalescent remain unable to easily account for unsampled lineages. The Empidonax difficilis/Empidonax occidentalis complex of small tyrannid flycatchers (Aves: Tyrannidae) is a classic example of widely distributed species with limited phenotypic geographic variation that was broken into two largely cryptic (or "sibling") lineages following extensive study. Though the group is well-characterized north of the US Mexico border, the evolutionary distinctiveness and phylogenetic relationships of southern populations remain obscure. In this article, we use dense genomic and geographic sampling across the majority of the range of the E. difficilis/E. occidentalis complex to assess whether current taxonomy and species limits reflect underlying evolutionary patterns, or whether they are an artifact of historically biased or incomplete sampling. We find that additional samples from Mexico render the widely recognized species-level lineage E. occidentalis paraphyletic, though it retains support in the best-fit species delimitation model from clustering analyses. We further identify a highly divergent unrecognized lineage in a previously unsampled portion of the group's range, which a cline analysis suggests is more reproductively isolated than the currently recognized species E. difficilis and E. occidentalis. Our phylogeny supports a southern origin of these taxa. Our results highlight the pervasive impacts of biased geographic sampling, even in well-studied vertebrate groups like birds, and illustrate what is a common problem when attempting to define species in the face of recent divergence and reticulate evolution.

Cryptic diversity in the Mexican highlands: Thousands of UCE loci help illuminate phylogenetic relationships, species limits and divergence times of montane rattlesnakes (Viperidae: Crotalus).

With the continued adoption of genome-scale data in evolutionary biology comes the challenge of adequately harnessing the information to make accurate phylogenetic inferences. Coalescent-based methods of species tree inference have become common, and concatenation has been shown in simulation to perform well, particularly when levels of incomplete lineage sorting are low. However, simulation conditions are often overly simplistic, leaving empiricists with uncertainty regarding analytical tools. We use a large ultraconserved element data set (>3,000 loci) from rattlesnakes of the Crotalus triseriatus group to delimit lineages and estimate species trees using concatenation and several coalescent-based methods. Unpartitioned and partitioned maximum likelihood and Bayesian analysis of the concatenated matrix yield a topology identical to coalescent analysis of a subset of the data in bpp. ASTRAL analysis on a subset of the more variable loci also results in a tree consistent with concatenation and bpp, whereas the SVDquartets phylogeny differs at additional nodes. The size of the concatenated matrix has a strong effect on species tree inference using SVDquartets, warranting additional investigation on optimal data characteristics for this method. Species delimitation analyses suggest up to 16 unique lineages may be present within the C. triseriatus group, with divergences occurring during the Neogene and Quaternary. Network analyses suggest hybridization within the group is relatively rare. Altogether, our results reaffirm the Mexican highlands as a biodiversity hotspot and suggest that coalescent-based species tree inference on data subsets can provide a strongly supported species tree consistent with concatenation of all loci with a large amount of missing data.

Deep divergence of Red-crowned Ant Tanager (Habia rubica: Cardinalidae), a multilocus phylogenetic analysis with emphasis in Mesoamerica.

Many neotropical species have a complex history of diversification as a result of the influence of geographical, ecological, climatic, and geological factors that determine the distribution of populations within a lineage. Phylogeography identifies such populations, determines their geographic distributions, and quantifies the degree of genetic divergence. In this work we explored the genetic structure of Habia rubica populations, a polytypic taxon with 17 subspecies described, in order to obtain hypotheses about their evolutionary history and processes of diversification. We undertook multilocus analyses using sequences of five molecular markers (ND2, ACOI-I9, MUSK, FGB-I5 and ODC), and sampling from across the species' distribution range, an area encompassing from Central Mexico throughout much of South America. With these data, we obtained a robust phylogenetic hypothesis, a species delimitation analysis, and estimates of divergence times for these lineages. The phylogenetic hypothesis of concatenated molecular markers shows that H. rubica can be divided in three main clades: the first includes Mexican Pacific coast populations, the second is formed by population from east of Mexico to Panama and the third comprises the South American populations. Within these clades we recognize seven principal phylogroups whose limits have a clear correspondence with important geographical discontinuities including the Isthmus of Tehuantepec in southern Mexico, the Talamanca Cordillera, and the Isthmus of Panama in North America. In South America, we observed a marked separation of two phylogroups that include the populations that inhabit mesic forests in western and central South America (Amazon Forest) and those inhabiting the seasonal forest from the eastern and northern regions of the South America (Atlantic Forest). These areas are separated by an intervening dry vegetation "diagonal" (Chaco, Cerrado and Caatinga). The geographic and genetic structure of these phylogroups describes a history of diversification more active and complex in the northern distribution of this species, producing at least seven well-supported lineages that could be considered species.

Species delimitation and biogeography of the gnatcatchers and gnatwrens (Aves: Polioptilidae).

The New World avian family Polioptilidae (gnatcatchers and gnatwrens) is distributed from Argentina to Canada and includes 15 species and more than 60 subspecies. No study to date has evaluated phylogenetic relationships within this family and the historical pattern of diversification within the group remains unknown. Moreover, species limits, particularly in widespread taxa that show geographic variation, remain unclear. In this study, we delimited species and estimated phylogenetic relationships using multilocus data for the entire family. We then used the inferred diversity along with alternative taxonomic classification schemes to evaluate how lumping and splitting of both taxa and geographical areas influenced biogeographic inference. Species-tree analyses grouped Polioptilidae into four main clades: Microbates, Ramphocaenus, a Polioptila guianensis complex, and the remaining members of Polioptila. Ramphocaenus melanurus was sister to the clade containing M. cinereiventris and M. collaris, which formed a clade sister to all species within Polioptila. Polioptila was composed of two clades, the first of which included the P. guianensis complex; the other contained all remaining species in the genus. Using multispecies coalescent modeling, we inferred a more than 3-fold increase in species diversity, of which 87% represent currently recognized species or subspecies. Much of this diversity corresponded to subspecies that occur in the Neotropics. We identified three polyphyletic species, and delimited 4-6 previously undescribed candidate taxa. Probabilistic modeling of geographic ranges on the species tree indicated that the family likely had an ancestral origin in South America, with all three genera independently colonizing North America. Support for this hypothesis, however, was sensitive to the taxonomic classification scheme used and the number of geographical areas allowed. Our study proposes the first phylogenetic hypothesis for Polioptilidae and provides genealogical support for the reclassification of species limits. Species limits and the resolution of geographical areas that taxa inhabit influence the inferred spatial diversification history.

Phylogenomic insights into the diversification of salamanders in the Isthmura bellii group across the Mexican highlands.

Mountain formation in Mexico has played an important role in the diversification of many Mexican taxa. The Trans-Mexican Volcanic Belt in particular has served as both a cradle of diversification and conduit for dispersal. We investigated the evolutionary history of the Isthmura bellii group of salamanders, a widespread amphibian across the Mexican highlands, using sequence capture of ultraconserved elements. Results suggest that the I. bellii group probably originated in southeastern Mexico in the late Miocene and later dispersed across the Trans-Mexican Volcanic Belt and into the Sierra Madre Occidental. Pre-Pleistocene uplift of the Trans-Volcanic Belt likely promoted early diversification by serving as a mesic land-bridge across central Mexico. These findings highlight the importance of the Trans-Volcanic Belt in generating Mexico's rich biodiversity.

A Migratory Divide in the Painted Bunting (Passerina ciris).

In the painted bunting (Passerina ciris), a North American songbird, populations on the Atlantic coast and interior southern United States are known to be allopatric during the breeding season, but efforts to map connectivity with wintering ranges have been largely inconclusive. Using genomic and morphological data from museum specimens and banded birds, we found evidence of three genetically differentiated painted bunting populations with distinct wintering ranges and molt-migration phenologies. In addition to confirming that the Atlantic coast population remains allopatric throughout the annual cycle, we identified an unexpected migratory divide within the interior breeding range. Populations breeding in Louisiana winter on the Yucatán Peninsula and are parapatric with other interior populations that winter in mainland Mexico and Central America. Across the interior breeding range, genetic ancestry is also associated with variation in wing length, suggesting that selection may be promoting morphological divergence in populations with different migration strategies.

Cryptic speciation and gene flow in a migratory songbird Species Complex: Insights from the Red-Eyed Vireo (Vireo olivaceus).

Migratory species that alternate between sympatry and allopatry over the course of an annual cycle are promising subjects for studies seeking to understand the process of speciation in the absence of strict geographic isolation. Here we sought to identify cryptic species and assess rates of gene flow in a clade of neotropical migrant songbirds in which geography and taxonomy are currently out of sync: the Red-Eyed Vireo (V. olivaceus) Species Complex. Phylogenetic, clustering, and statistical species delimitation analyses found that V. olivaceusincludes two non-sister lineages migrating in opposite directions across the equator. Analyses of gene flow identified low levels of introgression between two species pairs, but none between northern and southern olivaceus. We also identified substantial well-supported conflicts between nuclear and mitochondrial topologies. Although the geographic distribution of mito-nuclear discordance is suggestive of hybridization and mitochondrial capture, we found no evidence of introgression in the nuclear genome of populations with discordant mitochondrial gene trees. Our study finds that species boundaries match breeding range and migratory phenology rather than the existing taxonomy in this group, and demonstrates the utility of genomic data in inferring species boundaries in recently diverged clades.

The biogeographic and evolutionary history of an endemic clade of Middle American sparrows: Melozone and Aimophila (Aves: Passerellidae).

The large number of endemic species in Middle America is frequently attributed to the interplay of geographical barriers and historical climatic changes in the region. This process promotes genetic divergence between populations, and given enough time, may yield new species. Animals that inhabit mid-elevation or highland habitats may be disproportionately affected in this way. Genetic analyses of animals in this region allow us to better understand how historical patterns of isolation have influenced the generation of new species in this biodiversity hotspot. We studied the biogeography and systematics of two closely related genera of sparrows (Passerellidae): Melozone and Aimophila. Collectively, this group is distributed from the southwestern United States and southward as far as central Costa Rica. We sampled 81 individuals of 8 Melozone and 2 Aimophila species, from 19 localities distributed throughout their ranges. We reconstructed phylogenetic relationships and time-calibrated species trees using multilocus sequence data comprised of one mitochondrial gene and five nuclear genes. We conducted an ancestral area reconstruction analysis to determine the probability of ancestral range at each divergent event. Despite analyzing six loci, we were unable to obtain a fully resolved phylogenetic tree. We recovered four main lineages: lineage 1 includes four Melozone species distributed north of Isthmus of Tehuantepec (M. albicollis, M. crissalis, M. aberti, M. fusca); lineage 2 includes three Melozone species distributed south of the Isthmus of Tehuantepec (M. biarcuata, M. cabanisi, M. leucotis); lineage 3 lineage consists of a single species endemic to the Pacific coast of Mexico (M. kieneri); and lineage 4 includes the more widely distributed sparrows in the genus Aimophila. Our analyses suggest that these genera probably originated during the late Miocene in the Madrean Highlands of southern Mexico. We identified dispersal as the prevalent cause of speciation in this clade with most lineages dispersing to their current distributions from southern Mexico either to the north following a developing and expanding Madro-Tertiary flora, or to the south across the Isthmus of Tehuantepec. A similar pattern of dispersal from this biogeographic region has been reported in other taxa including fishes, reptiles, and birds. Our results reveal that the four lineages identified represent geographically coherent and ecologically similar assemblages of taxa. Finally, when our genetic results are considered, along with apparent differences in morphology and song, the allopatric forms M. b. cabanisi and M. l. occipitalis warrant recognition as biological species.

How Many Kinds of Birds Are There and Why Does It Matter?

Estimates of global species diversity have varied widely, primarily based on variation in the numbers derived from different inventory methods of arthropods and other small invertebrates. Within vertebrates, current diversity metrics for fishes, amphibians, and reptiles are known to be poor estimators, whereas those for birds and mammals are often assumed to be relatively well established. We show that avian evolutionary diversity is significantly underestimated due to a taxonomic tradition not found in most other taxonomic groups. Using a sample of 200 species taken from a list of 9159 biological species determined primarily by morphological criteria, we applied a diagnostic, evolutionary species concept to a morphological and distributional data set that resulted in an estimate of 18,043 species of birds worldwide, with a 95% confidence interval of 15,845 to 20,470. In a second, independent analysis, we examined intraspecific genetic data from 437 traditional avian species, finding an average of 2.4 evolutionary units per species, which can be considered proxies for phylogenetic species. Comparing recent lists of species to that used in this study (based primarily on morphology) revealed that taxonomic changes in the past 25 years have led to an increase of only 9%, well below what our results predict. Therefore, our molecular and morphological results suggest that the current taxonomy of birds understimates avian species diversity by at least a factor of two. We suggest that a revised taxonomy that better captures avian species diversity will enhance the quantification and analysis of global patterns of diversity and distribution, as well as provide a more appropriate framework for understanding the evolutionary history of birds.

Hidden histories of gene flow in highland birds revealed with genomic markers.

Genomic studies are revealing that divergence and speciation are marked by gene flow, but it is not clear whether gene flow has played a prominent role during the generation of biodiversity in species-rich regions of the world where vicariance is assumed to be the principal mode by which new species form. We revisit a well-studied organismal system in the Mexican Highlands, Aphelocoma jays, to test for gene flow among Mexican sierras. Prior results from mitochondrial DNA (mtDNA) largely conformed to the standard model of allopatric divergence, although there was also evidence for more obscure histories of gene flow in a small sample of nuclear markers. We tested for these 'hidden histories' using genomic markers known as ultraconserved elements (UCEs) in concert with phylogenies, clustering algorithms and newer introgression tests specifically designed to detect ancient gene flow (e.g. ABBA/BABA tests). Results based on 4303 UCE loci and 2500 informative SNPs are consistent with varying degrees of gene flow among highland areas. In some cases, gene flow has been extensive and recent (although perhaps not ongoing today), whereas in other cases there is only a trace signature of ancient gene flow among species that diverged as long as 5 million years ago. These results show how a species complex thought to be a model for vicariance can reveal a more reticulate history when a broader portion of the genome is queried. As more organisms are studied with genomic data, we predict that speciation-with-bouts-of-gene-flow will turn out to be a common mode of speciation.

Polyphyly of Hylophilus and a new genus for the Tawny-crowned Greenlet (Aves: Passeriformes: Vireonidae).

Once a catch-all taxon for various small, greenish passerines (Sclater 1881), today the genus Hylophilus Temminck contains 15 species of Neotropical greenlets in the avian family Vireonidae (Clements et al. 2013). Although Hylophilus species do share some common anatomical proportions and plumage features (Baird 1866; Ridgway 1904), some striking and concordant differences in habitat, voice, and iris color led Ridgely and Tudor (1989) to posit that the genus might contain sufficient diversity to warrant splitting into multiple genera.

A multilocus phylogeny of a major New World avian radiation: the Vireonidae.

The family Vireonidae represents one of the most widespread and well-known New World avian radiations, but a robust species-level phylogeny of the group is lacking. Here, we infer a phylogeny of Vireonidae using multilocus data obtained from 221 individuals from 46 of 52 vireonid species (representing all four genera) and five "core Corvoidea" outgroups. Our results show Vireonidae to be monophyletic, consistent with a single colonization of the New World by an Asian ancestor. Cyclarhis and Vireolanius are monophyletic genera that diverged early from the rest of Vireonidae. Hylophilus is polyphyletic, represented by three distinct clades concordant with differences in morphology, habitat, and voice. The poorly known South American species Hylophilus sclateri is embedded within the genus Vireo. Vireo, in turn, consists of several well-supported intrageneric clades. Overall, tropical vireonid species show much higher levels of intraspecific genetic structure than temperate species and several currently recognized species are probably comprised of multiple cryptic species.

A comprehensive multilocus assessment of sparrow (Aves: Passerellidae) relationships.

The New World sparrows (Emberizidae) are among the best known of songbird groups and have long-been recognized as one of the prominent components of the New World nine-primaried oscine assemblage. Despite receiving much attention from taxonomists over the years, and only recently using molecular methods, was a "core" sparrow clade established allowing the reconstruction of a phylogenetic hypothesis that includes the full sampling of sparrow species diversity. In this paper, we use mitochondrial DNA gene sequences from all 129 putative species of sparrow and four additional (nuclear) loci for a subset of these taxa to resolve both generic and species level relationships. Hypotheses derived from our mitochondrial (2184 base pairs) and nuclear (5705 base pairs) DNA data sets were generally in agreement with respect to clade constituency but differed somewhat with respect to among-clade relationships. Sparrow diversity is defined predominantly by eight well-supported clades that indicate a lack of monophyly for at least three currently recognized genera. Ammodramus is polyphyletic and requires the naming of two additional genera. Spizella is also polyphyletic with Tree Sparrow (Spizella arborea) as a taxonomic "outlier". Pselliophorus is embedded within a larger Atlapetes assemblage and should be merged with that group. This new hypothesis of sparrow relationships will form the basis for future comparative analyses of variation within songbirds.

Extensive gene flow characterizes the phylogeography of a North American migrant bird: Black-headed Grosbeak (Pheucticus melanocephalus).

We describe range-wide phylogeographic variation in the Black-headed Grosbeak (Pheucticus melanocephalus), a songbird that is widely distributed across North American scrublands and forests. Phylogenetic analysis of mitochondrial DNA (mtDNA, n=424) revealed three geographically structured clades. One widespread clade occurs throughout the Rocky Mountains, Great Basin, and Mexican Plateau, a second clade is found on the Pacific coast and in coastal ranges; and, a third in the Sierra Madre del Sur of Oaxaca and Guerrero. Some geographical structuring occurs in Mexican Plateau and Sierra Madre Oriental mtDNA clade, presumably because these populations have been more stable over time than northern populations. Multiple mitochondrial groups are found sympatrically in the Okanogan River Valley in Washington, the eastern Sierra Nevada, and the Transvolcanic Belt across central Mexico, indicating that there is a potential for introgression. Analyses of 12 nuclear loci did not recover the same geographically structured clades. Population analyses show high levels of gene flow in nucDNA from the Interior into the Sierra Madre del Sur and Pacific population groups, possibly indicating expansion of the Interior population at the expense of peripheral populations.

Phylogenetics and diversification of tanagers (Passeriformes: Thraupidae), the largest radiation of Neotropical songbirds.

Thraupidae is the second largest family of birds and represents about 4% of all avian species and 12% of the Neotropical avifauna. Species in this family display a wide range of plumage colors and patterns, foraging behaviors, vocalizations, ecotypes, and habitat preferences. The lack of a complete phylogeny for tanagers has hindered the study of this evolutionary diversity. Here, we present a comprehensive, species-level phylogeny for tanagers using six molecular markers. Our analyses identified 13 major clades of tanagers that we designate as subfamilies. In addition, two species are recognized as distinct branches on the tanager tree. Our topologies disagree in many places with previous estimates of relationships within tanagers, and many long-recognized genera are not monophyletic in our analyses. Our trees identify several cases of convergent evolution in plumage ornaments and bill morphology, and two cases of social mimicry. The phylogeny produced by this study provides a robust framework for studying macroevolutionary patterns and character evolution. We use our new phylogeny to study diversification processes, and find that tanagers show a background model of exponentially declining diversification rates. Thus, the evolution of tanagers began with an initial burst of diversification followed by a rate slowdown. In addition to this background model, two later, clade-specific rate shifts are supported, one increase for Darwin's finches and another increase for some species of Sporophila. The rate of diversification within these two groups is exceptional, even when compared to the overall rapid rate of diversification found within tanagers. This study provides the first robust assessment of diversification rates for the Darwin's finches in the context of the larger group within which they evolved.

A comprehensive species-level molecular phylogeny of the New World blackbirds (Icteridae).

The New World blackbirds (Icteridae) are among the best known songbirds, serving as a model clade in comparative studies of morphological, ecological, and behavioral trait evolution. Despite wide interest in the group, as yet no analysis of blackbird relationships has achieved comprehensive species-level sampling or found robust support for most intergeneric relationships. Using mitochondrial gene sequences from all ∼108 currently recognized species and six additional distinct lineages, together with strategic sampling of four nuclear loci and whole mitochondrial genomes, we were able to resolve most relationships with high confidence. Our phylogeny is consistent with the strongly-supported results of past studies, but it also contains many novel inferences of relationship, including unexpected placement of some newly-sampled taxa, resolution of relationships among major clades within Icteridae, and resolution of genus-level relationships within the largest of those clades, the grackles and allies. We suggest taxonomic revisions based on our results, including restoration of Cacicus melanicterus to the monotypic Cassiculus, merging the monotypic Ocyalus and Clypicterus into Cacicus, restoration of Dives atroviolaceus to the monotypic Ptiloxena, and naming Curaeus forbesi to a new genus, Anumara. Our hypothesis of blackbird phylogeny provides a foundation for ongoing and future evolutionary analyses of the group.