Complete species-level phylogeny of the leaf warbler (Aves: Phylloscopidae) radiation

The formation of the Indo-Pacific montane avifauna

The processes generating the earth's montane biodiversity remain a matter of debate. Two contrasting hypotheses have been advanced to explain how montane populations form: via direct colonization from other mountains, or, alternatively, via upslope range shifts from adjacent lowland areas. We seek to reconcile these apparently conflicting hypotheses by asking whether a species' ancestral geographic origin determines its mode of mountain colonization. Island-dwelling passerine birds at the faunal crossroads between Eurasia and Australo-Papua provide an ideal study system. We recover the phylogenetic relationships of the region's montane species and reconstruct their ancestral geographic ranges, elevational ranges, and migratory behavior. We also perform genomic population studies of three super-dispersive montane species/clades with broad island distributions. Eurasian-origin species populated archipelagos via direct colonization between mountains. This mode of colonization appears related to ancestral adaptations to cold and seasonal climates, specifically short-distance migration. Australo-Papuan-origin mountain populations, by contrast, evolved from lowland ancestors, and highland distribution mostly precludes their further colonization of island mountains. Our study explains much of the distributional variation within a complex biological system, and provides a synthesis of two seemingly discordant hypotheses for montane community formation.

Mitochondrial genome characteristics of six Phylloscopus species and their phylogenetic implication

The mitochondrial genomes of six Phylloscopus species-small insectivores belonging to the Phylloscopidae family-were obtained using the Illumina sequencing platform. The mitogenomes were closed circular molecules 16,922-17,007 bp in size, containing 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and two control regions (CR1 and remnant CR2). The gene orders were conserved in 35 sampled Phylloscopus mitogenomes in the GenBank database, with a gene rearrangement of cytb-trnT-CR1-trnP-nad6-trnE-remnant CR2-trnF-rrnS. The average base compositions of the six Phylloscopus mitogenomes were 29.43% A, 32.75% C, 14.68% G, and 23.10% T, with the A+T content slightly higher than that of G+C. ATG and TAA were the most frequent initiating and terminating codons, respectively. Several conserved boxes were identified in CR1, including C-string in domain I; F, E, D, and C boxes, as well as bird similarity and B boxes, in domain II; and CSB1 in domain III. Tandem repeats were observed in remnant CR2 of the Phylloscopus fuscatus and Phylloscopus proregulus mitogenomes. A phylogenetic analysis with maximum likelihood (ML) and Bayesian inference (BI) methods, based on 13 protein-coding genes and two rRNA genes, indicated that the Phylloscopus species was divided into two larger clades, with a splitting time approximately 11.06 million years ago (mya). The taxa of Phylloscopus coronatus/Phylloscopus burkii and Phylloscopus inornatus/P. proregulus were located at the basal position of the different clades. The phylogenetic result of the cox1 gene showed that Seicercus was nested within Phylloscopus. The complete set of mitogenomes of the Phylloscopus species provides potentially useful resources for the further exploration of the taxonomic status and phylogenetic history of Phylloscopidae.

Inversions maintain differences between migratory phenotypes of a songbird

Structural rearrangements have been shown to be important in local adaptation and speciation, but have been difficult to reliably identify and characterize in non-model species. Here we combine long reads, linked reads and optical mapping to characterize three divergent chromosome regions in the willow warbler Phylloscopus trochilus, of which two are associated with differences in migration and one with an environmental gradient. We show that there are inversions (0.4-13 Mb) in each of the regions and that the divergence times between inverted and non-inverted haplotypes are similar across the regions (~1.2 Myrs), which is compatible with a scenario where inversions arose in either of two allopatric populations that subsequently hybridized. The improved genomes allow us to detect additional functional differences in the divergent regions, providing candidate genes for migration and adaptations to environmental gradients.

Speciation and population divergence in a mutualistic seed dispersing bird

Bird-mediated seed dispersal is crucial for the regeneration and viability of ecosystems, often resulting in complex mutualistic species networks. Yet, how this mutualism drives the evolution of seed dispersing birds is still poorly understood. In the present study we combine whole genome re-sequencing analyses and morphometric data to assess the evolutionary processes that shaped the diversification of the Eurasian nutcracker (Nucifraga), a seed disperser known for its mutualism with pines (Pinus). Our results show that the divergence and phylogeographic patterns of nutcrackers resemble those of other non-mutualistic passerine birds and suggest that their early diversification was shaped by similar biogeographic and climatic processes. The limited variation in foraging traits indicates that local adaptation to pines likely played a minor role. Our study shows that close mutualistic relationships between bird and plant species might not necessarily act as a primary driver of evolution and diversification in resource-specialized birds.

Genomic and phylogeographic analyses indicate that resource-specialization did not play a major role in the diversification and speciation of seed dispersing nutcrackers

Most Genomic Loci Misrepresent the Phylogeny of an Avian Radiation Because of Ancient Gene Flow

Phylogenetic trees based on genome-wide sequence data may not always represent the true evolutionary history for a variety of reasons. One process that can lead to incorrect reconstruction of species phylogenies is gene flow, especially if interspecific gene flow has affected large parts of the genome. We investigated phylogenetic relationships within a clade comprising eight species of passerine birds (Phylloscopidae, Phylloscopus, leaf warblers) using one de novo genome assembly and 78 resequenced genomes. On the basis of hypothesis-exclusion trials based on D-statistics, phylogenetic network analysis, and demographic inference analysis, we identified ancient gene flow affecting large parts of the genome between one species and the ancestral lineage of a sister species pair. This ancient gene flow consistently caused erroneous reconstruction of the phylogeny when using large amounts of genome-wide sequence data. In contrast, the true relationships were captured when smaller parts of the genome were analyzed, showing that the "winner-takes-all democratic majority tree" is not necessarily the true species tree. Under this condition, smaller amounts of data may sometimes avoid the effects of gene flow due to stochastic sampling, as hidden reticulation histories are more likely to emerge from the use of larger data sets, especially whole-genome data sets. In addition, we also found that genomic regions affected by ancient gene flow generally exhibited higher genomic differentiation but a lower recombination rate and nucleotide diversity. Our study highlights the importance of considering reticulation in phylogenetic reconstructions in the genomic era.[Bifurcation; introgression; recombination; reticulation; Phylloscopus.].

Chromosome-Level Genome Assembly of the Common Chaffinch (Aves: Fringilla coelebs): A Valuable Resource for Evolutionary Biology

The common chaffinch, Fringilla coelebs, is one of the most common, widespread, and well-studied passerines in Europe, with a broad distribution encompassing Western Europe and parts of Asia, North Africa, and the Macaronesian archipelagos. We present a high-quality genome assembly of the common chaffinch generated using Illumina shotgun sequencing in combination with Chicago and Hi-C libraries. The final genome is a 994.87-Mb chromosome-level assembly, with 98% of the sequence data located in chromosome scaffolds and a N50 statistic of 69.73 Mb. Our genome assembly shows high completeness, with a complete BUSCO score of 93.9% using the avian data set. Around 7.8% of the genome contains interspersed repetitive elements. The structural annotation yielded 17,703 genes, 86.5% of which have a functional annotation, including 7,827 complete universal single-copy orthologs out of 8,338 genes represented in the BUSCO avian data set. This new annotated genome assembly will be a valuable resource as a reference for comparative and population genomic analyses of passerine, avian, and vertebrate evolution.

A lost world in Wallacea: Description of a montane archipelagic avifauna

Birds are the best-known animal class, with only about five or six new species descriptions per year since 1999. Integrating genomic and phenotypic research with arduous fieldwork in remote regions, we describe five new songbird species and five new subspecies from a small area near Sulawesi, Indonesia, all collected in a single 6-week expedition. Two factors contributed to the description of this large number of species from such a small geographic area: (i) Knowledge of Quaternary Period land connections helped pinpoint isolated islands likely to harbor substantial endemism and (ii) studying accounts of historic collectors such as Alfred Wallace facilitated the identification of undercollected islands. Our findings suggest that humans’ understanding of biogeographically complex regions such as Wallacea remains incomplete.

'Ghost introgression' as a cause of deep mitochondrial divergence in a bird species complex

In the absence of nuclear-genomic differentiation between two populations, deep mitochondrial divergence (DMD) is a form of mito-nuclear discordance. Such instances of DMD are rare and might variably be explained by unusual cases of female-linked selection, by male-biased dispersal, by 'speciation reversal' or by mitochondrial capture through genetic introgression. Here we analyze DMD in an Asian Phylloscopus leaf warbler (Aves: Phylloscopidae) complex. Bioacoustic, morphological and genomic data demonstrate close similarity between the taxa affinis and occisinensis, even though DMD previously led to their classification as two distinct species. Using population genomic and comparative genomic methods on 45 whole genomes, including historical reconstructions of effective population size, genomic peaks of differentiation and genomic linkage, we infer that the form affinis is likely the product of a westward expansion in which it replaced a now-extinct congener that was the donor of its mtDNA and small portions of its nuclear genome. This study provides strong evidence of 'ghost introgression' as the cause of DMD, and we suggest that 'ghost introgression' may be a widely overlooked phenomenon in nature.

A striking new species of leaf warbler from the Lesser Sundas as uncovered through morphology and genomics

Leaf warblers (Aves; Phylloscopidae) are a diverse clade of insectivorous, canopy-dwelling songbirds widespread across the Old World. The taxonomy of Australasian leaf warblers is particularly complex, with multiple species-level divergences between island taxa in the region requiring further scrutiny. We use a combination of morphology, bioacoustics, and analysis of thousands of genome-wide markers to investigate and describe a new species of Phylloscopus leaf warbler from the island of Rote in the Lesser Sundas, Indonesia. We show that this new Rote Leaf Warbler is morphologically and genomically highly distinct from its congenerics, but do not find vocal differentiation between different island taxa. We discuss the behaviour and ecology of this highly distinctive new species, and make recommendations about its conservation status. We believe this constitutes the first description of a novel bird species that is partly based on insights from massive amounts of genome-wide DNA markers.