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The Solomon Islands host a diverse terrestrial vertebrate fauna which has played a formative role in the development of speciation theory. Yet, despite over a century of biological exploration in the region, there are many islands for which we have incomplete knowledge of the vertebrate fauna. In 2019, we spent 20 days on Tetepare Island in the Western Province, Solomon Islands. Tetepare has a long history of conservation action by local communities and it is now the largest uninhabited tropical island in the world. We recorded 57 species of birds, 13 mammals, 5 amphibians, and 21 reptiles. Of these, we documented six species for the first time on Tetepare by western scientists: one frog, three non-avian reptiles, and two mammals. These findings point to a continued need for basic biological inventory work to inform research, local conservation efforts, and to increase published knowledge of the biodiversity in the Solomon Islands. Keywords: amphibians, birds, mammals, Melanesia, squamates, tropical South Pacific, Whitney South Sea Expedition, THE SOLOMON ARCHIPELAGO is a biodiverse region that is well known for its unique composition of terrestrial vertebrates (mammals, squamates, amphibians, and birds). Due in part to its high degree [...]

Secondary contact between closely related taxa represents a "moment of truth" for speciation—an opportunity to test the efficacy of reproductive isolation that evolved in allopatry and to identify the genetic, behavioral, and/or ecological barriers that separate species in sympatry. Sex chromosomes are known to rapidly accumulate differences between species, an effect that may be exacerbated for neo-sex chromosomes that are transitioning from autosomal to sex-specific inheritance. Here we report that, in the Solomon Islands, two closely related bird species in the honeyeater family—Myzomela cardinalis and Myzomela tristrami—carry neo-sex chromosomes and have come into recent secondary contact after ~1.1 my of geographic isolation. Hybrids of the two species were first observed in sympatry ~100 years ago. To determine the genetic consequences of hybridization, we use population genomic analyses of individuals sampled in allopatry and in sympatry to characterize gene flow in the contact zone. Using genome-wide estimates of diversity, differentiation, and divergence, we find that the degree and direction of introgression varies dramatically across the genome. For sympatric birds, autosomal introgression is bidirectional, with phenotypic hybrids and phenotypic parentals of both species showing admixed ancestry. In other regions of the genome, however, the story is different. While introgression on the Z/neo-Z-linked sequence is limited, introgression of W/neo-W regions and mitochondrial sequence (mtDNA) is highly asymmetric, moving only from the invading M. cardinalis to the resident M. tristrami. The recent hybridization between these species has thus enabled gene flow in some genomic regions but the interaction of admixture, asymmetric mate choice, and/or natural selection has led to the variation in the amount and direction of gene flow at sex-linked regions of the genome. Author summary: When an invasive species colonizes an island and interacts with a closely related resident species, we are provided with a rare opportunity to study the consequences of interbreeding and the factors that keep species distinct. Regions of the genome that evolve rapidly and/or influence mate choice may be especially likely to act as incidental barriers to gene flow. The red Myzomela cardinalis, birds in the honeyeater family, have invaded Makira in the Solomon Islands, coming into contact with the endemic, all black Myzomela tristrami. We used population genomic analyses of individuals in geographic isolation, and those in geographic contact, to understand the history of these two species and the consequences of their recent range overlap. We found that sex-specific regions of the genome (i.e., sex chromosomes) were either limited in their ability to move between species, or only moved in one direction, from the invading M. cardinalis to the resident M. tristrami. This work highlights how certain regions of the genome may be especially important in defining species boundaries and the generation and maintenance of biodiversity. [ABSTRACT FROM AUTHOR]

Body size is a key morphological attribute, often used to delimit species boundaries among closely related taxa. But body size can evolve in parallel, reaching similar final states despite independent evolutionary and geographic origins, leading to faulty assumptions of evolutionary history. Here, we document parallel evolution in body size in the widely distributed leaf-nosed bat genus Hipposideros , which has misled both taxonomic and evolutionary inference. We sequenced reduced representation genomic loci and measured external morphological characters from three closely related species from the Solomon Islands archipelago, delimited by body size. Species tree reconstruction confirms the paraphyly of two morphologically designated species. The nonsister relationship between large-bodied H. dinops lineages found on different islands indicates that large-bodied ecomorphs have evolved independently at least twice in the history of this radiation. A lack of evidence for gene flow between sympatric, closely related taxa suggests the rapid evolution of strong reproductive isolating barriers between morphologically distinct populations. Our results position Solomon Islands Hipposideros as a novel vertebrate system for studying the repeatability of parallel evolution under natural conditions. We conclude by offering testable hypotheses for how geography and ecology could be mediating the repeated evolution of large-bodied Hipposideros lineages in the Solomon Islands. [ABSTRACT FROM AUTHOR]

The Oriental Dwarf Kingfisher species‐complex of South and Southeast Asia comprises two forms, the dark‐backed Ceyx erithaca of India and Indochina and the rufous‐backed Ceyx rufidorsa of Java and the Lesser Sunda Islands. Between these two extremes, the large area of Sundaland and the Philippines is occupied by individuals that have a rufous back, characteristic of C. rufidorsa, but exhibit a range of phenotypes that are intermediate between C. erithaca and C. rufidorsa. These potential intermediates have intrigued avian taxonomists for generations. To investigate the species dynamics of the two forms and understand the demographic history of the intermediates, we generated a genome‐scale dataset (ddRAD) representing multiple individuals across the entire range of the complex. Our findings support the distinctiveness of the two forms based on back colour. Demographic analysis suggests the two populations were isolated c. 820 000 years ago followed by secondary contact c. 140 000 years ago, with asymmetrical dispersal of C. rufidorsa into C. erithaca. Although some limited introgression appears to have occurred more recently between the two taxa in the northern parts of their range, we were unable to find any association of recent hybridization with the intermediate plumages of C. rufidorsa. We also found no support for the commonly recognized Borneo subspecies motleyi. [ABSTRACT FROM AUTHOR]

Many organisms possess multiple discrete genomes (i.e. nuclear and organellar), which are inherited separately and may have unique and even conflicting evolutionary histories. Phylogenetic reconstructions from these discrete genomes can yield different patterns of relatedness, a phenomenon known as cytonuclear discordance. In many animals, mitonuclear discordance (i.e. discordant evolutionary histories between the nuclear and mitochondrial genomes) has been widely documented, but its causes are often considered idiosyncratic and inscrutable. We show that a case of mitonuclear discordance in Todiramphus kingfishers can be explained by extensive genome‐wide incomplete lineage sorting (ILS), likely a result of the explosive diversification history of this genus. For these kingfishers, quartet frequencies reveal that the nuclear genome is dominated by discordant topologies, with none of the internal branches in our consensus nuclear tree recovered in >50% of genome‐wide gene trees. Meanwhile, a lack of inter‐species shared ancestry, non‐significant pairwise tests for gene flow, and little evidence for meaningful migration edges between species, leads to the conclusion that gene flow cannot explain the mitonuclear discordance we observe. This lack of evidence for gene flow combined with evidence for extensive genome‐wide gene tree discordance, a hallmark of ILS, leads us to conclude that the mitonuclear discordance we observe likely results from ILS, specifically deep coalescence of the mitochondrial genome. Based on this case study, we hypothesize that similar demographic histories in other 'great speciator' taxa across the Indo‐Pacific likely predispose these groups to high levels of ILS and high likelihoods of mitonuclear discordance. [ABSTRACT FROM AUTHOR]

The Great Horned Owl (Bubo virginianus) inhabits myriad habitats throughout the Americas and shows complex patterns of individual and geographic morphological variation. The owl family Strigidae is known to follow ecogeographic rules, such as Gloger's rule. Although untested at the species level, these ecogeographic rules may affect B. virginianus plumage coloration and body size. Previous studies have indicated that, despite this species' morphological variability, little genetic differentiation exists across parts of their range. This study uses reduced representation genome-wide nuclear and complete mitochondrial DNA sequence data to assess range-wide relationships among B. virginianus populations and the disputed species status of B. v. magellanicus (Magellanic or Lesser Horned Owl) of the central and southern Andes. We found shallow phylogenetic relationships generally structured latitudinally to the north of the central Andes, and a deep divergence between a southern and northern clade close to the Marañón Valley in the central Andes, a common biogeographic barrier. We identify evidence of gene flow between B. v. magellanicus and other subspecies based on mitonuclear discordance and F-branch statistics. Overall differences in morphology, plumage coloration, voice, and genomic divergence support species status for B. v. magellanicus. [ABSTRACT FROM AUTHOR]

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White‐eyes are an iconic avian radiation of small passerines that are mainly distributed across the eastern hemisphere tropics and subtropics. Species diversity of white‐eyes is particularly high on oceanic islands, and many species are restricted to single islands or island groups. The high rate of species diversification of white‐eyes ranks them among the fastest radiations known in birds, but whether their accelerated diversification was the result of repeatedly colonizing islands remains unexplored. We used a newly estimated timetree for nearly all zosteropids and phylogenetic comparative methods to estimate and compare diversification rates between island and continental lineages. We show that island white‐eyes have similar extinction rates, yet higher speciation rates compared with continental white‐eyes. In addition, we find higher rates of transitions from islands to continents. Our results show the importance of islands, such as Wallacean and Melanesian archipelagos of the Indo‐Pacific, in facilitating high rates of speciation within this remarkable clade. [ABSTRACT FROM AUTHOR]

Sky islands, or montane forest separated by different lowland habitats, are highly fragmented regions that potentially limit gene flow between isolated populations. In the sky islands of the Madrean Archipelago (Arizona, USA), various taxa display different phylogeographic patterns, from unrestricted gene flow among sky islands to complex patterns with multiple distinct lineages. Using genomic-level approaches allows the investigation of differential patterns of gene flow, selection, and genetic differentiation among chromosomes and specific genomic regions between sky island populations. Here, we used thousands of SNPs to investigate the putative contact zone of divergent Brown Creeper (Certhia americana) lineages in the Madrean Archipelago sky islands. We found the two lineages to be completely allopatric (during the breeding season) with a lack of hybridization and gene flow between lineages and no genetic structure among sky islands within lineages. Additionally, the two lineages inhabit different climatic and ecosystem conditions and have many local primary song dialects in the southern Arizona mountain ranges. We identified a positive relationship between genetic differentiation and chromosome size, but the sex chromosome (Z) was not found to be an outlier. Differential patterns of genetic differentiation per chromosome may be explained by genetic drift-- possibly in conjunction with non-random mating and non-random gene flow--due to variance in recombination rates among chromosomes. Keywords: contact zone, chromosomal patterns, next-generation sequencing, sky islands. Des llots forestiers en altitude (<< sky islands >>), c'est-a-dire des zones forestieres en montagne qui sont separees par differents habitats en basses-terres, constituent des regions tres fragmentees qui limitent potentiellement le flux genique entre des populations isolees. Dans les llots forestiers du Madrean Archipelago (Arizona, Etats-Unis), divers taxons presentent differentes distributions phylogeographiques, allant d'un flux genique sans restriction entre les llots forestiers jusqu'a des distributions complexes presentant plusieurs lignees distinctes. L'emploi d'approches genomiques permet l'etude de differentes situations de flux genique, de selection et de differenciation genetique parmi les chromosomes et au sein de regions chromosomiques specifiques entre les populations. Dans ce travail, les auteurs ont employe des milliers de marqueurs SNP pour etudier une possible zone de contact entre des lignees divergentes du grimpereau brun (Certhia americana) au sein des llots forestiers du Madrean Archipelago. Deux lignees se sont averees completement allopatriques (au cours de la saison de reproduction) en ne presentant aucune hybridation ou flux genique entre les lignees et aucune structure genetique entre les llots forestiers parmi ces lignees. De plus, deux lignees occupent differentes niches en matiere de climat et d'ecosysteme, de maniere a ce qu'elles presentent plusieurs dialectes de chants primaires dans les chalnes de montagnes du sud de l'Arizona. Les auteurs ont identifie une relation positive entre la differenciation genetique et la taille des chromosomes, mais le chromosome sexuel (Z) n'etait pas hors norme. Une differenciation genetique distincte en fonction des chromosomes pourrait s'expliquer par la derive genetique--possiblement en conjonction avec de l'accouplement non-aleatoire et un flux genique non-aleatoire--attribuable a une variance dans les taux de recombinaison entre les chromosomes. [Traduit par la Redaction] Mots-cles : zone de contact, sequen^age de nouvelle generation, distributions chromosomiques, llots forestiers en altitude., Introduction Understanding the processes driving lineage divergence and limiting gene flow across species boundaries has been a longstanding focus of evolutionary biology (Mayr 1942). Highly fragmented landscapes escalate restrictions to [...]