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Abstract Tropical and subtropical trees provide key ecosystem services but are facing global population decline due to logging, habitat degradation, land conversion, and climate change. Vatica guangxiensis used to be a characteristic timber species of China's tropical forests but is now terminally endangered (280 individuals) and fragmented into three relictual populations in southwest China. Generating genome‐wide DNA for ∼82% of all living tree individuals of this species complex, we found evidence for a late Pliocene division into two species‐level lineages that have not had gene flow for approximately 3 million years. All three relictual populations exhibited a loss of genetic diversity and recent bottlenecks. In addition, forward simulations indicated a likely population collapse in all three populations within the next century. Our study generates a model framework for the integration of genomic evidence—including evolutionary history, current genetic variation, and future projections—into conservation planning.

Summary: Aedes albopictus is a successful disease vector due to its ability to survive in a wide range of habitats. Despite its ubiquity and impact on public health, little is known about its differential gene flow capabilities across different city habitats. We obtained a comprehensive dataset of >27,000 genome-wide DNA markers across 105 wild-caught Ae. albopictus individuals from Singapore, a dengue-endemic tropical city with heterogeneous landscapes from densely populated urban areas to forests. Despite Singapore’s challenging small-scale heterogeneity, our landscape-genomic approach indicated that dense urban areas are characterized by higher Aedes gene flow rates than managed parks and forests. We documented the incidence of Wolbachia infections of Ae. albopictus involving two strains (wAlbA and wAlbB). Our results dispel the misconception that substantial dispersal of Ae. albopictus is limited to urban greenery, with wide implications for vector management and critical insights into urban planning strategies to combat dengue transmission.

Wildlife crossings are implemented in many countries to facilitate the dispersal of animals among habitats fragmented by roads. However, the efficacy of different types of habitat corridors remains poorly understood. We used a comprehensive sampling regime in two lowland dipterocarp forest areas in peninsular Malaysia to sample pairs of small mammal individuals in three treatment types: (1) viaduct sites, at which sampling locations were separated by a highway but connected by a vegetated viaduct; (2) non-viaduct sites, at which sampling locations were separated by a highway and not connected by a viaduct; and (3) control sites, at which there was no highway fragmenting the forest. For four small mammal species, the common tree shrew Tupaia glis, Rajah’s spiny rat Maxomys rajah, Whitehead’s spiny rat Maxomys whiteheadi and dark-tailed tree rat Niviventer cremoriventer, we used genome-wide markers to assess genetic diversity, gene flow and genetic structure. The differences in genetic distance across sampling settings among the four species indicate that they respond differently to the presence of highways and viaducts. Viaducts connecting forests separated by highways appear to maintain higher population connectivity than forest fragments without viaducts, at least in M. whiteheadi, but apparently not in the other species.

Abstract Resource partitioning may facilitate the coexistence of sympatric species with similar ecological requirements. Here, we study a colony of unusual echolocating birds called swiftlets, which nest underground on an island off the coast of Singapore. The colony comprises two congeneric swiftlet species, black‐nest swiftlets (Aerodramus maximus) and edible‐nest swiftlets (A. fuciphagus), nesting at high densities and in close proximity. Bioacoustic recordings and monitoring of nesting biology at the site across multiple seasons revealed significant differences in echolocation calls as well as survival rates between the species, with the larger black‐nest swiftlet nesting at locations with the highest fledging rates. We also observe an additional off‐season breeding peak by the smaller species, the edible‐nest swiftlet. Unexpectedly, off‐season egg‐hatching rates were significantly higher compared with the rates during the shared breeding season (mean difference = 14%). Our study on the breeding biology of these echolocating cave‐dwelling birds provides an example of spatial and temporal strategies that animals employ to partition resources within a confined habitat.

Much confusion has surrounded the taxonomy of the Collared Scops Owl (Otus bakkamoena) complex, distributed widely across tropical and subtropical Asia. Often divided into three species, modern taxonomies disagree on its treatment, as a lack of deep mitochondrial DNA divergence is seemingly in contrast with patterns of vocal differentiation. Analysing a dataset of territorial calls of 122 individuals across Asia, we identified a vocal leapfrog pattern in which owl populations at the eastern and western ends of the distribution sound more similar to each other but are separated by different-sounding populations in between. The boundaries between vocal types are not congruent with traditional species boundaries. Our data allow for a re-drawing of species boundaries and reveal that Collared Scops Owls follow a biogeographic pattern rare in Southeast Asian birds. However, this pattern is shared with several other owl complexes in that peninsular Malaysian populations form part of a continental Asian species centred further north in Southeast Asia rather than forming part of a Sundaic species centred in the adjacent Indonesian Archipelago.

Human activities have precipitated a rise in the levels of introgressive gene flow among animals. The investigation of conspecific populations at different time points may shed light on the magnitude of human-mediated introgression. We used the red junglefowl Gallus gallus, the wild ancestral form of the chicken, as our study system. As wild junglefowl and domestic chickens readily admix, conservationists fear that domestic introgression into junglefowl may compromise their wild genotype. By contrasting the whole genomes of 51 chickens with 63 junglefowl from across their natural range, we found evidence of a loss of the wild genotype across the Anthropocene. When comparing against the genomes of junglefowl from approximately a century ago using rigorous ancient-DNA protocols, we discovered that levels of domestic introgression are not equal among and within modern wild populations, with the percentage of domestic ancestry around 20–50%. We identified a number of domestication markers in which chickens are deeply differentiated from historic junglefowl regardless of breed and/or geographic provenance, with eight genes under selection. The latter are involved in pathways dealing with development, reproduction and vision. The wild genotype is an allelic reservoir that holds most of the genetic diversity of G. gallus, a species which is immensely important to human society. Our study provides fundamental genomic infrastructure to assist in efforts to prevent a further loss of the wild genotype through introgression of domestic alleles. Author summary The red junglefowl Gallus gallus from tropical Asia is the ancestral form of the chicken, which is arguably the most important domestic animal on Earth. Here we discovered an increase in genetic exchange between red junglefowl and chickens in recent years, making wild populations increasingly domestic genomically. By using whole genome sequences of chickens and red junglefowl from two time points, we show that domestic introgression has increased across the wild range at varying levels over the course of a century. We also identified genes that might have played a role in the domestication of the species using the samples from a century ago, in which domestic contribution was lower than in modern day samples. We found eight genes under selection which are involved in development, reproduction and vision, and which might be fundamental to the nature of domestic chickens as distinct from their ancestral wild counterparts. Our study brings to light the current and ongoing loss of the wild junglefowl genotype, suggesting that efforts may be needed to safeguard its full genetic diversity.

Abstract Impending anthropogenic climate change will severely impact coastal organisms at unprecedented speed. Knowledge on organisms’ evolutionary responses to past sea‐level fluctuations and estimation of their evolutionary potential is therefore indispensable in efforts to mitigate the effects of future climate change. We sampled tens of thousands of genomic markers of ~300 individuals in two of the four extant horseshoe crab species across the complex archipelagic Singapore Straits. Carcinoscorpius rotundicauda Latreille, a less mobile mangrove species, has finer population structure and lower genetic diversity compared with the dispersive deep‐sea Tachypleus gigas Müller. Even though the source populations of both species during the last glacial maximum exhibited comparable effective population sizes, the less dispersive C. rotundicauda seems to lose genetic diversity much more quickly because of population fragmentation. Contra previous studies’ results, we predict that the more commonly sighted C. rotundicauda faces a more uncertain conservation plight, with a continuing loss in evolutionary potential and higher vulnerability to future climate change. Our study provides important genomic baseline data for the redirection of conservation measures in the face of climate change and can be used as a blueprint for assessment and mitigation of the adverse effects of impending sea‐level rise in other systems.

Abstract Urgent conservation action for terminally endangered species is sometimes hampered by taxonomic uncertainty, especially in illegally traded animals that are often cross‐bred in captivity. To overcome these problems, we used a genomic approach to analyze historical DNA from museum samples across the Asian Pied Starling (Gracupica contra) complex in tropical Asia, a popular victim of the ongoing songbird crisis whose distinct Javan population (“Javan Pied Starling”) is extinct in the wild and subject to admixture in captivity. Comparing genomic profiles across the entire distribution, we detected three deeply diverged lineages at the species level characterized by a lack of genomic intermediacy near areas of contact. Our study demonstrates that the use of historical DNA can be instrumental in delimiting species in situations of taxonomic uncertainty, especially when modern admixture may obfuscate species boundaries. Results of our research will enable conservationists to commence a dedicated ex situ breeding program for the Javan Pied Starling, and serve as a blueprint for similar conservation problems involving terminally endangered species subject to allelic infiltration from close congeners.

Abstract Background The Elegant Pitta (Pitta elegans) complex displays a remarkable diversity of morphological and bioacoustic traits across five taxa currently recognized as subspecies. They differ in plumage characteristics (such as red versus black belly patches; supercilium color and extent; and white versus black throats), in lifestyle (resident versus migratory) and in vocalizations. We investigated the morphological, bioacoustic and ecological differences across all taxa after recent studies demostrated the importance of these traits in recognizing biological species limits across pittas. Methods Morphometric analysis was carried out by measuring tarsus, wing, tail and bill lengths of 15 specimens at the Natural History Museum, UK, and plumages were inspected across 106 unique individuals from four different repositories. Bioacoustic analysis was based on 134 range-wide sound recordings. Two types of calls, territorial calls and alarm calls, were analyzed using different sets of parameters. Principal component analysis and the Isler Criterion were applied to the measurements. Playback trials were conducted to explore the levels of response of each taxon to the call types of the other taxa. Results The territorial call of concinna exhibits a distinct two-element motif, while elegans, maria and virginalis utter a three-element motif in which the first two elements are given in quick succession. On the other hand, vigorsii, produces both two-element and three-element motifs with longer breaks in between elements. As further corroborated by the playback trials, the three taxa elegans, virginalis and maria form a tight vocal cluster, whereas each concinna and vigorsii are distinct. The alarm call turned out to be less diagnostic even though most taxa did roughly separate into different vocal clusters. Morphometric analysis failed to produce strong differences, but plumage distinctions among multiple taxa are pronounced. Conclusions We suggest splitting the Elegant Pitta into three biological species based on bioacoustic and—less so—plumage evidence: (1) Temminck’s Elegant Pitta P. elegans (including subspecies elegans, virginalis and maria), (2) Wallace’s Elegant Pitta P. concinna (monotypic), and (3) Banda Elegant Pitta P. vigorsii (monotypic).

Abstract The red junglefowl Gallus gallus is the ancestor of the domestic chicken and arguably the most important bird species on Earth. Continual gene flow between domestic and wild populations has compromised its gene pool, especially since the last century when human encroachment and habitat loss would have led to increased contact opportunities. We present the first combined genomic and morphological admixture assessment of a native population of red junglefowl, sampled from recolonized parts of its former range in Singapore, partly using whole genomes resequenced from dozens of individuals. Crucially, this population was genomically anchored to museum samples from adjacent Peninsular Malaysia collected ~110–150 years ago to infer the magnitude of modern domestic introgression across individuals. We detected a strong feral–wild genomic continuum with varying levels of domestic introgression in different subpopulations across Singapore. Using a trait scoring scheme, we determined morphological thresholds that can be used by conservation managers to successfully identify individuals with low levels of domestic introgression, and selected traits that were particularly useful for predicting domesticity in genomic profiles. Our study underscores the utility of combined genomic and morphological approaches in population management and suggests a way forward to safeguard the allelic integrity of wild red junglefowl in perpetuity.

Abstract Background Quaternary climate fluctuations are an engine of biotic diversification. Global cooling cycles, such as the Last Glacial Maximum (LGM), are known to have fragmented the ranges of higher-latitude fauna and flora into smaller refugia, dramatically reducing species ranges. However, relatively less is known about the effects of cooling cycles on tropical biota. Results We analyzed thousands of genome-wide DNA markers across an assemblage of three closely related understorey-inhabiting scrubwrens (Sericornis and Aethomyias; Aves) from montane forest along an elevational gradient on Mt. Wilhelm, the highest mountain of Papua New Guinea. Despite species-specific differences in elevational preference, we found limited differentiation within each scrubwren species, but detected a strong genomic signature of simultaneous population expansions at 27-29 ka, coinciding with the onset of the LGM. Conclusion The remarkable synchronous timing of population expansions of all three species demonstrates the importance of global cooling cycles in expanding highland habitat. Global cooling cycles have likely had strongly different impacts on tropical montane areas versus boreal and temperate latitudes, leading to population expansions in the former and serious fragmentation in the latter.

Horseshoe crabs have been morphologically stable across evolutionary time. Here, the authors generate a chromosome-level assembly for the mangrove horseshoe crab, with implications for innate immunity, and challenging assumptions about the role of genome duplication in adaptive radiation.

Abstract Habitat fragmentation is a major extinction driver. Despite dramatically increasing fragmentation across the globe, its specific impacts on population connectivity across species with differing life histories remain difficult to characterize, let alone quantify. Here, we investigate patterns of population connectivity in six songbird species from Singapore, a highly fragmented tropical rainforest island. Using massive panels of genome‐wide single nucleotide polymorphisms across dozens of samples per species, we examined population genetic diversity, inbreeding, gene flow and connectivity among species along a spectrum of ecological specificities. We found a higher resilience to habitat fragmentation in edge‐tolerant and forest‐canopy species as compared to forest‐dependent understorey insectivores. The latter exhibited levels of genetic diversity up to three times lower in Singapore than in populations from contiguous forest elsewhere. Using dense genomic and geographic sampling, we identified individual barriers such as reservoirs that effectively minimize gene flow in sensitive understorey birds, revealing that terrestrial forest species may exhibit levels of sensitivity to fragmentation far greater than previously expected. This study provides a blueprint for conservation genomics at small scales with a view to identifying preferred locations for habitat corridors, flagging candidate populations for restocking with translocated individuals and improving the design of future reserves.

Although Blakiston's Fish Owl (Bubo blakistoni) is widely treated as a single species, marked differences in the structure of pair duets between continental and insular populations have been documented. However, no study has quantitatively assessed these vocal differences. We obtained 192 duets from 22 pairs of Blakiston's Fish Owl: 15 pairs of B. b. blakistoni from the Japanese island of Hokkaido and the Russian Kuril island of Kunashir, and seven pairs of B. b. doerriesi from Primorye on the Russian mainland. This is a sizeable dataset for such a large, retiring, and rare owl. We conducted bioacoustic examinations of 14 vocal parameters using principal component analysis and the Isler criterion to quantitatively test species boundaries within the B. blakistoni complex. We found that the insular populations on Hokkaido and Kunashir emerged as vocally similar to each other but markedly different from the continental populations of B. blakistoni, corresponding closely with presently accepted subspecies limits. Bioacoustic differences in the duets of the insular and continental groups are greater than the pairwise comparisons of territorial vocalisations between other sympatric owl species. Based on the reproductive importance of vocal duets in owl biology, we propose the taxonomic elevation of the continental subspecies to species level as Northern Fish Owl B. doerriesi. Our study corroborates the importance of bioacoustics in ascertaining species boundaries in owls and has important implications for the management of the two newly delimited species, each likely to be assessed as Endangered. Both species should be managed independently to optimise conservation outcomes.

Abstract The southern river terrapin, Batagur affinis is one of the world's 25 most endangered freshwater turtle species. The major portion of the global population is currently found in peninsular Malaysia, with the only remnant Indochinese population in southern Cambodia. For more than a decade, wild nests in this remnant Cambodian population have been fenced and hatchlings reared in captivity. Here we amplified 10 microsatellite markers from all 136 captive individuals, obtained 2,658 presumably unlinked and neutral single nucleotide polymorphisms from 72 samples with ddRAD‐seq, and amplified 784 bp of mtDNA from 50 samples. Our results reveal that the last Indochinese population comprised only four kinship groups as of 2012, with all offspring sired from

Abstract Background The taxonomy of the Collared Owlet (Glaucidium brodiei) species complex is confused owing to great individual variation in plumage colouration seemingly unrelated to their distribution. Although generally recognised as a single species, vocal differences among the subspecies have been noted by field recordists. However, there is no study assessing the vocal differences among these four subspecies. Methods We obtained 76 sound recordings of the G. brodiei species complex comprising all four subspecies. We conducted bioacoustic examinations using principal component analysis and the Isler criterion to quantitatively test species boundaries within the G. brodiei complex. In addition, we compared plumage colouration among 13 specimens of the G. brodiei complex deposited at the Natural History Museum at Tring, UK and the Lee Kong Chian Natural History Museum, Singapore to ascertain the presence of plumage differences across taxa. Results We found the Bornean and Sumatran populations vocally similar to each other, but distinctly different from the mainland and Taiwan populations. The vocal pattern seems to corroborate plumage distinctions in the colouration of neck collars: the Bornean and Sumatran taxa share a white neck collar, whereas the continental and Taiwan taxa share a rufous neck collar. Conclusions We propose the taxonomic elevation of the Sumatran and Bornean populations to species level as Sunda Owlet G. sylvaticum, with one subspecies on Sumatra (G. s. sylvaticum) and Borneo (G. s. borneense) each. Our study corroborates the importance of bioacoustics in ascertaining species boundaries in non-passerines, and emphasises the significance of incorporating multiple species delimitation approaches when making taxonomic decisions.

Abstract Background Allopatric speciation has played a particularly important role in archipelagic settings where populations evolve in isolation after colonizing different islands. The Indo-Australasian island realm is an unparalleled natural laboratory of biotic diversification. Here we explore how the level of earth-historic isolation has influenced genetic differentiation across the region by investigating phylogeographic patterns in the Pitta sordida species complex. Results We generated a de novo genome and compared population genomics of 29 individuals of Pitta sordida from the entire distributional range and we reconstructed phylogenetic relationship using mitogenomes, a multi-nuclear gene dataset and single nucleotide polymorphisms (SNPs). We found deep divergence between an eastern and a western group of taxa across Indo-Australasia. Within both groups we have identified major lineages that are geographically separated into Philippines, Borneo, western Sundaland, and New Guinea, respectively. Although these lineages are genetically well-differentiated, suggesting a long-term isolation, there are signatures of extensive gene flow within each lineage throughout the Pleistocene, despite the wide geographic range occupied by some of them. We found little evidence of hybridization or introgression among the studied taxa, but forsteni from Sulawesi makes an exception. This individual, belonging to the eastern clade, is genetically admixed between the western and eastern clades. Geographically this makes sense as Sulawesi is not far from Borneo that houses a population of hooded pittas that belongs to the western clade. Conclusions We found that geological vicariance events cannot explain the current genetic differentiation in the Pitta sordida species complex. Instead, the glacial-interglacial cycles may have played a major role therein. During glacials the sea level could be up to 120 m lower than today and land bridges formed within both the Sunda Shelf and the Sahul Shelf permitting dispersal of floral and faunal elements. The geographic distribution of hooded pittas shows the importance of overwater, “stepping-stone” dispersals not only to deep-sea islands, but also from one shelf to the other. The most parsimonious hypothesis is an Asian ancestral home of the Pitta sordida species complex and a colonization from west to east, probably via Wallacea.

Abstract We assess the magnitude and the extent of recent change of significant human footprint within protected areas, key biodiversity areas and the habitat range of 308 lowland forest specialist birds in Sundaland, a global hotspot of biodiversity in Southeast Asia. Using the most recent human footprint dataset, we find that 70% of Sundaland has been heavily modified by humans. This represents a 55% increase in areas under intense human pressure since 1993. Areas under intense human pressure covered on average 50% of the extent of key biodiversity areas, 78% of each protected area and 38% of the range of lowland forest specialist birds. The results imply that the actual level of protection by protected areas is only one‐third to half of that on paper once human footprint is accounted for. While all protected areas were impacted by human pressures, those managed strictly for biodiversity conservation presented the largest increases. These results highlight an exceptionally high human footprint across Sundaland and an impending further deepening of the biodiversity crisis across the region.

Disentangling multiple drivers of species declines can be difficult yet is critical to species conservation. Here, the authors parse the relative contributions of deforestation and trapping to declines of native birds in Southeast Asia, finding that the extinction risk of trapped species may be underestimated.

Abstract Background Pleistocene climatic fluctuations are known to be an engine of biotic diversification at higher latitudes, but their impact on highly diverse tropical areas such as the Andes remains less well-documented. Specifically, while periods of global cooling may have led to fragmentation and differentiation at colder latitudes, they may – at the same time – have led to connectivity among insular patches of montane tropical habitat with unknown consequences on diversification. In the present study we utilized ~5.5 kb of DNA sequence data from eight nuclear loci and one mitochondrial gene alongside diagnostic morphological and bioacoustic markers to test the effects of Pleistocene climatic fluctuations on diversification in a complex of Andean tyrant-flycatchers of the genus Elaenia. Results Population genetic and phylogenetic approaches coupled with coalescent simulations demonstrated disparate levels of gene flow between the taxon chilensis and two parapatric Elaenia taxa predominantly during the last glacial period but not thereafter, possibly on account of downward shifts of montane forest habitat linking the populations of adjacent ridges. Additionally, morphological and bioacoustic analyses revealed a distinct pattern of character displacement in coloration and vocal traits between the two sympatric taxa albiceps and pallatangae, which were characterized by a lack of gene flow. Conclusion Our study demonstrates that global periods of cooling are likely to have facilitated gene flow among Andean montane Elaenia flycatchers that are more isolated from one another during warm interglacial periods such as the present era. We also identify a hitherto overlooked case of plumage and vocal character displacement, underpinning the complexities of gene flow patterns caused by Pleistocene climate change across the Andes.

Lymphatic filariasis and loiasis are diseases caused by insect-borne filarial nematodes. Here, Suh et al. identify a retrotransposon that is present in the genomes of these nematodes and seven tropical bird lineages, indicating two waves of horizontal gene transfer around 17–25 million years ago.

Archipelagoes serve as important ‘natural laboratories’ which facilitate the study of island radiations and contribute to the understanding of evolutionary processes. The white-eye genus Zosterops is a classical example of a ‘great speciator’, comprising c. 100 species from across the Old World, most of them insular. We achieved an extensive geographic DNA sampling of Zosterops by using historical specimens and recently collected samples. Using over 700 genome-wide loci in conjunction with coalescent species tree methods and gene flow detection approaches, we untangled the reticulated evolutionary history of Zosterops, which comprises three main clades centered in Indo-Africa, Asia, and Australasia, respectively. Genetic introgression between species permeates the Zosterops phylogeny, regardless of how distantly related species are. Crucially, we identified the Indonesian archipelago, and specifically Borneo, as the major center of diversity and the only area where all three main clades overlap, attesting to the evolutionary importance of this region.