Ancient DNA preservation in subfossil specimens provides a unique opportunity to retrieve genetic information from the past. As ancient DNA extracts are generally dominated by molecules originating from environmental microbes, capture techniques are often used to economically retrieve orthologous sequence data at the population scale. Post-mortem DNA damage, especially the deamination of cytosine residues into uracils, also considerably inflates sequence error rates unless ancient DNA extracts are treated with the USER enzymatic mix prior to library construction. While both approaches have recently gained popularity in ancient DNA research, the impact of USER-treatment on capture efficacy still remains untested. In this study, we applied hyRAD capture to eight ancient equine subfossil specimens from France (1st-17th century CE), including horses, donkeys and their first-generation mule hybrids. We found that USER-treatment could reduce capture efficacy and introduce significant experimental bias. It differentially affected the size distribution of on-target templates following capture with two distinct hyRAD probe sets in a manner that was not driven by differences in probe sizes and DNA methylation levels. Finally, we recovered unbalanced proportions of donkey-specific and horse-specific alleles in mule capture sequence data, due to the combined effects of USER-treatment, probe sets and reference bias. Our work demonstrates that while USER-treatment can improve the quality of ancient DNA sequence data, it can also significantly affect hyRAD capture outcomes, introducing bias in the sequence data that is difficult to predict based on simple molecular probe features. Such technical batch effects may prove easier to model and correct for using capture with synthetic probes of controlled sizes and diversity content.

Conservation benefits from incorporating genomics to explore the impacts of population declines, inbreeding, loss of genetic variation and hybridization. Here we use the near-extinct Mariana Islands reedwarbler radiation to showcase how ancient DNA approaches can allow insights into the population dynamics of extinct species and threatened populations for which historical museum specimens or material with low DNA yield (e.g., scats, feathers) are the only sources for DNA. Despite their having paraphyletic mtDNA, nuclear SNPs support the distinctiveness of critically endangered Acrocephalus hiwae and the other three species in the radiation that went extinct between the 1960s and 1990s. Two extinct species, A. yamashinae and A. luscinius, were deeply divergent from each other and from a third less differentiated lineage containing A. hiwae and extinct A. nijoi. Both mtDNA and SNPs suggest that the two isolated populations of A. hiwae from Saipan and Alamagan Islands are sufficiently distinct to warrant subspecies recognition and separate conservation management. We detected no significant differences in genetic diversity or inbreeding between Saipan and Alamagan, nor strong signatures of geographic structuring within either island. However, the implications of possible signatures of inbreeding in both Saipan and Alamagan, and long-term population declines in A. hiwae that predate modern anthropogenic threats require further study with denser population sampling. Our study highlights the value conservation genomics studies of island radiations have as windows onto the possible future for the world’s biota as climate change and habitat destruction increasingly fragments their ranges and contributes to rapid declines in population abundances.

Cycles of glacial expansion and contraction throughout the Pleistocene drove increases and decreases, respectively, in the geographical range and population size of many animal species. Genetic data have revealed that during glacial maxima the distribution of many Eurasian animals was restricted to small refugial areas, from which species expanded to reoccupy parts of their former range as the climate warmed. It has been suggested that the extinct eastern moa (Emeus crassus)—a large, flightless bird from New Zealand—behaved analogously during glacial maxima, possibly surviving only in a restricted area of lowland habitat in the southern South Island of New Zealand during the Last Glacial Maximum (LGM). However, previous studies have lacked the power and geographical sampling to explicitly test this hypothesis using genetic data. Here we analyse 46 ancient mitochondrial genomes from Late Pleistocene and Holocene bones of the eastern moa from across their post-LGM distribution. Our results are consistent with a post-LGM increase in the population size and genetic diversity of eastern moa. We also demonstrate that genetic diversity was higher in eastern moa from the southern extent of their range, supporting the hypothesis that they expanded from a single glacial refugium following the LGM.

A species complex is an assemblage of closely related species with blurred boundaries, and from which species could arise from different speciation processes and/or a speciation continuum. Such a complex can provide an opportunity to investigate evolutionary mechanisms acting on speciation. The Chrysanthemum zawadskii species complex in China, a monophyletic group of Chrysanthemum, consists of seven species with considerable morphological variation, diverse habitats and different distribution patterns. Here, we used Hyb-Seq data to construct a well-resolved phylogeny of the C. zawadskii complex. Then, we performed comparative analyses of variation patterns in morphology, ecology and distribution to investigate the roles of geography and ecology in this complex’s diversification. Lastly, we implemented divergence time estimation, species distribution modelling and ancestral area reconstruction to trace the evolutionary history of this complex. We concluded that the C. zawadskii complex originated in the Qinling–Daba mountains during the early Pliocene and then spread west and northward along the mountain ranges to northern China. During this process, geographical and ecological factors imposing different influences resulted in the current diversification and distribution patterns of this species complex, which is composed of both well-diverged species and diverging lineages on the path of speciation.

Aim Phenotypes promoting dispersal over ecological timescales may have macroevolutionary consequences, such as long-distance dispersal and diversification. However, whether dispersal traits explain the distribution of pantropical plant groups remains unclear. Here we reconstruct the biogeographical history of a tree clade to assess whether seed dispersal traits and biome-switching explain the clade’s pantropical distribution. Location Pantropical. Taxon The Pterocarpus clade (Leguminosae/Fabaceae). Methods We sequenced 303 nuclear loci using target capture and generated a time-calibrated phylogenomic tree. We also generated a corroborative time-calibrated phylogenetic tree from data-mined Sanger-sequencing data. We then collated distribution data and seed dispersal morphology traits to compare trait-dependent and trait-independent biogeographical models, allowing us to infer whether dispersal traits influenced Pterocarpus’ spatio-temporal evolution. Finally, using the results of these model tests, we estimated the ancestral ranges and biomes of Pterocarpus species to better understand their biogeographical history, and assessed the degree and direction of biome-switching over the course of their diversification. Results We recovered well-supported phylogenetic relationships within Pterocarpus, within which there were two subclades – one neotropical and the other palaeotropical. Our divergence date estimates suggested that Pterocarpus diversified from around 12 Ma, during the Miocene. Trait-dependent biogeographical models were rejected for both range and biome evolution within Pterocarpus, but models including dispersal were supported. Pterocarpus’ ancestral node shared a range across the new-world and old-world tropics, followed by divergence into palaeotropical and neotropical clades. Biome-switching occurred most frequently into rainforest and grassland. Main conclusions Our analyses suggest that Pterocarpus underwent infrequent cross-continental dispersal and establishment into novel biomes. While this was minimally impacted by seed dispersal traits, biome-switching following long-distance dispersal and climate change have played an important role in diversification within Pterocarpus since the Miocene. Indeed, rare events of long-distance dispersal likely explain the wide distributions of many pantropical plant species.