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Rapid global warming is severely impacting Arctic ecosystems and is predicted to transform the abundance, distribution and genetic diversity of Arctic species, though these linkages are poorly understood. We address this gap in knowledge using palaeogenomics to examine how earlier periods of global warming influenced the genetic diversity of Atlantic walrus (Odobenus rosmarus rosmarus), a species closely associated with sea ice and shallow-water habitats. We analysed 82 ancient and historical Atlantic walrus mitochondrial genomes (mitogenomes), including now-extinct populations in Iceland and the Canadian Maritimes, to reconstruct the Atlantic walrus' response to Arctic deglaciation. Our results demonstrate that the phylogeography and genetic diversity of Atlantic walrus populations was initially shaped by the last glacial maximum (LGM), surviving in distinct glacial refugia, and subsequently expanding rapidly in multiple migration waves during the late Pleistocene and early Holocene. The timing of diversification and establishment of distinct populations corresponds closely with the chronology of the glacial retreat, pointing to a strong link between walrus phylogeography and sea ice. Our results indicate that accelerated ice loss in the modern Arctic may trigger further dispersal events, likely increasing the connectivity of northern stocks while isolating more southerly stocks putatively caught in small pockets of suitable habitat. [ABSTRACT FROM AUTHOR]

The world’s oceans are currently facing major stressors in the form of overexploitation and anthropogenic climate change. The Baltic Sea was home to the first “industrial” fishery ∼800 y ago targeting the Baltic herring, a species that is still economically and culturally important today. Yet, the early origins of marine industries and the long-term ecological consequences of historical and contemporary fisheries remain debated. Here, we study long-term population dynamics of Baltic herring to evaluate the past impacts of humans on the marine environment. We combine modern whole-genome data with ancient DNA (aDNA) to identify the earliest-known long-distance herring trade in the region, illustrating that extensive fish trade began during the Viking Age. We further resolve population structure within the Baltic and observe demographic independence for four local herring stocks over at least 200 generations. It has been suggested that overfishing at Øresund in the 16th century resulted in a demographic shift from autumn-spawning to spring-spawning herring dominance in the Baltic. We show that while the Øresund fishery had a negative impact on the western Baltic herring stock, the demographic shift to spring-spawning dominance did not occur until the 20th century. Instead, demographic reconstructions reveal population trajectories consistent with expected impacts of environmental change and historical reports on shifting fishing targets over time. This study illustrates the joint impact of climate change and human exploitation on marine species as well as the role historical ecology can play in conservation and management policies. [ABSTRACT FROM AUTHOR]

Fish are the most diverse group of vertebrates, fulfil important ecological functions and are of significant economic interest for aquaculture and wild fisheries. Advances in DNA extraction methods, sequencing technologies and bioinformatic applications have advanced genomic research for nonmodel organisms, allowing the field of fish ancient DNA (aDNA) to move into the genomics era. This move is enabling researchers to investigate a multitude of new questions in evolutionary ecology that could not, until now, be addressed. In many cases, these new fields of research have relevance to evolutionary applications, such as the sustainable management of fisheries resources and the conservation of aquatic animals. Here, we focus on the application of fish aDNA to (a) highlight new research questions, (b) outline methodological advances and current challenges, (c) discuss how our understanding of fish ecology and evolution can benefit from aDNA applications and (d) provide a future perspective on how the field will help answer key questions in conservation and management. We conclude that the power of fish aDNA will be unlocked through the application of continually improving genomic resources and methods to well‐chosen taxonomic groups represented by well‐dated archaeological samples that can provide temporally and/or spatially extensive data sets. [ABSTRACT FROM AUTHOR]

Abstract Horses are the most common grave goods found in Icelandic Viking Age graves. Horse skeletons have previously been sexed based on pelvis shape and the presence of canine teeth in male horses over 4–5 years of age. Morphological data has shown that all horses from Icelandic burials that were amenable to sexing were male. Yet the use of morphological methods to determine sex is problematic since they rely on finding a well-preserved pelvis and/or robust canine teeth. Furthermore, quantitative data underlying the features of the horse pelvis used for sexing is lacking and canine teeth have been reported to occur in mares. In this study we build upon and extend recently developed methodologies to make use of shotgun sequencing of ancient DNA (aDNA) for molecular sexing of Viking Age horse remains. With minimal sequencing effort we identified the sex of the largest collection (n = 22) of Viking Age Icelandic horses studied to date, sourced from both burial (n = 19) and non-burial (n = 3) sites. Our results revealed a male to female sex bias ratio of 18:1 in burial sites, versus 0:3 in non-burial sites. These findings support the significant over-representation of male horses in Viking Age graves in Iceland, yet show that –albeit rare– mares could also be selected for ritual burial in Viking Age Iceland. This cost-effective method provides statistical confidence to allow for sexing of highly fragmented archaeological specimens with low endogenous DNA content. [ABSTRACT FROM AUTHOR]

The field of ancient DNA (aDNA) typically uses between 50 and 200 mg of minimum input weight of bone material for the extraction of DNA from archaeological remains. While laboratory and analysis techniques have focused on improved efficiency of extracting useable sequence data from older and poorer quality remains, bone material input requirements have rarely been critically evaluated. Here, we present the aDNA analysis of 121 size-constrained Atlantic herring remains – weighing between <10 and 70 mg – that were individually sequenced to explore the capacity of successful aDNA retrieval from small archaeological remains. We statistically evaluate the relationship between bone weight and several response variables, including library success, endogenous DNA content, and library complexity, i.e., the number of unique molecules that are obtained. Remarkably, we find no relationship between bone weight and library success, levels of endogenous DNA, or library complexity. Our results imply that – at least in the case of fish bone – even minute bones can yield positive results and that the presumed minimum sample size required should be re-evaluated. Archaeological site, instead of bone size, is the primary driver of DNA sequence quality. Our work expands the number of specimens considered suitable for aDNA analyses, and therefore facilitates efforts to minimize the destructive impact of aDNA research and mediate some of the ethical concerns surrounding destructive analysis. • Whole-genome ancient DNA (aDNA) sequences have been successfully recovered from bones weighing less than 10 mg. • ADNA sequence quality is not significantly associated with starting bone weight. • Using small amounts of bone material can mitigate some ethical issues posed by destructive sampling. • Researchers should interrogate the amount of material and species investigated for aDNA research. [ABSTRACT FROM AUTHOR]

The impacts of early ecological globalisation may have had profound economic and environmental consequences for human settlements and animal populations. Here, we review the extent of such historical impacts by investigating the medieval trade of walrus (Odobenus rosmarus rosmarus) ivory. We use an interdisciplinary approach including chaîne opératoire , ancient DNA (aDNA), stable isotope and zooarchaeological analysis of walrus rostra (skull sections) to identify their biological source and subsequent trade through Indigenous and urban networks. This approach complements and improves the spatial resolution of earlier aDNA observations, and we conclude that almost all medieval European finds of walrus rostra likely derived from Greenland. We further find that shifting urban nodes redistributed the traded ivory and that the latest medieval rostra finds were from smaller, often female, walruses of a distinctive DNA clade, which is especially prevalent in northern Greenland. Our results suggest that more and smaller animals were targeted at increasingly untenable distances, which reflects a classic pattern of resource depletion. We consider how the trade of walrus and elephant ivory intersected, and evaluate the extent to which emergent globalisation and the "resource curse" contributed to the abandonment of Norse Greenland. • Walrus ivory for medieval art was traded as tusks in modified walrus skulls. • The modification of skulls followed a consistent, sequential treatment. • aDNA and stable isotopes show that Greenland supplied most European walrus skulls. • The latest medieval walruses were small and of a clade common in north Greenland. • Serial depletion of walruses may have impacted the resilience of Norse Greenland. [ABSTRACT FROM AUTHOR]