Einarsson, A. | Search bioRxiv

bioRxiv2025

Environmental DNA Reveals Reykjavik's Human and Ecological History

Iceland was among the last large islands settled by humans, with colonization (Landnam) in the late 9th century CE (Common Era) and is often portrayed as an ecological disaster driven by the Norse settlers. Here, we revisit this narrative through environmental DNA (eDNA) and multiproxy analyses of sediment cores from Lake Tjornin in central Reykjavik, one of Icelands earliest and longest-occupied settlements. Originally a marine embayment, Tjornin became a freshwater lake around 660 CE. Our record reveals a human presence decades before the long-accepted arrival date of 877 CE, marked by the Landnam volcanic tephra. Early settlement brought livestock, barley cultivation, and other introduced taxa that enhanced nutrient cycling and unexpectedly increased local biodiversity. Contrary to the conventional view of rapid deforestation, eDNA shows that birch and willow expanded during the settlement period, likely supported by deliberate management. Pronounced ecological and land use shifts occurred after 1200 CE, but these were coeval with the Little Ice Age cooling, compounded by volcanic eruptions, storm surges, and plague, rather than anthropogenic degradation. Crop cultivation ceased, arboreal taxa retracted, and grazing pressure maintained open landscapes. Even more profound ecological changes came after c. 1750 CE with urbanization and industrialization, as wastewater discharge, heavy-metal pollution, and fossil fuel use reshaped Tjornins ecosystem. These findings challenge the prevailing model of Norse-induced environmental collapse, revealing instead a dynamic human-environment relationship shaped by both cultural practices and external stressors. By applying eDNA to a long-occupied urban catchment, we demonstrate the power of genomic methods to refine settlement chronologies, reassess ecological baselines and changes, and integrate natural and cultural histories. This approach offers a model for revisiting human-environment interactions in urban centers worldwide.

genomics↗

bioRxiv2023

Shared features underlying compact genomes and extreme habitat use in chironomid midges

Non-biting midges (family Chironomidae) are found throughout the world in a diverse array of aquatic and terrestrial habitats, can often tolerate harsh conditions such as hypoxia or desiccation, and have consistently compact genomes. Yet we know little about the shared molecular basis for these attributes and how they have evolved across the family. Here, we address these questions by first creating high-quality, annotated reference assemblies for Tanytarsus gracilentus (subfamily Chironominae, tribe Tanytarsini) and Parochlus steinenii (subfamily Podonominae). Using these and other publicly available assemblies, we created a time-calibrated phylogenomic tree for family Chironomidae with outgroups from order Diptera. We used this phylogeny to test for features associated with compact genomes, as well as examining patterns of gene family evolution and positive selection that may underlie chironomid habitat tolerances. Our results suggest that compact genomes evolved in the most recent common ancestor of Chironomidae and Ceratopogonidae, and that this occurred mainly through reductions in non-coding regions (introns, intergenic sequences, and repeat elements). Gene families that significantly expanded in Chironomidae included biological processes that may relate to tolerance of stressful environments, such as temperature homeostasis, inflammatory response, melanization defense response, and trehalose transport. We identified a number of genes with evidence for positive selection in Chironomidae, notably sulfonylurea receptor, peroxiredoxin-1, and protein kinase D. Our results help to understand the genomic basis for the small genomes and extreme habitat use in this widely distributed group. Significance StatementChironomid midges are known for having small genomes and being able to tolerate many forms of environmental stress, yet little is known of the shared features of their genomes that may underlie these traits. We found that reductions in non-coding regions coincide with small chironomid genomes, and we identified duplicated and/or selected genes that may equip chironomids to tolerate harsh conditions. These results describe the key genomic changes in chironomid midges that may explain their ability to inhabit a range of extreme habitats across the world.

genomics↗