Biology subjects

Dietz, R.

Publications and source records attributed to Dietz, R..

5 recordsLinked to original sources

bioRxiv2026

Contemporary hybridization and localized genomic differentiation between grey seal subspecies

Grey seals are divided into two subspecies, Halichoerus grypus grypus in the Baltic Sea and H. grypus atlantica in the North Atlantic Ocean. Historically, intense hunting caused local extinctions of grey seals across their range and promoted geographical isolation of the subspecies. However, recent population recovery and recolonization have renewed their overlap in a contact zone in Danish and Swedish waters. Here, using whole-genome sequencing data from 119 individuals, we investigate the demographic history of grey seals, the divergence of the subspecies, and genomic signatures of local adaptation and potential hybridization in the contact zone. We estimate that divergence began approximately 10,000 years ago, with gene flow ceasing 2000 years ago. We detect peaks of high genetic differentiation near genes with putative functions in osmo- and thermoregulation, consistent with salinity and temperature differences between the Baltic Sea and the North Atlantic. As evidence of the geographic isolation breaking up, we report a hybrid individual in the southwest Baltic contact zone, with Baltic maternal and Atlantic paternal ancestry, and identify a migrant of Baltic origin in the North Sea. Our study illustrates how local environmental variation and long-term hunting pressure have contributed to divergence between mammal subspecies over a short evolutionary timescale, with recent population recovery, recolonization and hybridization reshaping gene flow dynamics. Broadly, our work emphasizes the importance of studying evolutionary processes amid anthropogenic influences, including both disturbances and conservation successes, where demographic fluctuations, range shifts, altered gene flow, and adaptation to changing environments interact in complex, potentially consequential ways.

evolutionary biology↗

bioRxiv2023

Climate change introduces threatened killer whale populations and conservation challenges to the Arctic

The Arctic is the fastest-warming region on the planet, and sea ice loss has opened new habitat for sub-Arctic species such as the killer whale (Orcinus orca). As apex predators, killer whales can cause significant ecosystem-scale changes, however, we know very little about killer whales in the Arctic. Setting conservation priorities for killer whales and their Arctic prey species requires knowledge of their evolutionary history and demography. We found that there are two highly genetically distinct, non-interbreeding populations of killer whales using the eastern Canadian Arctic--one population is newly identified as globally distinct. The effective sizes of both populations recently declined, and both are vulnerable to inbreeding and reduced adaptive potential. Furthermore, we present evidence that human-caused mortalities, particularly ongoing harvest, pose an ongoing threat to these populations. The certainty of substantial environmental change in the Arctic complicates conservation and management significantly. Killer whales bring top-down pressure to Arctic food webs, however, they also merit conservation concern. The opening of the Arctic to killer whales exemplifies the magnitude of complex decisions surrounding local peoples, wildlife conservation, and resource management as the effects of climate change are realized.

genomics↗

bioRxiv2022

Unprecedented shift in Canadian High Arctic polar bear food web unsettles four millennia of stability

Stable carbon ({delta}13C) and nitrogen ({delta}15N) isotope analysis was conducted on modern and archaeological polar bear bone collagen from the Canadian Arctic Archipelago to investigate potential changes in polar bear foraging ecology over four-millennia. Polar bear{delta} 13C values showed a significant decline in the modern samples relative to all archaeological time-bins, indicating a disruption in the sources of production that support the food web, occurring after the Industrial Revolution. The trophic structure, indicated through{delta} 15N, remained unaltered throughout all time periods. The lower{delta} 13C observed in the modern samples indicates a change in the relative importance of pelagic (supported by open-water phytoplankton) over sympagic (supported by sea ice-associated algae) primary production. The consistency in polar bear{delta} 13C through the late Holocene includes climatic shifts such as the Medieval Warm Period (MWP, A.D. 950-1250) and the early stages of the Little Ice Age (LIA, A.D. 1300-1850). These findings suggest that polar bears inhabit a food web that is more pelagic and less sympagic today than it was through the Late Holocene. We suggest that modern, anthropogenic warming has already affected food web structure in the Canadian Arctic Archipelago when modern data are contextualized with a deep time perspective. Research HighlightsO_LIModern polar bear bone collagen{delta} 13C suggests recent decline in ice associated prey. C_LIO_LIArchaeological polar bear bone collagen suggests food web stability for millennia. C_LIO_LINo change in sea-ice association through the Medieval Warm Period and Little Ice Age. C_LIO_LIRecent isotopic shifts are unusual relative to the stability of ancient samples. C_LIO_LIModern Arctic warming has isotopically observable impacts that past events did not. C_LI OR Significance StatementThe lack of behavioral plasticity of both polar bears and their principal prey, ringed seals, make these species particularly vulnerable to declining sea ice. While the Lancaster Sound food web has demonstrated stability through past climate fluctuations, the speed and magnitude of ongoing changes in the Arctic has had an observable effect on the source of primary production. Given that past climate fluctuations are referenced as an argument to minimize the importance of modern anthropogenic warming, it is important to take opportunities to position contemporary climate change relative to the archaeological record. Here we present a unique illustration of the effects of past and present warming on polar bear diet and the marine food web in the Canadian Arctic Archipelago.

ecology↗

bioRxiv2022

Impact of Holocene environmental change on the evolutionary ecology of an Arctic top predator

The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea-ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. By integrating genomics, isotopic analysis, morphometrics, and ecological modelling, we investigate how Holocene environmental changes affected the evolutionary ecology of polar bears around Greenland. We show that throughout the last [~]11,000 years, Greenlandic polar bears have been heavily influenced by changes in sea-surface temperature (SST) and sea-ice cover. Most notable are major reductions in effective population size at the beginning of the Holocene and during the Holocene Thermal Maximum [~]6 kya, which coincide with increases in annual mean SST, reduction in sea-ice covers, declines in suitable habitat, and shifts in suitable habitat northwards. Furthermore, we show how individuals sampled from west and east Greenland are genetically, morphologically, and ecologically distinct. We find bears sampled in west Greenland to be larger, more genetically diverse and have diets dominated by ringed seals, whereas bears from east Greenland are smaller and less diverse with more varied diets, putatively driven by regional biotic differences. Taken together, we provide novel insights into the vulnerability of polar bears to environmental change, and how the Arctic marine ecosystem plays a vital role in shaping the evolutionary and ecological trajectories of its inhabitants. TeaserMultivariate investigations of the environments role in the evolutionary ecology of Greenlandic polar bears.

evolutionary biology↗

bioRxiv2019

Sex identification of ancient pinnipeds using the dog genome

Determining the male and female representation in zooarchaeological material from hunted animal species is essential, to fully investigate the effects and means of prehistoric hunting practices, and may further provide valuable biological information on past animal life-history, behaviour and demography. However, the fragmented nature of the zooarchaeological record and a lack of clear diagnostic skeletal markers, often prevents such inference. Here, we test the usability of the dog nuclear genome (CanFam3.1) for sex identification of pinnipeds. First, a contemporary sample set (n=72) of ringed seals (Pusa hispida), with known sex was used to test the genetic sex identification method. By quantifying the proportion of X chromosome reads, as the chrX/chr1 ratio, the ratios clustered in two clearly distinguishable sex groups. Of the 72 individuals, 69 were identified to the accurate sex, which proves a high reliability of the genetic method. Second, random down sampling of a subset of the ringed seal samples to different read number, suggests at least 5000 DNA sequence reads mapped to the reference genome as the lower limit for which this method is applicable. Finally, applying this standard, sex identification was successfully carried out on a broad set of ancient pinniped samples, including walruses (Odobenus rosmarus), grey seals (Halichoerus grypus) and harp seals (Pagophilus groenlandicus), which all showed clearly distinct male and female chrX/chr1 ratio groups.

genomics↗