Ursula Siebert

Understanding how demography and natural selection interact during colonization of novel environments is a central question in evolutionary biology. The Baltic Sea region combines one of the world's strongest salinity gradients with a well‐characterized postglacial history of less than ~12,000 years. The harbour porpoise ( Phocoena phocoena ) is distributed across this gradient as three populations—the North Sea, Belt Sea and Proper Baltic Sea populations. Using whole genome resequencing data from 59 individuals, we reconstructed the demographic history of Baltic colonization and identified genomic signatures of local adaptation. Demographic modelling supported a sequential colonization in which the Belt Sea population diverged first from an ancestral North Sea population, followed by an independent divergence of the Proper Baltic Sea population, with two equally supported timing hypotheses placing initial colonization either during the Yoldia Sea (~11,800 years ago) or the Baltic Sea period (~8000 years ago). The Proper Baltic Sea population showed drift‐dominated divergence consistent with a founder effect, while two discrete genomic islands of differentiation with selective sweep signatures were identified between North and Belt Sea populations, pointing to recent positive selection. Both regions contain osmoregulatory candidate genes, most notably SCNN1D, encoding part of the epithelial Na ⁺ channels, a key regulator of sodium homeostasis. A non‐synonymous mutation in SCNN1D showed striking allele frequency divergence along the salinity gradient, confirmed across ~400 individuals. Together, these results reveal how genetic drift and divergent selection interact to drive rapid adaptation to a brackish environment, and identify SCNN1D as a compelling candidate for cetacean osmoregulatory adaptation.

The Eurasian otter ( Lutra lutra ) is a semiaquatic, freshwater top predator of conservation concern due to its significant global population decline in the last century. Following its recovery and recolonization in parts of Europe, the population faces ongoing threats, including habitat loss and fragmentation due to human activities, climate change, prey depletion, and exposure to emerging contaminants. Accurately identifying its diet is crucial for understanding ecological interactions and proposing effective management strategies. DNA metabarcoding based on high‐throughput sequencing is a reliable diet analysis tool with better resolution than traditional methods. This study, for the first time, applied two 16S rRNA primers targeting different prey classes on the dietary spectrum of two Eurasian otters populations returning to Northern Germany (Schleswig‐Holstein and Lower Saxony). DNA fragments of prey items from the gut contents of 156 otters collected between 2005 and 2022 were sequenced. Fifty‐five operational taxonomic units (OTUs) were identified in the dietary remains, including freshwater and marine fish, anurans, caudates, and water birds. Otters in the study area are opportunistic predators with wide dietary plasticity, feeding on the most abundant species. Nine‐spined sticklebacks, common roach, and common frogs were important prey items, and marine fish species were detected in the diet of some of the investigated otters. The otters' diet differed between Lower Saxony and Schleswig‐Holstein, between sexes, and a slight difference was observed between adults and subadults. This study provides new insights into the diet composition of otters and their ability to exploit a variety of resources in their habitat. This information is vital for understanding their chances of survival in an environment that is continuously changing due to human impacts and for developing effective management tools.

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.

The hooded seal ( Cystophora cristata ) is an Arctic phocid seal occasionally observed far outside its native range, including the European Atlantic shelf seas. This study presents the movements and diving behaviour of two female hooded seal pups after rehabilitation and release in the German North Sea. We tracked the animals using satellite telemetry to evaluate post-release survival and movement behaviour. Within one month, one seal travelled through the North Sea to the coast of United Kingdom, and then further northward to the Norwegian west coast, suggesting a successful return to Arctic waters. In contrast, the second seal remained in the North Sea and exhibited shallower and shorter dives over time, with extensive surface resting. She was ultimately found in poor condition in the United Kingdom and placed in permanent captivity. These cases highlight the species’ high dispersal capacity, yet also underline the challenges vagrant individuals face in suboptimal non-native habitats. The contrasting outcomes suggest that rehabilitation and release of such Arctic vagrants should be assessed case-by-case, considering the animal’s age, health, and timing of the release in relation to the expected prey availability. This study emphasizes the importance of satellite telemetry in evaluating post-release success and contributes to the broader discussion on the viability and ethics of rehabilitating extralimital marine mammals.

Amphibian populations are undergoing dramatic global declines, with infectious diseases recognized as major contributors. While chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), and disease caused by ranaviruses are well known, herpesviruses in amphibians remain comparatively neglected. We conducted a passive survey using carcasses collected between 2022 and 2025 in Schleswig-Holstein, northern Germany. Dead amphibians (n = 187) were dissected. Skin, kidney, liver, and brain samples were screened for Bd, ranaviruses, bufonid herpesvirus 1 (BfHV1), and ranid herpesvirus 3 (RaHV3) by PCR. BfHV1 was detected in nearly half of the Bufo bufo (common toads; 48.6%), while RaHV3 was identified in 23.6% of the Rana temporaria (common frogs) examined. Bd was detected in a single B. bufo, while ranaviruses were not detected. BfHV1 was present in skin, liver, kidney, and brain samples, whereas RaHV3 was detected exclusively in skin samples. No macroscopical or histological lesions characteristic of herpesviruses or Bd were found. However, the carcass-based approach frequently limited detailed examination due to compromised sample quality. Our findings confirm the presence of amphibian herpesviruses (BfHV1 and RaHV3) in the region without associated lesions, raising questions about their potential to cause systemic infections. Furthermore, our results highlight the limitations of carcass-based surveillance and underscore the need for complementary diagnostic approaches, such as immunohistochemistry and meta-omics.

Live trapping is a common method in wildlife research and management, yet it poses inherent risks to animal welfare. This study systematically evaluated injury incidence and severity in coypus ( Myocastor coypus ) and raccoons ( Procyon lotor ) captured using three commercially available live trap types: a standard wooden box trap (WBT), a metallic, sheet metal trap (SMT), and a wire grid trap (WGT). A total of 55 coypus and 45 raccoons were examined following a trap confinement duration of a maximum of six hours. Injuries were assessed using standardized necropsy protocols and categorized by anatomical location, severity, and presumed cause. Results showed species-specific injury patterns, with raccoons exhibiting more frequent and severe injuries than coypus. Raccoons primarily sustained skin lesions and dental trauma, consistent with their manipulative, escape-oriented behavior, while coypu injuries were predominantly localized to the snout and incisors. Although not statistically significant, trap design influenced injury profiles: the WBT was associated with severe injuries in raccoons, particularly to the forelimbs and dentition, while the WGT prompted intense escape behaviors without a proportional increase in trauma. The SMT resulted in fewer external injuries but did present species-specific risks, such as claw-abrasion and tail entrapment. Approximately 93% of raccoons and 55% of coypus exhibited external injuries, including 14 severe cases and 5 confirmed fractures. These findings underscore the importance of species-specific trap assessment and design optimization to mitigate animal suffering. Given the limitations of traditional injury scoring systems and behavioral indicators when applied to wild animals, this study highlights the need for integrated, evidence-based welfare assessments in field settings. Future research should prioritize refinement of trapping methods and standardized welfare evaluation frameworks to support ethical and effective wildlife management.