Explore the vast range of titles available.

The prevailing paleobiogeographic hypothesis suggests that many steppe and tundra-steppe taxa currently found in Central Asia expanded into Europe during Pleistocene glacial periods, when open habitats dominated. However, previous studies have shown that one such species, the European narrow-headed vole ( Stenocranius anglicus ), diverged from its Asiatic counterparts over 200 thousand years ago, implying its prolonged isolation and survival in European refugia through the Eemian interglacial period. To test whether this was an exception or part of a broader pattern, we analysed the mitochondrial genomes from 33 Late Pleistocene and Holocene small hamster (Cricetinae) remains from Central and Western Europe, the Balkans, and Anatolia, all previously identified morphologically as grey dwarf hamster ( Nothocricetulus migratorius ). Contrary to expectations, 16 Late Pleistocene Central European samples were assigned to the hairy-footed hamster ( Cricetiscus sungorus ), a species currently restricted to northern Kazakhstan and southern Russia, whereas 17 samples from the Balkans and Anatolia belonged to the grey dwarf hamster. In both cases, the Late Pleistocene samples formed clades sister to modern populations; however, with relatively recent divergence times. This suggests population continuity or repeated expansion of hamsters from Asiatic sources rather than long-term isolation in Europe, as previously observed in narrow-headed voles. Our findings indicate that steppe species, despite occupying similar ecological niches, respond to past climate change in a species-specific manner. Therefore, broad generalisations regarding their evolutionary history may be misleading.

Background The systematics of extant hamsters (Cricetinae) have been increasingly clarified, due to advances in molecular phylogenetics. In contrast, their relationships with their fossil relatives have remained relatively unclear. Furthermore, studies on the biogeographical history and divergence times of the main groups of extant hamsters have so far been limited to molecular phylogenies and node dating approaches. Results Here, we present the first ‘total-evidence’ analysis of hamsters that combines extinct and extant taxa, based on a comprehensive dataset covering 82 species (~ 75% of the total known diversity of 109 species). We performed a relaxed-clock Bayesian phylogenetic reconstruction and used the resulting tip-dated tree to estimate ancestral geographic ranges. Our results confirm ‘† Kowalskia’ as a synonym of † Neocricetodon , support the previously suggested non-monophyly of † Allocricetus , † Cricetulodon , and ‘† Cricetinus’ and reveal several fossil taxa as potential close relatives of the crown group. We recover a Pliocene origin of the crown hamsters, considerably younger than previous estimates of a late/middle Miocene origin. Our biogeographic reconstructions suggest a Central and Eastern European origin of the entire group, with crown hamsters emerging in the region around the Black Sea and the Eastern Mediterranean. Subsequent dispersal events into Western Europe and East Central Asia may be linked to the expansion of open vegetation. Conclusions Based on a total-evidence phylogenetic reconstruction, we highlight necessary taxonomical revisions for several fossil cricetine taxa and explore the biogeographical evolution of the group. Importantly, our estimated divergence dates reveal a substantially younger group of crown hamsters than previously assumed.

In late 2022, SARS-CoV-2 Omicron subvariants have become highly diversified, and XBB is spreading rapidly around the world. Our phylogenetic analyses suggested that XBB emerged through the recombination of two cocirculating BA.2 lineages, BJ.1 and BM.1.1.1 (a progeny of BA.2.75), during the summer of 2022. XBB.1 is the variant most profoundly resistant to BA.2/5 breakthrough infection sera to date and is more fusogenic than BA.2.75. The recombination breakpoint is located in the receptor-binding domain of spike, and each region of the recombinant spike confers immune evasion and increases fusogenicity. We further provide the structural basis for the interaction between XBB.1 spike and human ACE2. Finally, the intrinsic pathogenicity of XBB.1 in male hamsters is comparable to or even lower than that of BA.2.75. Our multiscale investigation provides evidence suggesting that XBB is the first observed SARS-CoV-2 variant to increase its fitness through recombination rather than substitutions. XBB is the first recombinant, globally dominant variant of SARS-CoV-2. Here, the authors examine the variant’s origins and virological properties, showing it is the first example of SARS-CoV-2 improving its fitness through recombination.

The genus status of Urocricetus was defined recently based on morphological and molecular data. Even though the amount of evidence for a separate phylogenetic position of this genus among Cricetinae continues to increase, there is still no consensus on its relationship to other groups. Here we give the first comprehensive description of the U. kamensis karyotype (2 n  = 30, NF a  = 50) including results of comparative cytogenetic analysis and detailed examination of its phylogenetic position by means of numerous molecular markers. The molecular data strongly indicated that Urocricetus is a distant sister group to Phodopus . Comparative cytogenetic data showed significant reorganization of the U. kamensis karyotype compared to karyotypes of all other hamsters investigated earlier. The totality of findings undoubtedly means that Urocricetus belongs to a separate divergent lineage of Cricetinae.

During the current coronavirus disease 2019 (COVID-19) pandemic, a variety of mutations have accumulated in the viral genome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and, at the time of writing, four variants of concern are considered to be potentially hazardous to human society 1 . The recently emerged B.1.617.2/Delta variant of concern is closely associated with the COVID-19 surge that occurred in India in the spring of 2021 (ref. 2 ). However, the virological properties of B.1.617.2/Delta remain unclear. Here we show that the B.1.617.2/Delta variant is highly fusogenic and notably more pathogenic than prototypic SARS-CoV-2 in infected hamsters. The P681R mutation in the spike protein, which is highly conserved in this lineage, facilitates cleavage of the spike protein and enhances viral fusogenicity. Moreover, we demonstrate that the P681R-bearing virus exhibits higher pathogenicity compared with its parental virus. Our data suggest that the P681R mutation is a hallmark of the virological phenotype of the B.1.617.2/Delta variant and is associated with enhanced pathogenicity. The P681R mutation in the spike protein renders the Delta variant more pathogenic than prototypic SARS-CoV-2 in infected hamsters, and facilitates spike protein cleavage and enhances viral fusogenicity.

At the end of 2019, a novel coronavirus (severe acute respiratory syndrome coronavirus 2; SARS-CoV-2) was detected in Wuhan, China, that spread rapidly around the world, with severe consequences for human health and the global economy. Here, we assessed the replicative ability and pathogenesis of SARS-CoV-2 isolates in Syrian hamsters. SARS-CoV-2 isolates replicated efficiently in the lungs of hamsters, causing severe pathological lung lesions following intranasal infection. In addition, microcomputed tomographic imaging revealed severe lung injury that shared characteristics with SARS-CoV-2−infected human lung, including severe, bilateral, peripherally distributed, multilobular ground glass opacity, and regions of lung consolidation. SARS-CoV-2−infected hamsters mounted neutralizing antibody responses and were protected against subsequent rechallenge with SARS-CoV-2. Moreover, passive transfer of convalescent serum to naïve hamsters efficiently suppressed the replication of the virus in the lungs even when the serum was administrated 2 d postinfection of the serum-treated hamsters. Collectively, these findings demonstrate that this Syrian hamster model will be useful for understanding SARS-CoV-2 pathogenesis and testing vaccines and antiviral drugs.

Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (Cricetulus barabensis), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein substitution D614G became dominant during the coronavirus disease 2019 (COVID-19) pandemic 1 , 2 . However, the effect of this variant on viral spread and vaccine efficacy remains to be defined. Here we engineered the spike D614G substitution in the USA-WA1/2020 SARS-CoV-2 strain, and found that it enhances viral replication in human lung epithelial cells and primary human airway tissues by increasing the infectivity and stability of virions. Hamsters infected with SARS-CoV-2 expressing spike(D614G) (G614 virus) produced higher infectious titres in nasal washes and the trachea, but not in the lungs, supporting clinical evidence showing that the mutation enhances viral loads in the upper respiratory tract of COVID-19 patients and may increase transmission. Sera from hamsters infected with D614 virus exhibit modestly higher neutralization titres against G614 virus than against D614 virus, suggesting that the mutation is unlikely to reduce the ability of vaccines in clinical trials to protect against COVID-19, and that therapeutic antibodies should be tested against the circulating G614 virus. Together with clinical findings, our work underscores the importance of this variant in viral spread and its implications for vaccine efficacy and antibody therapy. The SARS-CoV-2 variant expressing spike(D641G) shows increased infectivity in human lung epithelial cells and in hamster and primary human upper airway tissues, but is more susceptible to neutralization by antibodies raised against SARS-CoV-2.

The emergence of the Omicron variant of SARS-CoV-2 is an urgent global health concern 1 . In this study, our statistical modelling suggests that Omicron has spread more rapidly than the Delta variant in several countries including South Africa. Cell culture experiments showed Omicron to be less fusogenic than Delta and than an ancestral strain of SARS-CoV-2. Although the spike (S) protein of Delta is efficiently cleaved into two subunits, which facilitates cell–cell fusion 2 , 3 , the Omicron S protein was less efficiently cleaved compared to the S proteins of Delta and ancestral SARS-CoV-2. Furthermore, in a hamster model, Omicron showed decreased lung infectivity and was less pathogenic compared to Delta and ancestral SARS-CoV-2. Our multiscale investigations reveal the virological characteristics of Omicron, including rapid growth in the human population, lower fusogenicity and attenuated pathogenicity. In vitro studies in human cell lines and in vivo studies in a hamster model show that the SARS-CoV-2 Omicron variant is less pathogenic than both the Delta variant and an ancestral strain of SARS-CoV-2.

The recent emergence of B.1.1.529, the Omicron variant 1 , 2 , has raised concerns of escape from protection by vaccines and therapeutic antibodies. A key test for potential countermeasures against B.1.1.529 is their activity in preclinical rodent models of respiratory tract disease. Here, using the collaborative network of the SARS-CoV-2 Assessment of Viral Evolution (SAVE) programme of the National Institute of Allergy and Infectious Diseases (NIAID), we evaluated the ability of several B.1.1.529 isolates to cause infection and disease in immunocompetent and human ACE2 (hACE2)-expressing mice and hamsters. Despite modelling data indicating that B.1.1.529 spike can bind more avidly to mouse ACE2 (refs.  3 , 4 ), we observed less infection by B.1.1.529 in 129, C57BL/6, BALB/c and K18-hACE2 transgenic mice than by previous SARS-CoV-2 variants, with limited weight loss and lower viral burden in the upper and lower respiratory tracts. In wild-type and hACE2 transgenic hamsters, lung infection, clinical disease and pathology with B.1.1.529 were also milder than with historical isolates or other SARS-CoV-2 variants of concern. Overall, experiments from the SAVE/NIAID network with several B.1.1.529 isolates demonstrate attenuated lung disease in rodents, which parallels preliminary human clinical data. A collaborative study demonstrates that, compared with previous SARS-CoV-2 variants, B.1.1.529 isolates cause less infection and disease in mice and hamsters, in agreement with preliminary data from studies in humans.