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Antarctica harbours some of the most isolated and extreme environments on Earth, concealing a largely unexplored and unique component of the global animal virosphere. To understand the diversity and evolutionary histories of viruses in these polar species, we determined the viromes of gill metatranscriptomes from 11 Antarctic fish species with 248 samples collected from the Ross Sea region spanning the Perciformes, Gadiformes, and Scorpaeniformes orders. The continent's shift southward and cooling temperatures >20 million years ago led to a reduction in biodiversity and subsequent radiation of some marine fauna, such as the notothenioid fishes. Despite decreased host species richness in polar regions, we revealed a surprisingly complex virome diversity in Ross Sea fish, with the types and numbers of viruses per host species and individuals sampled comparable to that of fish in warmer marine environments with higher host community diversity. We also observed a higher number of closely related viruses likely representing instances of recent and historic host-switching events among the Perciformes (all notothenioids) than in the Gadiformes, suggesting that rapid speciation events within this order generated closely related host species with few genetic barriers to cross-species transmission. Additionally, we identified novel genomic variation in an arenavirus with a split nucleoprotein sequence containing a stable helical structure, indicating potential adaptation of viral proteins to extreme temperatures. These findings enhance our understanding of virus evolution and virus-host interactions in response to environmental shifts, especially in less diverse ecosystems that are more vulnerable to the impacts of anthropogenic and climate changes., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press.)

Background: Accelerating biodiversity loss necessitates monitoring the potential pathogens of vulnerable species. With a third of New Zealand's avifauna considered at risk of extinction, a greater understanding of the factors that influence microbial transmission in this island ecosystem is needed. We used metatranscriptomics to determine the viruses, as well as other microbial organisms (i.e. the infectomes), of seven bird species, including the once critically endangered black robin (Petroica traversi), on two islands in the remote Chatham Islands archipelago, New Zealand., Results: We identified 19 likely novel avian viruses across nine viral families. Black robins harboured viruses from the Flaviviridae, Herpesviridae, and Picornaviridae, while introduced starlings (Sturnus vulgaris) and migratory seabirds (Procellariiformes) carried viruses from six additional viral families. Potential cross-species virus transmission of a novel passerivirus (family: Picornaviridae) between native (black robins and grey-backed storm petrels) and introduced (starlings) birds was also observed. Additionally, we identified bacterial genera, apicomplexan parasites, as well as a novel megrivirus linked to disease outbreaks in other native New Zealand birds. Notably, island effects were outweighed by host taxonomy as a significant driver of viral composition, even among sedentary birds., Conclusions: These findings underscore the value of surveillance of avian populations to identify and minimise escalating threats of disease emergence and spread in these island ecosystems. Importantly, they contribute to our understanding of the potential role of introduced and migratory birds in the transmission of microbes and associated diseases, which could impact vulnerable island-endemic species., (© 2024. The Author(s).)

The lesser short-tailed bat ( Mystacina tuberculata ) and the long-tailed bat ( Chalinolobus tuberculatus ) are Aotearoa New Zealand's only native extant terrestrial mammals and are believed to have migrated from Australia. Long-tailed bats arrived in New Zealand an estimated two million years ago and are closely related to other Australian bat species. Lesser short-tailed bats, in contrast, are the only extant species within the Mystacinidae and are estimated to have been living in isolation in New Zealand for the past 16-18 million years. Throughout this period of isolation, lesser short-tailed bats have become one of the most terrestrial bats in the world. Through a metatranscriptomic analysis of guano samples from eight locations across New Zealand, we aimed to characterise the viromes of New Zealand's bats and determine whether viruses have jumped between these species over the past two million years. High viral richness was observed among long-tailed bats with viruses spanning seven different viral families. In contrast, no bat-specific viruses were identified in lesser short-tailed bats. Both bat species harboured an abundance of likely dietary- and environment-associated viruses. We also identified alphacoronaviruses in long-tailed bat guano that had previously been identified in lesser short-tailed bats, suggesting that these viruses had jumped the species barrier after long-tailed bats migrated to New Zealand. Of note, an alphacoronavirus species discovered here possessed a complete genome of only 22,416 nucleotides with entire deletions or truncations of several non-structural proteins, thereby representing what may be the shortest genome within the Coronaviridae identified to date. Overall, this study has revealed a diverse range of novel viruses harboured by New Zealand's only native terrestrial mammals, in turn expanding our understanding of bat viral dynamics and evolution globally., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press.)

Fish viromes often provide insights into the origin and evolution of viruses affecting tetrapods, including those associated with imporant human diseases. However, despite fish being the most diverse vertebrate group, their viruses are still understudied. We investigated the viromes of fish on Chatham Island (Rēkohu), a geographically isolated island housing 9% of New Zealand's threatened endemic fish species. Using metatranscriptomics, we analyzed samples from seven host species across 16 waterbodies. We identified 19 fish viruses, including 16 potentially novel species, expanding families such as the Coronaviridae, Hantaviridae, Poxviridae, and the recently proposed Tosoviridae. Surprisingly, virome composition was not influenced by the ecological factors measured and smelt (Retropinna retropinna) viromes were consistent across lakes despite differences in host life history, seawater influence, and community richness. Overall, fish viromes across Rēkohu were highly diverse and revealed a long history of co-divergence between host and virus despite their unique and geographically isolated ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Tuatara (Sphenodon punctatus) are one of the most phylogenetically isolated vertebrate species and provide a unique host system to study virus evolution. While the tuatara genome, sequenced in 2020, revealed many endogenous viral elements, we know little of the exogenous viruses that infect tuatara. We performed a metatranscriptomics study of tuatara cloaca samples from a wild population on Takapourewa (Stephens Island), Aotearoa New Zealand. From these data we identified 49 potentially novel viral species that spanned 19 RNA viral families and/or orders, the vast majority (48) of which were likely dietary-related. Notably, using a protein structure homology search, we identified a highly divergent novel virus within the Picornaviridae which may directly infect tuatara. Additionally, two endogenous tuatara adintoviruses were characterised that exhibited long-term viral-host co-divergence. Overall, our results indicate that the tuatara cloacal virome is highly diverse, likely due to a large number of dietary-related viruses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The Nidovirales comprise a genetically diverse group of positive-sense single-stranded RNA virus families that infect a range of invertebrate and vertebrate hosts. Recent metagenomic studies have identified nido-like virus sequences, particularly those related to the Coronaviridae , in a range of aquatic hosts including fish, amphibians, and reptiles. We sought to identify additional members of the Coronaviridae in both bony and jawless fish through a combination of total RNA sequencing (meta-transcriptomics) and data mining of published RNA sequencing data and from this reveal more of the long-term patterns and processes of coronavirus evolution. Accordingly, we identified a number of divergent viruses that fell within the Letovirinae subfamily of the Coronaviridae , including those in a jawless fish-the pouched lamprey. By mining fish transcriptome data, we identified additional virus transcripts matching these viruses in bony fish from both marine and freshwater environments. These new viruses retained sequence conservation in the RNA-dependant RNA polymerase across the Coronaviridae but formed a distinct and diverse phylogenetic group. Although there are broad-scale topological similarities between the phylogenies of the major groups of coronaviruses and their vertebrate hosts, the evolutionary relationship of viruses within the Letovirinae does not mirror that of their hosts. For example, the coronavirus found in the pouched lamprey fell within the phylogenetic diversity of bony fish letoviruses, indicative of past host switching events. Hence, despite possessing a phylogenetic history that likely spans the entire history of the vertebrates, coronavirus evolution has been characterised by relatively frequent cross-species transmission, particularly in hosts that reside in aquatic habitats., (© The Author(s) 2021. Published by Oxford University Press.)

Rubella virus (RuV) is the causative agent of rubella ("German measles") and remains a global health concern. Until recently, RuV was the only known member of the genus Rubivirus and the only virus species classified within the Matonaviridae family of positive-sense RNA viruses. Recently, two new rubella-like matonaviruses, Rustrela virus and Ruhugu virus , have been identified in several mammalian species, along with more divergent viruses in fish and reptiles. To screen for the presence of additional novel rubella-like viruses, we mined published transcriptome data using genome sequences from Rubella , Rustrela , and Ruhugu viruses as baits. From this, we identified a novel rubella-like virus in a transcriptome of Tetronarce californica -order Torpediniformes (Pacific electric ray)-that is more closely related to mammalian Rustrela virus than to the divergent fish matonavirus and indicative of a complex pattern of cross-species virus transmission. Analysis of host reads confirmed that the sample analysed was indeed from a Pacific electric ray, and two other viruses identified in this animal, from the Arenaviridae and Reoviridae , grouped with other fish viruses. These findings indicate that the evolutionary history of the Matonaviridae is more complex than previously thought and highlights the vast number of viruses that remain undiscovered.