Karyotypic stasis and swarming influenced the evolution of viral tolerance in a species-rich bat radiation

Comparative genomics provides insights into chromosomal evolution and immunological adaptation in horseshoe bats

Horseshoe bats are natural hosts of zoonotic viruses, yet the genetic basis of their antiviral immunity is poorly understood. Here we generated two new chromosomal-level genome assemblies for horseshoe bat species (Rhinolophus) and three close relatives, and show that, during their diversification, horseshoe bats underwent extensive chromosomal rearrangements and gene expansions linked to segmental duplications. These expansions have generated new adaptive variations in type I interferons and the interferon-stimulated gene ANXA2R, which potentially enhance antiviral states, as suggested by our functional assays. Genome-wide selection screens, including of candidate introgressed regions, uncover numerous putative molecular adaptations linked to immunity, including in viral receptors. By expanding taxon coverage to ten horseshoe bat species, we identify new variants of the SARS-CoV-2 receptor ACE2, and report convergent functionally important residues that could explain wider patterns of susceptibility across mammals. We conclude that horseshoe bats have numerous signatures of adaptation, including some potentially related to immune response to viruses, in genomic regions with diverse and multiscale mutational changes.

How many mammal species are there now? Updates and trends in taxonomic, nomenclatural, and geographic knowledge

The Mammal Diversity Database (MDD) is an open-access resource providing up-to-date taxonomic, nomenclatural, and geographic data for global mammal species. Since its launch in 2018, the MDD has transformed the traditionally static process of updating mammalian taxonomy into regular online releases reflecting the latest published research. To build on this foundation, we here present version 2.0 of the MDD (MDD2), which catalogues 6,759 living and recently extinct mammal species, representing net increases of 4.1% and 24.8% over MDD version 1.0 and Mammal Species of the World, 3rd edition (MSW3), respectively. Additionally, we identify a net increase of 68.8% (+2,754; 3,149 splits + de novo, 395 lumps) species since 1980 at a rate of ~65 species/year based on past totals from 14 mammalian compendia, leading to projections of ~7,084 species by 2030 and ~8,382 by 2050 if these trends continue. Key updates in MDD2 include: (i) codings of US state, country, continent, and biogeographic realm geographic categories for each species; (ii) a comprehensive nomenclatural dataset for 50,230 valid and synonymous species-rank names, curated with type locality and specimen information for the first time; and (iii) integration between the MDD and the databases Hesperomys and Batnames for greater data accuracy and completeness. These updates bridge critical gaps in the taxonomic and nomenclatural information needed for ongoing revisions and assessments of mammalian species diversity. Using these data, we evaluate temporal and geographic trends over the past 267 years, identifying four major time periods of change in mammalian taxonomy and nomenclature: (i) the initial monographic description of traditionally charismatic species (1758-1880); (ii) the peak of descriptive taxonomy, describing subspecies, and publishing in journals (1881-1939); (iii) the shift toward revisionary taxonomy and polytypic species (1940-1999); and (iv) the current technology-driven period of integrative revisionary taxonomy (2000-present). Geographically, new species recognition since MSW3 has been concentrated in equatorial, mountainous, and island regions, highlighting areas of high mammal endemism (e.g., Madagascar, Philippines, Andes, East Africa, Himalayas, Atlantic Forests). However, gaps in 21st century taxonomic activity are identified in West and Central Africa, India, and some parts of Indonesia. Currently lagging conservation assessments are alarming, with 25% of the MDD2-recognized mammal species allocated to the 'understudied' conservation threat categories of Data Deficient (11%) or Not Evaluated (14%), underscoring the need for greater taxonomic integration with conservation organizations. Governance advancements in MDD2 include the establishment of external taxonomic subcommittees to guide data collection and curation, a rewritten website that improves access and scalability, a cross-platform application that provides offline access, and new partnerships to continue linking MDD data to global biodiversity infrastructure. By providing up-to-date mammalian taxonomic and nomenclatural data-including links to the text of original name descriptions, type localities, and type specimen collections-the MDD provides an integrative resource for mammalogists and conservationists to more easily track the status of their study organisms.

The Genomic Landscape, Causes, and Consequences of Extensive Phylogenomic Discordance in Murine Rodents

A species tree is a central concept in evolutionary biology whereby a single branching phylogeny reflects relationships among species. However, the phylogenies of different genomic regions often differ from the species tree. Although tree discordance is widespread in phylogenomic studies, we still lack a clear understanding of how variation in phylogenetic patterns is shaped by genome biology or the extent to which discordance may compromise comparative studies. We characterized patterns of phylogenomic discordance across the murine rodents-a large and ecologically diverse group that gave rise to the laboratory mouse and rat model systems. Combining recently published linked-read genome assemblies for seven murine species with other available rodent genomes, we first used ultraconserved elements (UCEs) to infer a robust time-calibrated species tree. We then used whole genomes to examine finer-scale patterns of discordance across ∼12 million years of divergence. We found that proximate chromosomal regions tended to have more similar phylogenetic histories. There was no clear relationship between local tree similarity and recombination rates in house mice, but we did observe a correlation between recombination rates and average similarity to the species tree. We also detected a strong influence of linked selection whereby purifying selection at UCEs led to appreciably less discordance. Finally, we show that assuming a single species tree can result in substantial deviation from the results with gene trees when testing for positive selection under different models. Collectively, our results highlight the complex relationship between phylogenetic inference and genome biology and underscore how failure to account for this complexity can mislead comparative genomic studies.

Extensive longevity and DNA virus-driven adaptation in nearctic Myotis bats

The genus Myotis is one of the largest clades of bats, and exhibits some of the most extreme variation in lifespans among mammals alongside unique adaptations to viral tolerance and immune defense. To study the evolution of longevity-associated traits and infectious disease, we generated near-complete genome assemblies and cell lines for 8 closely related species of Myotis. Using genome-wide screens of positive selection, analyses of structural variation, and functional experiments in primary cell lines, we identify new patterns of adaptation contributing to longevity, cancer resistance, and viral interactions in bats. We find that Myotis bats have some of the most significant variation in cancer risk across mammals and demonstrate a unique DNA damage response in primary cells of the long-lived M. lucifugus. We also find evidence of abundant adaptation in response to DNA viruses - but not RNA viruses - in Myotis and other bats in sharp contrast with other mammals, potentially contributing to the role of bats as reservoirs of zoonoses. Together, our results demonstrate how genomics and primary cells derived from diverse taxa uncover the molecular bases of extreme adaptations in non-model organisms.

Distinct Genes with Similar Functions Underlie Convergent Evolution in Myotis Bat Ecomorphs

Convergence offers an opportunity to explore to what extent evolution can be predictable when genomic composition and environmental triggers are similar. Here, we present an emergent model system to study convergent evolution in nature in a mammalian group, the bat genus Myotis. Three foraging strategies-gleaning, trawling, and aerial hawking, each characterized by different sets of phenotypic features-have evolved independently multiple times in different biogeographic regions in isolation for millions of years. To investigate the genomic basis of convergence and explore the functional genomic changes linked to ecomorphological convergence, we sequenced and annotated 17 new genomes and screened 16,426 genes for positive selection and associations between relative evolutionary rates and foraging strategies across 30 bat species representing all Myotis ecomorphs across geographic regions as well as among sister groups. We identify genomic changes that describe both phylogenetic and ecomorphological trends. We infer that colonization of new environments may have first required changes in genes linked to hearing sensory perception, followed by changes linked to fecundity and development, metabolism of carbohydrates, and heme degradation. These changes may be linked to prey acquisition and digestion and match phylogenetic trends. Our findings also suggest that the repeated evolution of ecomorphs does not always involve changes in the same genes but rather in genes with the same molecular functions such as developmental and cellular processes.

Signals of positive selection in genomes of palearctic Myotis-bats coexisting with a fungal pathogen

Disease can act as a driving force in shaping genetic makeup across populations, even species, if the impacts influence a particularly sensitive part of their life cycles. White-nose disease is caused by a fungal pathogen infecting bats during hibernation. The mycosis has caused massive population declines of susceptible species in North America, particularly in the genus Myotis. However, Myotis bats appear to tolerate infection in Eurasia, where the fungal pathogen has co-evolved with its bat hosts for an extended period of time. Therefore, with susceptible and tolerant populations, the fungal disease provides a unique opportunity to tease apart factors contributing to tolerance at a genomic level to and gain an understanding of the evolution of non-harmful in host-parasite interactions. To investigate if the fungal disease has caused adaptation on a genomic level in Eurasian bat species, we adopted both whole-genome sequencing approaches and a literature search to compile a set of 300 genes from which to investigate signals of positive selection in genomes of 11 Eurasian bats at the codon-level. Our results indicate significant positive selection in 38 genes, many of which have a marked role in responses to infection. Our findings suggest that white-nose syndrome may have applied a significant selective pressure on Eurasian Myotis-bats in the past, which can contribute their survival in co-existence with the pathogen. Our findings provide an insight on the selective pressure pathogens afflict on their hosts using methodology that can be adapted to other host-pathogen study systems.

The genome sequence of Daubenton's bat, Myotis daubentonii (Kuhl, 1817)

We present a genome assembly from an individual male Myotis daubentonii (Daubenton's bat; Chordata; Mammalia; Chiroptera; Vespertilionidae). The genome sequence is 2,127.8 megabases in span. Most of the assembly is scaffolded into 23 chromosomal pseudomolecules, including the X and Y sex chromosomes. The mitochondrial genome has also been assembled and is 17.34 kilobases in length.