The phylogenetic and taxonomic relationships among the Old World leaf-nosed bats (Hipposideridae) and the closely related horseshoe bats (Rhinolophidae) remain unresolved. In this study, we generated a novel approximately 10-kb molecular data set of 19 nuclear exon and intron gene fragments for 40 bat species to elucidate the phylogenetic relationships within the families Rhinolophidae and Hipposideridae. We estimated divergence times and explored potential reasons for any incongruent phylogenetic signal. We demonstrated the effects of outlier taxa and genes on phylogenetic reconstructions and compared the relative performance of intron and exon data to resolve phylogenetic relationships. Phylogenetic analyses produced a well-resolved phylogeny, supporting the familial status of Hipposideridae and demonstrated the paraphyly of the largest genus, Hipposideros. A fossil-calibrated timetree and biogeographical analyses estimated that Rhinolophidae and Hipposideridae diverged in Africa during the Eocene approximately 42 Ma. The phylogram, the timetree, and a unique retrotransposon insertion supported the elevation of the subtribe Rhinonycterina to family level and which is diagnosed herein. Comparative analysis of diversification rates showed that the speciose genera Rhinolophus and Hipposideros underwent diversification during the Mid-Miocene Climatic Optimum. The intron versus exon analyses demonstrated the improved nodal support provided by introns for our optimal tree, an important finding for large-scale phylogenomic studies, which typically rely on exon data alone. With the recent outbreak of Middle East respiratory syndrome, caused by a novel coronavirus, the study of these species is urgent as they are considered the natural reservoir for emergent severe acute respiratory syndrome (SARS)-like coronaviruses. It has been shown that host phylogeny is the primary factor that determines a virus's persistence, replicative ability, and can act as a predictor of new emerging disease. Therefore, this newly resolved phylogeny can be used to direct future assessments of viral diversity and to elucidate the origin and development of SARS-like coronaviruses in mammals.

It is commonly, although not universally, accepted that most intra and interspecific genome sequence variations are more or less neutral, whereas a large fraction of organism-level phenotypic variations are adaptive. Gene expression levels are molecular phenotypes that bridge the gap between genotypes and corresponding organism-level phenotypes. Yet, it is unknown whether natural variations in gene expression levels are mostly neutral or adaptive. Here we address this fundamental question by genome-wide profiling and comparison of gene expression levels in nine yeast strains belonging to three closely related Saccharomyces species and originating from five different ecological environments. We find that the transcriptome-based clustering of the nine strains approximates the genome sequence-based phylogeny irrespective of their ecological environments. Remarkably, only ∼0.5% of genes exhibit similar expression levels among strains from a common ecological environment, no greater than that among strains with comparable phylogenetic relationships but different environments. These and other observations strongly suggest that most intra and interspecific variations in yeast gene expression levels result from the accumulation of random mutations rather than environmental adaptations. This finding has profound implications for understanding the driving force of gene expression evolution, genetic basis of phenotypic adaptation, and general role of stochasticity in evolution.

Through their unique use of sophisticated laryngeal echolocation bats are considered sensory specialists amongst mammals and represent an excellent model in which to explore sensory perception. Although several studies have shown that the evolution of vision is linked to ecological niche adaptation in other mammalian lineages, this has not yet been fully explored in bats. Recent molecular analysis of the opsin genes, which encode the photosensitive pigments underpinning color vision, have implicated high-duty cycle (HDC) echolocation and the adoption of cave roosting habits in the degeneration of color vision in bats. However, insufficient sampling of relevant taxa has hindered definitive testing of these hypotheses. To address this, novel sequence data was generated for the SWS1 and MWS/LWS opsin genes and combined with existing data to comprehensively sample species representing diverse echolocation types and niches (SWS1 n = 115; MWS/LWS n = 45). A combination of phylogenetic analysis, ancestral state reconstruction, and selective pressure analyses were used to reconstruct the evolution of these visual pigments in bats and revealed that although both genes are evolving under purifying selection in bats, MWS/LWS is highly conserved but SWS1 is highly variable. Spectral tuning analyses revealed that MWS/LWS opsin is tuned to a long wavelength, 555-560 nm in the bat ancestor and the majority of extant taxa. The presence of UV vision in bats is supported by our spectral tuning analysis, but phylogenetic analyses demonstrated that the SWS1 opsin gene has undergone pseudogenization in several lineages. We do not find support for a link between the evolution of HDC echolocation and the pseudogenization of the SWS1 gene in bats, instead we show the SWS1 opsin is functional in the HDC echolocator, Pteronotus parnellii. Pseudogenization of the SWS1 is correlated with cave roosting habits in the majority of pteropodid species. Together these results demonstrate that the loss of UV vision in bats is more widespread than was previously considered and further elucidate the role of ecological niche specialization in the evolution of vision in bats.

Diet is a key factor in determining and structuring animal diversity and adaptive radiations. The mammalian fossil record preserves phenotypic evidence of many dietary shifts, whereas genetic changes followed by dietary diversification in mammals remain largely unknown. To test whether living mammals preserve molecular evidence of dietary shifts, we examined the trehalase gene (Treh), which encodes an enzyme capable of digesting trehalose from insect blood, in bats and other mammals with diverse diets. Bats represent the largest dietary radiation among all mammalian orders, with independent origins of frugivory, nectarivory, carnivory, omnivory, and even sanguivory in an otherwise insectivorous clade. We found that Treh has been inactivated in unrelated bat lineages that independently radiated into noninsectivorous niches. Consistently, purifying selection has been markedly relaxed in noninsectivorous bats compared with their insectivorous relatives. Enzymatic assays of intestinal trehalase in bats suggest that trehalase activity tends to be lost or markedly reduced in noninsectivorous bats compared with their insectivorous relatives. Furthermore, our survey of Treh in 119 mammal species, which represent a deeper evolutionary timeframe, additionally identified a number of other independent losses of Treh in noninsectivorous species, recapitulating the evolutionary pattern that we found in bats. These results document a molecular record of dietary diversification in mammals, and suggest that such molecular signatures of dietary shifts would help us understand both historical and modern changes of animal diets.

Sensory systems are attractive evolutionary models to address how organisms adapt to local environments that can cause ecological speciation. However, tests of these evolutionary models have focused on visual, auditory, and olfactory senses. Here, we show local adaptation of bitter taste receptor genes in two neighboring populations of a wild mammal-the blind mole rat Spalax galili-that show ecological speciation in divergent soil environments. We found that basalt-type bitter receptors showed higher response intensity and sensitivity compared with chalk-type ones using both genetic and cell-based functional analyses. Such functional changes could help animals adapted to basalt soil select plants with less bitterness from diverse local foods, whereas a weaker reception to bitter taste may allow consumption of a greater range of plants for animals inhabiting chalk soil with a scarcity of food supply. Our study shows divergent selection on food resources through local adaptation of bitter receptors, and suggests that taste plays an important yet underappreciated role in speciation.

WUS and WOX5, which are expressed, respectively, in the organizing center (OC) and the quiescent center (QC), are essential for shoot/root apical stem-cell maintenance in flowering plants. However, little is known about how these stem-cell factors evolved their functions in flowering plants. Here, we show that the WUS/WOX5 proteins acquired two distinct capabilities by a two-step functional innovation process in the course of plant evolution. The first-step is the apical stem-cell maintenance activity of WUS/WOX5, which originated in the common ancestor of ferns and seed plants, as evidenced by the interspecies complementation experiments, showing that ectopic expression of fern Ceratopteris richardii WUS-like (CrWUL) surrounding OC/QC, or exclusive OC-/QC-expressed gymnosperms/angiosperms WUS/WOX5 in Arabidopsis wus-1 and wox5-1 mutants, could rescue their phenotypes. The second-step is the intercellular mobility that emerged in the common ancestor of seed plants after divergence from the ferns. Evidence for this includes confocal imaging of GFP fusion proteins, showing that WUS/WOX5 from seed plants, rather than from the fern CrWUL, can migrate into cells adjacent to the OC/QC. Evolutionary analysis showed that the WUS-like gene was duplicated into two copies prior to the divergence of gymnosperms/angiosperms. Then the two gene copies (WUS and WOX5) have undergone similar levels of purifying selection, which is consistent with their conserved functions in angiosperm shoot/root stem-cell maintenance and floral organ formation. Our results highlight the critical roles and the essential prerequisites that the two-step functional innovation of these genes performs and represents in the origin of flowering plants.

Obligate scavenging on the dead and decaying animal matter is a rare dietary specialization that in extant vertebrates is restricted to vultures. These birds perform essential ecological services, yet many vulture species have undergone recent steep population declines and are now endangered. To test for molecular adaptations underlying obligate scavenging in vultures, and to assess whether genomic features might have contributed to their population declines, we generated high-quality genomes of the Himalayan and bearded vultures, representing both independent origins of scavenging within the Accipitridae, alongside a sister taxon, the upland buzzard. By comparing our data to published sequences from other birds, we show that the evolution of obligate scavenging in vultures has been accompanied by widespread positive selection acting on genes underlying gastric acid production, and immunity. Moreover, we find evidence of parallel molecular evolution, with amino acid replacements shared among divergent lineages of these scavengers. Our genome-wide screens also reveal that both the Himalayan and bearded vultures exhibit low levels of genetic diversity, equating to around a half of the mean genetic diversity of other bird genomes examined. However, demographic reconstructions indicate that population declines began at around the Last Glacial Maximum, predating the well-documented dramatic declines of the past three decades. Taken together, our genomic analyses imply that vultures harbor unique adaptations for processing carrion, but that modern populations are genetically depauperate and thus especially vulnerable to further genetic erosion through anthropogenic activities.

The escape of DNA from mitochondria into the nuclear genome (nuclear mitochondrial DNA, NUMT) is an ongoing process. Although pervasively observed in eukaryotic genomes, their evolutionary trajectories in a mammal-wide context are poorly understood. The main challenge lies in the orthology assignment of NUMTs across species due to their fast evolution and chromosomal rearrangements over the past 200 million years. To address this issue, we systematically investigated the characteristics of NUMT insertions in 45 mammalian genomes and established a novel, synteny-based method to accurately predict orthologous NUMTs and ascertain their evolution across mammals. With a series of comparative analyses across taxa, we revealed that NUMTs may originate from nonrandom regions in mtDNA, are likely found in transposon-rich and intergenic regions, and unlikely code for functional proteins. Using our synteny-based approach, we leveraged 630 pairwise comparisons of genome-wide microsynteny and predicted the NUMT orthology relationships across 36 mammals. With the phylogenetic patterns of NUMT presence-and-absence across taxa, we constructed the ancestral state of NUMTs given the mammal tree using a coalescent method. We found support on the ancestral node of Fereuungulata within Laurasiatheria, whose subordinal relationships are still controversial. This study broadens our knowledge on NUMT insertion and evolution in mammalian genomes and highlights the merit of NUMTs as alternative genetic markers in phylogenetic inference.

Horizontal transfer of transposable elements (TEs) is an important mechanism contributing to genetic diversity and innovation. Bats (order Chiroptera) have repeatedly been shown to experience horizontal transfer of TEs at what appears to be a high rate compared with other mammals. We investigated the occurrence of horizontally transferred (HT) DNA transposons involving bats. We found over 200 putative HT elements within bats; 16 transposons were shared across distantly related mammalian clades, and 2 other elements were shared with a fish and two lizard species. Our results indicate that bats are a hotspot for horizontal transfer of DNA transposons. These events broadly coincide with the diversification of several bat clades, supporting the hypothesis that DNA transposon invasions have contributed to genetic diversification of bats.

The olfactory receptor (OR) gene families, which govern mammalian olfaction, have undergone extensive expansion and contraction through duplication and pseudogenization. Previous studies have shown that broadly defined environmental adaptations (e.g., terrestrial vs. aquatic) are correlated with the number of functional and non-functional OR genes retained. However, to date, no study has examined species-specific gene duplications in multiple phylogenetically divergent mammals to elucidate OR evolution and adaptation. Here, we identify the OR gene families driving adaptation to different ecological niches by mapping the fate of species-specific gene duplications in the OR repertoire of 94 diverse mammalian taxa, using molecular phylogenomic methods. We analyze >70,000 OR gene sequences mined from whole genomes, generated from novel amplicon sequencing data, and collated with data from previous studies, comprising one of the largest OR studies to date. For the first time, we demonstrate statistically significant patterns of OR species-specific gene duplications associated with the presence of a functioning vomeronasal organ. With respect to dietary niche, we uncover a novel link between a large number of duplications in OR family 5/8/9 and herbivory. Our results also highlight differences between social and solitary niches, indicating that a greater OR repertoire expansion may be associated with a solitary lifestyle. This study demonstrates the utility of species-specific duplications in elucidating gene family evolution, revealing how the OR repertoire has undergone expansion and contraction with respect to a number of ecological adaptations in mammals.