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The recent influx of genomic data has provided greater insights into the molecular basis for regressive evolution, or vestigialization, through gene loss and pseudogenization. As such, the analysis of gene degradation patterns has the potential to provide insights into the evolutionary history of regressed anatomical traits. We specifically applied these principles to the xenarthran radiation (anteaters, sloths, armadillos), which is characterized by taxa with a gradation in regressed dental phenotypes. Whether the pattern among extant xenarthrans is due to an ancient and gradual decay of dental morphology or occurred repeatedly in parallel is unknown. We tested these competing hypotheses by examining 11 core dental genes in most living species of Xenarthra, characterizing shared inactivating mutations and patterns of relaxed selection during their radiation. Here we report evidence of independent and distinct events of dental gene loss in the major xenarthran subclades. First, we found strong evidence of complete enamel loss in the common ancestor of sloths and anteaters, suggested by the inactivation of five enamel-associated genes (AMELX, AMTN, MMP20, ENAM, ACP4). Next, whereas dental regression appears to have halted in sloths, presumably a critical event that ultimately permitted adaptation to an herbivorous lifestyle, anteaters continued losing genes on the path towards complete tooth loss. Echoes of this event are recorded in the genomes of all living anteaters, being marked by a 2-bp deletion in a gene critical for dentinogenesis (DSPP) and a putative shared 1-bp insertion in a gene linked to tooth retention (ODAPH). By contrast, in the two major armadillo clades, genes pertaining to the dento-gingival junction and amelogenesis appear to have been independently inactivated prior to losing all or some enamel. These genomic data provide evidence for multiple pathways and rates of anatomical regression, and underscore the utility of using pseudogenes to reconstruct evolutionary history when fossils are sparse.

Transposable elements (TE) play critical roles in shaping genome evolution. Highly repetitive TE sequences are also a major source of assembly gaps making it difficult to fully understand the impact of these elements on host genomes. The increased capacity of long-read sequencing technologies to span highly repetitive regions promises to provide new insights into patterns of TE activity across diverse taxa. Here we report the generation of highly contiguous reference genomes using PacBio long-read and Omni-C technologies for three species of Passerellidae sparrow. We compared these assemblies to three chromosome-level sparrow assemblies and nine other sparrow assemblies generated using a variety of short- and long-read technologies. All long-read based assemblies were longer (range: 1.12 to 1.41 Gb) than short-read assemblies (0.91 to 1.08 Gb) and assembly length was strongly correlated with the amount of repeat content. Repeat content for Bell's sparrow (31.2% of genome) was the highest level ever reported within the order Passeriformes, which comprises over half of avian diversity. The highest levels of repeat content (79.2% to 93.7%) were found on the W chromosome relative to other regions of the genome. Finally, we show that proliferation of different TE classes varied even among species with similar levels of repeat content. These patterns support a dynamic model of TE expansion and contraction even in a clade where TEs were once thought to be fairly depauperate and static. Our work highlights how the resolution of difficult-to-assemble regions of the genome with new sequencing technologies promises to transform our understanding of avian genome evolution.

The little pocket mouse, Perognathus longimembris, and its nine congeners are small heteromyid rodents found in arid and seasonally arid regions of Western North America. The genus is characterized by behavioral and physiological adaptations to dry and often harsh environments, including nocturnality, seasonal torpor, food caching, enhanced osmoregulation, and a well-developed sense of hearing. Here we present a genome assembly of Perognathus longimembris longimembris generated from PacBio HiFi long read and Omni-C chromatin-proximity sequencing as part of the California Conservation Genomics Project. The assembly has a length of 2.35 Gb, contig N50 of 11.6 Mb, scaffold N50 of 73.2 Mb, and includes 93.8% of the BUSCO Glires genes. Interspersed repetitive elements constitute 41.2% of the genome. A comparison with the highly endangered Pacific pocket mouse, P. l. pacificus, reveals broad synteny. These new resources will enable studies of local adaptation, genetic diversity, and conservation of threatened taxa.

The Steller's jay is a familiar bird of western forests from Alaska south to Nicaragua. Here, we report a draft reference assembly for the species generated from PacBio HiFi long-read and Omni-C chromatin-proximity sequencing data as part of the California Conservation Genomics Project (CCGP). Sequenced reads were assembled into 352 scaffolds totaling 1.16 Gb in length. Assembly metrics indicate a highly contiguous and complete assembly with a contig N50 of 7.8 Mb, scaffold N50 of 25.8 Mb, and BUSCO completeness score of 97.2%. Repetitive elements span 16.6% of the genome including nearly 90% of the W chromosome. Compared with high-quality assemblies from other members of the family Corvidae, the Steller's jay genome contains a larger proportion of repetitive elements than 4 crow species (Corvus), but a lower proportion of repetitive elements than the California scrub-jay (Aphelocoma californica). This reference genome will serve as an essential resource for future studies on speciation, local adaptation, phylogeography, and conservation genetics in this species of significant biological interest.

The California quail (Callipepla californica) is an iconic native bird of scrub and oak woodlands in California and the Baja Peninsula of Mexico. Here, we report a draft reference assembly for the species generated from PacBio HiFi long read and Omni-C chromatin-proximity sequencing data as part of the California Conservation Genomics Project (CCGP). Sequenced reads were assembled into 321 scaffolds totaling 1.08 Gb in length. Assembly metrics indicate a highly contiguous and complete assembly with a contig N50 of 5.5 Mb, scaffold N50 of 19.4 Mb, and BUSCO completeness score of 96.5%. Transposable elements (TEs) occupy 16.5% of the genome, more than previous Odontophoridae quail assemblies but in line with estimates of TE content for recent long-read assemblies of chicken and Peking duck. Together these metrics indicate that the present assembly is more complete than prior reference assemblies generated for Odontophoridae quail. This reference will serve as an essential resource for studies on local adaptation, phylogeography, and conservation genetics in this species of significant biological and recreational interest.

Interactions between genes can influence how selection acts on sequence variation. In gene regulatory networks, genes that affect the expression of many other genes may be under stronger evolutionary constraint than genes whose expression affects fewer partners. While this has been studied for individual tissue types, we know less about the effects of regulatory networks on gene evolution across different tissue types. We use RNA-sequencing and genomic data collected from Mus musculus domesticus to construct and compare gene co-expression networks for 10 tissue types. We identify tissue-specific expression and local regulatory variation, and we associate these components of gene expression variation with sequence polymorphism and divergence. We found that genes with higher connectivity across tissues and genes associated with a greater number of cross-tissue modules showed significantly lower genetic diversity and lower rates of protein evolution. Consistent with this pattern, "hub" genes across multiple tissues also showed evidence of greater evolutionary constraint. Using allele-specific expression, we found that genes with cis-regulatory variation had lower average connectivity and higher levels of tissue specificity. Taken together, these results are consistent with strong purifying selection acting on genes with high connectivity within and across tissues.

Changes in cis-regulatory regions are thought to play a major role in the genetic basis of adaptation. However, few studies have linked cis-regulatory variation with adaptation in natural populations. Here, using a combination of exome and RNA-seq data, we performed expression quantitative trait locus (eQTL) mapping and allele-specific expression analyses to study the genetic architecture of regulatory variation in wild house mice (Mus musculus domesticus) using individuals from five populations collected along a latitudinal cline in eastern North America. Mice in this transect showed clinal patterns of variation in several traits, including body mass. Mice were larger in more northern latitudes, in accordance with Bergmann's rule. We identified 17 genes where cis-eQTLs were clinal outliers and for which expression level was correlated with latitude. Among these clinal outliers, we identified two genes (Adam17 and Bcat2) with cis-eQTLs that were associated with adaptive body mass variation and for which expression is correlated with body mass both within and between populations. Finally, we performed a weighted gene co-expression network analysis (WGCNA) to identify expression modules associated with measures of body size variation in these mice. These findings demonstrate the power of combining gene expression data with scans for selection to identify genes involved in adaptive phenotypic evolution, and also provide strong evidence for cis-regulatory elements as essential loci of environmental adaptation in natural populations.

The end-Cretaceous extinction led to a massive faunal turnover, with placental mammals radiating in the wake of nonavian dinosaurs. Fossils indicate that Cretaceous stem placentals were generally insectivorous, whereas their earliest Cenozoic descendants occupied a variety of dietary niches. It is hypothesized that this dietary radiation resulted from the opening of niche space, following the extinction of dinosaurian carnivores and herbivores. We provide the first genomic evidence for the occurrence and timing of this dietary radiation in placental mammals. By comparing the genomes of 107 placental mammals, we robustly infer that chitinase genes (CHIAs), encoding enzymes capable of digesting insect exoskeletal chitin, were present as five functional copies in the ancestor of all placental mammals, and the number of functional CHIAs in the genomes of extant species positively correlates with the percentage of invertebrates in their diets. The diverse repertoire of CHIAs in early placental mammals corroborates fossil evidence of insectivory in Cretaceous eutherians, with descendant lineages repeatedly losing CHIAs beginning at the Cretaceous/Paleogene (K/Pg) boundary as they radiated into noninsectivorous niches. Furthermore, the timing of gene loss suggests that interordinal diversification of placental mammals in the Cretaceous predates the dietary radiation in the early Cenozoic, helping to reconcile a long-standing debate between molecular timetrees and the fossil record. Our results demonstrate that placental mammal genomes, including humans, retain a molecular record of the post-K/Pg placental adaptive radiation in the form of numerous chitinase pseudogenes.

House mice (Mus musculus) arrived in the Americas only recently in association with European colonization (~400-600 generations), but have spread rapidly and show evidence of local adaptation. Here, we take advantage of this genetic model system to investigate the genomic basis of environmental adaptation in house mice. First, we documented clinal patterns of phenotypic variation in 50 wild-caught mice from a latitudinal transect in Eastern North America. Next, we found that progeny of mice from different latitudes, raised in a common laboratory environment, displayed differences in a number of complex traits related to fitness. Consistent with Bergmann's rule, mice from higher latitudes were larger and fatter than mice from lower latitudes. They also built bigger nests and differed in aspects of blood chemistry related to metabolism. Then, combining exomic, genomic, and transcriptomic data, we identified specific candidate genes underlying adaptive variation. In particular, we defined a short list of genes with cis-eQTL that were identified as candidates in exomic and genomic analyses, all of which have known ties to phenotypes that vary among the studied populations. Thus, wild mice and the newly developed strains represent a valuable resource for future study of the links between genetic variation, phenotypic variation, and climate.

Understanding the genetic architecture of speciation is a major goal in evolutionary biology. Hybrid dysfunction is thought to arise most commonly through negative interactions between alleles at two or more loci. Divergence between interacting regulatory elements that affect gene expression (i.e., regulatory divergence) may be a common route for these negative interactions to arise. We review here how regulatory divergence between species can result in hybrid dysfunction, including recent theoretical support for this model. We then discuss the empirical evidence for regulatory divergence between species and evaluate evidence for misregulation as a source of hybrid dysfunction. Finally, we review unresolved questions in gene regulation as it pertains to speciation and point to areas that could benefit from future research.

Replicated clines across environmental gradients can be strong evidence of adaptation. House mice (Mus musculus domesticus) were introduced to the Americas by European colonizers and are now widely distributed from Tierra del Fuego to Alaska. Multiple aspects of climate, such as temperature, vary predictably across latitude in the Americas. Past studies of North American populations across latitudinal gradients provided evidence of environmental adaptation in traits related to body size, metabolism, and behavior and identified candidate genes using selection scans. Here, we investigate genomic signals of environmental adaptation on a second continent, South America, and ask whether there is evidence of parallel adaptation across multiple latitudinal transects in the Americas. We first identified loci across the genome showing signatures of selection related to climatic variation in mice sampled across a latitudinal transect in South America, accounting for neutral population structure. Consistent with previous results, most candidate SNPs were in putatively regulatory regions. Genes that contained the most extreme outliers relate to traits such as body weight or size, metabolism, immunity, fat, eye function, and the cardiovascular system. We then compared these results with the results of analyses of published data from two transects in North America. While most candidate genes were unique to individual transects, we found significant overlap among candidate genes identified independently in the three transects. These genes are diverse, with functions relating to metabolism, immunity, cardiac function, and circadian rhythm, among others. We also found parallel shifts in allele frequency in candidate genes across latitudinal gradients. Finally, combining data from all three transects, we identified several genes associated with variation in body weight. Overall, our results provide strong evidence of shared responses to selection and identify genes that likely underlie recent environmental adaptation in house mice across North and South America. Author summary: Since their arrival with European colonizers, house mice have successfully spread throughout the Americas. There is strong evidence that populations in North America have adapted in that time, including parallel evolution of phenotypes across latitude (e.g., body size, behavior) as well as significant overlap of genes that show signals of selection. Here, we investigate the genetics of environmental adaptation in South America. We found that populations in South America are genetically distinct from populations in North America. We identified candidate genes for environmental adaptation with links to traits like body size, metabolism, immunity, eye function, thermoregulation and the cardiovascular system. We then bring together data from three transects across two continents to determine if environmental adaptation is predictable, with shared genetic responses. We found that most responses to selection do not involve changes in amino acid sequence and therefore are likely due to changes in gene regulation. We also found that while most candidate genes are unique to individual transects, there was more overlap than expected by chance. In addition, we observed parallel shifts in allele frequency among shared candidate genes, i.e., shifts in the same direction across different latitudinal gradients. These results suggest that there is a shared response to selection and identify a core set of candidate genes that likely contribute to environmental adaptation. Finally, we combine the data from all three transects to identify genes associated with variation in body weight. These findings highlight the value of studying wild populations of this important genetic model system. [ABSTRACT FROM AUTHOR]

Genes involved in reproduction often evolve rapidly at the sequence level due to postcopulatory sexual selection (PCSS) driven by male–male competition and male–female sexual conflict, but the impact of PCSS on gene expression has been under‐explored. Further, though multiple tissues contribute to male reproductive success, most studies have focused on the testes. To explore the influence of mating system variation on reproductive tract gene expression in natural populations, we captured adult males from monogamous Peromyscus californicus and polygynandrous P. boylii and P. maniculatus. We generated RNAseq libraries, quantified gene expression in the testis, seminal vesicle, epididymis, and liver, and identified 3627 mating system‐associated differentially expressed genes (MS‐DEGs), where expression shifted in the same direction in P. maniculatus and P. boylii relative to P. californicus. Gene expression variation was most strongly associated with mating behaviour in the seminal vesicles, where 89% of differentially expressed genes were MS‐DEGs, including the key seminal fluid proteins Svs2 and Pate4. We also used published rodent genomes to test for positive and relaxed selection on Peromyscus‐expressed genes. Though we did not observe more overlap than expected by chance between MS‐DEGs and positively selected genes, 203 MS‐DEGs showed evidence of positive selection. Fourteen reproductive genes were under tree‐wide positive selection but convergent relaxed selection in P. californicus and Microtus ochrogaster, a distantly related monogamous species. Changes in transcript abundance and gene sequence evolution in association with mating behaviour suggest that male mice may respond to sexual selection intensity by altering aspects of sperm motility, sperm‐egg binding and copulatory plug formation. [ABSTRACT FROM AUTHOR]

One approach to understanding the process of speciation is to characterize the genetic architecture of post-zygotic isolation. As gene regulation requires interactions between loci, negative epistatic interactions between divergent regulatory elements might underlie hybrid incompatibilities and contribute to reproductive isolation. Here, we take advantage of a cross between house mouse subspecies, where hybrid dysfunction is largely unidirectional, to test several key predictions about regulatory divergence and reproductive isolation. Regulatory divergence between Mus musculus musculus and M. m. domesticus was characterized by studying allele-specific expression in fertile hybrid males using mRNA-sequencing of whole testes. We found extensive regulatory divergence between M. m. musculus and M. m. domesticus, largely attributable to cis-regulatory changes. When both cis and trans changes occurred, they were observed in opposition much more often than expected under a neutral model, providing strong evidence of widespread compensatory evolution. We also found evidence for lineage-specific positive selection on a subset of genes related to transcriptional regulation. Comparisons of fertile and sterile hybrid males identified a set of genes that were uniquely misexpressed in sterile individuals. Lastly, we discovered a nonrandom association between these genes and genes showing evidence of compensatory evolution, consistent with the idea that regulatory interactions might contribute to Dobzhansky-Muller incompatibilities and be important in speciation.

Recognition of individuals by scent is widespread across animal taxa. Though animals can often discriminate chemical blends based on many compounds, recent work shows that specific protein pheromones are necessary and sufficient for individual recognition via scent marks in mice. The genetic nature of individuality in scent marks (e.g. coding versus regulatory variation) and the evolutionary processes that maintain diversity are poorly understood. The individual signatures in scent marks of house mice are the protein products of a group of highly similar paralogs in the major urinary protein (Mup) gene family. Using the offspring of wild-caught mice, we examine individuality in the major urinary protein (MUP) scent marks at the DNA, RNA and protein levels. We show that individuality arises through a combination of variation at amino acid coding sites and differential transcription of central Mup genes across individuals, and we identify eSNPs in promoters. There is no evidence of post-transcriptional processes influencing phenotypic diversity as transcripts accurately predict the relative abundance of proteins in urine samples. The match between transcripts and urine samples taken six months earlier also emphasizes that the proportional relationships across central MUP isoforms in urine is stable. Balancing selection maintains coding variants at moderate frequencies, though pheromone diversity appears limited by interactions with vomeronasal receptors. We find that differential transcription of the central Mup paralogs within and between individuals significantly increases the individuality of pheromone blends. Balancing selection on gene regulation allows for increased individuality via combinatorial diversity in a limited number of pheromones.

In mammals, intrinsic postzygotic isolation has been well studied in males but has been less studied in females, despite the fact that female gametogenesis and pregnancy provide arenas for hybrid sterility or inviability that are absent in males. Here, we asked whether inviability or sterility is observed in female hybrids of Mus musculus domesticus and M. m. musculus, taxa which hybridize in nature and for which male sterility has been well characterized. We looked for parent-of-origin growth phenotypes by measuring adult body weights in F1 hybrids. We evaluated hybrid female fertility by crossing F1 females to a tester male and comparing multiple reproductive parameters between intrasubspecific controls and intersubspecific hybrids. Hybrid females showed no evidence of parent-of-origin overgrowth or undergrowth, providing no evidence for reduced viability. However, hybrid females had smaller litter sizes, reduced embryo survival, fewer ovulations, and fewer small follicles relative to controls. Significant variation in reproductive parameters was seen among different hybrid genotypes, suggesting that hybrid incompatibilities are polymorphic within subspecies. Differences in reproductive phenotypes in reciprocal genotypes were observed and are consistent with cyto-nuclear incompatibilities or incompatibilities involving genomic imprinting. These findings highlight the potential importance of reduced hybrid female fertility in the early stages of speciation.

Facial recognition plays a key role in human interactions, and there has been great interest in understanding the evolution of human abilities for individual recognition and tracking social relationships. Individual recognition requires sufficient cognitive abilities and phenotypic diversity within a population for discrimination to be possible. Despite the importance of facial recognition in humans, the evolution of facial identity has received little attention. Here we demonstrate that faces evolved to signal individual identity under negative frequency-dependent selection. Faces show elevated phenotypic variation and lower between-trait correlations compared with other traits. Regions surrounding face-associated single nucleotide polymorphisms show elevated diversity consistent with frequency-dependent selection. Genetic variation maintained by identity signalling tends to be shared across populations and, for some loci, predates the origin of Homo sapiens. Studies of human social evolution tend to emphasize cognitive adaptations, but we show that social evolution has shaped patterns of human phenotypic and genetic diversity as well.

One approach to understanding the genetic basis of speciation is to scan the genomes of recently diverged taxa to identify highly differentiated regions. The house mouse, Mus musculus, provides a useful system for the study of speciation. Three subspecies (M. m. castaneus, M. m. domesticus, and M. m. musculus) diverged ∼350 KYA, are distributed parapatrically, show varying degrees of reproductive isolation in laboratory crosses, and hybridize in nature. We sequenced the testes transcriptomes of multiple wild-derived inbred lines from each subspecies to identify highly differentiated regions of the genome, to identify genes showing high expression divergence, and to compare patterns of differentiation among subspecies that have different demographic histories and exhibit different levels of reproductive isolation. Using a sliding-window approach, we found many genomic regions with high levels of sequence differentiation in each of the pairwise comparisons among subspecies. In all comparisons, the X chromosome was more highly differentiated than the autosomes. Sequence differentiation and expression divergence were greater in the M. m. domesticus-M. m. musculus comparison than in either pairwise comparison with M. m. castaneus, which is consistent with laboratory crosses that show the greatest reproductive isolation between M. m. domesticus and M. m. musculus. Coalescent simulations suggest that differences in estimates of effective population size can account for many of the observed patterns. However, there was an excess of highly differentiated regions relative to simulated distributions under a wide range of demographic scenarios. Overlap of some highly differentiated regions with previous results from QTL mapping and hybrid zone studies points to promising candidate regions for reproductive isolation.

The analysis of introgression of genomic regions between divergent populations provides an excellent opportunity to determine the genetic basis of reproductive isolation during the early stages of speciation. However, hybridization and subsequent gene flow must be relatively common in order to localize individual loci that resist introgression. In this study, we used next-generation sequencing to study genome-wide patterns of genetic differentiation between two hybridizing subspecies of rabbits (Oryctolagus cuniculus algirus and O. c. cuniculus) that are known to undergo high rates of gene exchange. Our primary objective was to identify specific genes or genomic regions that have resisted introgression and are likely to confer reproductive barriers in natural conditions. On the basis of 326,000 polymorphisms, we found low to moderate overall levels of differentiation between subspecies, and fewer than 200 genomic regions dispersed throughout the genome showing high differentiation consistent with a signature of reduced gene flow. Most differentiated regions were smaller than 200 Kb and contained very few genes. Remarkably, 30 regions were each found to contain a single gene, facilitating the identification of candidate genes underlying reproductive isolation. This gene-level resolution yielded several insights into the genetic basis and architecture of reproductive isolation in rabbits. Regions of high differentiation were enriched on the X-chromosome and near centromeres. Genes lying within differentiated regions were often associated with transcription and epigenetic activities, including chromatin organization, regulation of transcription, and DNA binding. Overall, our results from a naturally hybridizing system share important commonalities with hybrid incompatibility genes identified using laboratory crosses in mice and flies, highlighting general mechanisms underlying the maintenance of reproductive barriers.

Post-copulatory sexual selection in the form of sperm competition is known to influence the evolution of male reproductive proteins in mammals. The relationship between sperm competition and regulatory evolution, however, remains to be explored. Protamines and transition nuclear proteins are involved in the condensation of sperm chromatin and are expected to affect the shape of the sperm head. A hydrodynamically efficient head allows for fast swimming velocity and, therefore, more competitive sperm. Previous comparative studies in rodents have documented a significant association between the level of sperm competition (as measured by relative testes mass) and DNA sequence evolution in both the coding and promoter sequences of protamine 2. Here, we investigate the influence of sexual selection on protamine and transition nuclear protein mRNA expression in the testes of eight mouse species that differ widely in levels of sperm competition. We also examined the relationship between relative gene expression levels and sperm head shape, assessed using geometric morphometrics. We found that species with higher levels of sperm competition express less protamine 2 in relation to protamine 1 and transition nuclear proteins. Moreover, there was a significant association between relative protamine 2 expression and sperm head shape. Reduction in the relative abundance of protamine 2 may increase the competitive ability of sperm in mice, possibly by affecting sperm head shape. Changes in gene regulatory sequences thus seem to be the basis of the evolutionary response to sexual selection in these proteins.

The genetic basis of hybrid male sterility in house mice is complex, highly polygenic, and strongly X linked. Previous work suggested that there might be interactions between the Mus musculus musculus X and the M. m. domesticus Y with a large negative effect on sperm head morphology in hybrid males with an F1 autosomal background. To test this, we introgressed the M. m. domesticus Y onto a M. m. musculus background and measured the change in sperm morphology, testis weight, and sperm count across early backcross generations and in 11th generation backcross males in which the opportunity for X-autosome incompatibilities is effectively eliminated. We found that abnormality in sperm morphology persists in M. m. domesticus Y introgression males, and that this phenotype is rescued by M. m. domesticus introgressions on the X chromosome. In contrast, the severe reductions in testis weight and sperm count that characterize F1 males were eliminated after one generation of backcrossing. These results indicate that X-Y incompatibilities contribute specifically to sperm morphology. In contrast, X-autosome incompatibilities contribute to low testis weight, low sperm count, and sperm morphology. Restoration of normal testis weight and sperm count in first generation backcross males suggests that a small number of complex incompatibilities between loci on the M. m. musculus X and the M. m. domesticus autosomes underlie F1 male sterility. Together, these results provide insight into the genetic architecture of F1 male sterility and help to explain genome-wide patterns of introgression across the house mouse hybrid zone.

Speciation is a fundamental evolutionary process, the knowledge of which is crucial for understanding the origins of biodiversity. Genomic approaches are an increasingly important aspect of this research field. We review current understanding of genome-wide effects of accumulating reproductive isolation and of genomic properties that influence the process of speciation. Building on this work, we identify emergent trends and gaps in our understanding, propose new approaches to more fully integrate genomics into speciation research, translate speciation theory into hypotheses that are testable using genomic tools and provide an integrative definition of the field of speciation genomics.

More than tools for managing physical and digital objects, museum collection management systems (CMS) serve as platforms for structuring, integrating, and making accessible the rich data embodied by natural history collections. Here we describe Arctos, a scalable community solution for managing and publishing global biological, geological, and cultural collections data for research and education. Specific goals are to: (1) Describe the core features and implementation of Arctos for a broad audience with respect to the biodiversity informatics principles that enable high quality research; (2) Highlight the unique aspects of Arctos; (3) Illustrate Arctos as a model for supporting and enhancing the Digital Extended Specimen concept; and (4) Emphasize the role of the Arctos community for improving data discovery and enabling cross-disciplinary, integrative studies within a sustainable governance model. In addition to detailing Arctos as both a community of museum professionals and a collection database platform, we discuss how Arctos achieves its richly annotated data by creating a web of knowledge with deep connections between catalog records and derived or associated data. We also highlight the value of Arctos as an educational resource. Finally, we present the financial model of fiscal sponsorship by a nonprofit organization, implemented in 2022, to ensure the long-term success and sustainability of Arctos. [ABSTRACT FROM AUTHOR]

Wing pattern evolution in Heliconius butterflies provides some of the most striking examples of adaptation by natural selection. The genes controlling pattern variation are classic examples of Mendelian loci of large effect, where allelic variation causes large and discrete phenotypic changes and is responsible for both convergent and highly divergent wing pattern evolution across the genus. We characterize nucleotide variation, genotype-by-phenotype associations, linkage disequilibrium (LD), and candidate gene expression patterns across two unlinked genomic intervals that control yellow and red wing pattern variation among mimetic forms of Heliconius erato. Despite very strong natural selection on color pattern, we see neither a strong reduction in genetic diversity nor evidence for extended LD across either patterning interval. This observation highlights the extent that recombination can erase the signature of selection in natural populations and is consistent with the hypothesis that either the adaptive radiation or the alleles controlling it are quite old. However, across both patterning intervals we identified SNPs clustered in several coding regions that were strongly associated with color pattern phenotype. Interestingly, coding regions with associated SNPs were widely separated, suggesting that color pattern alleles may be composed of multiple functional sites, conforming to previous descriptions of these loci as "supergenes." Examination of gene expression levels of genes flanking these regions in both H. erato and its co-mimic, H. melpomene, implicate a gene with high sequence similarity to a kinesin as playing a key role in modulating pattern and provides convincing evidence for parallel changes in gene regulation across co-mimetic lineages. The complex genetic architecture at these color pattern loci stands in marked contrast to the single casual mutations often identified in genetic studies of adaptation, but may be more indicative of the type of genetic changes responsible for much of the adaptive variation found in natural populations.