Showing papers in "Journal of Heredity in 2023"

The revised reference genome of the leopard gecko (Eublepharis macularius) provides insight into the considerations of genome phasing and assembly.

Abstract: Genomic resources across squamate reptiles (lizards and snakes) have lagged behind other vertebrate systems and high-quality reference genomes remain scarce. Of the 23 chromosome-scale reference genomes across the order, only 12 of the ~60 squamate families are represented. Within geckos (infraorder Gekkota), a species-rich clade of lizards, chromosome-level genomes are exceptionally sparse representing only two of the seven extant families. Using the latest advances in genome sequencing and assembly methods, we generated one of the highest quality squamate genomes to date for the leopard gecko, Eublepharis macularius (Eublepharidae). We compared this assembly to the previous, short-read only, E. macularius reference genome published in 2016 and examined potential factors within the assembly influencing contiguity of genome assemblies using PacBio HiFi data. Briefly, the read N50 of the PacBio HiFi reads generated for this study was equal to the contig N50 of the previous E. macularius reference genome at 20.4 kilobases. The HiFi reads were assembled into a total of 132 contigs, which was further scaffolded using HiC data into 75 total sequences representing all 19 chromosomes. We identified 9 of the 19 chromosomal-scaffolds were assembled as a near-single contig, while the other 10 chromosomes were each scaffolded together from multiple contigs. We qualitatively identified that percent repeat content within a chromosome broadly affects its assembly contiguity prior to scaffolding. This genome assembly signifies a new age for squamate genomics where high-quality reference genomes rivaling some of the best vertebrate genome assemblies can be generated for a fraction previous cost estimates. This new E. macularius reference assembly is available on NCBI at JAOPLA010000000.

Where to draw the line? Expanding the delineation of conservation units to highly mobile taxa.

Abstract: Conservation units (CUs) are an essential tool for maximizing evolutionary potential and prioritizing areas across a species' range for protection when implementing conservation and management measures. However, current workflows for identifying CUs on the basis of neutral and adaptive genomic variation largely ignore information contained in patterns of isolation by distance (IBD), frequently the primary signal of population structure in highly mobile taxa, such as birds, bats, and marine organisms with pelagic larval stages. While individuals located on either end of a species' distribution may exhibit clear genetic, phenotypic, and ecological differences, IBD produces subtle changes in allele frequencies across space, making it difficult to draw clear boundaries for conservation purposes in the absence of discrete population structure. Here, we highlight potential pitfalls that arise when applying common methods for delineating CUs to continuously distributed organisms and review existing methods for detecting subtle breakpoints in patterns of IBD that can indicate barriers to gene flow in highly mobile taxa. In addition, we propose a new framework for identifying CUs in all organisms, including those characterized by continuous genomic differentiation, and suggest several possible ways to harness the information contained in patterns of IBD to guide conservation and management decisions.

A highly contiguous genome assembly for the California quail (Callipepla californica)

Abstract: Abstract 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.

Management of diversity and inbreeding when importing new stock into an inbred population.

Abstract: This article relates to breeding programs that seek to manage genetic diversity. The method maximises a multicomponent objective function, applicable across breeding scenarios. However, this paper focuses on breeding decisions following immigration of ten unrelated individuals into a highly inbred simulated population (F≈0.34). We use Optimal Contribution Selection to maximise retention of genetic diversity. However, some treatments add Coancestry Assortative Mating (CAM). This helps to avoid early dilution of immigrant genetic material, maximising its ability to contribute to genetic diversity in the longer term. After 20 generations, this resulted in considerably increased genetic diversity, with mean coancestries 59% of what random pairing gave. To manage progeny inbreeding, common practice is to reject matings above an upper limit. As a sub-optimal rules-based approach, this resulted in 26% decreased genetic diversity and 8% increased inbreeding in the long term, compared to random pairing. In contrast, including mean progeny inbreeding as a continuous variable in the overall objective function decreased final inbreeding by 37% compared to random pairing. Adding some emphasis on selection for a single trait resulted in a similar pattern of effects on coancestry and inbreeding, with 12% higher trait response under CAM. Results indicate the properties of alternative methods, but we encourage users to do their own investigations of particular scenarios, such as including inbreeding depression. Practical implementation of these methods is discussed: they have been widely adopted in domestic animal breeding and are highly flexible to accommodate a wide range of technical and logistical objectives and constraints.

"Type D" killer whale genomes reveal long-term small population size and low genetic diversity.

Abstract: Genome sequences can reveal the extent of inbreeding in small populations. Here, we present the first genomic characterization of type D killer whales, a distinctive eco/morphotype with a circumpolar, subantarctic distribution. Effective population size is the lowest estimated from any killer whale genome and indicates a severe population bottleneck. Consequently, type D genomes show among the highest level of inbreeding reported for any mammalian species (FROH ≥ 0.65). Detected recombination cross-over events of different haplotypes are up to an order of magnitude rarer than in other killer whale genomes studied to date. Comparison of genomic data from a museum specimen of a type D killer whale that stranded in New Zealand in 1955, with 3 modern genomes from the Cape Horn area, reveals high covariance and identity-by-state of alleles, suggesting these genomic characteristics and demographic history are shared among geographically dispersed social groups within this morphotype. Limitations to the insights gained in this study stem from the nonindependence of the 3 closely related modern genomes, the recent coalescence time of most variation within the genomes, and the nonequilibrium population history which violates the assumptions of many model-based methods. Long-range linkage disequilibrium and extensive runs of homozygosity found in type D genomes provide the potential basis for both the distinctive morphology, and the coupling of genetic barriers to gene flow with other killer whale populations.

Reference genome of the long-jawed orb-weaver, Tetragnatha versicolor (Araneae: Tetragnathidae)

Abstract: Abstract Climate-driven changes in hydrological regimes are of global importance and are particularly significant in riparian ecosystems. Riparian ecosystems in California provide refuge to many native and vulnerable species within a xeric landscape. California Tetragnatha spiders play a key role in riparian ecosystems, serving as a link between terrestrial and aquatic elements. Their tight reliance on water paired with the widespread distributions of many species make them ideal candidates to better understand the relative role of waterways versus geographic distance in shaping the population structure of riparian species. To assist in better understanding population structure, we constructed a reference genome assembly for Tetragnatha versicolor using long-read sequencing, scaffolded with proximity ligation Omni-C data. The near-chromosome-level assembly is comprised of 174 scaffolds spanning 1.06 Gb pairs, with a scaffold N50 of 64.1 Mb pairs and BUSCO completeness of 97.6%. This reference genome will facilitate future study of T. versicolor population structure associated with the rapidly changing environment of California.

Gene expression reveals immune response strategies of naïve Hawaiian honeycreepers experimentally infected with introduced avian malaria

Abstract: Abstract The unprecedented rise in the number of new and emerging infectious diseases in the last quarter century poses direct threats to human and wildlife health. The introduction to the Hawaiian archipelago of Plasmodium relictum and the mosquito vector that transmits the parasite has led to dramatic losses in endemic Hawaiian forest bird species. Understanding how mechanisms of disease immunity to avian malaria may evolve is critical as climate change facilitates increased disease transmission to high elevation habitats where malaria transmission has historically been low and the majority of the remaining extant Hawaiian forest bird species now reside. Here, we compare the transcriptomic profiles of highly susceptible Hawai‘i ‘amakihi (Chlorodrepanis virens) experimentally infected with P. relictum to those of uninfected control birds from a naïve high elevation population. We examined changes in gene expression profiles at different stages of infection to provide an in-depth characterization of the molecular pathways contributing to survival or mortality in these birds. We show that the timing and magnitude of the innate and adaptive immune response differed substantially between individuals that survived and those that succumbed to infection, and likely contributed to the observed variation in survival. These results lay the foundation for developing gene-based conservation strategies for Hawaiian honeycreepers by identifying candidate genes and cellular pathways involved in the pathogen response that correlate with a bird’s ability to recover from malaria infection.

Heat challenge elicits stronger physiological and gene expression responses than starvation in symbiotic Oculina arbuscula.

Abstract: Heterotrophy has been shown to mitigate coral-algal dysbiosis (coral bleaching) under heat challenge, but the molecular mechanisms underlying this phenomenon remain largely unexplored. Here, we quantified coral physiology and gene expression of fragments from 13 genotypes of symbiotic Oculina arbuscula after a 28-d feeding experiment under (1) fed, ambient (24 °C); (2) unfed, ambient; (3) fed, heated (ramp to 33 °C); and (4) unfed, heated treatments. We monitored algal photosynthetic efficiency throughout the experiment, and after 28 d, profiled coral and algal carbohydrate and protein reserves, coral gene expression, algal cell densities, and chlorophyll-a and chlorophyll-c2 pigments. Contrary to previous findings, heterotrophy did little to mitigate the impacts of temperature, and we observed few significant differences in physiology between fed and unfed corals under heat challenge. Our results suggest the duration and intensity of starvation and thermal challenge play meaningful roles in coral energetics and stress response; future work exploring these thresholds and how they may impact coral responses under changing climate is urgently needed. Gene expression patterns under heat challenge in fed and unfed corals showed gene ontology enrichment patterns consistent with classic signatures of the environmental stress response. While gene expression differences between fed and unfed corals under heat challenge were subtle: Unfed, heated corals uniquely upregulated genes associated with cell cycle functions, an indication that starvation may induce the previously described, milder "type B" coral stress response. Future studies interested in disentangling the influence of heterotrophy on coral bleaching would benefit from leveraging the facultative species studied here, but using the coral in its symbiotic and aposymbiotic states.

A lizard is never late: Squamate genomics as a recent catalyst for understanding sex chromosome and microchromosome evolution

Abstract: Abstract In 2011, the first high-quality genome assembly of a squamate reptile (lizard or snake) was published for the green anole. Dozens of genome assemblies were subsequently published over the next decade, yet these assemblies were largely inadequate for answering fundamental questions regarding genome evolution in squamates due to their lack of contiguity or annotation. As the “genomics age” was beginning to hit its stride in many organismal study systems, progress in squamates was largely stagnant following the publication of the green anole genome. In fact, zero high-quality (chromosome-level) squamate genomes were published between the years 2012 and 2017. However, since 2018, an exponential increase in high-quality genome assemblies has materialized with 24 additional high-quality genomes published for species across the squamate tree of life. As the field of squamate genomics is rapidly evolving, we provide a systematic review from an evolutionary genomics perspective. We collated a near-complete list of publicly available squamate genome assemblies from more than half-a-dozen international and third-party repositories and systematically evaluated them with regard to their overall quality, phylogenetic breadth, and usefulness for continuing to provide accurate and efficient insights into genome evolution across squamate reptiles. This review both highlights and catalogs the currently available genomic resources in squamates and their ability to address broader questions in vertebrates, specifically sex chromosome and microchromosome evolution, while addressing why squamates may have received less historical focus and has caused their progress in genomics to lag behind peer taxa.

Genetic rescue remains underused for aiding recovery of federally listed vertebrates in the United States

Abstract: Abstract Restoring gene flow among fragmented populations is discussed as a potentially powerful management strategy that could reduce inbreeding depression and cause genetic rescue. Yet, examples of assisted migration for genetic rescue remain sparse in conservation, prompting several outspoken calls for its increased use in genetic management of fragmented populations. We set out to evaluate the extent to which this strategy is underused and to determine how many imperiled species would realistically stand to benefit from genetic rescue, focusing on federally threatened or endangered vertebrate species in the United States. We developed a “genetic rescue suitability index (GR index)” based on concerns about small population problems relative to risks associated with outbreeding depression and surveyed the literature for 222 species. We found that two-thirds of these species were good candidates for consideration of assisted migration for the purpose of genetic rescue according to our suitability index. Good candidate species spanned all taxonomic groups and geographic regions, though species with more missing data tended to score lower on the suitability index. While we do not recommend a prescriptive interpretation of our GR index, we used it here to establish that assisted migration for genetic rescue is an underused strategy. For example, we found in total, “genetic rescue” was only mentioned in 11 recovery plans and has only been implemented in 3 of the species we surveyed. A potential way forward for implementation of this strategy is incorporating genetic rescue as a priority in USFWS recovery documentation. In general, our results suggest that although not appropriate for all imperiled species, many more species stand to benefit from a conservation strategy of assisted migration for genetic rescue than those for which it has previously been considered or implemented.

Whole-genome resequencing data support a single introduction of the invasive white pine sawfly, <i>Diprion similis</i>

Abstract: Abstract Biological introductions are unintended “natural experiments” that provide unique insights into evolutionary processes. Invasive phytophagous insects are of particular interest to evolutionary biologists studying adaptation, as introductions often require rapid adaptation to novel host plants. However, adaptive potential of invasive populations may be limited by reduced genetic diversity—a problem known as the “genetic paradox of invasions.” One potential solution to this paradox is if there are multiple invasive waves that bolster genetic variation in invasive populations. Evaluating this hypothesis requires characterizing genetic variation and population structure in the invaded range. To this end, we assemble a reference genome and describe patterns of genetic variation in the introduced white pine sawfly, Diprion similis. This species was introduced to North America in 1914, where it has rapidly colonized the thin-needled eastern white pine (Pinus strobus), making it an ideal invasion system for studying adaptation to novel environments. To evaluate evidence of multiple introductions, we generated whole-genome resequencing data for 64 D. similis females sampled across the North American range. Both model-based and model-free clustering analyses supported a single population for North American D. similis. Within this population, we found evidence of isolation-by-distance and a pattern of declining heterozygosity with distance from the hypothesized introduction site. Together, these results support a single-introduction event. We consider implications of these findings for the genetic paradox of invasion and discuss priorities for future research in D. similis, a promising model system for invasion biology.

Evolutionary potential mitigates extinction risk under climate change in the endangered southwestern willow flycatcher

Abstract: The complexity of global anthropogenic change makes forecasting species responses and planning effective conservation actions challenging. Additionally, important components of a species' adaptive capacity, such as evolutionary potential, are often not included in quantitative risk assessments due to lack of data. While genomic proxies for evolutionary potential in at-risk species are increasingly available, they have not yet been included in extinction risk assessments at a species-wide scale. In this study, we used an individual-based, spatially explicit, dynamic eco-evolutionary simulation model to evaluate the extinction risk of an endangered desert songbird, the southwestern willow flycatcher (Empidonax traillii extimus), in response to climate change. Using data from long-term demographic and habitat studies in conjunction with genome-wide ecological genomics research, we parameterized simulations that include 418 sites across the breeding range, genomic data from 225 individuals, and climate change forecasts spanning 3 generalized circulation models and 3 emissions scenarios. We evaluated how evolutionary potential, and the lack of it, impacted population trajectories in response to climate change. We then investigated the compounding impact of drought and warming temperatures on extinction risk through the mechanism of increased nest failure. Finally, we evaluated how rapid action to reverse greenhouse gas emissions would influence population responses and species extinction risk. Our results illustrate the value of incorporating evolutionary, demographic, and dispersal processes in a spatially explicit framework to more comprehensively evaluate the extinction risk of threatened and endangered species and conservation actions to promote their recovery.

2023 AGA Award Outcomes

Abstract: Journal Article 2023 AGA Award Outcomes Get access Journal of Heredity, Volume 114, Issue 3, May 2023, Pages 295–296, https://doi.org/10.1093/jhered/esad024 Published: 25 May 2023 Article history Corrected and typeset: 25 May 2023 Published: 25 May 2023

Assembly of the largest squamate reference genome to date: the western fence lizard, Sceloporus occidentalis.

Abstract: Spiny lizards (genus Sceloporus) have long served as important systems for studies of behavior, thermal physiology, dietary ecology, vector biology, speciation, and biogeography. The western fence lizard, Sceloporus occidentalis, is found across most of the major biogeographical regions in the western United States and northern Baja California, Mexico, inhabiting a wide range of habitats, from grassland to chaparral to open woodlands. As small ectotherms, Sceloporus lizards are particularly vulnerable to climate change, and S. occidentalis has also become an important system for studying the impacts of land use change and urbanization on small vertebrates. Here, we report a new reference genome assembly for S. occidentalis, as part of the California Conservation Genomics Project (CCGP). Consistent with the reference genomics strategy of the CCGP, we used Pacific Biosciences HiFi long reads and Hi-C chromatin-proximity sequencing technology to produce a de novo assembled genome. The assembly comprises a total of 608 scaffolds spanning 2,856 Mb, has a contig N50 of 18.9 Mb, a scaffold N50 of 98.4 Mb, and BUSCO completeness score of 98.1% based on the tetrapod gene set. This reference genome will be valuable for understanding ecological and evolutionary dynamics in S. occidentalis, the species status of the California endemic island fence lizard (S. becki), and the spectacular radiation of Sceloporus lizards.

A chromosome-scale high-contiguity genome assembly of the cheetah (Acinonyx jubatus)

Abstract: Abstract The cheetah (Acinonyx jubatus, SCHREBER 1775) is a large felid and is considered the fastest land animal. Historically, it inhabited open grassland across Africa, the Arabian Peninsula, and southwestern Asia; however, only small and fragmented populations remain today. Here, we present a de novo genome assembly of the cheetah based on PacBio continuous long reads and Hi-C proximity ligation data. The final assembly (VMU_Ajub_asm_v1.0) has a total length of 2.38 Gb, of which 99.7% are anchored into the expected 19 chromosome-scale scaffolds. The contig and scaffold N50 values of 96.8 Mb and 144.4 Mb, respectively, a BUSCO completeness of 95.4% and a k-mer completeness of 98.4%, emphasize the high quality of the assembly. Furthermore, annotation of the assembly identified 23,622 genes and a repeat content of 40.4%. This new highly contiguous and chromosome-scale assembly will greatly benefit conservation and evolutionary genomic analyses and will be a valuable resource, e.g., to gain a detailed understanding of the function and diversity of immune response genes in felids.

A chromosome-scale reference genome assembly of the great sand eel, Hyperoplus lanceolatus

Abstract: Abstract Despite increasing sequencing efforts, numerous fish families still lack a reference genome, which complicates genetic research. One such understudied family is the sand lances (Ammodytidae, literally: “sand burrower”), a globally distributed clade of over 30 fish species that tend to avoid tidal currents by burrowing into the sand. Here, we present the first annotated chromosome-level genome assembly of the great sand eel (Hyperoplus lanceolatus). The genome assembly was generated using Oxford Nanopore Technologies long sequencing reads and Illumina short reads for polishing. The final assembly has a total length of 808.5 Mbp, of which 97.1% were anchored into 24 chromosome-scale scaffolds using proximity-ligation scaffolding. It is highly contiguous with a scaffold and contig N50 of 33.7 and 31.3 Mbp, respectively, and has a BUSCO completeness score of 96.9%. The presented genome assembly is a valuable resource for future studies of sand lances, as this family is of great ecological and commercial importance and may also contribute to studies aiming to resolve the suprafamiliar taxonomy of bony fishes.

Chromosome-level reference genome of stinkwort, Dittrichia graveolens (L.) Greuter: a resource for studies on invasion, range expansion, and evolutionary adaptation under global change.

Abstract: Dittrichia graveolens (L.) Greuter, or stinkwort, is a weedy annual plant within the family Asteraceae. The species is recognized for the rapid expansion of both its native and introduced ranges: in Europe, it has expanded its native distribution northward from the Mediterranean basin by nearly 7 degrees latitude since the mid-20th century, while in California and Australia the plant is an invasive weed of concern. Here, we present the first de novo Dittrichia graveolens genome assembly (1N=9 chromosomes), including complete chloroplast (151,013 bp) and partial mitochondrial genomes (22,084 bp), created using Pacific Biosciences HiFi reads and Dovetail Omni-C data. The final primary assembly is 835 Mbp in length, of which 98.1% are represented by nine scaffolds ranging from 66 to 119 Mbp. The contig N50 is 74.9 Mbp and the scaffold N50 is 96.9 Mbp, which, together with a 98.8% completeness based on the BUSCO embryophyta10 database containing 1614 orthologs, underscores the high quality of this assembly. This pseudomolecule-scale genome assembly is a valuable resource for our fundamental understanding of the genomic consequences of range expansion under global change, as well as comparative genomic studies in the Asteraceae.

Genome assemblies and comparison of two Neotropical spiral gingers: Costus pulverulentus and C. lasius

Abstract: Abstract The spiral gingers (Costus L.) are a pantropical genus of herbaceous perennial monocots; the Neotropical clade of Costus radiated rapidly in the past few million years into over 60 species. The Neotropical spiral gingers have a rich history of evolutionary and ecological research that can motivate and inform modern genetic investigations. Here, we present the first 2 chromosome-level genome assemblies in the genus, for C. pulverulentus and C. lasius, and briefly compare their synteny. We assembled the C. pulverulentus genome from a combination of short-read data, Chicago and Dovetail Hi-C chromatin-proximity sequencing, and alignment with a linkage map. We annotated the genome by mapping a C. pulverulentus transcriptome and querying mapped transcripts against a protein database. We assembled the C. lasius genome with Pacific Biosciences HiFi long reads and alignment to the C. pulverulentus genome. These 2 assemblies are the first published genomes for non-cultivated tropical plants. These genomes solidify the spiral gingers as a model system and will facilitate research on the poorly understood genetic basis of tropical plant diversification.

A highly contiguous reference genome for the Steller's jay (Cyanocitta stelleri).

Abstract: 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 four 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.

Estimating phylogenies from genomes: A beginners review of commonly used genomic data in vertebrate phylogenomics.

Abstract: Despite the increasing feasibility of sequencing whole genomes from diverse taxa, a persistent problem in phylogenomics is the selection of appropriate genetic markers or loci for a given taxonomic group or research question. In this review, we aim to streamline the decision-making process when selecting specific markers to use in phylogenomic studies by introducing commonly used types of genomic markers, their evolutionary characteristics, and their associated uses in phylogenomics. Specifically, we review the utilities of ultraconserved elements (including flanking regions), anchored hybrid enrichment loci, conserved nonexonic elements, untranslated regions, introns, exons, mitochondrial DNA, single nucleotide polymorphisms, and anonymous regions (nonspecific regions that are evenly or randomly distributed across the genome). These various genomic elements and regions differ in their substitution rates, likelihood of neutrality or of being strongly linked to loci under selection, and mode of inheritance, each of which are important considerations in phylogenomic reconstruction. These features may give each type of marker important advantages and disadvantages depending on the biological question, number of taxa sampled, evolutionary timescale, cost effectiveness, and analytical methods used. We provide a concise outline as a resource to efficiently consider key aspects of each type of genetic marker. There are many factors to consider when designing phylogenomic studies, and this review may serve as a primer when weighing options between multiple potential phylogenomic markers.

Juvenile Idiopathic Epilepsy in Arabian Horses is not a Single Gene Disorder.

Abstract: Valued for their temperament, beauty, athletic ability, and exhibition in the show ring, Arabian horses are an important component of the horse industry. Juvenile Idiopathic Epilepsy (JIE), a seizure disorder, is most often reported in Arabian foals from birth to six months of age. Affected foals exhibit tonic-clonic seizures lasting as long as five minutes and risking secondary complications like temporary blindness and disorientation. Some foals outgrow this condition, while others die or suffer lifelong complications if not treated. Previous work suggested a strong genetic component to JIE and proposed JIE to be a single-gene trait. In this work we conducted a GWAS in 60 cases of JIE and 120 genetically matched controls, identifying loci suggesting JIE is not caused by a single locus. Coat color (chestnut, grey) phenotypes were used as positive control traits to assess the efficacy of GWAs in this population. Future work will attempt to future define candidate regions and explore a polygenic mode of inheritance.

Conservation genomics: Current applications and future directions.

Abstract: In October 2021, during a fortuitous lull in the number of covid cases, over 150 masked and vaccinated conservation genomicists met at Snowbird, Utah, for AGA’s 2021 President’s Symposium (https://www.theaga.org/agatwentytwentyone). For many of us, this was our first travel in close to 2 yr and certainly the first attendance of a meeting of this size since the onset of the pandemic. The audience was primed with excitement to survey advances in the field of conservation ­genomics. Throughout 2 d of excellent talks, we explored adaptation to climate change, genetic monitoring and genetic rescue, genomics of disease, and conservation genomics in action. In the last decades, the field of conservation genomics has vastly increased our ability to address pressing questions about threats to biodiversity and to predict the likely outcomes of organisms responding to a changing world (Stefanoudis et al. 2021; Chen et al. 2022; Theissinger et al. 2023). The causes for these rapid advances in our field are many, including the types and amount of data we can now collect from species in the wild, the analytical advances that allow us to query responses at the scale of entire genomes, and the integration of data from different sources (e.g. environmental, historical, demographic) with genomic datasets to better inform conservation. These themes repeatedly emerged throughout the symposium talks and contributed papers and highlight how the synergy between them has so quickly moved conservation genetics from an established discipline focused on genetic variation to a new field of conservation genomics—one that aims to predict organismal responses to global change and propose management responses in that framework (Hogg et al. 2022; Andrews et al. 2023; Meek et al. 2023).

A tale of two paths: The evolution of mitochondrial recombination in bivalves with doubly uniparental inheritance

Abstract: In most animals, mitochondrial DNA is strictly maternally inherited and non-recombining. One exception to this pattern is called doubly uniparental inheritance (DUI), a phenomenon involving the independent transmission of female and male mitochondrial genomes. DUI is known only from the molluskan class Bivalvia. The phylogenetic distribution of male-transmitted mitochondrial DNA (M mtDNA) in bivalves is consistent with several evolutionary scenarios, including multiple independent gains, losses, and varying degrees of recombination with female-transmitted mitochondrial DNA (F mtDNA). In this study, we use phylogenetic methods to test M mtDNA origination hypotheses and infer the prevalence of mitochondrial recombination in bivalves with DUI. Phylogenetic modeling using site concordance factors supported a single origin of M mtDNA in bivalves coupled with recombination acting over long evolutionary timescales. Ongoing mitochondrial recombination is present in Mytilida and Venerida, which results in a pattern of concerted evolution of F mtDNA and M mtDNA. Mitochondrial recombination could be favored to offset the deleterious effects of asexual inheritance and maintain mitonuclear compatibility across tissues. Cardiida and Unionida have gone without recent recombination, possibly due to an extension of the COX2 gene in male mitochondrial DNA. The loss of recombination could be connected to the role of M mtDNA in sex determination or sexual development. Our results support that recombination events may occur throughout the mitochondrial genomes of DUI species. Future investigations may reveal more complex patterns of inheritance of recombinants, which could explain the retention of signal for a single origination of M mtDNA in protein-coding genes.

Book Review: Conservation and the Genomics of Populations: Third edition.

Abstract: Fred W. Allendorf, W. Chris Funk, Sally N. Aitken, Margaret Byrne, and Gordon Luikart. Oxford University Press, 2022. The familiar story of Noah is timeworn, maybe a bit cliched, and probably overused. But it does remind one how often conservationists reference the fable as a tale of our own time and why. We recognize now that we cannot create diversity; we can only conserve what natural selection has honed fit for purpose over 3.8 billion years of evolution. And what we mean by conservation today explicitly comprises genetic variation at the individual, population, species, and phylogenic scales. So, “conservation” is really “conservation genetics”, and the preservation of biodiversity is the goal. And if N = 2 is not enough after all, how many are? A sort of brute force genetic conservation might be effected by preserving as much native habitat and as many survivors as possible, as fast as possible, and leaving them be. But as that is rarely possible, modern conservation, and this book, aims for a fine-tuned approach. If we are to manage what diversity we have left, much less hope for survival into the distant future, we must understand the genetic dynamics of these living, breeding organisms contending with their environments. The general principles explained in Conservation and the Genomics of Populations help us discover and understand what natural selection has evolved and what we have broken, and how, perhaps, we might fix it. This latest edition of a text long recognized for its outstanding quality covers the basics of population genetics, describes what happens when population sizes are reduced, and outlines how to bring this understanding to bear on conservation management. All the nuts and bolts of how to preserve as much genetic diversity as possible. The idea of saving all living things is not new, but the methods are different.

A draft reference genome assembly of the Pipevine Swallowtail butterfly, Battus philenor hirsuta.

Abstract: The California Pipevine Swallowtail Butterfly, Battus philenor hirsuta, and its host plant, the California Pipevine or Dutchman's Pipe, Aristolochia californica Torr., are an important California endemic species pair. While this species pair is an ideal system to study co-evolution, genomic resources for both are lacking. Here, we report a new, chromosome-level assembly of B. philenor hirsuta as part of the California Conservation Genomics Project (CCGP). Following the sequencing and assembly strategy of the CCGP, we used Pacific Biosciences HiFi long reads and Hi-C chromatin proximity sequencing technology to produce a de novo assembled genome. Our genome assembly, the first for any species in the genus, contains 109 scaffolds spanning 443 mega base (Mb) pairs, with a contig N50 of 14.6 Mb, a scaffold N50 of 15.2 Mb, and BUSCO complete score of 98.9%. In combination with the forthcoming A. californica reference genome, the B. philenor hirsuta genome will be a powerful tool for documenting landscape genomic diversity and plant-insect co-evolution in a rapidly changing California landscape.

In Memoriam: Robert K. Wayne, a pioneer of evolutionary genomics for wildlife with an emphasis on endangered species.

Abstract: Robert (Bob) Keith Wayne lost his battle with cancer in his home on 26 December 2022 with his wife, Dr. Blaire Van Valkenburgh, by his side. This essay, written by his former graduate students, highlights the foundation that survives Bob and our vision of continuing his efforts in building a future for endangered species.

Reference genome for the American rubyspot damselfly, Hetaerina americana

Abstract: Abstract Damselflies and dragonflies (Order: Odonata) play important roles in both aquatic and terrestrial food webs and can serve as sentinels of ecosystem health and predictors of population trends in other taxa. The habitat requirements and limited dispersal of lotic damselflies make them especially sensitive to habitat loss and fragmentation. As such, landscape genomic studies of these taxa can help focus conservation efforts on watersheds with high levels of genetic diversity, local adaptation, and even cryptic endemism. Here, as part of the California Conservation Genomics Project (CCGP), we report the first reference genome for the American rubyspot damselfly, Hetaerina americana, a species associated with springs, streams and rivers throughout California. Following the CCGP assembly pipeline, we produced two de novo genome assemblies. The primary assembly includes 1,630,044,487 base pairs, with a contig N50 of 5.4 Mb, a scaffold N50 of 86.2 Mb, and a BUSCO completeness score of 97.6%. This is the seventh Odonata genome to be made publicly available and the first for the subfamily Hetaerininae. This reference genome fills an important phylogenetic gap in our understanding of Odonata genome evolution, and provides a genomic resource for a host of interesting ecological, evolutionary, and conservation questions for which the rubyspot damselfly genus Hetaerina is an important model system.

Limited, asymmetric hybridization between coastal cutthroat trout and steelhead in a Northern California river.

Abstract: Hybridization between coastal cutthroat trout (Oncorhynchus clarkii clarkii) and steelhead (O. mykiss) was assessed in the Smith River, California. Individuals were categorized as pure or as one of 10 hybrid classes using 30 'diagnostic' single-nucleotide polymorphisms positioned on 26 separate chromosomes. Most of the individuals examined (n = 876), were pure coastal cutthroat trout (n = 634) or pure steelhead (n = 213), and 29 individuals were identified as having hybrid ancestry. Among hybrids, first generation hybrids (n = 15) and coastal cutthroat trout backcrosses (n = 12) were the most common. No individuals were identified as backcrosses to SH, suggesting the presence of genetic or behavioral mechanisms constraining such backcrosses, or the growth and survival of their progeny. Mitochondrial DNA of 14 of 15 F1 hybrids was of steelhead origin, suggesting that hybridization was driven primarily by sneak-mating of male coastal cutthroat trout with female steelhead. Evaluation of classical phenotypic characters for coastal cutthroat trout and steelhead (i.e., jaw slash, maxillary length, and hyoid teeth) were not reliable by themselves for identification of either pure parental fish or hybrids. In contrast, analysis with geometric morphometrics revealed distinctive body shapes for pure coastal cutthroat trout and steelhead, and the combination of classical traits and geometric morphology was mostly accurate in distinguishing them. However, first generation hybrids and backcrosses overlapped completely with parental types, highlighting challenges in hybrid identification using phenotypic traits.

Reference genome of California walnut, Juglans californica, and resemblance with other genomes in the order Fagales.

Abstract: Juglans californica, California walnut, is a vulnerable small tree that is locally abundant but restricted to woodland and chaparral habitats of Southern California threatened by urbanization and land use change. This species is the dominant species in a unique woodland ecosystem in California. It is one of two endemic California walnut species (family Juglandaceae). The other species, Northern California black walnut (J. hindsii), has been suggested controversially to be a variety of J. californica. Here, we report a new, chromosome-level assembly of J. californica as part of the California Conservation Genomics Project (CCGP). Consistent with the CCGP common methodology across ~150 genomes, we used Pacific Biosciences HiFi long reads and Omni-C chromatin-proximity sequencing technology to produce a de novo assembled genome. The assembly comprises 137 scaffolds spanning 551,065,703 base pairs, has a contig N50 of 30 Mb, a scaffold N50 of 37 Mb, and BUSCO complete score of 98.9%. Additionally, the mitochondrial genome has 701,569 base pairs. In addition, we compare this genome with other existing high quality Juglans and Quercus genomes, which are in the same order (Fagales) and show relatively high synteny within the Juglans genomes. Future work will utilize the J. californica genome to determine its relationship with the Northern California walnut and assess the extent to which these two endemic trees might be at risk from fragmentation and/or climate warming.

Limited evidence for extensive genetic differentiation between X and Y chromosomes in Hybognathus amarus (Cypriniformes:Leuciscidae).

Abstract: Sex determination systems and genetic sex differentiation across fishes are highly diverse but are unknown for most Cypriniformes, including Rio Grande silvery minnow (Hybognathus amarus). In this study, we aimed to detect and validate sex-linked markers to infer sex determination system and to demonstrate the utility of combining several methods for sex-linked marker detection in non-model organisms. To identify potential sex-linked markers, Nextera-tagmented reductively-amplified DNA (nextRAD) libraries were generated from 66 females, 64 males and 60 larvae of unknown sex. These data were combined with female and male de novo genomes from Nanopore long read sequences. We identified five potential unique male nextRAD-tags and one potential unique male contig, suggesting an XY sex determination system. We also identified two SNPs in the same contig with values of FST, allele frequencies and heterozygosity conforming with expectations of an XY system. Through PCR we validated the marker containing the sex-linked SNPS and a single nextRAD-tag sex-associated marker but it was not male-specific. Instead, more copies of this locus in the male genome were suggested by enhanced amplification in males. Results are consistent with an XY system with low differentiation between sex determining regions. Further research is needed to confirm the level of differentiation between the sex chromosomes. Nonetheless, this study highlighted the power of combining reduced-representation and whole-genome sequencing for identifying sex-linked markers, especially when reduced representation sequencing does not include extensive variation between sexes, either because such variation is not present or not captured.