Biology subjects

Tigano, A.

Publications and source records attributed to Tigano, A..

11 recordsLinked to original sources

bioRxiv2025

Whole genome analyses of the endangered Northern abalone (Haliotis kamtschatkana) reveal population differentiation and a genomic signature of a dramatic population decline

Despite widespread declines of many wildlife species, the effects of population decline on the genetic health and the recovery potential of affected species is still poorly understood, especially beyond a few charismatic species. The Northern abalone (or Pinto abalone; Haliotis kamtschatkana) is a marine gastropod mollusc of social, cultural and historical economic importance in the Pacific Northwest of North America that experienced a decline in population density due to commercial harvest and is currently listed as endangered in Canada under the Species at Risk Act. Previous genetic investigations based on microsatellites and reduced-representation approaches concluded that Northern abalone is panmictic throughout its range, from Alaska to California, and identified high levels of genetic variation with no indication of population decline. Using whole genome resequencing data from Northern abalone sampled across the northern part of the species range, we instead identified both: 1) significant differentiation between two genetic groups, albeit very concentrated in the genome; and 2) a strong signature of a dramatic population decline, without evidence of genetic inbreeding. Even though demographic reconstructions showed a timid signal of recent population expansion, the pervasive excess of rare alleles identified (including a high occurrence of singletons) may pose a genetic load risk, potentially hindering the species recovery. We also found evidence of historical, rather than current, connectivity throughout the area investigated. These results are important for management decisions and highlight the utility of whole genome data in conservation, especially in species with historically large effective population sizes like the Northern abalone.

evolutionary biology↗

bioRxiv2024

Genetic differentiation is constrained to chromosomal inversions and putative centromeres in locally adapted populations with higher gene flow

The impact of genome structure on adaptation is a growing focus in evolutionary biology, revealing an important role for structural variation and recombination landscapes in shaping genetic diversity across genomes and among populations. This is particularly relevant when local adaptation occurs despite gene flow, where clustering of differentiated loci can maintain locally adapted variants by reducing recombination between them. However, the limited genomic resources for non-model species, including reference genomes and recombination maps, has constrained our understanding of these patterns. In this study, we leverage the Atlantic silverside--a non-model fish with extensive local adaptation across a steep latitudinal gradient--as an ideal system to explore how genome structure influences adaptation under varying levels of gene flow, using a newly available reference genome and multiple recombination maps. Analyzing 168 genomes from four populations, we found a continuum of genome-wide differentiation increasing from south to north, reflecting higher connectivity among southern populations and reduced gene flow at northern latitudes. With increasing gene flow, the number and clustering of FST outlier loci also increased, with differentiated loci tightly clustered in large haploblocks harboring inversions and smaller peaks overlapping putative centromeres. Notably, sequence divergence was only evident in inversions, supporting their role in adaptive divergence with gene flow, whereas centromeres appeared differentiated because of low recombination and reduced diversity, with no indication of elevated sequence divergence. Our results support the hypothesis that clustered genomic architectures evolve with high gene flow and enhance our understanding of how inversions and centromeres are linked to different evolutionary processes. Significance StatementHow populations preserve favorable combinations of genes adapted to their local environment despite reproducing with populations adapted to different conditions is a longstanding question in evolutionary biology. By analyzing the genomes of 168 Atlantic silverside fish from four populations, we found that when populations adapted to different environments frequently interbreed, genetic differences concentrate in specific parts of the genome, particularly in chromosomal inversions--where segments of DNA are flipped. These inversions help preserve locally adapted gene combinations, enabling populations to maintain differences essential for survival in their habitats. This research enhances our understanding of genomic adaptation, a fundamental evolutionary question with increasing relevance as environmental changes pose new challenges globally.

evolutionary biology↗

bioRxiv2022

Temperature-dependent gene regulatory divergence underlies local adaptation with gene flow in the Atlantic silverside

Gene regulatory divergence is thought to play an important role in adaptation, yet its extent and underlying mechanisms remain largely elusive under scenarios of local adaptation with gene flow. Local adaptation is widespread in marine species despite generally high connectivity and often associated with tightly-linked genomic architectures, such as chromosomal inversions. To investigate gene regulatory evolution under gene flow and the role of discrete genomic regions associated with local adaptation to a steep thermal gradient, we generated RNA-seq data from Atlantic silversides (Menidia menidia) from two locally adapted populations and their F1 hybrids, reared under two different temperatures. We found substantial divergence in gene expression and thermal plasticity, with up to 31% of genes being differentially expressed, and primarily trans-rather than cis-regulatory divergence between populations, despite ongoing gene flow. Substantially reduced thermal plasticity, temperature-dependent gene misexpression and the disruption of co-expression networks in hybrids point toward a role of regulatory incompatibilities in maintaining local adaptation, particularly under colder temperatures, which appear more challenging for this species. Adaptive chromosomal inversions seem to play an important role in gene regulatory divergence through the accumulation of regulatory incompatibilities but are not consistently enriched for divergently regulated genes. Together, these results highlight that gene regulation can diverge substantially among populations connected by strong gene flow in marine environments, partly due to the accumulation of temperature-dependent regulatory incompatibilities within inversions.

evolutionary biology↗

bioRxiv2021

Background selection under evolving recombination rates

Background selection (BGS), the effect that purifying selection exerts on sites linked to deleterious alleles, is expected to be ubiquitous across eukaryotic genomes. The effects of BGS reflect the interplay of the rates and fitness effects of deleterious mutations with recombination. A fundamental assumption of BGS models is that recombination rates are invariant over time. However, in some lineages recombination rates evolve rapidly, violating this central assumption. Here, we investigate how recombination rate evolution affects genetic variation under BGS. We show that recombination rate evolution modifies the effects of BGS in a manner similar to a localised change in the effective population size, potentially leading to an underestimation of the genome-wide effects of selection. Furthermore, we find evidence that recombination rate evolution in the ancestors of modern house mice may have impacted inferences of the genome-wide effects of selection in that species.

evolutionary biology↗

bioRxiv2021

Comparative linkage mapping uncovers massive chromosomal inversions that suppress recombination between locally adapted fish populations

The role of recombination in genome evolution has long been studied in theory, but until recently empirical investigations had been limited to a small number of model species. Here we compare the recombination landscape and genome collinearity between two populations of the Atlantic silverside (Menidia menidia), a small fish distributed across the steep latitudinal climate gradient of the North American Atlantic coast. Using ddRADseq, we constructed separate linkage maps for locally adapted populations from New York and Georgia and their inter-population lab cross. First, we used one of the linkage maps to improve the current silverside genome assembly by anchoring three large unplaced scaffolds to two chromosomes. Second, we estimated sex-specific recombination rates, finding 2.75-fold higher recombination rates in females than males--one of the most extreme examples of heterochiasmy in a fish. While recombination occurs relatively evenly across female chromosomes, it is restricted to only the terminal ends of male chromosomes. Furthermore, comparisons of female linkage maps revealed suppressed recombination along several massive chromosomal inversions spanning nearly 16% of the genome and segregating between locally adapted populations. Finally, we discerned significantly higher recombination rates across chromosomes in the northern population. In addition to providing valuable resources for ongoing evolutionary and comparative genomic studies, our findings represent a striking example of structural variation that impacts recombination between adaptively divergent populations, providing empirical support for theorized genomic mechanisms facilitating adaptation despite gene flow.

evolutionary biology↗

bioRxiv2021

Chromosome size affects sequence divergence between species through the interplay of recombination and selection

The structure of the genome shapes the distribution of genetic diversity and sequence divergence. To investigate how the relationship between chromosome size and recombination rate affects sequence divergence between species, we combined empirical analyses and evolutionary simulations. We estimated pairwise sequence divergence among 15 species from three different Mammalian clades - Peromyscus rodents, Mus mice, and great apes - from chromosome-level genome assemblies. We found a strong significant negative correlation between chromosome size and sequence divergence in all species comparisons within the Peromyscus and great apes clades, but not the Mus clade, suggesting that the dramatic chromosomal rearrangements among Mus species may have masked the ancestral genomic landscape of divergence in many comparisons. Our evolutionary simulations showed that the main factor determining differences in divergence among chromosomes of different size is the interplay of recombination rate and selection, with greater variation in larger populations than in smaller ones. In ancestral populations, shorter chromosomes harbor greater nucleotide diversity. As ancestral populations diverge, diversity present at the onset of the split contributes to greater sequence divergence in shorter chromosomes among daughter species. The combination of empirical data and evolutionary simulations revealed that chromosomal rearrangements, demography, and divergence times may also affect the relationship between chromosome size and divergence, and deepen our understanding of the role of genome structure on the evolution of species divergence.

evolutionary biology↗

bioRxiv2020

Chromosome-level assembly of the Atlantic silverside genome reveals extreme levels of sequence diversity and structural genetic variation

The levels and distribution of standing genetic variation in a genome can provide a wealth of insights about the adaptive potential, demographic history, and genome structure of a population or species. As structural variants are increasingly associated with traits important for adaptation and speciation, investigating both sequence and structural variation is essential for wholly tapping this potential. Using a combination of shotgun sequencing, 10X Genomics linked reads and proximity-ligation data (Chicago and Hi-C), we produced and annotated a chromosome-level genome assembly for the Atlantic silverside (Menidia menidia) - an established ecological model for studying the phenotypic effects of natural and artificial selection - and examined patterns of genomic variation across two individuals sampled from different populations with divergent local adaptations. Levels of diversity varied substantially across each chromosome, consistently being highly elevated near the ends (presumably near telomeric regions) and dipping to near zero around putative centromeres. Overall, our estimate of the genome-wide average heterozygosity in the Atlantic silverside is the highest reported for a fish, or any vertebrate, to date (1.32-1.76% depending on inference method and sample). Furthermore, we also found extreme levels of structural variation, affecting ~23% of the total genome sequence, including multiple large inversions (> 1 Mb and up to 12.6 Mb) associated with previously identified haploblocks showing strong differentiation between locally adapted populations. These extreme levels of standing genetic variation are likely associated with large effective population sizes and may help explain the remarkable adaptive divergence among populations of the Atlantic silverside.

genomics↗

bioRxiv2020

Multiple evolutionary pathways to achieve thermal adaptation in small mammals

Phenotypic plasticity enables an immediate response to changing conditions, but for most species, evolutionary change through adaptation will be more important for long-term survival. Warming climate and increasing desertification urges the identification of genes involved in heat-and dehydration-tolerance to better inform and target biodiversity conservation efforts. Comparisons among extant desert adapted species can highlight parallel or convergent patterns of genome evolution through the identification of shared signatures of selection. We generate chromosome-level genome assembly for the canyon mouse (Peromyscus crinitus) and test for signature of parallel evolution by comparing signatures of selective sweeps across population-level genomic resequencing data from another desert specialist deer mouse (P. eremicus) and a widely-distributed habitat generalist (P. maniculatus), that may locally adapted to arid conditions. We identify few shared candidate loci involved in desert adaptation and do not find support for a shared pattern of parallel evolution. Instead, we hypothesize divergent molecular mechanisms of desert adaptation among deer mice, potentially tied to species-specific historical demography, which may limit or enhance adaptation. We identify a number of candidate loci experiencing selective sweeps in the P. crinitus genome that are implicated in osmoregulation (Trypsin, Prostasin) and metabolic regulation (Kallikrein, eIF2-alpha kinase GCN2, APPL1/2), which may be important to accommodating hot and dry environmental conditions.

evolutionary biology↗

bioRxiv2019

Comparative and population genomics approaches reveal the basis of adaptation to deserts in a small rodent

Organisms that live in deserts offer the opportunity to investigate how species adapt to environmental conditions that are lethal to most plants and animals. In the hot deserts of North America, high temperatures and lack of water are conspicuous challenges for organisms living there. The cactus mouse (Peromyscus eremicus) displays several adaptations to these conditions, including low metabolic rate, heat tolerance, and the ability to maintain homeostasis under extreme dehydration. To investigate the genomic basis of desert adaptation in cactus mice, we built a chromosome-level genome assembly and resequenced 26 additional cactus mouse genomes from two locations in southern California (USA). Using these data, we integrated comparative, population, and functional genomic approaches. We identified 16 gene families exhibiting significant contractions or expansions in the cactus mouse compared to 17 other Myodontine rodent genomes, and found 232 sites across the genome associated with selective sweeps. Functional annotations of candidate gene families and selective sweeps revealed a pervasive signature of selection at genes involved in the synthesis and degradation of proteins, consistent with the evolution of cellular mechanisms to cope with protein denaturation caused by thermal and hyperosmotic stress. Other strong candidate genes included receptors for bitter taste, suggesting a dietary shift towards chemically defended desert plants and insects, and a growth factor involved in lipid metabolism, potentially involved in prevention of dehydration. Understanding how species adapted to the recent emergence of deserts in North America will provide an important foundation for predicting future evolutionary responses to increasing temperatures, droughts and desertification in the cactus mouse and other species.

evolutionary biology↗

bioRxiv2019

Higher quality de novo genome assemblies from degraded museum specimens: a linked-read approach to museomics

AO_SCPLOWBSTRACTC_SCPLOWHigh-throughput sequencing technologies are a proposed solution for accessing the molecular data in historic specimens. However, degraded DNA combined with the computational demands of short-read assemblies has posed significant laboratory and bioinformatics challenges. Linked-read or synthetic long-read sequencing technologies, such as 10X Genomics, may provide a cost-effective alternative solution to assemble higher quality de novo genomes from degraded specimens. Here, we compare assembly quality (e.g., genome contiguity and completeness, presence of orthogroups) between four published genomes assembled from a single shotgun library and four deer mouse (Peromyscus spp.) genomes assembled using 10X Genomics technology. At a similar price-point, these approaches produce vastly different assemblies, with linked-read assemblies having overall higher quality, measured by larger N50 values and greater gene content. Although not without caveats, our results suggest that linked-read sequencing technologies may represent a viable option to build de novo genomes from historic museum specimens, which may prove particularly valuable for extinct, rare, or difficult to collect taxa.

genomics↗

bioRxiv2018

A complex copy number variant underlies differences in both colour plumage and cold adaptation in a dimorphic seabird.

Colour morphs associated with different physiological adaptations offer unique opportunities to study the genomic basis of otherwise elusive adaptive traits. These complex balanced polymorphisms are often controlled by groups of tightly linked genes, and understanding how these supergenes evolve and are maintained is an active area of research in evolutionary biology (Schwander et al. 2014, Thompson and Jiggins 2014). Within the Atlantic, the common murre (Uria aalge, a colonial seabird) displays a plumage colour dimorphism ( bridled and unbridled) that seems to be associated with differences in thermal adaptation (Birkhead 1984; Reiertsen et al. 2012). The genes associated with bridling and how these genes affect thermal adaptation are unknown. Using whole genome resequencing, we investigate the genomic basis of differences in colouration and thermal adaptation between the two morphs, and how the association between the two traits is maintained despite random mating. We identify a 60 kb genomic region of high differentiation laying in the intergenic area amongst three candidate genes for colouration and thermal adaptation: retinoic acid receptor beta (RARB), thyroid hormone receptor beta (THRB), and nuclear receptor subfamily 1 group D member 2 (NR1D2 or Rev-erb{beta}). Differentiation is due to a complex copy number variant (CNV) that suppresses recombination locally. We show that this CNV acts as a supergene and maintain association between regulatory elements likely affecting gene expression of one or more of the identified candidate genes. Our analyses also provide insights into the origin of the dimorphism: while copy number proliferation in the unbridled haplotype was potentially mediated by transposable elements (TEs), the bridled haplotype seems to have introgressed from the more cold-adapted sister species, the thick-billed murre (U. lomvia). Our results highlight the role of copy number variants in adaptation, especially when association among traits is maintained in the face of gene flow. They also shed light into the molecular mechanisms of adaptive thermogenesis in birds, which is poorly understood.\n\nHighlightsO_LIDifferences in plumage colour in Atlantic common murres are associated with different thermal adaptations\nC_LIO_LIA single region is highly differentiated between bridled and unbridled morphs\nC_LIO_LIA complex copy number variant in a non-coding region underlies the dimorphism\nC_LIO_LITransposable elements and adaptive introgression from the thick-billed murre seem to explain the origin of the dimorphism\nC_LI

evolutionary biology↗