Biology subjects

Akopyan, M.

Publications and source records attributed to Akopyan, M..

5 recordsLinked to original sources

bioRxiv2026

Recombination accelerates adaptation across genetic architectures and demographic histories

According to classic population genetics theory, recombination shapes the efficacy of natural selection. However, whether variation in recombination rate itself translates into meaningful differences in adaptive capacity remains poorly understood. Here, we used forward-time simulations to examine polygenic adaptation in populations colonizing novel environments. We varied recombination rate eightfold, modeled QTL effect size distributions using three gamma distributions, and compared constant and contracted population sizes. Across all conditions, higher recombination rates modestly accelerated adaptation, reducing the time to reach a new phenotypic optimum by 2-15%. The benefit was substantially greater in constant-size populations than in those that had experienced a contraction, but did not differ across genetic architectures. To understand the mechanism of this acceleration, we tracked linkage disequilibrium among adaptation-related QTL throughout adaptation. We found that across simulations, beneficial alleles were consistently in repulsion phase with one another and in coupling phase with deleterious alleles, both signatures of Hill-Robertson interference. Higher recombination attenuated both forms of interference, indicating that the benefit of recombination operated primarily through relieving interference among QTL. These results implicate interference among linked loci as the primary constraint on polygenic adaptation in this context, and demographic history as a critical modulator of the benefit of recombination.

evolutionary biology↗

bioRxiv2024

Divergent reference genomes compromise the reconstruction of demographic histories, selection scans, and population genetic summary statistics

Characterizing genetic variation in natural populations is vital to evolutionary biology, however many non-model species lack genomic resources. Here, we demonstrate that reference bias significantly affects population genomic analyses by mapping whole genome sequence data from gray foxes (Urocyon cinereoargenteus) to a conspecific reference and two heterospecific canid genomes (dog and Arctic fox). Mapping to the conspecific genome improved read pairing by [~]5%, detected 26-32% more SNPs, and 33-35% more singletons. Nucleotide diversity estimates increased over 30%, FST increased from 0.189 to 0.197, and effective population size estimates were 30-60% higher with the conspecific reference. Recombination rates varied by up to 3-fold at chromosome ends with heterospecific references. Importantly, FST outlier detection differed markedly, with heterospecific genomes identifying twice as many unique outlier windows. These findings highlight the impact of reference genome choice and the importance of conspecific genomic resources for accurate evolutionary inference. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=198 SRC="FIGDIR/small/625554v2_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@1d717adorg.highwire.dtl.DTLVardef@537c85org.highwire.dtl.DTLVardef@1142d10org.highwire.dtl.DTLVardef@19a9f06_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIA species-specific reference genome improves read mapping and variant detection C_LIO_LIReference bias underestimates genetic diversity and differentiation C_LIO_LIDivergent reference genomes distort demographic histories and recombination landscapes C_LIO_LIUnique FST outliers are detected across references, affecting functional interpretations C_LI

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↗

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

Genetic isolation by distance underlies color pattern divergence in red-eyed treefrogs (Agalychnis callidryas)

Investigating the spatial distribution of genetic and phenotypic variation can provide insights into the evolutionary processes that shape diversity in natural systems. We characterized patterns of genetic and phenotypic diversity to learn about drivers of color-pattern diversification in red-eyed treefrogs (Agalychnis callidryas) in Costa Rica. Along the Pacific coast, red-eyed treefrogs have conspicuous leg color patterning that transitions from orange in the north to purple in the south. We measured phenotypic variation of frogs, with increased sampling at sites where the orange-to-purple transition occurs. At the transition zone, we discovered the co-occurrence of multiple color-pattern morphs. To explore possible causes of this variation, we generated a SNP dataset to analyze population genetic structure, measure genetic diversity, and infer the processes that mediate genotype-phenotype dynamics. We investigated how patterns of genetic relatedness correspond with individual measures of color pattern along the coast, including testing for the role of hybridization in geographic regions where orange and purple phenotypic groups co-occur. We found no evidence that color-pattern polymorphism in the transition zone arose through recent hybridization. Instead, a strong pattern of genetic isolation by distance (IBD) indicates that color-pattern variation was either retained through other processes such as ancestral color polymorphisms or ancient secondary contact, or else it was generated by novel mutations. We found that phenotype changes along the Pacific coast more than would be expected based on genetic divergence and geographic distance alone. Combined, our results suggest the possibility of selective pressures acting on color pattern at a small geographic scale.

evolutionary biology↗