Biology subjects

Bradburd, G. S.

Publications and source records attributed to Bradburd, G. S..

10 recordsLinked to original sources

bioRxiv2025

Longevity in plants impacts phylogenetic and population dynamics

Many long-lived plant species exhibit notable patterns in phylogenies, such as short molecular branch lengths and high gene-tree conflict. However, it is not clear what biological properties of long-lived plant species or concomitant processes acting within these lineages generate these patterns. To explore this mystery, we implemented an agent-based model and conducted simulations to investigate how longevity affects molecular evolution and population dynamics. Through these simulations, we demonstrated that the patterns exhibited in empirical datasets for long-lived species can be explained by their lifespan and overlapping generations. We also show that somatic mutations can exacerbate these patterns, although evidence for substantive rates in empirical systems high enough to impact phylogenetic patterns is scarce. We discuss several empirical datasets containing life history shifts that exhibit diverse phylogenomic patterns. The variation produced through different parameterizations of our simulations reflects the diversity of patterns found in empirical datasets. Our results have broad implications for phylogenomic patterns and population genetics in general, as well as for specifically explaining patterns of evolution in long-lived lineages.

evolutionary biology↗

bioRxiv2025

Drivers of genetic diversity across the marine tree of life

Why do some species have more genetic diversity than others? This question is one of the greatest remaining mysteries in evolutionary biology, yet we still know little about what factors predict genetic diversity among species. Efforts to quantify diversity or understand its distribution have been hampered by a lack of genomic data analyzed in a consistent way with statistical approaches that can move beyond the population level to generate species-wide estimates of genetic diversity. We address this critical gap by generating standardized estimates of genomic-level genetic diversity for 93 species sampled over 9,000 localities. Because marine species have evolved a strikingly diverse array of biological traits that have long been hypothesized to affect species-level genetic diversity, we focus our study on marine taxa. For each species, we aggregated biotic traits related to life history and abiotic features of the species range. We show that genetic diversity increases with species range extent and planktonic dispersal. We hypothesize that these traits increase a species ability to avoid or recover from bottlenecks, thereby maintaining genetic diversity. Our findings provide insights into how biotic and abiotic factors interact to shape genomic variation in the ocean, and offer a predictive framework for understanding marine biodiversity in the face of global change. Significance statementSpecies exhibit vast trait diversity that allows populations to persist. However, diversity in these traits -- e.g., how organisms reproduce, disperse, and feed -- is not easily linked to what is known of genomic diversity, even in well-studied organisms. We investigate a diverse assemblage of marine species to begin to build a predictive framework for how species traits drive genomic diversity across the worlds oceans. We find that species with larger geographic ranges have higher genomic diversity. More dispersive species also harbor higher diversity, suggesting that greater dispersal facilitates resilience to environmental change. As available datasets increase, our ability to understand fundamental links between trait and genetic diversity and how they shape species responses to environmental change will continue to improve.

evolutionary biology↗

bioRxiv2024

Asymmetric gene flow maintains an abundant range center

Species are restricted to finite ranges, and when they are in demographic equilibrium with the environment this implies a failure to adapt at the range periphery. There are several competing evolutionary hypotheses for the maintenance and persistence of range edges. One hypothesis is gene swamping of edge populations, in which migrants from the center carrying alleles adapted to the range center but maladaptive along the edge hamper local adaptation. A competing explanation is dispersal limitation, in which reduced migration to the periphery keeps edge populations small, causing drift to dominate over selection. It has proven difficult to assess these potential generative scenarios due to the inherent complexity of species ranges. In this study, we leverage range-wide genomic sequencing data to investigate the evolution of range edges in an empirical system - Haustorius canadensis, the Canadian shovel bug. We find increased genetic drift and inbreeding on the range edges and detect signatures of asymmetric migration towards the range center. The inferred directionality of migration is consistent with the direction of the dominant current regimes in the North Atlantic. We conclude that anisotropic dispersal towards the range center leaves progressively fewer migrants to replenish peripheral populations, consistent with the migration limitation hypothesis, and generates the appearance of an abundant center.

evolutionary biology↗

bioRxiv2024

The Roles of Drift and Selection on Short Stamen Loss in Arabidopsis thaliana along an Elevational Gradient in the Spanish Pyrenees

Traits that have lost function sometimes persist through evolutionary time. These traits may persist if there is not enough standing genetic variation for the trait to allow a response to selection, if selection against the trait is weak relative to drift, or if the trait has a residual function. To determine the evolutionary processes shaping whether nonfunctional traits are retained or lost, we investigated short stamens in 16 populations of Arabidopsis thaliana along an elevational cline in northeast Spain. We found a cline in short stamen number from retention of short stamens in high elevation populations to incomplete loss in low elevation populations. We did not find evidence that limited genetic variation constrains the loss of short stamens at high elevations, nor evidence for divergent selection on short stamens between high and low elevations. Finally, we identified loci associated with short stamens in northeast Spain that are different from loci associated with variation in short stamen number across latitudes from a previous study. Overall, we did not identify the evolutionary mechanisms contributing to an elevational cline in short stamen number but did identify different genetic loci underlying variation in short stamen along similar phenotypic clines. Teaser textThe evolutionary mechanisms underlying loss or retention of traits that have lost function are poorly understood. Short stamens in Arabidopsis thaliana provide a compelling system to investigate the roles of genetic drift and selection in trait loss across latitudinal and elevational clines. This study investigates how drift and selection shape short stamen loss in 16 populations of A. thaliana along an elevational gradient in Northeast Spain. An investigation of the loci underlying variation in short stamen number suggests variants in different genes may cause trait loss in similar phenotypic clines within a species.

evolutionary biology↗

bioRxiv2024

Pitfalls and windfalls of detecting demographic declines using population genetics in long-lived species

Detecting recent demographic changes is a crucial component of species conservation and management, as many natural populations face declines due to anthropogenic habitat alteration and climate change. Genetic methods allow researchers to detect changes in effective population size (Ne) from sampling at a single timepoint. However, in species with long lifespans, there is a lag between the start of a decline in a population and the resulting decrease in genetic diversity. This lag slows the rate at which diversity is lost, and therefore makes it difficult to detect recent declines using genetic data. However, the genomes of old individuals can provide a window into the past, and can be compared to those of younger individuals, a contrast that may help reveal recent demographic declines. To test whether comparing the genomes of young and old individuals can help infer recent demographic bottlenecks, we use forward-time, individual-based simulations with varying mean individual lifespans and extents of generational overlap. We find that age information can be used to aid in the detection of demographic declines when the decline has been severe. When average lifespan is long, comparing young and old individuals from a single timepoint has greater power to detect a recent (within the last 50 years) bottleneck event than comparing individuals sampled at different points in time. Our results demonstrate how longevity and generational overlap can be both a hindrance and a boon to detecting recent demographic declines from population genomic data.

evolutionary biology↗

bioRxiv2024

A geographic history of human genetic ancestry

Describing the distribution of genetic variation across individuals is a fundamental goal of population genetics. In humans, traditional approaches for describing population genetic variation often rely on discrete genetic ancestry labels, which, despite their utility, can obscure the complex, multifaceted nature of human genetic history. These labels risk oversimplifying ancestry by ignoring its temporal depth and geographic continuity, and may therefore conflate notions of race, ethnicity, geography, and genetic ancestry. Here, we present a method that capitalizes on the rich genealogical information encoded in genomic tree sequences to infer the geographic locations of the shared ancestors of a sample of sequenced individuals. We use this method to infer the geographic history of genetic ancestry of a set of human genomes sampled from Europe, Asia, and Africa, accurately recovering major population movements on those continents. Our findings demonstrate the importance of defining the spatial-temporal context of genetic ancestry to describing human genetic variation and caution against the oversimplified interpretations of genetic data prevalent in contemporary discussions of race and ancestry.

genetics↗

bioRxiv2023

A spatial approach to jointly estimate Wright's neighborhood size and long-term effective population size

Spatially continuous patterns of genetic differentiation, which are common in nature, are often poorly described by existing population genetic theory or methods that assume panmixia or discrete, clearly definable populations. There is therefore a need for statistical approaches in population genetics that can accommodate continuous geographic structure, and that ideally use georeferenced individuals as the unit of analysis, rather than populations or subpopulations. In addition, researchers are often interested describing the diversity of a population distributed continuously in space, and this diversity is intimately linked to the dispersal potential of the organism. A statistical model that leverages information from patterns of isolation-by-distance to jointly infer parameters that control local demography (such as Wrights neighborhood size), and the long-term effective size (Ne) of a population would be useful. Here, we introduce such a model that uses individual-level pairwise genetic and geographic distances to infer Wrights neighborhood size and long-term Ne. We demonstrate the utility of our model by applying it to complex, forward-time demographic simulations as well as an empirical dataset of the Red Sea clownfish (Amphiprion bicinctus). The model performed well on simulated data relative to alternative approaches and produced reasonable empirical results given the natural history of clownfish. The resulting inferences provide important insights into the population genetic dynamics of spatially structure populations.

evolutionary biology↗

bioRxiv2022

Metadata preservation and stewardship for genomic data is possible, but must happen now

Genetic diversity within species represents a fundamental yet underappreciated level of biodiversity. Because genetic diversity can indicate species and population resilience to changing climate, its measurement is relevant to many national and global conservation policy targets. Many studies of evolutionary biology, molecular ecology and conservation genetics produce large amounts of genome-scale genetic diversity data for wild populations. While open data policies have ensured an abundance of freely available genomic data stored in the databases of the International Nucleotide Sequence Database Collaboration (INSDC), only about 13% of current accessions have the associated spatial and temporal metadata in INSDC necessary to be reused in monitoring programs, macrogenetic studies, or for acknowledging the sovereignty of nations or Indigenous Peoples. We undertook a "distributed datathon" to quantify the availability of these missing metadata in sources external to the INSDC and to test the hypothesis that these metadata decay with time. We also worked to remediate these missing metadata by extracting them, when present, from associated published papers, online repositories, and/or from direct communication with authors. Starting with 848 programmatically identified candidate datasets (INSDC BioProjects), we manually determined that 561 contained samples from wild populations. We successfully restored spatiotemporal metadata (locality name and/or geospatial coordinates and collection year) for 78% of these 561 datasets (N = 440 BioProjects comprising 45,105 individuals or BioSamples from 762 species in 17 phyla). We also quantified the availability of 33 additional categories of metadata in sources external to the INSDC. Information about associated publications and the type of habitat from which the samples were taken was the most easily found; information about sampling permits was the most challenging to locate. Looking at papers and online repositories was much more fruitful than contacting authors, who only replied to our email requests 45% of the time. Overall, 23% of our email queries to authors discovered useful metadata. Importantly, we found that the probability of retrieving spatiotemporal metadata declines significantly with the age of the dataset, with a 13.5% yearly decrease for metadata located in published papers or online repositories and up to a 22% yearly decrease for metadata that were only available from authors. This observable metadata decay, mirrored in studies of other types of biological data, should motivate swift updates to data sharing policies and researcher practices to ensure that the valuable context provided by metadata is not lost forever.

bioinformatics↗

bioRxiv2022

Modeling the Evolution of Rates of Continuous Trait Evolution

AO_SCPLOWBSTRACTC_SCPLOWRates of phenotypic evolution vary markedly across the tree of life, from the accelerated evolution apparent in adaptive radiations to the remarkable evolutionary stasis exhibited by so-called "living fossils". Such rate variation has important consequences for large-scale evolutionary dynamics, generating vast disparities in phenotypic diversity across space, time, and taxa. Despite this, most methods for estimating trait evolution rates assume rates vary deterministically with respect to some variable of interest or change infrequently during a clades history. These assumptions may cause underfitting of trait evolution models and mislead hypothesis testing. Here, we develop a new trait evolution model that allows rates to vary gradually and stochastically across a clade. Further, we extend this model to accommodate generally decreasing or increasing rates over time, allowing for flexible modeling of "early/late bursts" of trait evolution. We implement a Bayesian method, termed "evolving rates" (evorates for short), to efficiently fit this model to comparative data. Through simulation, we demonstrate that evorates can reliably infer both how and in which lineages trait evolution rates varied during a clades history. We apply this method to body size evolution in cetaceans, recovering substantial support for an overall slowdown in body size evolution over time with recent bursts among some oceanic dolphins and relative stasis among beaked whales of the genus Mesoplodon. These results unify and expand on previous research, demonstrating the empirical utility of evorates.

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↗