Biology subjects

Moyle, L. C.

Publications and source records attributed to Moyle, L. C..

At least 19 recordsLinked to original sources

bioRxiv2026

Large phenological advances and delays over 124 years of climate change alter co-flowering among North American Viola

Shifts in flowering phenology are one of the most well studied plant responses to global climate change. Many studies have documented these shifts and their drivers, including some that describe altered patterns of co-flowering among taxonomically diverse species within communities. In comparison, few analyses have examined systematic changes in co-flowering between closely related, interfertile species, where co-flowering can have unique evolutionary consequences. To address such shifts in co-flowering among close relatives, we investigate phenological responses to climate change and its effect on patterns of co-flowering over the past 124 years in 52 species of North America violets (Viola). This genus has many co-occurring species that reproductively interact via shared pollinators and hybridization. We use [~]14,000 herbarium records along with environmental and species trait data to model the magnitude of recent flowering phenology shifts, environmental variables and/or species traits associated with these shifts, and resulting changes in co-flowering among species. While both the magnitude and direction of phenological shifts varied among Viola species, nearly half (25/52) show significant changes in flowering day. Regardless of whether flowering was advanced or delayed, flowering date was most consistently associated with local mean temperature. Of six species-level traits, geographical region also significantly predicted flowering shifts, consistent with environment and geography together explaining broad phenological responses across this group. These shifts have produced significant changes to pairwise patterns of co-flowering among species--ranging from a 59 day increase in co-flowering to complete loss of co-flowering overlap. Sympatric pairs specifically have experienced both increases and decreases in co-flowering, within a significant geographic pattern of increased co-flowering mainly in eastern US and decreased co-flowering common in western US. Because Viola species are generalist pollinated and already known to hybridize, these new co-flowering patterns could further undermine reproductive barriers among species in this genus.

evolutionary biology↗

bioRxiv2025

Reinforcement and selection against migrants maintain sperm competitive and genetic differences among populations of Drosophila pseudoobscura

Sexual interactions among closely related species can select for divergence in reproductive traits as a mechanism to avoid the costs of hybridization. This selection, termed reinforcement, produces a canonical pattern of stronger isolation in populations that are sympatric with congeners, versus in allopatric populations. While reinforcement has been observed in many systems, the resulting pattern might be transient. There must be selection against migrants between allopatry and sympatry--akin to local reproductive adaptation--for a pattern of stronger sympatric isolation to be maintained. We tested for evidence of this selection against migrants in the context of sperm competition, in Drosophila pseudoobscura. Previously we showed an advantage of sympatric genotypes in sympatric contexts, via their elevated reproductive isolation (conspecific sperm precedence) against congeneric D. persimilis. Here, using experimental crosses that simulated migration between populations that are naturally sympatric and allopatric with D. persimilis, we show that sympatric genotypes are at a sperm-competitive disadvantage against allopatric male genotypes. This selection against sympatric males in allopatry, combined with the advantage of sympatric genotypes in sympatry, produce a scenario for strong selection against migrants between these two geographic contexts. This is accompanied by population differentiation in reproductive gene expression and allele frequency variation between allopatry and sympatry, including genes with known roles in sperm competition. While some of these changes are parallel among sympatric or allopatric contexts, most are unique to individual populations and might reflect the unique ways that selection has acted on sperm competition genes in different sympatric populations.

evolutionary biology↗

bioRxiv2025

Endemic and invasion dynamics of wild tomato species on the Gal&aacutepagos Islands, across two centuries of collection records

O_LIWe aggregated digitized herbarium and other collection records--spanning >225 years since 1795--to assess the biological, geographical, and historical factors shaping distributions of three wild tomato species on the Galapagos Islands, and to infer future threats to the two endemic species (Solanum cheesmaniae and S. galapagense) and risks posed by their invasive congener (S. pimpinellifolium). C_LIO_LICombining >400 unique geolocated Galapagos records with bioclimate data and species distribution modelling, we quantified the geo-spatial distribution of each species, bracketed the historical timing and location of introductions of the invasive species, characterized species bioclimate envelopes, and projected suitable habitat overlap. C_LIO_LIWe infer that dispersal limitation and alternative selective histories shape current species distributions, and that anthropogenic change has and will continue to have different impacts on the two endemic species--closely associated with their different geographic and environmental distributions. We also identify plausible avenues for, and limits to, future invasive expansion. C_LIO_LIThese data vastly extend the temporal and spatial reach of our direct historical inferences, provide a critical complement to genomic analyses of contemporary Galapagos populations, and demonstrate that scientific collections are especially valuable for interpreting factors shaping species distributions on high-endemism islands with recent rapid environmental change. C_LI

evolutionary biology↗

bioRxiv2024

Gene expression and pollen performance indicate altered postmating selection between Solanum species with different mating systems

Postmating prezygotic (PMPZ) traits play an important role in mating success, especially in species where gametes from multiple males compete. Despite this, the effect of mating system transitions, and attendant shifts in the intensity of sexual selection, on specific PMPZ traits and their underlying loci is still poorly understood. Here we assessed differences in pollen PMPZ traits and tissue-specific gene expression (in leaf, pollen, and style) between two closely related plant species with different mating systems--Solanum lycopersicum (selfing) & Solanum pennellii (outcrossing). We focused on species differences in loci with known roles in pollen tube growth rate, including pectin methylesterases (PMEs) and their inhibitors (PMEIs), and in- vitro & in-vivo pollen tube growth rates. Among the gene expression differences observed between species, we found that the expression domain of pollen-biased genes was much narrower in the selfing species S. lycopersicum compared to the outcrossing species S. pennellii, including for most reproductive PMEs and PMEIs. In addition, S. pennellii had faster pollen tube growth rates in-vivo, while S. lycopersicum had faster in-vitro pollen tube growth rates. We propose that the lower expression of pollen tube development genes in S. lycopersicum style tissue, and reduced in-vivo pollen performance, is a result of reduced allocation to stylar mechanisms that modulate pollen tube growth, potentially consistent with relaxed selection on cryptic female choice in the selfing species. Article SummaryThis study investigates the evidence for differential postmating sexual selection in plants, by analyzing reproductive gene expression and pollen performance in two Solanum species with different mating systems. It finds that species differ systematically in pollen tube growth rates, and that pollen ( male)-biased genes have higher secondary expression in stylar ( female) tissues in the outcrossing species. These observations are consistent with the outcrossing species experiencing stronger selection on female reproductive tract traits that influence male postmating performance. This study evaluates key expectations of sexual selection on postmating traits but does so in the uncommon context of flowering plants.

evolutionary biology↗

bioRxiv2024

Females drive postmating reproductive trait evolution across Drosophila species, but not via remating rate

While traits that contribute to premating sexual interactions are known to be wildly diverse, much less is known about the diversity of postmating (especially female) reproductive traits and the mechanisms shaping this diversity. To assess the rate, pattern, and potential drivers of postmating reproductive trait evolution, we analyzed male and female traits across up to 30 Drosophila species within a phylogenetic comparative framework. In addition to postmating reproductive morphology (e.g., sperm length, reproductive tract length and mass), we also quantified mating behaviors including female remating rate--a common proxy for the strength of postmating sexual selection. We found evidence for strong coevolution between male and female postmating traits (specifically sperm length and sperm storage organ size). However, remating rate was not associated with the rate of evolution or exaggeration of either male or female postmating reproductive morphology, once phylogenetic relatedness was accounted for. We infer that female-mediated and intersexual selection predominantly drive the evolution of our postmating morphological traits, including via divergent male and female interests in controlling paternity. In comparison, remating rate has a complex and likely secondary role in shaping this evolution, in part because this trait can be both a driver and a product of postmating selection.

evolutionary biology↗

bioRxiv2024

Long-sperm precedence and other cryptic female choices in Drosophila melanogaster

Females that mate multiply make postmating choices about which sperm fertilize their eggs (cryptic female choice); however, the male characteristics they use to make such choices remain unclear. In this study, we sought to understand female sperm use patterns by evaluating whether Drosophila melanogaster females adjust sperm use (second male paternity) in response to four main factors: male genotype, male courtship effort, male pheromone alteration, and male postmating reproductive morphology. Our experiment was replicated across four different D. melanogaster lines, in a full factorial design, including a pheromone manipulation in which second males were perfumed to resemble heterospecific (D. yakuba) males. We found that females prefer longer sperm--regardless of mating order--in almost all contexts; this observed pattern of long-sperm precedence is consistent with female postmating choice of high-fitness male traits. Nonetheless, we also found that this general preference can be plastically altered by females in response to effects including perfuming treatment; this differential female sperm use is between otherwise identical males, and therefore solely female-mediated. Furthermore, our finding that females exercise choice using diverse criteria suggests a possible mechanism for the maintenance of variation in sexually selected male traits. Teaser textHow do females make choices about which sperm will fertilize their eggs? In this study, we assess four geographically diverse Drosophila melanogaster lines to show that females strongly prefer long sperm--a pattern consistent with female preference for high-fitness males. In addition, we perfumed males to show that females can adjust this general preference based on other factors, including pheromones. Because this adjustment occurs between genotypically identical males, it is entirely female-mediated.

evolutionary biology↗

bioRxiv2022

CAGEE: computational analysis of gene expression evolution

Despite the increasing abundance of whole transcriptome data, few methods are available to analyze global gene expression across phylogenies. Here, we present a new software package (CAGEE) for inferring patterns of increases and decreases in gene expression across a phylogenetic tree, as well as the rate at which these changes occur. In contrast to previous methods that treat each gene independently, CAGEE can calculate genome-wide rates of gene expression, along with ancestral states for each gene. The statistical approach developed here makes it possible to infer lineage-specific shifts in rates of evolution across the genome, in addition to possible differences in rates among multiple tissues sampled from the same species. We demonstrate the accuracy and robustness of our method on simulated data, and apply it to a dataset of ovule gene expression collected from multiple self-compatible and self-incompatible species in the genus Solanum to test hypotheses about the evolutionary forces acting during mating system shifts. These comparisons allow us to highlight the power of CAGEE, demonstrating its utility for use in any empirical system and for the analysis of most morphological traits. Our software is available at https://github.com/hahnlab/CAGEE/.

bioinformatics↗

bioRxiv2021

Testing potential mechanisms of conspecific sperm precedence in Drosophila pseudoobscura

Drosophila pseudoobscura females that co-occur with sister species D. persimilis show elevated fertilization by conspecific sperm when they mate with both a heterospecific and a conspecific male. This phenomenon, known as conspecific sperm precedence (CSP), has evolved as a mechanism to avoid maladaptive hybridization with D. persimilis. In this study, we assessed pericopulatory (during mating) and postcopulatory (after mating) traits in crosses with sympatric or allopatric D. pseudoobscura females and conspecific or heterospecific males to evaluate potential mechanisms of CSP in this system. We observed shorter copulation duration in crosses with sympatric females, but found no difference in quantity of sperm transferred or female reproductive tract toxicity between sympatry and allopatry. Our data also support the hypothesis that parasperm, a short, sterile sperm morph, can protect fertile eusperm from the D. pseudoobscura female reproductive tract, though it is unclear how this might affect patterns of sperm use in sympatry vs. allopatry. Overall, these results suggest that copulation duration could potentially contribute to the elevated CSP observed in sympatry.

evolutionary biology↗

bioRxiv2020

Highly contiguous assemblies of 101 drosophilid genomes

Over 100 years of studies in Drosophila melanogaster and related species in the genus Drosophila have facilitated key discoveries in genetics, genomics, and evolution. While high-quality genome assemblies exist for several species in this group, they only encompass a small fraction of the genus. Recent advances in long read sequencing allow high quality genome assemblies for tens or even hundreds of species to be generated. Here, we utilize Oxford Nanopore sequencing to build an open community resource of high-quality assemblies for 101 lines of 95 drosophilid species encompassing 14 species groups and 35 sub-groups with an average contig N50 of 10.5 Mb and greater than 97% BUSCO completeness in 97/101 assemblies. These assemblies, along with detailed wet lab protocol and assembly pipelines, are released as a public resource and will serve as a starting point for addressing broad questions of genetics, ecology, and evolution within this key group.

evolutionary biology↗

bioRxiv2020

Reproductive proteins evolve faster than non-reproductive proteins among Solanum species

Elevated rates of evolution in reproductive proteins are commonly observed in animal species, and are thought to be driven by the action of sexual selection and sexual conflict acting specifically on reproductive traits. Whether similar patterns are broadly observed in other biological groups is equivocal. Here we examine patterns of protein divergence among wild tomato species (Solanum section Lycopersicon), to understand forces shaping the evolution of reproductive genes in this diverse, rapidly evolving plant clade. By comparing rates of molecular evolution among loci expressed in reproductive and non-reproductive tissues, our aims were to test if: a) reproductive-specific loci evolve more rapidly, on average, than non-reproductive loci; male-specific loci evolve at different rates than female-specific loci; c) genes expressed exclusively in gametophytic (haploid) tissue evolve differently from genes expressed in sporophytic (diploid) tissue or in both tissue types; and d) mating system variation (a potential proxy for the expected strength of sexual selection and/or sexual conflict) affects patterns of protein evolution. We observed elevated evolutionary rates in reproductive proteins. However this pattern was most evident for female- rather than male-specific loci, both broadly and for individual loci inferred to be positively selected. These elevated rates might be facilitated by greater tissue-specificity of reproductive proteins, as faster rates were also associated with more narrow expression domains. In contrast we found little evidence that evolutionary rates are consistently different in loci experiencing haploid selection (gametophytic-exclusive loci), or in lineages with quantitatively different mating systems. Overall while reproductive protein evolution is generally elevated in this diverse plant group, some specific patterns of evolution are more complex than those reported in other (largely animal) systems, and include a more prominent role for female-specific loci among adaptively evolving genes.

evolutionary biology↗

bioRxiv2020

Reconstructing the history and biological consequences of a plant invasion on the Galapagos islands

The introduction of non-native species into new habitats is one of the foremost risks to global biodiversity. Here, we evaluate a recent invasion of wild tomato (Solanum pimpinellifolium) onto the Galapagos islands from a population genomic perspective, using a large panel of novel collections from the archipelago as well as historical accessions from mainland Ecuador and Peru. We infer a recent invasion of S. pimpinellifolium on the islands, largely the result of a single event from central Ecuador which, despite its recency, has rapidly spread onto several islands in the Galapagos. By reconstructing patterns of local ancestry throughout the genomes of invasive plants, we uncover evidence for recent hybridization and introgression between S. pimpinellifolium and the closely related endemic species Solanum cheesmaniae. Two large introgressed regions overlap with known fruit color loci involved in carotenoid biosynthesis. Instead of red fruits, admixed individuals with endemic haplotypes at these loci have orange fruit colors that are typically characteristic of the endemic species. We therefore infer that introgression explains the observed trait convergence. Moreover, we infer roles for two independent loci in driving this pattern, and a likely history of selection favoring the repeated phenotypic transition from red to orange fruits. Together, our data reconstruct a complex history of invasion, expansion, and gene flow among wild tomatoes on the Galapagos islands. These findings provide critical data on the evolutionary importance of hybridization during colonization and its role in influencing conservation outcomes. Significance StatementThe isolation and unique diversity of the Galapagos Islands provide numerous natural experiments that have enriched our understanding of evolutionary biology. Here we use population genomic sequencing to reconstruct the timing, path, and consequences of a biological invasion by wild tomato onto the Galapagos. We infer that invasive populations originated from a recent human-mediated migration event from central Ecuador. Our data also indicate that invasive populations are hybridizing with endemic populations, and that this has led to some invasive individuals adopting both fruit color genes and the fruit color characteristic of the endemic island species. Our results demonstrate how hybridization can shape patterns of trait evolution over very short time scales, and characterize genetic factors underlying invasive success.

evolutionary biology↗

bioRxiv2020

A shift to shorter cuticular hydrocarbons causes sexual isolation in the Drosophila americana species group

Because sensory signals often evolve rapidly, they could be instrumental in the emergence of reproductive isolation between species. However, pinpointing their specific contribution to isolating barriers, and the mechanisms underlying their divergence, remains challenging. Here we demonstrate sexual isolation due to divergence in chemical signals between two populations of Drosophila americana (SC and NE) and one population of D. novamexicana, and dissect its underlying phenotypic and genetic mechanisms. Mating trials revealed strong sexual isolation between Drosophila novamexicana males and SC Drosophila americana females, as well as more moderate bi-directional isolation between D. americana populations. Mating behavior data indicates SC D. americana males have the highest courtship efficiency and, unlike males of the other populations, are accepted by females of all species. Quantification of cuticular hydrocarbon (CHC) profiles--chemosensory signals that are used for species recognition and mate finding in Drosophila--shows that the SC D. americana population differs from the other populations primarily on the basis of compound carbon chain-length. Moreover, manipulation of male CHC composition via heterospecific perfuming--specifically perfuming D. novamexicana males with SC D. americana males--abolishes their sexual isolation from these D. americana females. Of a set of candidates, a single gene--elongase CG17821--had patterns of gene expression consistent with a role in CHC differences between species. Sequence comparisons indicate D. novamexicana and our Nebraska (NE) D. americana population share a derived CG17821 truncation mutation that could also contribute to their shared "short" CHC phenotype. Together, these data suggest an evolutionary model for the origin and spread of this allele and its consequences for CHC divergence and sexual isolation in this group.

evolutionary biology↗

bioRxiv2020

Inferring the genetic basis of sex determination from the genome of a dioecious nightshade

Dissecting the genetic mechanisms underlying dioecy (i.e. separate female and male individuals) is critical for understanding the evolution of this pervasive reproductive strategy. Nonetheless, the genetic basis of sex determination remains unclear in many cases, especially in systems where dioecy has arisen recently. Within the economically important plant genus Solanum ([~]2000 species), dioecy is thought to have evolved independently at least 4 times across roughly 20 species. Here, we generate the first genome sequence of a dioecious Solanum and use it to ascertain the genetic basis of sex determination in this species. We de novo assembled and annotated the genome of S. appendiculatum (assembly size: [~]750 Mb; scaffold N50: 0.92 Mb; [~]35,000 genes), identified sex-specific sequences and their locations in the genome, and inferred that males in this species are the heterogametic sex. We also analyzed gene expression patterns in floral tissues of males and females, finding [~]100 genes that are differentially expressed between the sexes. These analyses, together with observed patterns of gene-family evolution specific to S. appendiculatum, consistently implicate a suite of genes from the regulatory network controlling pectin degradation and modification in the expression of sex. Furthermore, the genome of a species with a relatively young sex determination system provides the foundational resources for future studies on the independent evolution of dioecy in this speciose clade.

evolutionary biology↗

bioRxiv2019

Local extirpation is pervasive among populations of Galapagos endemic tomatoes

The Galapagos Islands are home to incredible endemic biodiversity that is of high conservation interest. Two such endemic species are the Galapagos tomatoes: Solanum cheesmaniae and Solanum galapagense. Both are known from historical location records, but like many endemic plant species on the Galapagos, their current conservation status is unclear. We revisited previously documented sites of endemic species on San Cristobal, Santa Cruz, and Isabela, and document the disappearance of >80% of these populations. In contrast, we find that two invasive relatives (Solanum pimpinellifolium and Solanum lycopersicum) are now highly abundant, and in some cases--based on morphological observations--might be hybridizing with endemics. Our findings suggest that expanding human developments and putative interspecific hybridization are among the major factors affecting the prevalence of invasives and the threatened persistence of the endemic populations.

evolutionary biology↗

bioRxiv2019

Transposable elements that cause dysgenesis also contribute to postzygotic isolation in the Drosophila virilis clade

Mismatches between parental genomes in selfish elements are frequently hypothesized to underlie hybrid dysfunction and drive speciation. However, because the genetic basis of most hybrid incompatibilities is unknown, testing the contribution of selfish elements to reproductive isolation is difficult. Here we evaluated the role of transposable elements (TEs) in hybrid incompatibilities between Drosophila virilis and D. lummei by experimentally comparing hybrid incompatibility in a cross where active TEs are present in D. virilis (TE+) and absent in D. lummei, to a cross where these TEs are absent from both D. virilis (TE-) and D. lummei genotypes. Using genomic data, we confirmed copy number differences in TEs between the D. virilis (TE+) strain and both the D. virilis (TE-) strain and D. lummei. We observed F1 postzygotic reproductive isolation exclusively in the interspecific cross involving TE+ D. virilis but not in crosses involving TE- D. virilis. This mirrors intraspecies dysgenesis where atrophied testes only occur when TE+ D. virilis is the paternal parent. A series of backcross experiments, that accounted for alternative models of hybrid incompatibility, showed that both F1 hybrid incompatibility and intrastrain dysgenesis are consistent with the action of TEs rather than genic interactions. Thus, our data suggest that this TE mechanism manifests as two different incompatibility phenotypes. A further Y-autosome interaction contributes to additional, sex-specific, inviability in one direction of this cross combination. These experiments demonstrate that TEs that cause intraspecies dysgenesis can increase reproductive isolation between closely related lineages, thereby adding to the processes that consolidate speciation.

evolutionary biology↗

bioRxiv2019

Regional differences in the abiotic environment contribute to genomic divergence within a wild tomato species

The wild currant tomato Solanum pimpinellifolium inhabits a wide range of abiotic habitats across its native range of Ecuador and Peru. Although it has served as a key genetic resource for the improvement of domestic cultivars, little is known about the genetic basis of traits underlying local adaptation in this species, nor what abiotic variables are most important for driving differentiation. Here we use redundancy analysis (RDA) and other multivariate statistical methods (structural equation modeling (SEM) and generalized dissimilarity modeling (GDM)) to quantify the relationship of genomic variation (6,830 single nucleotide polymorphisms) with climate and geography, among 140 wild accessions. RDA, SEM, and GDM each identified environment as explaining more genomic variation than geography, suggesting that local adaptation to heterogeneous abiotic habitats may be an important source of genetic diversity in this species. Environmental factors describing temporal variation in precipitation and evaporative demand explained the most SNP variation among accessions, indicating that these forces may represent key selective agents. Lastly, by studying how SNP-environment associations vary throughout the genome (44,064 SNPs), we mapped the location and investigated the functions of loci putatively contributing to climatic adaptations. Together our findings indicate an important role for selection imposed by the abiotic environment in driving genomic differentiation between populations.

evolutionary biology↗

bioRxiv2019

Intraspecific genetic variation underlying postmating reproductive barriers between species in the wild tomato clade (Solanum sect. Lycopersicon)

A goal of speciation genetics is to understand how the genetic components underlying interspecific reproductive barriers originate within species. Unilateral incompatibility (UI) is a postmating prezygotic barrier in which pollen rejection in the female reproductive tract (style) occurs in only one direction of an interspecific cross. Natural variation in the strength of UI has been observed among populations within species in the wild tomato clade. In some cases, molecular loci underlying self-incompatibility (SI) are associated with this variation in UI, but the mechanistic connection between these intra- and inter-specific pollen rejection behaviors is poorly understood in most instances. We generated an F2 population between SI and SC genotypes of a single species, Solanum pennellii, to examine the genetic basis of intraspecific variation in the strength of UI against other species, and to determine whether loci underlying SI are genetically associated with this variation. We found that F2 individuals vary in the rate at which UI rejection occurs. One large effect QTL detected for this trait co-localized with the SI-determining S-locus. Moreover, individuals that expressed S-RNase--the S-locus protein involved in SI pollen rejection--in their styles had much more rapid UI responses compared to those without S-RNase protein. Our analysis shows that intraspecific variation at mate choice loci--in this case at loci that prevent self-fertilization--can contribute to variation in the strength of interspecific isolation, including postmating prezygotic barriers. Understanding the nature of such standing variation can provide insight into the accumulation of these barriers between diverging lineages.

evolutionary biology↗

bioRxiv2019

Spatial proximity determines post-speciation introgression in Solanum

An increasing number of phylogenomic studies have documented a clear footprint of post-speciation introgression among closely-related species. Nonetheless, systematic genome-wide studies of factors influencing the likelihood of introgression remain rare. Here, we use an a priori hypothesis-testing framework, and introgression statistics, to evaluate the prevalence and frequency of introgression. Specifically, with whole genome sequences from 32 lineages of wild tomato species, we assess the effect of three factors on introgression: genetic relatedness, geographical proximity, and mating system differences. Using multiple trios within the ABBA-BABA test, we find that one of our factors, geographic proximity, is consistently associated with evidence for recent introgression between species. Of 14 species pairs with proximate versus distant population comparisons, 12 showed evidence of introgression; in ten of these cases, this was more prevalent between geographically-closer populations. We found no evidence that introgression varies systematically with increasing genetic divergence between lineages or with mating system differences, although we have limited power to address the latter effect. While our analysis indicates that recent post-speciation introgression is frequent in this group, estimated levels of genetic exchange are modest (0.05-1.5% of the genome), so the relative importance of hybridization in shaping the evolutionary trajectories of these species could be limited. Regardless, similar clade-wide analyses of genomic introgression would be valuable for disentangling the major ecological, reproductive, and historical determinants of post-speciation gene flow, and for assessing the relative importance of introgression as a source of evolutionary change. IMPACT STATEMENTThe formation of new species is traditionally viewed as a tree-like branching process, in which species are discrete branches that no longer share an ongoing genealogical connection with other, equally discrete, species. Recently this view has been challenged by numerous studies examining genealogical patterns across entire genomes (all the DNA of an organism); these studies suggest that the exchange of genes between different species (known as introgression) is much more common than previously appreciated. This unexpected observation raises questions about which conditions are most important in determining whether species continue to exchange genes after they diverge. Factors such as physical proximity, differences in reproductive mechanisms, and time since species shared a common ancestor, might all contribute to determining the prevalence of introgression. But to evaluate the general importance of these factors requires more than individual cases; many species comparisons, that differ systematically in one or more of these conditions, are needed. Here we use whole-genome information from 32 lineages to evaluate patterns of introgression among multiple species in a single, closely related group--the wild tomatoes of south America. We contrast these patterns among pairs of lineages that differ in their geographical proximity, reproductive system, and time since common ancestry, to assess the individual influence of each condition on the prevalence of introgression. We find that only one of our factors--geographical proximity--is consistently associated with greater evidence for recent introgression, indicating that this is largely shaped by the geographical opportunity for hybridization, rather than other plausible biological processes. Our study is one of the first to systematically assess the influence of general ecological and evolutionary conditions on the frequency of post-speciation introgression. It also provides a straightforward, generalizable, hypothesis-testing framework for similar systematic analyses of introgression in groups of other organisms in the future.

evolutionary biology↗