Genomic evidence for human-mediated introgressive hybridization and selection in the developed breed.

BACKGROUND: The pig (Sus Scrofa) is one of the oldest domesticated livestock species that has undergone extensive improvement through modern breeding. European breeds have advantages in lean meat development and highly-productive body type, whereas Asian breeds possess extraordinary fat deposition and reproductive performance. Consequently, Eurasian breeds have been extensively used to develop modern commercial breeds for fast-growing and high prolificacy. However, limited by the sequencing technology, the genome architecture of some nascent developed breeds and the human-mediated impact on their genomes are still unknown. RESULTS: Through whole-genome analysis of 178 individuals from an Asian locally developed pig breed, Beijing Black pig, and its two ancestors from two different continents, we found the pervasive inconsistent gene trees and species trees across the genome of Beijing Black pig, which suggests its introgressive hybrid origin. Interestingly, we discovered that this developed breed has more genetic relationships with European pigs and an unexpected introgression from Asian pigs to this breed, which indicated that human-mediated introgression could form the porcine genome architecture in a completely different type compared to native introgression. We identified 554 genomic regions occupied 63.30 Mb with signals of introgression from the Asian ancestry to Beijing Black pig, and the genes in these regions enriched in pathways associated with meat quality, fertility, and disease-resistant. Additionally, a proportion of 7.77% of genomic regions were recognized as regions that have been under selection. Moreover, combined with the results of a genome-wide association study for meat quality traits in the 1537 Beijing Black pig population, two important candidate genes related to meat quality traits were identified. DNAJC6 is related to intramuscular fat content and fat deposition, and RUFY4 is related to meat pH and tenderness. CONCLUSIONS: Our research provides insight for analyzing the origins of nascent developed breeds and genome-wide selection remaining in the developed breeds mediated by humans during modern breeding.

Genetic introgression from commercial European pigs to the indigenous Chinese Lijiang breed and associated changes in phenotypes.

BACKGROUND: Gene flow is crucial for enhancing economic traits of livestock. In China, breeders have used hybridization strategies for decades to improve livestock performance. Here, we performed whole-genome sequencing of a native Chinese Lijiang pig (LJP) breed. By integrating previously published data, we explored the genetic structure and introgression of genetic components from commercial European pigs (EP) into the LJP, and examined the impact of this introgression on phenotypic traits. RESULTS: Our analysis revealed significant introgression of EP breeds into the LJP and other domestic pig breeds in China. Using a haplotype-based approach, we quantified introgression levels and compared EP to LJP and other Chinese domestic pigs. The results show that EP introgression is widely prevalent in Chinese domestic pigs, although there are significant differences between breeds. We propose that LJP could potentially act as a mediator for the transmission of EP haplotypes. We also examined the correlation between EP introgression and the number of thoracic vertebrae in LJP and identified VRTN and STUM as candidate genes for this trait. CONCLUSIONS: Our study provides evidence of introgressed European haplotypes in the LJP breed and describes the potential role of EP introgression on phenotypic changes of this indigenous breed.

Hybrid speciation driven by multilocus introgression of ecological traits.

Hybridization allows adaptations to be shared among lineages and may trigger the evolution of new species1,2. However, convincing examples of homoploid hybrid speciation remain rare because it is challenging to demonstrate that hybridization was crucial in generating reproductive isolation3. Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies. We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years. This is despite pervasive and ongoing gene flow with one parent, Heliconius pardalinus, which homogenizes 99% of their genomes. The remaining 1% introgressed from the other parent, Heliconius melpomene, and is scattered widely across the H. elevatus genome in islands of divergence from H. pardalinus. These islands contain multiple traits that are under disruptive selection, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Collectively, these traits place H. elevatus on its own adaptive peak and permit coexistence with both parents. Our results show that speciation was driven by introgression of ecological traits, and that speciation with gene flow is possible with a multilocus genetic architecture.

Long-read sequencing of extrachromosomal circular DNA and genome assembly of a Solanum lycopersicum breeding line revealed active LTR retrotransposons originating from S. Peruvianum L. introgressions.

Transposable elements (TEs) are a major force in the evolution of plant genomes. Differences in the transposition activities and landscapes of TEs can vary substantially, even in closely related species. Interspecific hybridization, a widely employed technique in tomato breeding, results in the creation of novel combinations of TEs from distinct species. The implications of this process for TE transposition activity have not been studied in modern cultivars. In this study, we used nanopore sequencing of extrachromosomal circular DNA (eccDNA) and identified two highly active Ty1/Copia LTR retrotransposon families of tomato (Solanum lycopersicum), called Salsa and Ketchup. Elements of these families produce thousands of eccDNAs under controlled conditions and epigenetic stress. EccDNA sequence analysis revealed that the major parts of eccDNA produced by Ketchup and Salsa exhibited low similarity to the S. lycopersicum genomic sequence. To trace the origin of these TEs, whole-genome nanopore sequencing and de novo genome assembly were performed. We found that these TEs occurred in a tomato breeding line via interspecific introgression from S. peruvianum. Our findings collectively show that interspecific introgressions can contribute to both genetic and phenotypic diversity not only by introducing novel genetic variants, but also by importing active transposable elements from other species.

Traditional multilocus phylogeny fails to fully resolve Palearctic ground squirrels (Spermophilus) relationships but reveals a new species endemic to West Siberia.

Previous efforts to reconstruct evolutionary history of Palearctic ground squirrels within the genus Spermophilus have primarily relied on a single mitochondrial marker for phylogenetic data. In this study, we present the first phylogeny with comprehensive taxon sampling of Spermophilus via a conventional multilocus approach utilizing five mitochondrial and five nuclear markers. Through application of the multispecies coalescent model, we constructed a species tree revealing four distinct clades that diverged during the Late Miocene. These clades are 1) S. alaschanicus and S. dauricus from East Asia; 2) S. musicus and S. pygmaeus from East Europe and northwestern Central Asia; 3) the subgenus Colobotis found across Central Asia and its adjacent regions and encompassing S. brevicauda, S. erythrogenys, S. fulvus, S. major, S. pallidicauda, S. ralli, S. relictus, S. selevini, and S. vorontsovi sp. nov.; and 4) a Central/Eastern Europe and Asia Minor clade comprising S. citellus, S. taurensis, S. xanthoprymnus, S. suslicus, and S. odessanus. The latter clade lacked strong support owing to uncertainty of taxonomic placement of S. odessanus and S. suslicus. Resolving relationships within the subgenus Colobotis, which radiated rapidly, remains challenging likely because of incomplete lineage sorting and introgressive hybridization. Most of modern Spermophilus species diversified during the Early-Middle Pleistocene (2.2-1.0 million years ago). We propose a revised taxonomic classification for the genus Spermophilus by recognizing 18 species including a newly identified one (S. vorontsovi sp. nov.), which is found only in a limited area in the southeast of West Siberia. Employing genome-wide single-nucleotide polymorphism genotyping, we substantiated the role of the Ob River as a major barrier ensuring robust isolation of this taxon from S. erythrogenys. Despite its inherent limitations, the traditional multilocus approach remains a valuable tool for resolving relationships and can provide important insights into otherwise poorly understood groups. It is imperative to recognize that additional efforts are needed to definitively determine phylogenetic relationships between certain species of Palearctic ground squirrels.

Adaptive introgression of a visual preference gene.

Visual preferences are important drivers of mate choice and sexual selection, but little is known of how they evolve at the genetic level. In this study, we took advantage of the diversity of bright warning patterns displayed by Heliconius butterflies, which are also used during mate choice. Combining behavioral, population genomic, and expression analyses, we show that two Heliconius species have evolved the same preferences for red patterns by exchanging genetic material through hybridization. Neural expression of regucalcin1 correlates with visual preference across populations, and disruption of regucalcin1 with CRISPR-Cas9 impairs courtship toward conspecific females, providing a direct link between gene and behavior. Our results support a role for hybridization during behavioral evolution and show how visually guided behaviors contributing to adaptation and speciation are encoded within the genome.

Secondary Contact, Introgressive Hybridization, and Genome Stabilization in Sticklebacks.

Advances in genomic studies have revealed that hybridization in nature is pervasive and raised questions about the dynamics of different genetic and evolutionary factors following the initial hybridization event. While recent research has proposed that the genomic outcomes of hybridization might be predictable to some extent, many uncertainties remain. With comprehensive whole-genome sequence data, we investigated the genetic introgression between 2 divergent lineages of 9-spined sticklebacks (Pungitius pungitius) in the Baltic Sea. We found that the intensity and direction of selection on the introgressed variation has varied across different genomic elements: while functionally important regions displayed reduced rates of introgression, promoter regions showed enrichment. Despite the general trend of negative selection, we identified specific genomic regions that were enriched for introgressed variants, and within these regions, we detected footprints of selection, indicating adaptive introgression. Geographically, we found the selection against the functional changes to be strongest in the vicinity of the secondary contact zone and weaken as a function of distance from the initial contact. Altogether, the results suggest that the stabilization of introgressed variation in the genomes is a complex, multistage process involving both negative and positive selection. In spite of the predominance of negative selection against introgressed variants, we also found evidence for adaptive introgression variants likely associated with adaptation to Baltic Sea environmental conditions.

The role of introgressive hybridization in shaping the geographically isolated gene pools of wax palm populations (genus Ceroxylon).

The speciation continuum is the process by which genetic groups diverge until they reach reproductive isolation. It has become common in the literature to show that this process is gradual and flickering, with possibly many instances of secondary contact and introgression after divergence has started. The level of divergence might vary among genomic regions due to, among others, the different forces and roles of selection played by the shared regions. Through hybrid capture, we sequenced ca. 4,000 nuclear regions in populations of six species of wax palms, five of which form a monophyletic group (genus Ceroxylon, Arecaceae: Ceroxyloideae). We show that in this group, the different populations show varying degrees of introgressive hybridization, and two of them are backcrosses of the other three 'pure' species. This is particularly interesting because these three species are dioecious, have a shared main pollinator, and have slightly overlapping reproductive seasons but highly divergent morphologies. Our work supports shows wax palms diverge under positive and background selection in allopatry, and hybridize due to secondary contact and inefficient reproductive barriers, which sustain genetic diversity. Introgressed regions are generally not under positive selection. Peripheral populations are backcrosses of other species; thus, introgressive hybridization is likely modulated by demographic effects rather than selective pressures. In general, these species might function as an 'evolutionary syngameon' where expanding, peripheral, small, and isolated populations maintain diversity by crossing with available individuals of other wax palms. In the Andean context, species can benefit from gained variation from a second taxon or the enhancement of population sizes by recreating a common genetic pool.

Role of genetic introgression in introducing mutant alleles in Bos indicus cattle and prevalence of lethal genetic disorders in Bos taurus × Bos indicus and Bos indicus cattle in India.

Fertility is an important trait associated with reproductive performance and animal welfare concern. Lethal alleles affect fertility through early embryonic death, abortions, and stillbirth depending on the genetic expression of the allele. Holstein Friesian and Jersey are two major Bos taurus breeds used widely for increasing milk yield along with purebreds of Bos indicus breeds like Gir, Kankrej, Sahiwal, and Tharparkar. In the present study, prevalence of lethal mutants in crossbred Holstein Friesian (CBHF, n = 2435), crossbred Jersey (CBJY, n = 2874), Gir (n = 3288), Kankrej (n = 593), Sahiwal (n = 965), and Tharparkar (n = 18) were studied. Heterozygous carrier animals were identified for bovine leukocyte adhesion deficiency (BLAD), Citrullinemia, complex vertebral malformation (CVM), Brachyspina, Holstein Haplotype 1 (HH1), Holstein Haplotype 3 (HH3),Holstein Haplotype 4 (HH4) and Jersey Haplotype 1 (JH1). Breed purity analysis confirmed inheritance of Bos taurus genes contributing to the presence of lethal mutant alleles like BLAD, Citrullinemia, HH1, and JH1 in apparently phenotypic Bos indicus animals. Screening and elimination of heterozygous carrier bulls/cows is essential to control fertility loss associated with lethal alleles.

Past human expansions shaped the spatial pattern of Neanderthal ancestry.

The worldwide expansion of modern humans (Homo sapiens) started before the extinction of Neanderthals (Homo neanderthalensis). Both species coexisted and interbred, leading to slightly higher introgression in East Asians than in Europeans. This distinct ancestry level has been argued to result from selection, but range expansions of modern humans could provide an alternative explanation. This hypothesis would lead to spatial introgression gradients, increasing with distance from the expansion source. We investigate the presence of Neanderthal introgression gradients after past human expansions by analyzing Eurasian paleogenomes. We show that the out-of-Africa expansion resulted in spatial gradients of Neanderthal ancestry that persisted through time. While keeping the same gradient orientation, the expansion of early Neolithic farmers contributed decisively to reducing the Neanderthal introgression in European populations compared to Asian populations. This is because Neolithic farmers carried less Neanderthal DNA than preceding Paleolithic hunter-gatherers. This study shows that inferences about past human population dynamics can be made from the spatiotemporal variation in archaic introgression.

Genomic introgressions from African rice (Oryza glaberrima) in Asian rice (O. sativa) lead to the identification of key QTLs for panicle architecture.

BACKGROUND: Developing high yielding varieties is a major challenge for breeders tackling the challenges of climate change in agriculture. The panicle (inflorescence) architecture of rice is one of the key components of yield potential and displays high inter- and intra-specific variability. The genus Oryza features two different crop species: Asian rice (Oryza sativa L.) and the African rice (O. glaberrima Steud.). One of the main morphological differences between the two independently domesticated species is the structure (or complexity) of the panicle, with O. sativa displaying a highly branched panicle, which in turn produces a larger number of grains than that of O. glaberrima. The gene regulatory network that governs intra- and interspecific panicle diversity is still under-studied. RESULTS: To identify genetic factors linked to panicle architecture diversity in the two species, we used a set of 60 Chromosome Segment Substitution Lines (CSSLs) issued from third generation backcross (BC3DH) and carrying genomic segments from O. glaberrima cv. MG12 in the genetic background of O. sativa Tropical Japonica cv. Caiapó. Phenotypic data were collected for rachis and primary branch length, primary, secondary and tertiary branch number and spikelet number. A total of 15 QTLs were localized on chromosomes 1, 2, 3, 7, 11 and 12, QTLs associated with enhanced secondary and tertiary branch numbers were detected in two CSSLs. Furthermore, BC4F3:5 lines carrying different combinations of substituted segments were produced to decipher the effects of the identified QTL regions on variations in panicle architecture. A detailed analysis of phenotypes versus genotypes was carried out between the two parental genomes within these regions in order to understand how O. glaberrima introgression events may lead to alterations in panicle traits. CONCLUSION: Our analysis led to the detection of genomic variations between O. sativa cv. Caiapó and O. glaberrima cv. MG12 in regions associated with enhanced panicle traits in specific CSSLs. These regions contain a number of key genes that regulate panicle development in O. sativa and their interspecific genomic variations may explain the phenotypic effects observed.

Community-wide genome sequencing reveals 30 years of Darwin's finch evolution.

A fundamental goal in evolutionary biology is to understand the genetic architecture of adaptive traits. Using whole-genome data of 3955 of Darwin's finches on the Galápagos Island of Daphne Major, we identified six loci of large effect that explain 45% of the variation in the highly heritable beak size of Geospiza fortis, a key ecological trait. The major locus is a supergene comprising four genes. Abrupt changes in allele frequencies at the loci accompanied a strong change in beak size caused by natural selection during a drought. A gradual change in Geospiza scandens occurred across 30 years as a result of introgressive hybridization with G. fortis. This study shows how a few loci with large effect on a fitness-related trait contribute to the genetic potential for rapid adaptive radiation.

A case of forensic genomics in Uganda reveals animal ownership and low exotic genetic introgression in indigenous cattle.

BACKGROUND: The cattle industry contributes to Uganda's agricultural output. It faces challenges that include theft and parentage ascertainment. These challenges can benefit from recent molecular genomics and bioinformatics technologies. OBJECTIVES: We employed genomic analyses to establish potential ownership of a group of nine cattle that were being claimed by two farmers in Uganda. We investigated the genetic relationship of Ugandan cattle with regional indigenous breeds as well as exotic breeds that are currently present in Uganda. In addition, we investigated regions that are likely to be under selection in the Ugandan cattle. METHODS: Hair samples were collected from seven and two animals from farmers A and B, respectively. They were genotyped for 53,218 Single Nucleotide Polymorphism markers. To establish genetic relationships between the sampled animals, we performed genomic analyses including, principal component analysis (PCA), hierarchical clustering analysis and identity by state/descent. We also performed admixture and runs of homozygosity analyses to assess the ancestry composition and identify regions potentially under selection in Ugandan cattle, respectively. RESULTS: The seven animals from Farmer A were genetically close to each other but showed minimal relationship with the disputed animals. The two animals from Farmer B were genetically distant from each other but showed greater similarity to four of the disputed animals. Four of the disputed animals showed great dissimilarity from the animals of both farmers. Comparison of these with the reference breeds revealed minimal European exotic genetic introgression into these animals, but rather high similarity to the Sheko. Results also revealed high homozygosity in the major histocompatibility complex regions. CONCLUSIONS: Our results demonstrate the use of currently available genomic tools to empirically establish the ownership of cattle; these could be scaled up as a resourceful and viable tool that could be employed to support conflict resolution where reliable livestock identification is unavailable.

Einkorn genomics sheds light on history of the oldest domesticated wheat.

Einkorn (Triticum monococcum) was the first domesticated wheat species, and was central to the birth of agriculture and the Neolithic Revolution in the Fertile Crescent around 10,000 years ago1,2. Here we generate and analyse 5.2-Gb genome assemblies for wild and domesticated einkorn, including completely assembled centromeres. Einkorn centromeres are highly dynamic, showing evidence of ancient and recent centromere shifts caused by structural rearrangements. Whole-genome sequencing analysis of a diversity panel uncovered the population structure and evolutionary history of einkorn, revealing complex patterns of hybridizations and introgressions after the dispersal of domesticated einkorn from the Fertile Crescent. We also show that around 1% of the modern bread wheat (Triticum aestivum) A subgenome originates from einkorn. These resources and findings highlight the history of einkorn evolution and provide a basis to accelerate the genomics-assisted improvement of einkorn and bread wheat.

Morphological and molecular diversity in mid-late and late maturity genotypes of cauliflower.

Genetic diversity is the prerequisite for the success of crop improvement programmes. Keeping in view, the current investigation was undertaken to assess the agro-morphological and molecular diversity involving 36 diverse mid-late and late cauliflower genotypes following α-RBD design during winter season 2021-22. Six morphological descriptors predicted as polymorphic using Shannon diversity index with maximum for leaf margin (0.94). The genotypes grouped into nine clusters based on D2 analysis with four as monogenotypic and gross plant weight (32.38%) revealed maximum contribution towards the genetic diversity. Molecular diversity analysis revealed 2-7 alleles among 36 polymorphic simple sequence repeats (SSR) with average of 4.22. Primer BoESSR492 (0.77) showed maximum polymorphic information content (PIC) with mean of 0.58. SSR analysis revealed two clusters each with two subclusters with a composite pattern of genotype distribution. STRUCTURE analysis showed homogenous mixture with least amount of gene pool introgression within the genotypes. Thus, based on morphological and molecular studies, the diverse genotypes namely, DPCaCMS-1, DPCaf-W4, DPCaf-US, DPCaf-W131W, DPCaf-S121, DPCaf-18, DPCaf-13, DPCaf-29 and DPCaf-CMS5 can be utilized in hybridization to isolate potential transgressive segregants to broaden the genetic base of cauliflower or involve them to exploit heterosis.

Integrating sex-bias into studies of archaic introgression on chromosome X.

Evidence of interbreeding between archaic hominins and humans comes from methods that infer the locations of segments of archaic haplotypes, or 'archaic coverage' using the genomes of people living today. As more estimates of archaic coverage have emerged, it has become clear that most of this coverage is found on the autosomes- very little is retained on chromosome X. Here, we summarize published estimates of archaic coverage on autosomes and chromosome X from extant human samples. We find on average 7 times more archaic coverage on autosomes than chromosome X, and identify broad continental patterns in this ratio: greatest in European samples, and least in South Asian samples. We also perform extensive simulation studies to investigate how the amount of archaic coverage, lengths of coverage, and rates of purging of archaic coverage are affected by sex-bias caused by an unequal sex ratio within the archaic introgressors. Our results generally confirm that, with increasing male sex-bias, less archaic coverage is retained on chromosome X. Ours is the first study to explicitly model such sex-bias and its potential role in creating the dearth of archaic coverage on chromosome X.

Dissecting human population variation in single-cell responses to SARS-CoV-2.

Humans display substantial interindividual clinical variability after SARS-CoV-2 infection1-3, the genetic and immunological basis of which has begun to be deciphered4. However, the extent and drivers of population differences in immune responses to SARS-CoV-2 remain unclear. Here we report single-cell RNA-sequencing data for peripheral blood mononuclear cells-from 222 healthy donors of diverse ancestries-that were stimulated with SARS-CoV-2 or influenza A virus. We show that SARS-CoV-2 induces weaker, but more heterogeneous, interferon-stimulated gene activity compared with influenza A virus, and a unique pro-inflammatory signature in myeloid cells. Transcriptional responses to viruses display marked population differences, primarily driven by changes in cell abundance including increased lymphoid differentiation associated with latent cytomegalovirus infection. Expression quantitative trait loci and mediation analyses reveal a broad effect of cell composition on population disparities in immune responses, with genetic variants exerting a strong effect on specific loci. Furthermore, we show that natural selection has increased population differences in immune responses, particularly for variants associated with SARS-CoV-2 response in East Asians, and document the cellular and molecular mechanisms by which Neanderthal introgression has altered immune functions, such as the response of myeloid cells to viruses. Finally, colocalization and transcriptome-wide association analyses reveal an overlap between the genetic basis of immune responses to SARS-CoV-2 and COVID-19 severity, providing insights into the factors contributing to current disparities in COVID-19 risk.

Detecting introgressive hybridization to maintain genetic integrity in endangered large waterbird: a case study in milky stork.

Hybridization between milky stork (Mycteria cinerea) and painted stork (M. leucocephala) occurs frequently in captivity. Dusit Zoo is a captive breeding facility where storks with phenotypically ambiguous patterns have recently been observed, and their status remaining inconclusive. Here, we used a combination of phenotypic characters and genetic markers (cytochrome b and 14 microsatellite markers) to distinguish and identify hybrids from the two parental species (n = 114). Haplotype analysis revealed asymmetric mtDNA introgression from M. cinerea to M. leucocephala, with twelve morphologically classified M. leucocephala individuals carrying heterospecific mtDNA. Comprehensive biparental genetic assessments identified 33% of all three genetic clusters as admixed individuals, of which most were either F2 hybrids, backcrosses with M. leucocephala, or hybrids of unknown generation, implying weak premating isolation with the absence of intrinsic postzygotic isolation between parentals. Morphological analysis demonstrated that the absence or indistinctness of a black bar across the breast is the most noticeable trait to identify these hybrids. The endangered M. cinerea was found to have genomic contamination from M. leucocephala and vice versa, with at least 41 hybrid individuals being identified. These findings provide critical information for detecting hybrids and identifying suitable breeding stocks with genetic purity for future reintroduction and conservation management.

A weakly structured stem for human origins in Africa.

Despite broad agreement that Homo sapiens originated in Africa, considerable uncertainty surrounds specific models of divergence and migration across the continent1. Progress is hampered by a shortage of fossil and genomic data, as well as variability in previous estimates of divergence times1. Here we seek to discriminate among such models by considering linkage disequilibrium and diversity-based statistics, optimized for rapid, complex demographic inference2. We infer detailed demographic models for populations across Africa, including eastern and western representatives, and newly sequenced whole genomes from 44 Nama (Khoe-San) individuals from southern Africa. We infer a reticulated African population history in which present-day population structure dates back to Marine Isotope Stage 5. The earliest population divergence among contemporary populations occurred 120,000 to 135,000 years ago and was preceded by links between two or more weakly differentiated ancestral Homo populations connected by gene flow over hundreds of thousands of years. Such weakly structured stem models explain patterns of polymorphism that had previously been attributed to contributions from archaic hominins in Africa2-7. In contrast to models with archaic introgression, we predict that fossil remains from coexisting ancestral populations should be genetically and morphologically similar, and that only an inferred 1-4% of genetic differentiation among contemporary human populations can be attributed to genetic drift between stem populations. We show that model misspecification explains the variation in previous estimates of divergence times, and argue that studying a range of models is key to making robust inferences about deep history.

Prepping for climate change by introgressive hybridization.

Species and populations may adapt to climate change by microevolutionary processes. However, standing genetic variation can be insufficient for this to occur. An interesting new study of a system of rainbowfish species shows that intraspecific hybridization enriches gene pools with adaptive variation that may allow persistence in a changing climate.