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The wing patterns of butterflies and moths (Lepidoptera) are diverse and striking examples of evolutionary diversification by natural selection. Lepidopteran wing colour patterns are a key innovation, consisting of arrays of coloured scales. We still lack a general understanding of how these patterns are controlled and whether this control shows any commonality across the 160,000 moth and 17,000 butterfly species. Here, we use fine-scale mapping with population genomics and gene expression analyses to identify a gene, cortex, that regulates pattern switches in multiple species across the mimetic radiation in Heliconius butterflies. cortex belongs to a fast-evolving subfamily of the otherwise highly conserved fizzy family of cell-cycle regulators, suggesting that it probably regulates pigmentation patterning by regulating scale cell development. In parallel with findings in the peppered moth (Biston betularia), our results suggest that this mechanism is common within Lepidoptera and that cortex has become a major target for natural selection acting on colour and pattern variation in this group of insects.
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Mimetismo Biológico/genética , Mariposas Diurnas/genética , Genes de Insecto/genética , Pigmentación/genética , Alas de Animales/fisiología , Animales , Mimetismo Biológico/fisiología , Mariposas Diurnas/citología , Mariposas Diurnas/fisiología , Color , Evolución Molecular , Femenino , Regulación del Desarrollo de la Expresión Génica , Masculino , Fenotipo , Pigmentación/fisiología , Selección Genética/genéticaRESUMEN
BACKGROUND: The hybridizing field crickets, Gryllus firmus and Gryllus pennsylvanicus have several barriers that prevent gene flow between species. The behavioral pre-zygotic mating barrier, where males court conspecifics more intensely than heterospecifics, is important because by acting earlier in the life cycle it has the potential to prevent a larger fraction of hybridization. The mechanism behind such male mate preference is unknown. Here we investigate if the female cuticular hydrocarbon (CHC) profile could be the signal behind male courtship. RESULTS: While males of the two species display nearly identical CHC profiles, females have different, albeit overlapping profiles and some females (between 15 and 45%) of both species display a male-like profile distinct from profiles of typical females. We classified CHC females profile into three categories: G. firmus-like (F; including mainly G. firmus females), G. pennsylvanicus-like (P; including mainly G. pennsylvanicus females), and male-like (ML; including females of both species). Gryllus firmus males courted ML and F females more often and faster than they courted P females (p < 0.05). Gryllus pennsylvanicus males were slower to court than G. firmus males, but courted ML females more often (p < 0.05) than their own conspecific P females (no difference between P and F). Both males courted heterospecific ML females more often than other heterospecific females (p < 0.05, significant only for G. firmus males). CONCLUSIONS: Our results suggest that male mate preference is at least partially informed by female CHC profile and that ML females elicit high courtship behavior in both species. Since ML females exist in both species and are preferred over other heterospecific females, it is likely that this female type is responsible for most hybrid offspring production.
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Escamas de Animales/química , Cortejo , Gryllidae/fisiología , Hibridación Genética/fisiología , Hidrocarburos/análisis , Conducta Sexual Animal/fisiología , Escamas de Animales/metabolismo , Animales , Femenino , Gryllidae/genética , Hidrocarburos/metabolismo , Masculino , Reproducción/fisiologíaRESUMEN
BACKGROUND: Pre-zygotic barriers often involve some form of sexual selection, usually interpreted as female choice, as females are typically the choosier sex. However, males typically show some mate preferences, which are increasingly reported. Here we document previously uncharacterized male courtship behavior (effort and song) and cuticular hydrocarbon (CHC) profiles in the hybridizing crickets Gryllus firmus and G. pennsylvanicus. These two species exhibit multiple barriers to gene exchange that act throughout their life history, including a behavioral barrier that results in increased time to mate in heterospecific pairs. RESULTS: We demonstrated that male mate choice (as courtship effort allocation) plays a more important role in the prezygotic behavioral barrier than previously recognized. In gryllids females ultimately decide whether or not to mate, yet we found males were selective by regulating courtship effort intensity toward the preferred (conspecific) females. Females were also selective by mating with more intensely courting males, which happened to be conspecifics. We report no differences in courtship song between the two species and suggest that the mechanism that allows males to act differentially towards conspecific and heterospecific females is the cuticular hydrocarbon (CHC) composition. CHC profiles differed between males and females of both species, and there were clear differences in CHC composition between female G. firmus and G. pennsylvanicus but not between the males of each species. CONCLUSION: Although many barriers to gene exchange are known in this system, the mechanism behind the mate recognition leading to reduced heterospecific mating remains unknown. The CHC profiles might be the phenotypic cue that allow males to identify conspecifics and thus to adjust their courtship intensity accordingly, leading to differential mating between species.
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Gryllidae/fisiología , Animales , Cortejo , Femenino , Gryllidae/química , Gryllidae/genética , Hibridación Genética , Hidrocarburos/análisis , Hidrocarburos/metabolismo , Masculino , Preferencia en el Apareamiento Animal , Reproducción , Caracteres Sexuales , Vocalización AnimalRESUMEN
This commentary documents how federal funding agencies are changing the criteria by which they distribute taxpayer money intended for scientific research. Increasingly, STEMM (Science, Technology, Engineering, Mathematics, and Medicine) funding agencies are requiring applicants for funding to include a plan to advance DEI ("Diversity, Equity, and Inclusion") in their proposals and to dedicate a part of the research budget to its implementation. These mandates undermine the academic freedom of researchers and the unbiased generation of knowledge needed for a well-functioning democracy. Maintaining excellence in science is fundamental to the continuation of the U.S. as a global economic leader. Science provides a basis for solving important global challenges such as security, energy, climate, and health. Diverting funding from science into activities unrelated to the production of knowledge undermines science's ability to serve humankind. When funding agencies politicize science by using their power to further a particular ideological agenda, they contribute to public mistrust in science. Hijacking science funding to promote DEI is thus a threat to our society.
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Wing patterning in Heliconius butterflies is a longstanding example of both Müllerian mimicry and phenotypic radiation under strong natural selection. The loci controlling such patterns are "hotspots" for adaptive evolution with great allelic diversity across different species in the genus. We characterise nucleotide variation, genotype-by-phenotype associations, linkage disequilibrium, and candidate gene expression at two loci and across multiple hybrid zones in Heliconius melpomene and relatives. Alleles at HmB control the presence or absence of the red forewing band, while alleles at HmYb control the yellow hindwing bar. Across HmYb two regions, separated by approximately 100 kb, show significant genotype-by-phenotype associations that are replicated across independent hybrid zones. In contrast, at HmB a single peak of association indicates the likely position of functional sites at three genes, encoding a kinesin, a G-protein coupled receptor, and an mRNA splicing factor. At both HmYb and HmB there is evidence for enhanced linkage disequilibrium (LD) between associated sites separated by up to 14 kb, suggesting that multiple sites are under selection. However, there was no evidence for reduced variation or deviations from neutrality that might indicate a recent selective sweep, consistent with these alleles being relatively old. Of the three genes showing an association with the HmB locus, the kinesin shows differences in wing disc expression between races that are replicated in the co-mimic, Heliconius erato, providing striking evidence for parallel changes in gene expression between Müllerian co-mimics. Wing patterning loci in Heliconius melpomene therefore show a haplotype structure maintained by selection, but no evidence for a recent selective sweep. The complex genetic pattern contrasts with the simple genetic basis of many adaptive traits studied previously, but may provide a better model for most adaptation in natural populations that has arisen over millions rather than tens of years.
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Adaptación Fisiológica/genética , Genética de Población , Genoma/genética , Imitación Molecular/genética , Animales , Mariposas Diurnas/genética , Cromosomas Artificiales Bacterianos/genética , Regulación de la Expresión Génica , Genes de Insecto/genética , Sitios Genéticos/genética , Variación Genética , Genotipo , Proteínas de Insectos/genética , Proteínas de Insectos/metabolismo , Desequilibrio de Ligamiento/genética , Fenotipo , Filogenia , Dinámica Poblacional , Selección Genética/genética , Especificidad de la EspecieRESUMEN
BACKGROUND: Heliconius butterflies are an excellent system for studies of adaptive convergent and divergent phenotypic traits. Wing colour patterns are used as signals to both predators and potential mates and are inherited in a Mendelian manner. The underlying genetic mechanisms of pattern formation have been studied for many years and shed light on broad issues, such as the repeatability of evolution. In Heliconius melpomene, the yellow hindwing bar is controlled by the HmYb locus. MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression that have key roles in many biological processes, including development. miRNAs could act as regulators of genes involved in wing development, patterning and pigmentation. For this reason we characterised miRNAs in developing butterfly wings and examined differences in their expression between colour pattern races. RESULTS: We sequenced small RNA libraries from two colour pattern races and detected 142 Heliconius miRNAs with homology to others found in miRBase. Several highly abundant miRNAs were differentially represented in the libraries between colour pattern races. These candidates were tested further using Northern blots, showing that differences in expression were primarily due to developmental stage rather than colour pattern. Assembly of sequenced reads to the HmYb region identified hme-miR-193 and hme-miR-2788; located 2380 bp apart in an intergenic region. These two miRNAs are expressed in wings and show an upregulation between 24 and 72 hours post-pupation, indicating a potential role in butterfly wing development. A search for miRNAs in all available H. melpomene BAC sequences (~2.5 Mb) did not reveal any other miRNAs and no novel miRNAs were predicted. CONCLUSIONS: Here we describe the first butterfly miRNAs and characterise their expression in developing wings. Some show differences in expression across developing pupal stages and may have important functions in butterfly wing development. Two miRNAs were located in the HmYb region and were expressed in developing pupal wings. Future work will examine the expression of these miRNAs in different colour pattern races and identify miRNA targets among wing patterning genes.
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Mariposas Diurnas/genética , MicroARNs/genética , Alas de Animales/metabolismo , Animales , Northern Blotting , Mariposas Diurnas/crecimiento & desarrollo , Evolución Molecular , Femenino , Regulación del Desarrollo de la Expresión Génica/genética , Regulación del Desarrollo de la Expresión Génica/fisiología , Masculino , Alas de Animales/crecimiento & desarrolloRESUMEN
The evolution of pigmentation in vertebrates and flies has involved repeated divergence at a small number of genes related to melanin synthesis. Here, we study insect melanin synthesis genes in Heliconius butterflies, a group characterised by its diversity of wing patterns consisting of black (melanin), and yellow and red (ommochrome) pigmented scales. Consistent with their respective biochemical roles in Drosophila melanogaster, ebony is upregulated in non-melanic wing regions destined to be pigmented red whilst tan is upregulated in melanic regions. Wing regions destined to be pigmented yellow, however, are downregulated for both genes. This pattern is conserved across multiple divergent and convergent phenotypes within the Heliconii, suggesting a conserved mechanism for the development of black, red and yellow pattern elements across the genus. Linkage mapping of five melanin biosynthesis genes showed that, in contrast to other organisms, these genes do not control pattern polymorphism. Thus, the pigmentation genes themselves are not the locus of evolutionary change but lie downstream of a wing pattern regulatory factor. The results suggest a modular system in which particular combinations of genes are switched on whenever red, yellow or black pattern elements are favoured by natural selection for diverse and mimetic wing patterns.
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Mariposas Diurnas/genética , Regulación del Desarrollo de la Expresión Génica , Genes de Insecto , Pigmentos Biológicos/fisiología , Alas de Animales/crecimiento & desarrollo , Animales , Evolución Biológica , Biomimética , Tipificación del Cuerpo/genética , Mapeo Cromosómico , Melaninas/biosíntesis , Melaninas/genética , Selección GenéticaRESUMEN
Loss of developmental stability can lead to deviations from bilateral symmetry (i.e. Fluctuating Asymmetry - FA), and is thought to be caused by environmental and genetic factors associated with habitat loss and stress. Therefore, levels of FA might be a valuable tool to monitor wild populations if FA serves as an indicator of exposure to stress due to impacts of habitat loss and fragmentation. In studies examining FA and habitat fragmentation, FA levels are often explained by loss of genetic variation, though few studies have addressed FA's use as indicator of environmental impact. Here, we investigated whether habitat loss, genetic variation, and/or inbreeding affect the developmental instability in Brazilian Atlantic forest populations of a Neotropical water rat (Nectomys squamipes). We sampled individuals from eight sites within Atlantic forest remnants with different amounts of available forest habitat and assessed FA levels with geometric morphometric techniques using adult mandibles. We used observed heterozygosity (Ho) and inbreeding coefficient (Fis), from seven microsatellite markers, as a proxy of genetic variation at individual and population levels. Populations were not significantly different for shape or size FA levels. Furthermore, interindividual variation in both shape and size FA levels and interpopulational differences in size FA levels were best explained by chance. However, habitat amount was negatively associated with both interpopulational variance and average shape FA levels. This association was stronger in populations living in areas with <28% of forest cover, which presented higher variance and higher average FA, suggesting that Nectomys squamipes might have a tolerance threshold to small availability of habitat. Our work is one of the first to use FA to address environmental stress caused by habitat loss in small mammal populations from a Neotropical biome. We suggest that shape FA might serve as a conservation tool to monitor human impact on natural animal populations.
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In many animals, male seminal proteins influence gamete interactions and fertilization ability and are probably involved in barriers to gene flow between diverging lineages. Here we use a proteomic approach to identify seminal proteins that are transferred to females during copulation and that may be involved in fertilization barriers between two hybridizing field crickets (Gryllus firmus and Gryllus pennsylvanicus). Analyses of patterns of divergence suggest that much of the field cricket genome has remained undifferentiated following the evolution of reproductive isolation. By contrast, seminal protein genes are highly differentiated. Tests of selection reveal that positive selection is likely to be responsible for patterns of differentiation. Together, our observations suggest that some of the loci encoding seminal proteins may indeed play a role in fertilization barriers in field crickets.
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Especiación Genética , Gryllidae/genética , Proteómica/métodos , Proteínas de Plasma Seminal/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Cromatografía por Intercambio Iónico , Gryllidae/metabolismo , Masculino , Espectrometría de Masas , Polimorfismo de Nucleótido Simple , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteínas de Plasma Seminal/metabolismoRESUMEN
The genomic architecture of barriers to gene exchange during the speciation process is poorly understood. The genomic islands model suggests that loci associated with barriers to gene exchange prevent introgression of nearby genomic regions via linkage disequilibrium. But few analyses of the actual genomic location of non-introgressing loci in closely related species exist. In a previous study Maroja et al. showed that in the hybridizing field crickets, Gryllus firmus and G. pennsylvanicus, 50 non-introgressing loci are localized on two autosomal regions and the X chromosome, but they were not able to map the loci along the X chromosome because they used a male informative cross. Here, we localize the introgressing and non-introgressing loci on the X chromosome, and reveal that all X-linked non-introgressing loci are restricted to a 50-cM region with 10 of these loci mapped to a single location. We discuss the implications of this finding to speciation.
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Mapeo Cromosómico , Cromosomas de Insectos , Gryllidae/genética , Hibridación Genética , Cromosoma X/genética , Animales , Cruzamientos Genéticos , Femenino , Genes de Insecto , Sitios Genéticos , Desequilibrio de Ligamiento , MasculinoRESUMEN
The rapid evolution of sexual isolation in sympatry has long been associated with reinforcement (i.e., selection to avoid maladaptive hybridization). However, there are many species pairs in sympatry that have evolved rapid sexual isolation without known costs to hybridization. A major unresolved question is what evolutionary processes are involved in driving rapid speciation in such cases. Here, we focus on one such system; the Drosophila athabasca species complex, which is composed of three partially sympatric and interfertile semispecies: WN, EA, and EB. To study speciation in this species complex, we assayed sexual and genomic isolation within and between these semispecies in both sympatric and allopatric populations. First, we found no evidence of reproductive character displacement (RCD) in sympatric zones compared to distant allopatry. Instead, semispecies were virtually completely sexually isolated from each other across their entire ranges. Moreover, using spatial approaches and coalescent demographic simulations, we detected either zero or only weak heterospecific gene flow in sympatry. In contrast, within each semispecies we found only random mating and little population genetic structure, except between highly geographically distant populations. Finally, we determined that speciation in this system is at least an order of magnitude older than previously assumed, with WN diverging first, around 200K years ago, and EA and EB diverging 100K years ago. In total, these results suggest that these semispecies should be given full species status and we adopt new nomenclature: WN-D. athabasca, EA-D. mahican, and EB-D. lenape. While the lack of RCD in sympatry and interfertility do not support reinforcement, we discuss what additional evidence is needed to further decipher the mechanisms that caused rapid speciation in this species complex.
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The Heliconius butterflies are a widely studied adaptive radiation of 46 species spread across Central and South America, several of which are known to hybridize in the wild. Here, we present a substantially improved assembly of the Heliconius melpomene genome, developed using novel methods that should be applicable to improving other genome assemblies produced using short read sequencing. First, we whole-genome-sequenced a pedigree to produce a linkage map incorporating 99% of the genome. Second, we incorporated haplotype scaffolds extensively to produce a more complete haploid version of the draft genome. Third, we incorporated â¼20x coverage of Pacific Biosciences sequencing, and scaffolded the haploid genome using an assembly of this long-read sequence. These improvements result in a genome of 795 scaffolds, 275 Mb in length, with an N50 length of 2.1 Mb, an N50 number of 34, and with 99% of the genome placed, and 84% anchored on chromosomes. We use the new genome assembly to confirm that the Heliconius genome underwent 10 chromosome fusions since the split with its sister genus Eueides, over a period of about 6 million yr.
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Mariposas Diurnas/genética , Cromosomas de Insectos , Evolución Molecular , Genoma de los Insectos , Genómica , Hibridación Genética , Animales , Mapeo Cromosómico , Biología Computacional/métodos , Femenino , Ligamiento Genético , Sitios Genéticos , Tamaño del Genoma , Genómica/métodos , Haplotipos , Secuenciación de Nucleótidos de Alto Rendimiento , Masculino , Anotación de Secuencia Molecular , Polimorfismo de Nucleótido SimpleRESUMEN
Characterizing the extent of genomic differentiation between recently diverged lineages provides an important context for understanding the early stages of speciation. When such lineages form discrete hybrid zones, patterns of differential introgression allow direct estimates of which genome regions are likely involved in speciation and local adaptation. Here we use a backcross experimental design to construct a genetic linkage map for the field crickets Gryllus firmus and Gryllus pennsylvanicus, which interact in a well-characterized hybrid zone in eastern North America. We demonstrate that loci with major allele frequency differences between allopatric populations are not randomly distributed across the genome. Instead, most are either X-linked or map to a few small autosomal regions. Furthermore, the subset of those highly differentiated markers that exhibit restricted introgression across the cricket hybrid zone are also concentrated on the X chromosome (39 of 50 loci) and in a single 7-cM region of one autosome. Although the accumulation on the sex chromosome of genes responsible for postzygotic barriers is a well-known phenomenon, less attention has been given to the genomic distribution of genes responsible for prezygotic barriers. We discuss the implications of our results for speciation, both in the context of the role of sex chromosomes and also with respect to the likely causes of heterogeneous genomic divergence. Although we do not yet have direct evidence for the accumulation of ecological, behavioral, or fertilization prezygotic barrier genes on the X chromosome, faster-X evolution could make these barriers more likely to be X-linked.
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Cromosomas de Insectos/genética , Genes de Insecto , Ligamiento Genético , Gryllidae/genética , Cromosoma X/genética , Animales , Frecuencia de los GenesRESUMEN
Inositol 1,4,5-trisphosphate (IP3) regulates a host of biological processes from egg activation to cell death. When IP3-specific receptors (IP3Rs) bind to IP3, they release calcium from the ER into the cytoplasm, triggering a variety of cell type- and developmental stage-specific responses. Alternatively, inositol polyphosphate kinases can phosphorylate IP3; this limits IP3R activation by reducing IP3 levels, and also generates new signaling molecules altogether. These divergent pathways draw from the same IP3 pool yet cause very different cellular responses. Therefore, controlling the relative rates of IP3R activation vs. phosphorylation of IP3 is essential for proper cell functioning. Establishing a model system that sensitively reports the net output of IP3 signaling is crucial for identifying the controlling genes. Here we report that mutant alleles of wavy (wy), a classic locus of the fruit fly Drosophila melanogaster, map to IP3 3-kinase 2 (IP3K2), a member of the inositol polyphosphate kinase gene family. Mutations in wy disrupt wing structure in a highly specific pattern. RNAi experiments using GAL4 and GAL80(ts) indicated that IP3K2 function is required in the wing discs of early pupae for normal wing development. Gradations in the severity of the wy phenotype provide high-resolution readouts of IP3K2 function and of overall IP3 signaling, giving this system strong potential as a model for further study of the IP3 signaling network. In proof of concept, a dominant modifier screen revealed that mutations in IP3R strongly suppress the wy phenotype, suggesting that the wy phenotype results from reduced IP4 levels, and/or excessive IP3R signaling.
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Proteínas de Drosophila/genética , Drosophila/crecimiento & desarrollo , Drosophila/genética , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Mutación , Fenotipo , Fosfotransferasas (Aceptor de Grupo Alcohol)/genética , Alas de Animales/crecimiento & desarrollo , Alas de Animales/metabolismo , Alelos , Animales , Secuencia de Bases , Mapeo Cromosómico , Drosophila/metabolismo , Proteínas de Drosophila/metabolismo , Epistasis Genética , Orden Génico , Receptores de Inositol 1,4,5-Trifosfato/genética , Modelos Biológicos , Datos de Secuencia Molecular , Fosfotransferasas (Aceptor de Grupo Alcohol)/metabolismo , Unión Proteica , Sitios de Carácter Cuantitativo , Interferencia de ARN , Transducción de SeñalRESUMEN
PREMISE OF THE STUDY: We developed 10 novel microsatellite loci for Sagina nodosa, a diploid perennial arctic-alpine herb. To our knowledge, these are the first microsatellite loci for a Sagina species. ⢠METHODS AND RESULTS: We performed a low-coverage 454 next-generation sequencing of enriched genomic fragments derived from one individual to generate a massive library of contigs containing potential polymorphic microsatellites. We present data for 10 novel polymorphic microsatellite loci containing di-, tri-, tetra-, and hexanucleotide repeats with two to nine alleles per locus assessed in 29 individuals. ⢠CONCLUSIONS: These polymorphic microsatellite loci in S. nodosa will provide insights on the population structure and life history of S. nodosa in Isle Royale and other North American populations.
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PREMISE OF THE STUDY: Twelve microsatellite markers were developed for Primula mistassinica, a distylous, diploid arctic-alpine plant. The markers will be used to investigate the landscape genetics of a disjunct population on Isle Royale, Michigan, and the phylogeographic patterns of the species. ⢠METHODS AND RESULTS: We used Roche/454 high-throughput technology to sequence microsatellite-enriched regions in the P. mistassinica genome. We developed 12 polymorphic microsatellite primer sets. These loci contained di-, tri-, and tetranucleotide repeats with two to nine alleles per locus when assessed in 23 individuals. ⢠CONCLUSIONS: Understanding the historical movements of P. mistassinica will provide insight to the survival prospects of current Arctic plant populations, which face the pressures of global, anthropogenic climate change.
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Heliconius butterflies are an excellent system for understanding the genetic basis of phenotypic change. Here we document surprising diversity in the genetic control of a common phenotype. Two disjunct H. erato populations have each recruited the Cr and/or Sd loci that control similar yellow hindwing patterns, but the alleles involved partially complement one another indicating either multiple origins for the patterning alleles or developmental drift in genetic control of similar patterns. We show that in these H. erato populations cr and sd are epistatically interacting and that the parental origin of alleles can explain phenotypes of backcross individuals. In contrast, mimetic H. melpomene populations with identical phenotypes (H. m. rosina and H. m. amaryllis) do not show genetic complementation (F(1)s and F(2)s are phenotypically identical to parentals). Finally, we report hybrid female inviability in H. m. melpomene × H. m. rosina crosses (previously only female infertility had been reported) and presence of standing genetic variation for alternative color alleles at the Yb locus in true breeding H. melpomene melpomene populations (expressed when in a different genomic background) that could be an important source of variation for the evolution of novel phenotypes or a result of developmental drift. Although recent work has emphasized the simple genetic control of wing pattern in Heliconius, we show there is underlying complexity in the allelic variation and epistatic interactions between major patterning loci.
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Adaptación Biológica/genética , Mariposas Diurnas/genética , Pigmentación/genética , Alas de Animales/metabolismo , Animales , Mariposas Diurnas/anatomía & histología , Cruzamientos Genéticos , Epistasis Genética , Evolución Molecular , Femenino , Guyana Francesa , Genes de Insecto/genética , Sitios Genéticos/genética , Variación Genética , Genética de Población , Genotipo , Geografía , Infertilidad Femenina/genética , Masculino , Panamá , Fenotipo , Polimorfismo de Nucleótido Simple , Especificidad de la Especie , Alas de Animales/anatomía & histologíaRESUMEN
In recently diverged species, ancestral polymorphism and introgression can cause incongruence between gene and species trees. In the face of hybridization, few genomic regions may exhibit reciprocal monophyly, and these regions, usually evolving rapidly under selection, may be important for the maintenance of species boundaries. In animals with internal fertilization, genes encoding seminal protein are candidate barrier genes. Recently diverged hybridizing species such as the field crickets Gryllus firmus and G. pennsylvanicus, offer excellent opportunities to investigate the origins of barriers to gene exchange. These recently diverged species form a well-characterized hybrid zone, and share ancestral polymorphisms across the genome. We analyzed DNA sequence divergence for seminal protein loci, housekeeping loci, and mtDNA, using a combination of analytical approaches and extensive sampling across both species and the hybrid zone. We report discordant genealogical patterns and differential introgression rates across the genome. The most dramatic outliers, showing near-zero introgression and more structured species trees, are also the only two seminal protein loci under selection. These are candidate barrier genes with possible reproductive functions. We also use genealogical data to examine the demographic history of the field crickets and the current structure of the hybrid zone.
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Gryllidae/genética , Selección Genética , Alelos , Animales , Secuencia de Bases , Cartilla de ADN , ADN Mitocondrial/genética , Fertilización , Gryllidae/fisiología , Hibridación Genética , Masculino , FilogeniaRESUMEN
Tree-feeding insects that are widespread in north temperate regions are excellent models for studying how past glaciations have impacted differentiation and speciation. We used mitochondrial DNA (mtDNA) sequences and allele frequencies at nine microsatellite loci to examine genetic population structure across the current range of the spruce beetle (Dendroctonus rufipennis), an economically important insect in North America. Two major haplotype groups occur across northern North America, from Newfoundland to Alaska, on white spruce (Picea glauca), and a third distinctive haplotype group occurs throughout the Rocky Mountains on Engelmann spruce (Picea engelmannii). The two mtDNA lineages found in northern populations are 3-4% divergent from each other and from the lineages found in the Rocky Mountains. Analyses of microsatellite data also suggest the existence of major population groupings associated with different geographical regions. In the Pacific Northwest, concordant contact zones for genetically distinct populations of spruce beetles and their principal hosts appear to reflect recent secondary contact. Although we could detect no evidence of historical mtDNA gene flow between allopatric population groups, patterns of variation in the Pacific Northwest suggest recent hybridization and introgression. Together with the pollen record for spruce, they also suggest that beetles have spread from at least three glacial refugia. A minimum estimate of divergence time between the Rocky Mountain and northern populations was 1.7 Myr (million years), presumably reflecting the combined effects of isolation during multiple glacial cycles.
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Clima , Escarabajos/genética , Demografía , Especiación Genética , Variación Genética , Genética de Población , Filogenia , Animales , Secuencia de Bases , Teorema de Bayes , Análisis por Conglomerados , ADN Mitocondrial/genética , Frecuencia de los Genes , Geografía , Haplotipos/genética , Repeticiones de Microsatélite/genética , Modelos Genéticos , Datos de Secuencia Molecular , América del Norte , Picea , Análisis de Secuencia de ADNRESUMEN
In sexually reproducing organisms, male ejaculates are complex traits that are potentially subject to many different selection pressures. Recent experimental evidence supports the hypothesis that postmating sexual selection, and particularly sexual conflict, may play a key role in the evolution of the proteinaceous components of ejaculates. However, this evidence is based almost entirely on the study of Drosophila, a species with a mating system characterized by a high cost of mating for females. In this paper, we broaden our understanding of the role of selection on the evolution of seminal proteins by characterizing these proteins in field crickets, a group of insects in which females appear to benefit from mating multiply. We have used an experimental protocol that can be applied to other organisms for which complete genome sequences are not yet available. By combining an evolutionary expressed sequence tag screen of the male accessory gland in 2 focal species (Gryllus firmus and Gryllus pennsylvanicus) with a bioinformatics approach, we have been able to identify as many as 30 seminal proteins. Evolutionary analyses among 5 species of the genus Gryllus suggest that seminal protein genes evolve more rapidly than genes encoding proteins that are not involved with reproduction. The rates of synonymous substitution (dS) are similar in genes encoding seminal proteins and genes encoding "housekeeping" proteins. For the same comparison, the rate of fixation of nonsynonymous substitutions (dN) is 3 times higher in genes encoding seminal proteins, suggesting that the divergence of seminal proteins in field crickets has been accelerated by positive Darwinian selection. In spite of the contrasting characteristics of the Drosophila and Gryllus mating systems, the mean selection parameter omega and the proportion of loci estimated to be affected by positive selection are very similar.