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De novo transcriptome analysis profiles gene expression underlying seasonal polyphenism in butterfly wing patterns

ABSTRACT: In the eastern United States the buckeye butterfly, Junonia coenia, shows a seasonal wing color polyphenism where adults emerging in the spring are pale brown, while those emerging in the autumn are dark red. This variation can be artificially induced in laboratory colonies, thus making J. coenia a useful model system to examine the developmental basis of phenotypic plasticity. We used RNA-seq to generate the first set of assembled transcripts for this species while simultaneously quantifying relative gene expression associated with development of alternative seasonal color morphs. The assembled consolidated wing transcriptome was 77.55 Mb. 16,251 contigs of over 1000bp in length were assembled, of which 3,145 were differentially expressed between stages and/or color morphs. Depending on the developmental stage, between 547 and 1420 transcripts were significantly differentially expressed between brown and red wing morphs. These extensive differences in gene expression stand in stark contrast to the much smaller numbers found in previous studies on genetic wing pattern variation, and suggest that environmentally induced phenotypic shifts may arise from very broad systemic processes. Overall gene ontology (GO) analyses revealed that genes associated with structural constituents of ribosomes and oxygen transport were significantly upregulated in the pale brown morph, while genes associated with peptidase activity were very significantly upregulated in the dark red morph. Focused analyses of candidate endocrine and pigmentation pathways revealed a number of notable genes upregulated in the red morph, including several ecdysone-related genes and cinnabar, an ommochrome pigment gene implicated in color pattern variation in other butterflies. Surprisingly, we found numerous melanin-related transcripts, including tan and yellow-family genes, strongly upregulated in the red morph, leading us to speculate that red pigmentation in autumn J. coenia may include red or brown melanins in addition to ommochromes. While we identified several endocrine and pigmentation genes as obvious candidates for color morph differentiation, we speculate that the majority of gene expression differences we observed were due to thermal stress response. The buckeye transcriptome provides a basis for further developmental studies of phenotypic plasticity.

ORGANISM(S): Junonia coenia

PROVIDER: GSE54819 | GEO | 2014/02/15

SECONDARY ACCESSION(S): PRJNA237755

REPOSITORIES: GEO

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Project description:In the eastern United States the buckeye butterfly, Junonia coenia, shows a seasonal wing color polyphenism where adults emerging in the spring are pale brown, while those emerging in the autumn are dark red. This variation can be artificially induced in laboratory colonies, thus making J. coenia a useful model system to examine the developmental basis of phenotypic plasticity. We used RNA-seq to generate the first set of assembled transcripts for this species while simultaneously quantifying relative gene expression associated with development of alternative seasonal color morphs. The assembled consolidated wing transcriptome was 77.55 Mb. 16,251 contigs of over 1000bp in length were assembled, of which 3,145 were differentially expressed between stages and/or color morphs. Depending on the developmental stage, between 547 and 1420 transcripts were significantly differentially expressed between brown and red wing morphs. These extensive differences in gene expression stand in stark contrast to the much smaller numbers found in previous studies on genetic wing pattern variation, and suggest that environmentally induced phenotypic shifts may arise from very broad systemic processes. Overall gene ontology (GO) analyses revealed that genes associated with structural constituents of ribosomes and oxygen transport were significantly upregulated in the pale brown morph, while genes associated with peptidase activity were very significantly upregulated in the dark red morph. Focused analyses of candidate endocrine and pigmentation pathways revealed a number of notable genes upregulated in the red morph, including several ecdysone-related genes and cinnabar, an ommochrome pigment gene implicated in color pattern variation in other butterflies. Surprisingly, we found numerous melanin-related transcripts, including tan and yellow-family genes, strongly upregulated in the red morph, leading us to speculate that red pigmentation in autumn J. coenia may include red or brown melanins in addition to ommochromes. While we identified several endocrine and pigmentation genes as obvious candidates for color morph differentiation, we speculate that the majority of gene expression differences we observed were due to thermal stress response. The buckeye transcriptome provides a basis for further developmental studies of phenotypic plasticity. mRNA profiling of hind wings from 4 developmental stages of two color morphs (Rosa and Linea) of the buckeye butterfly (J. coenia), generated by deep sequencing, in triplicate, using Illumina GAII or HiSeq 2000.

Project description:Heliconius butterfly wing pattern diversity offers a unique opportunity to investigate how natural genetic variation can drive the evolution of complex adaptive phenotypes. Here we took a large-scale transcriptomic approach to identify the network of genes involved in Heliconius wing pattern development and variation. This included applying 147 microarrays representing the Heliconius transcriptome to assay shifts in gene expression across pupal development among several wing pattern morphs of Heliconius erato. We focused in particular on genes differentially expressed relative to the gene optix, which controls red pattern elements in wings. We combined expression results from three hindwing morphs from Peru and from dissected basal to apical wing elements in two forewing morphs to uncover two main classes of genes. First we looked for candidate upstream regulators of optix by determining transcripts expressed differently across basal to apical sections of the forewing prior to optix expression. Second, we assessed how optix regulates downstream gene expression by targeting transcripts with differential expression similar to optix, where expression differs among red wing pattern elements of both the forewing and hindwing. This study is an analysis of two distinct datasets generated using the same microarray platform. One dataset involved comparative analysis of forewing sections of different color morphs, while the other compared whole hindwings with different color patterns. For the forewing analysis we compared proximal, medial, and distal wing sections of two color pattern morphs: H. erato petiverana and a hybrid H. himera x H. erato etylus. The proximal section in H. erato petiverana is black and the hybrid form orange/red, the medial section is red in H. erato petiverana and pale yellow in the hybrid form, and the distal section is black in both races. For the hindwing analysis, we compared hindwing color pattern gene expression in three races that meet in a hybrid zone in Peru. H. erato emma has a rayed hindwing, H. erato favorinus has a yellow-barred hindwing, and H. erato amphritrite has a black hindwing. Wings were dissected at five time intervals: 1, 3, and 5 days after pupation, when orange/red ommochrome pigments were beginning to be expressed (~7 days after pupation), and when black melanin pigments were starting to pepper the center of the wings (~8 days after pupation). In the forewings, Days 1, 3, and 5 were at 12, 36, and 60 hours post-pupation. In the hindwings these stages were sampled at 24, 48, and 72 hours. Samples hybridized to microarrays included three replicates each of each race, stage, and wing section for forewings (3 replicates x 2 morphs x 3 wing sections x 5 stages, with one replicate wing missing for Day 1 H. e. petiverana = 87 samples) and four replicates of each stage and race for hindwings (4 replicates x 3 races x 5 stages = 60 samples). Total RNA was extracted and converted to cDNA. Cy3-labeling of samples, hybridization, and array scanning was performed according to NimbleGen protocols (2008): for the forewings this was performed at the City of Hope Functional Genomics Core, while the hindwings were run separately at NCSU.Samples were hybridized to NimbleGen HD2 12-plex arrays. These arrays include 12 identical subarrays with 135,000 60 bp probes each, each hybridizing a separate sample. Samples were distributed across arrays to prevent repeat conditions as much as possible and to space similar conditions in different regions of the slide. The array design involved two classes of probes. First there was a tiling component involving 89,310 probes tiled across three genomic intervals. Results from the tiling data were used for the initial discovery of the optix gene and are not the focus of the present study. The second component involved a representation of a set of 12,450 transcript contigs at 1-6X coverage for a total of 40,046 probes, with a mean coverage of 3-4 probes per contig. The number of probes for each contig depended on the ability to create suitable probes according to NimbleGen probe selection criteria and was limited by the small size of some transcripts and the minimum spacing criterion of 15 bp apart. Sequences of low complexity and high repeats with the rest of the genome (>5X representation), determined by comparison against 1.6 MB of genomic sequence available at the time, were avoided for designing probes. An additional 3,248 random probes were placed on the array for quality control.

Project description:We investigated gene expression levels in Heliconius erato butterflies with divergent wing patterns across a 656KB genomic interval linked to the red color pattern wing polymorphism. This included comparison of expression between two H. erato color pattern populations (H. e. petiverana and a H.e. etylus x H. himera hybrid) across three sections of the forewing that differed in pigmentation (the basal, mid, and distal wing sections) and five different stages of pupal development (Day 1, 3, 5 pupae and ommochrome and melanin pigmentation stages). These results allowed us to determine whether certain genes in this interval were differentially expressed between the wing pattern elements, and, therefore, potentially responsible for adaptive color pattern variation in these butterflies. Forewings from a total of 29 individuals, covering three biological replicates of five developmental time points for each of the two H. erato distinct phenotypes were dissected, with the only exception being that there were only two replicates of the day 1 hybrid phenotype. Individuals were reared at 25˚C and dissected at the following stages: a) day 1 = 12 hr after pupation; b) day 3 = 60 hr after pupation; c) day 5 = 108 hr after pupation; d) early ommochrome = ~ 156 hr after pupation when red scales in forewing partially mature, showing a pale orange color; and e) early melanin = ~ 180 hr after pupation melanic scales begin to turn black and are present primarily at the center of the wing. Using wing veins as landmarks, each forewing was cut into three sections corresponding to the color pattern boundaries: basal (F1), middle (F2), and apical (F3). A eight custom-designed Roche NimbleGen 12x135K format microarrays with probes spanning a 656,307bp genomic region (Roche NimbleGen Inc., Madison, Wisconsin, United States) were used to hybridize double stranded cDNA from 87 tissue samples. Repetitive sequence elements found more than five times across all currently available H. erato genomic sequences, including the probed region as well as additional genomic BAC sequences, were masked from the tiling region. The remaining unmasked non-repetitive genomic sequences were tiled using 60 bp probes staggered every 13 bp on average, with slight modifications to ensure probe quality, for a total of 48,547 probes. Microarry design and printing was performed by Roche NimbleGen. cDNA labeling, hybridization, and array scanning was performed by the City of Hope Microarray Facility (Duarte, California, United States). In addition to the probes from the red color pattern intervals, the arrays also include 40,763 probes across two other genomic intervals not addressed in this study, 45,046 probes representing 12450 transcripts from a recent transcriptome assembly at 1-6X coverage, and 3248 random probes. Results from the transcriptome and other color pattern intervals will be published separately, however, we analyzed all probes together for array normalization and quality control.

Project description:Developmental mechanisms play an important role in determining the costs, limits, and evolutionary consequences of phenotypic plasticity. One issue central to these claims is the metaphor of developmental “decoupling,” where alternate morphs result from evolutionarily independent developmental pathways. We test this assumption through a microarray study that explores differences in gene expression between alternate morphs relative to differences between sexes, a classic example of developmental decoupling. We then examine whether morph-biased genes are less conserved, relative to morph-shared genes, as predicted if developmental decoupling relaxes pleiotropic constraints on divergence. We focus on the developing horns and brains of two species of horned beetles with spectacular sexual- and morph-dimorphism in the expression of horns and fighting behavior. We find that patterns of gene expression were as divergent between morphs as they were between sexes. However, overall patterns of gene expression were also highly correlated across morphs and sexes. Morph-biased genes were more evolutionarily divergent, suggesting a role of relaxed pleiotropic constraints or relaxed selection. Together these results suggest that alternate morphs are somewhat developmentally decoupled, and that this decoupling has significant evolutionary consequences. However, alternative morphs may not be as developmentally decoupled as sometimes assumed and such hypotheses of development should be revisited and refined. We compared gene expression in three focal epidermal tissues (head, prothorax, legs) relative to a "control" tissue (dorsal abdominal epidermis) without any outgrowths. We also surveyed gene expression in the brain, relative to ganglionic neural tissue. We compared such patterns of gene expression between two male morphs (horned, fighter and hornless, sneaker males) and between males and females. We focused our array analyses (N = 48 arrays) on Onthophagus taurus (the species for which the array was designed), but also ran 19 arrays on thoracic tissue of Onthophagus nigriventris, a species which expresses thoracic horns as adults (O. taurus expresses head horns). Finally, we included a small subset of arrays (N = 4) directly hybridizing head epidermis tissue of O. taurus male morphs to validate our overall estimates of morph-biased expression. For more detail, refer to Snell-Rood et al. 2010, Evolution.

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De novo transcriptome analysis profiles gene expression underlying seasonal polyphenism in butterfly wing patterns

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