Project description:Caves are populated with a diverse fauna of highly adapted species that tend to exhibit a consistent suite of both regressive and constructive trait modifications. Because molecular studies of cave adaptation have largely concentrated on vertebrate models, our ability to recognize universalities in the genetic trajectories underlying cave adaptation remains limited. We have initiated efforts to elucidate the molecular evolution of the flightless small carrion beetle Ptomaphagus hirtus (Ptomaphagus hirtus), which represents one of the highly endemic signature inhabitants of the Mammoth Cave system of Kentucky. Ptomaphagus hirtus has been considered blind despite the presence of lateral eye rudiments. However, analysis of the Ptomaphagus hirtus adult head transcriptome by deep RNA sequencing reveals the conservation and expression of all essential insect phototransduction genes including a single long wavelength-sensitive opsin. Consistent with the preservation of visual ability, Ptomaphagus hirtus expresses all core members of the clock gene network and exhibits a similar degree of negative phototaxis as does a closely related flight-active species in light-dark choice assays. The structural reduction of the peripheral Ptomaphagus hirtus visual system is reflected by the lack of five eye pigmentation specific genes in the head transcriptome. Taken together our data suggest that wavelength contingent and probably also spatial vision have been lost in Ptomaphagus hirtus, while irradiance vision and contingent behavioral modules have remained preserved. We predict that the adaptive state of Ptomaphagus hirtus is representative for a large number of microphthalmic species adapted to the twilight zone of caves and other subterranean habitats Poly(A)+ transcripts were isolated from a pooled sample of 25 adult Ptomaphagus hirtus heads, reverse transcribed and sequenced on the Illumina GAII
Project description:Coding and non-coding mutations in DNA contribute significantly to phenotypic variability during evolution. However, less is known about the role of epigenetics in this process. Although previous studies have identified eye development genes associated with the loss of eyes phenotype in the Pachón blind cave morph of the Mexican tetra Astyanax mexicanus1-6, no inactivating mutations have been found in any of these genes2,3,7-10. Here we show that excess DNA methylation-based epigenetic silencing promotes eye degeneration in blind cave Astyanax mexicanus. By performing parallel analyses in Astyanax mexicanus cave and surface morphs and in the zebrafish Danio rerio, we have discovered that DNA methylation mediates eye-specific gene repression and globally regulates early eye development. The most significantly hypermethylated and down-regulated genes in the cave morph are also linked to human eye disorders, suggesting the function of these genes is conserved across the vertebrates. Our results show that changes in DNA methylation-based gene repression can serve as an important molecular mechanism generating phenotypic diversity during development and evolution.
Project description:Caves are populated with a diverse fauna of highly adapted species that tend to exhibit a consistent suite of both regressive and constructive trait modifications. Because molecular studies of cave adaptation have largely concentrated on vertebrate models, our ability to recognize universalities in the genetic trajectories underlying cave adaptation remains limited. We have initiated efforts to elucidate the molecular evolution of the flightless small carrion beetle Ptomaphagus hirtus (Ptomaphagus hirtus), which represents one of the highly endemic signature inhabitants of the Mammoth Cave system of Kentucky. Ptomaphagus hirtus has been considered blind despite the presence of lateral eye rudiments. However, analysis of the Ptomaphagus hirtus adult head transcriptome by deep RNA sequencing reveals the conservation and expression of all essential insect phototransduction genes including a single long wavelength-sensitive opsin. Consistent with the preservation of visual ability, Ptomaphagus hirtus expresses all core members of the clock gene network and exhibits a similar degree of negative phototaxis as does a closely related flight-active species in light-dark choice assays. The structural reduction of the peripheral Ptomaphagus hirtus visual system is reflected by the lack of five eye pigmentation specific genes in the head transcriptome. Taken together our data suggest that wavelength contingent and probably also spatial vision have been lost in Ptomaphagus hirtus, while irradiance vision and contingent behavioral modules have remained preserved. We predict that the adaptive state of Ptomaphagus hirtus is representative for a large number of microphthalmic species adapted to the twilight zone of caves and other subterranean habitats
Project description:Organisms adapt to and survive in environments with varying nutrient availability. Cis-regulatory changes play important roles in adaptation and phenotypic evolution. To what extent cis-regulatory elements contribute to metabolic adaptation is less understood. Here we have utilized a unique vertebrate model, Astyanax mexicanus, that survives in nutrient rich surface and nutrient deprived cave water to uncover gene regulatory networks in metabolic adaptation. We performed genome-wide analysis of accessible chromatin and histone modifications in the liver tissue of one surface and two independently derived cave populations, providing the first genome-wide epigenetic landscape in this organism. We find that many cis-regulatory elements differ between surface and the cavefish, while the two independently derived cave populations have evolved remarkably similar regulatory signatures. Changes in gene regulatory networks between the surface and cave morphotypes point to global changes in key metabolic pathways.
Project description:Organisms adapt to and survive in environments with varying nutrient availability. Cis-regulatory changes play important roles in adaptation and phenotypic evolution. To what extent cis-regulatory elements contribute to metabolic adaptation is less understood. Here we have utilized a unique vertebrate model, Astyanax mexicanus, that survives in nutrient rich surface and nutrient deprived cave water to uncover gene regulatory networks in metabolic adaptation. We performed genome-wide analysis of accessible chromatin and histone modifications in the liver tissue of one surface and two independently derived cave populations, providing the first genome-wide epigenetic landscape in this organism. We find that many cis-regulatory elements differ between surface and the cavefish, while the two independently derived cave populations have evolved remarkably similar regulatory signatures. Changes in gene regulatory networks between the surface and cave morphotypes point to global changes in key metabolic pathways.
Project description:we report a transcriptome-wide comparative investigation between surface and cave species in Sinocyclocheilus. De novo transcriptome assemblies were performed on surface and cave species; then the Sinocyclocheilus contigs were annotated with Gene Ontology. RNA-Seq assays revealed reduced transcription of a series of visual phototransduction and retinal disease related genes in cave-dwelling species compared with surface species. Degeneration of the retina in Sinocyclocheilus cavefish might occur in a lens-independent way by the down-regulation of several transcriptional factors, which have direct roles in retina development and maintenance, such as crx, rorb and Wnt pathway members. Examination of 2 different eye samples in 2 Sinocyclocheilus species.