Project description:Ecological speciation is a common mechanism by which new species arise. Despite great efforts, the role of gene expression in ecological divergence and speciation is poorly understood. Here, we conducted a genome-wide gene expression investigation of two Oryza species that are evolutionarily young and distinct in ecology and morphology. Using digital gene expression (DGE) technology and the paired-end RNA sequencing (RNA-Seq) method, we obtained 21,415 expressed genes across three reproduction-related tissues at two critical developmental stages. Of them, ~8% (1717) differed significantly in expression levels between the two species and these differentially expressed genes are randomly distributed across the genome. Moreover, 62% (1064) of the differentially expressed genes exhibited a signature of directional selection in at least one species. Importantly, the genes with differential expression between species evolved more rapidly at the 5â??flanking sequences than the genes without differential expression relative to coding sequences, suggesting that cis-regulatory changes are likely adaptive and play an important role in the ecological divergence of the two species. Finally, we showed evidence of significant differentiation between species in phenotype traits and observed that genes with differential expression were overrepresented with functional terms involving phenotypic and ecological differentiation between the two species, including reproduction- and stress-related characteristics. Our findings demonstrate that ecological speciation is associated with widespread and adaptive alterations in genome-wide gene expression and highlight the dominant role of regulatory evolution in ecological divergence and adaptation. We selected accessions representing typical Oryza rufipogon and O. nivara, which were sampled exclusively from South and Southeast Asia where the two species overlap. We chose to collect three types of tissues, i.e., flag leaves at the heading stage (2â??7 cm above the primary branch) (L), panicles at the heading stage (H) and panicles at the flowering stage (10â??15 cm above the primary branch) (F). Sample collection was repeated twice in two consecutive years (2009 and 2010) under the same controlled conditions. A total of 36 samples were sequenced by Illuminaâ??s digital gene expression (DGE) system, with each type of tissues collected from six individuals of each species as biological replicates. To access the quality of DGE technology, we also selected six samples representing three tissues from each of two individuals (one individual per species) for paired-end RNA-Seq sequencing.

Project description:It has long been recognized that species occupy a specific ecological niche within their ecosystem. The ecological niche is defined as the number of conditions and resources that limit species distribution. Within their ecological niche, species do not exist in a single physiological state but in a number of states we call the Natural Operating Range. In this paper we link ecological niche theory to physiological ecology by measuring gene expression levels of collembolans exposed to various natural conditions. The soil-dwelling collembolan Folsomia candida was exposed to 26 natural soils with different soil characteristics (soil type, land use, practice, etc). The animals were exposed for two days and gene expression levels were measured. The main factor found to regulate gene expression was the soil type (sand or clay), in which 18.5% of the measured genes were differentially expressed. Gene Ontology analysis showed animals exposed to sandy soils experience general stress, affecting cell homeostasis and replication. Multivariate analysis linking soil chemical data to gene expression data revealed that soil fertility influences gene expression. Land-use and practice had less influence on gene expression; only forest soils showed a different expression pattern. A variation in gene expression variation analysis showed overall low variance in gene expression. The large difference in response to soil type was caused by the soil physicochemical properties where F. candida experiences clay soils and sandy soils as very different from each other. This collembolan prefers fertile soils with high organic matter content, as soil fertility was found to correlate with gene expression and animals exposed to sandy soils (which, in general, have lower organic matter content) experience more general stress. Finally, we conclude that there is no such thing as a fixed physiological state for animals in their ecological niche and the boundary between the ecological niche and a stressed state depends on the genes/pathways investigated. Test animals were exposed to 26 natural soils + 2 control soils. 4 biological replicates per soil containing 25 grams of soil and 30 23-day-old animals per replicate, RNA was isolated after two days of exposure. for the micro-array hybridization design we made use of an interwoven loop design. from the four replicates per soil two were labeled with Cy3 and 2 with Cy5. It was made sure that now two replicates of the same soil were ever hybridized against the same soil.

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