RNA sequencing reveals small RNAs differentially expressed between incipient Japanese threespine sticklebacks

BACKGROUND: Non-coding small RNAs, ranging from 20 to 30 nucleotides in length, mediate the regulation of gene expression and play important roles in many biological processes. One class of small RNAs, microRNAs (miRNAs), are highly conserved across taxa and mediate the regulation of the chromatin state and the post-transcriptional regulation of messenger RNA (mRNA). Another class of small RNAs is the Piwi-interacting RNAs, which play important roles in the silencing of transposons and other functional genes. Although the biological functions of the different small RNAs have been elucidated in several laboratory animals, little is known regarding naturally occurring variation in small RNA transcriptomes among closely related species. RESULTS: We employed next-generation sequencing technology to compare the expression profiles of brain small RNAs between sympatric species of the Japanese threespine stickleback (Gasterosteus aculeatus). We identified several small RNAs that were differentially expressed between sympatric Pacific Ocean and Japan Sea sticklebacks. Potential targets of several small RNAs were identified as repetitive sequences. Female-biased miRNA expression from the old X chromosome was also observed, and it was attributed to the degeneration of the Y chromosome. CONCLUSIONS: Our results suggest that expression patterns of small RNA can differ between incipient species and may be a potential mechanism underlying differential mRNA expression and transposon activity

Phenotypic divergence and reproductive isolation between sympatric forms of Japanese threespine sticklebacks

The threespine stickleback (Gasterosteus aculeatus) species complex is well suited for identifying the types of phenotypic divergence and isolating barriers that contribute to reproductive isolation at early stages of speciation. In the present study, we characterize the patterns of genetic and phenotypic divergence as well as the types of isolating barriers that are present between two sympatric pairs of threespine sticklebacks in Hokkaido, Japan. One sympatric pair consists of an anadromous and a resident freshwater form and shows divergence in body size between the forms, despite the lack of genetic differentiation between them. The second sympatric pair consists of two anadromous forms, which originated before the last glacial period and are currently reproductively isolated. These two anadromous forms have diverged in many morphological traits as well as in their reproductive behaviours. Both sexual isolation and hybrid male sterility contribute to reproductive isolation between the anadromous species pair. We discuss the shared and unique aspects of phenotypic divergence and reproductive isolation in the Japanese sympatric pairs compared with postglacial stickleback species pairs. Further studies of these divergent species pairs will provide a deeper understanding of the mechanisms of speciation in sticklebacks. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 671–685

Divergence of male courtship displays between sympatric forms of anadromous threespine stickleback

Courtship displays are an important component of animal reproduction, and divergence in these displays can play an integral role in promoting or maintaining reproductive isolation between species. The courtship behaviour of the threespine stickleback (Gasterosteus aculeatus) has been extensively characterized. In Japan, there are two lineages of threespine stickleback that are genetically differentiated and reproductively isolated when found in regions of sympatry. We have previously shown that males of the Pacific Ocean lineage perform the zig-zag dance, while sympatric males of the Japan Sea lineage perform a different dance, which we have termed the rolling dance (Kitano et al., 2007, Biol. J. Linn. Soc. 91: 671-685). As a first step towards understanding the role of the courtship display in female mate choice and sexual isolation between this sympatric pair, we conducted a more detailed analysis of divergence between the courtship displays of the Pacific Ocean and Japan Sea males. Kinematic analysis revealed that the tempo of the zig-zag dance is two times faster than the tempo of the rolling dance. A detailed analysis of head movements during the courtship dance revealed that the Japan Sea males erect their gill covers, extend their red throats, and open their mouths more frequently during the rolling dance than the Pacific Ocean males do during the zig-zag dance. These results demonstrate that there is extensive divergence between sympatric Pacific Ocean and Japan Sea males in both the motor patterns and the tempo of their courtship displays. Thus, the Japanese sympatric stickleback pair provides a good system to study the role of courtship behaviour in speciation, as well as the genetic mechanisms that underlie the divergence of kinematics and motor patterns in courtship behaviour

Sex Differences in Recombination in Sticklebacks.

Recombination often differs markedly between males and females. Here we present the first analysis of sex-specific recombination in Gasterosteus sticklebacks. Using whole-genome sequencing of 15 crosses between G. aculeatus and G. nipponicus, we localized 698 crossovers with a median resolution of 2.3 kb. We also used a bioinformatic approach to infer historical sex-averaged recombination patterns for both species. Recombination is greater in females than males on all chromosomes, and overall map length is 1.64 times longer in females. The locations of crossovers differ strikingly between sexes. Crossovers cluster toward chromosome ends in males, but are distributed more evenly across chromosomes in females. Suppression of recombination near the centromeres in males causes crossovers to cluster at the ends of long arms in acrocentric chromosomes, and greatly reduces crossing over on short arms. The effect of centromeres on recombination is much weaker in females. Genomic differentiation between G. aculeatus and G. nipponicus is strongly correlated with recombination rate, and patterns of differentiation along chromosomes are strongly influenced by male-specific telomere and centromere effects. We found no evidence for fine-scale correlations between recombination and local gene content in either sex. We discuss hypotheses for the origin of sexual dimorphism in recombination and its consequences for sexually antagonistic selection and sex chromosome evolution

Thermal properties of hemp fiber filled polyamide 1010 biomass composites and the blend of these composites and polyamide 11 elastomer

The aim of this study is to improve the performance of all inedible plants-derived materials for new engineering materials such as structural materials and tribomaterials. Thermal properties of hemp fiber tilled polyamide 1010 biomass composites and the blend of these composites and plants-derived TPE, were investigated experimentally. These biomass composites were extruded by a twin screw extruder and compression or injection molded. Thermal properties such as dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of these biomass composites were evaluated. It was found that the addition of HF and the blend of bio-TPE With PA1010 have strong influence on the thermal properties such as DMA, TGA and DSC. In particular, IT has a good effect for the improvement of the thermal and mechanical properties. These properties of HF/PA1010/PA11E biomass composites are better than those of HF/PA1010/ITU ones

Effect of processing sequence on the dynamic viscoelastic properties of ternary biomass composites (Hemp fiber/PA1010/PA11E) in the molten state

For developing the new engineering materials such as structural materials and tribomaterials based on all plants-derived materials, we investigated the effect of processing sequence on the dynamic viscoelastic properties of the ternary biomass composites: 5mm cut hemp fiber (HF) filled polymer blend of plants-derived polyamide 1010 (PA1010) and polyamide 11 elastomer (PA11E) composites in the molten state. PA1010 and PA11E, which contain the polyether groups as soft segment, were made from plant-derived castor oil. The composition of the polymer blend of PA1010 and PA11E was fixed with 60/40 weight fraction. HF was surface-treated by two types of treatment: alkali treatment by NaOH solution and surface treatment by ureido silane coupling agent. The volume fraction of HF in the composites was fixed with 20vol.%. Five different processing sequences: (1) HF, PA1010 and PA11E were mixed simultaneously (Process A), (2) Re-mixing (second compounding) of the materials prepared by Process A (Process AR), (3) PA11E was blended with PA1010 (PA1010/PA11E blends) and then these blends were mixed with HF (Process B), (4) HF was mixed with PA1010 (HF/PA1010 composites) and then these composites were blended with PA11E (Process C), and (5) HF were mixed with PA11E (HF/PA11E composites) and then these composites were blended with PA1010 (Process D) were attempted for preparing the ternary biomass composites (HF/PA1010/PA11E) composites. These ternary biomass composites were extruded by a twin screw extruder and compression-molded. Their dynamic viscoelastic properties in the molten state were evaluated by oscillatory flow testing using a parallel plate type rheometer. It was found that those properties of the ternary biomass composites in the molten state are influenced so much by processing sequence. This is attributed to the change of internal microstructure of these composites such as the distribution and dispersion of HF. © 2016 Author(s).JSPS, Japan Society for the Promotion of Scienc

Influence of types of alkali treatment on the mechanical properties of hemp fiber reinforced polyamide 1010 composites

In order to develop the new engineering materials such as structural materials and tribomaterials based on all plants-derived materials, the purpose of this study is to investigate the influence of types of alkali treatment on the mechanical and tribological properties of hemp fiber (HF) reinforced plants-derived polyamide 1010 (HF/PA1010) biomass composites. HF were surface-treated by four types of surface treatments: (a) alkali treatment by sodium hydroxide (NaOH) solution, (b) alkali treatment by sodium chlorite (NaClO2) solution, (c) alkali treatment by NaOH solution and surface treatment by ureido silane coupling agent, and (d) alkali treatment by NaClO2 solution and surface treatment by ureido silane. The volume fraction of hemp fiber in the composites was fixed with 20vol.%. HF/PA1010 composites were extruded by a twin screw extruder and injection-molded. Mechanical properties such as tensile, bending and tribological properties by ring-on-plate type sliding wear testing were evaluated. It was found that the effect of the types of alkali treatment on the mechanical and tribological properties of the composites differed for each property. The mechanical and tribological properties are improved with both alkali treatments by NaOH and NaClO2 with or without the surface treatment by ureido silane coupling agent (A-1160). This may be attributed to the interfacial interaction and interphase adhesion between HF and PA1010 according to the type of these alkali treatments. The combination NaClO2 and A-1160 is the most effect improvement for the mechanical and tribological properties of HF/PA1010 biomass composites. It follows from these results that it may be possible to develop the new engineering materials with sufficient balance between mechanical and tribological properties. © 2016 Author(s)

The genomic landscape at a late stage of stickleback speciation: High genomic divergence interspersed by small localized regions of introgression

Speciation is a continuous process and analysis of species pairs at different stages of divergence provides insight into how it unfolds. Previous genomic studies on young species pairs have revealed peaks of divergence and heterogeneous genomic differentiation. Yet less known is how localised peaks of differentiation progress to genome-wide divergence during the later stages of speciation in the presence of persistent gene flow. Spanning the speciation continuum, stickleback species pairs are ideal for investigating how genomic divergence builds up during speciation. However, attention has largely focused on young postglacial species pairs, with little knowledge of the genomic signatures of divergence and introgression in older stickleback systems. The Japanese stickleback species pair, composed of the Pacific Ocean three-spined stickleback (Gasterosteus aculeatus) and the Japan Sea stickleback (G. nipponicus), which co-occur in the Japanese islands, is at a late stage of speciation. Divergence likely started well before the end of the last glacial period and crosses between Japan Sea females and Pacific Ocean males result in hybrid male sterility. Here we use coalescent analyses and Approximate Bayesian Computation to show that the two species split approximately 0.68–1 million years ago but that they have continued to exchange genes at a low rate throughout divergence. Population genomic data revealed that, despite gene flow, a high level of genomic differentiation is maintained across the majority of the genome. However, we identified multiple, small regions of introgression, occurring mainly in areas of low recombination rate. Our results demonstrate that a high level of genome-wide divergence can establish in the face of persistent introgression and that gene flow can be localized to small genomic regions at the later stages of speciation with gene flow