High altitude is an important driving force in animal evolution. However, the effect of altitude on gut microbial communities in reptiles has not been examined in detail. Here, we investigated the intestinal microbiota of three populations of the lizard Phrynocephalus vlangalii living at different altitudes using 16S rRNA gene sequencing. Bacteroidetes, Firmicutes, and Proteobacteria were the most abundant phyla. Bacteroides, Odoribacter, and Parabacteroides were the most abundant genera. Significant differences in the intestinal microbiota composition were found among the three populations from different altitudes. The proportions of Verrucomicrobia and Akkermansia decreased, whereas Bacteroides increased significantly with altitude. Greater abundance of Bacteroides at higher altitude led to the fractional increase in the phylum Bacteroides relative to other phyla. Hypoxia may be the main factor that caused intestinal microbiota variation in P. vlangalii along the altitude gradient. Overall, our study suggested that the community composition and structure of intestinal microbiota of the lizard P. vlangalii varied along altitudes, and such differences likely play a certain role in highland adaptation. Our findings warrant a further study that would determine whether ambient and body temperatures play a key role in the modulation of intestinal microbiota in reptiles.

Compared to straight fiber path laminates, variable-angle tow (VAT) laminates are known to redistribute the in-plane stress resultants for improving structural buckling response. The VAT laminates can also be used to improve the free vibration response by tailoring the structural elastic stiffness. This paper studies the prestressed vibration response of a stiffened, VAT laminated plate under a uniform end shortening. Because there are both spatially dependent stiffener and fiber path orientations for a stiffened, VAT laminated plate, a separate modeling of the plate and stiffeners is considered. This method avoids placing common nodes at stiffener–plate and stiffener–stiffener interfaces. This allows one to study mesh convergence for the plate and the stiffeners, separately. It also improves the efficiency and robustness of the finite element model. The finite element code based on the present method is verified extensively using examples that are either available in literature or are analyzed using commercial software. Parametric studies show that, depending on the in-plane load and boundary condition, the VAT laminates with linearly varying (LV) fiber paths can increase the prestressed vibration fundamental frequency when compared to the straight fiber path laminates. Optimization studies found that using nonlinearly varying fiber paths, when compared to the LV fiber paths, causes a significant increase in the buckling load but only a slight increase in the case of free or prestressed vibration fundamental frequencies. The VAT laminates appear to mainly tailor the panel’s elastic stiffness for improving the prestressed vibration response for the stiffened plates with clamped edges. However, for the simply supported stiffened plate, the VAT laminates are mainly used to change both the elastic and geometric stiffness matrices for improving the prestressed vibration response.