Transcriptome Analysis Reveals Olfactory System Expression Characteristics of Aquatic Snakes

A time-course transcriptome analysis revealing the potential molecular mechanism of early gonadal differentiation in the Chinese giant salamander

The Chinese giant salamander (CGS) Andrias davidianus is the largest extant amphibian and has recently become an important species for aquaculture with high economic value. Meanwhile, its wild populations and diversity are in urgent need of protection. Exploring the mechanism of its early gonadal differentiation will contribute to the development of CGS aquaculture and the recovery of its wild population. In this study, transcriptomic and phenotypic research was conducted on the critical time points of early gonadal differentiation of CGS. The results indicate that around 210 days post-hatching (dph) is the critical window for female CGS's gonadal differentiation, while 270 dph is that of male CGS. Besides, the TRPM1 gene may be the crucial gene among many candidates determining the sex of CGS. More importantly, in our study, key genes involved in CGS's gonadal differentiation and development are identified and their potential pathways and regulatory models at early stage are outlined. This is an initial exploration of the molecular mechanisms of CGS's early gonadal differentiation at multiple time points, providing essential theoretical foundations for its captive breeding and offering unique insights into the conservation of genetic diversity in wild populations from the perspective of sex development.

Genomic evidence reveals intraspecific divergence of the hot-spring snake (Thermophis baileyi), an endangered reptile endemic to the Qinghai-Tibet plateau

Understanding how and why species evolve requires knowledge on intraspecific divergence. In this study, we examined intraspecific divergence in the endangered hot-spring snake (Thermophis baileyi), an endemic species on the Qinghai-Tibet Plateau (QTP). Whole-genome resequencing of 58 sampled individuals from 15 populations was performed to identify the drivers of intraspecific divergence and explore the potential roles of genes under selection. Our analyses resolved three groups, with major intergroup admixture occurring in regions of group contact. Divergence probably occurred during the Pleistocene as a result of glacial climatic oscillations, Yadong-Gulu rift, and geothermal fields differentiation, while complex gene flow between group pairs reflected a unique intraspecific divergence pattern on the QTP. Intergroup fixed loci involved selected genes functionally related to divergence and local adaptation, especially adaptation to hot spring microenvironments in different geothermal fields. Analysis of structural variants, genetic diversity, inbreeding, and genetic load indicated that the hot-spring snake population has declined to a low level with decreased diversity, which is important for the conservation management of this endangered species. Our study demonstrated that the integration of demographic history, gene flow, genomic divergence genes, and other information is necessary to distinguish the evolutionary processes involved in speciation.

Differential gene expression patterns between the head and thorax of Gynaephora aureata are associated with high-altitude adaptation

Grassland caterpillars (Lepidoptera: Erebidae: Gynaephora) are important pests in alpine meadows of the Qinghai-Tibetan Plateau (QTP). These pests have morphological, behavioral, and genetic adaptations for survival in high-altitude environments. However, mechanisms underlying high-altitude adaptation in QTP Gynaephora species remain largely unknown. Here, we performed a comparative analysis of the head and thorax transcriptomes of G. aureata to explore the genetic basis of high-altitude adaptation. We detected 8,736 significantly differentially expressed genes (sDEGs) between the head and thorax, including genes related to carbohydrate metabolism, lipid metabolism, epidermal proteins, and detoxification. These sDEGs were significantly enriched in 312 Gene Ontology terms and 16 KEGG pathways. We identified 73 pigment-associated genes, including 8 rhodopsin-associated genes, 19 ommochrome-associated genes, 1 pteridine-associated gene, 37 melanin-associated genes, and 12 heme-associated genes. These pigment-associated genes were related to the formation of the red head and black thorax of G. aureata. A key gene, yellow-h, in the melanin pathway was significantly upregulated in the thorax, suggesting that it is related to the formation of the black body and contributed to the adaptation of G. aureata to low temperatures and high ultraviolet radiation in the QTP. Another key gene, cardinal, in the ommochrome pathway was significantly upregulated in the head and may be related to red warning color formation. We also identified 107 olfactory-related genes in G. aureata, including genes encoding 29 odorant-binding proteins, 16 chemosensory proteins, 22 odorant receptor proteins, 14 ionotropic receptors, 12 gustatory receptors, 12 odorant degrading enzymes, and 2 sensory neuron membrane proteins. Diversification of olfactory-related genes may be associated with the feeding habits of G. aureata, including larvae dispersal and searching for plant resources available in the QTP. These results provide new insights into high-altitude adaptation of Gynaephora in the QTP and may contribute to the development of new control strategies for these pests.

On the validity of Hebius sauteri maximus (Malnate, 1962) (Squamata, Natricidae), with the redescription of H. maximus comb. nov. and H. sauteri (Boulenger, 1909)

Hebius sauteri (Boulenger, 1909) has been long recognized as a widely distributed species with three subspecies, namely Hebius sauteri sauteri from Taiwan Island and southeastern China, Hebius sauteri bourreti (Malnate, 1962) from northern Vietnam, and Hebius sauteri maximus (Malnate, 1962) from Sichuan, southwestern China. However, the validity of these subspecies of the H. sauteri complex has not been evaluated. In the current study, we re-evaluate the taxonomic status of H. s. maximus based on morphological and molecular evidence. Molecular phylogenetic results indicate that H. s. maximus is a distantly diverged clade with respect to H. s. sauteri, and that H. s. maximus is morphologically distinguishable from the nominative subspecies. Therefore, our results support the validity of H. s. maximus and we elevate it to full species status, namely Hebius maximuscomb. nov. The distribution range of H. sauteri is revised according to our proposed taxonomic change. Furthermore, detailed redescription, natural history, and coloration of both H. sauteri and H. maximus and comments on the validity of H. s. bourreti are also provided.

Genome of Laudakia sacra Provides New Insights into High-Altitude Adaptation of Ectotherms

Anan’s rock agama (Laudakia sacra) is a lizard species endemic to the harsh high-altitude environment of the Qinghai–Tibet Plateau, a region characterized by low oxygen tension and high ultraviolet (UV) radiation. To better understand the genetic mechanisms underlying highland adaptation of ectotherms, we assembled a 1.80-Gb L. sacra genome, which contained 284 contigs with an N50 of 20.19 Mb and a BUSCO score of 93.54%. Comparative genomic analysis indicated that mutations in certain genes, including HIF1A, TIE2, and NFAT family members and genes in the respiratory chain, may be common adaptations to hypoxia among high-altitude animals. Compared with lowland reptiles, MLIP showed a convergent mutation in L. sacra and the Tibetan hot-spring snake (Thermophis baileyi), which may affect their hypoxia adaptation. In L. sacra, several genes related to cardiovascular remodeling, erythropoiesis, oxidative phosphorylation, and DNA repair may also be tailored for adaptation to UV radiation and hypoxia. Of note, ERCC6 and MSH2, two genes associated with adaptation to UV radiation in T. baileyi, exhibited L. sacra-specific mutations that may affect peptide function. Thus, this study provides new insights into the potential mechanisms underpinning high-altitude adaptation in ectotherms and reveals certain genetic generalities for animals’ survival on the plateau.