Phylogeography of the Mauremys mutica complex and the implications for conservation management.

For more than three decades, the Asian turtle crisis has resulted in the decline of every native species in China. For some species, such as the yellow pond turtle (Mauremys mutica), wild populations have dwindled to near functional extinction. Previous studies show there is deep genetic divergence of M. mutica sensu lato between populations north and south of the Pearl River Drainage but no data to show if phylogeographic structure occurs within these two main types. In this study, we found clear phylogeographic structure. In northern types, we found two main clades, corresponding to mainland China and island clades (Taiwan and Yaeyema Islands) with uncorrected p values of 0.00-2.0% divergence in our 2353 bp concatenated mtDNA data set. For the southern types, we found three main clades corresponding to Hainan, Mainland (Vietnam/Guangxi) and the Annam pond turtle (Mauremys annamensis) with divergence ranging from 1.0-1.8% among these three groups. Moreover, the identification of northern and southern types by phenotype was roughly 98% accurate, which, coupling with the deep genetic divergence in mtDNA (5.5-6.7%) and in the 6056 bp nuDNA data set (0.16-0.37%) provide sufficient evidence for northern M. mutica to be an independent species, and individuals from the southern clade should be regarded as subspecies of M. annamensis. Finally, we provide the most comprehensive database to date which can be used to determine the region of origin for captive stock. Making the large captive populations of M. mutica, under the right conditions, potentially valuable for restocking or augmentation of wild populations.

Chromosome-level analysis of the Mauremys mutica genome reveals adaptation of temperature-dependent sex-associated genes

Knowledge of the sex determination system and sex-associated genes has important implications in physiology, ecology and evolution, but the mechanisms underlying sexual determination systems in turtles has not been fully elucidated, due to their remarkable variability and a lack of reference genomes in some species. In this report, we describe the first genome assembled at the chromosome scale for Mauremys mutica using Illumina and high-throughput chromatin conformation capture (Hi-C) technology. A total of 280.42 Gb of clean data were generated using the Pacific Biosciences platforms, which represented approximately 119× coverage of the Mauremys mutica genome. The assembly comprised 2.23 Gb with a contig N50 of 8.53 Mb and scaffold N50 of 141.98 Mb. Genome Hi-C scaffolding resulted in 26 pseudochromosomes containing 99.98% of the total assembly. Genome annotation predicted 24,751 protein-coding genes, and 97.23% of them were annotated. Comparative genomics analysis indicated that the lizard-snake-tuatara clade diverged from the bird-crocodilian-turtle clade at approximately 283.1-320.5 Mya. Additionally, positive selection of genes and gene families related to calcium signaling, neuroactive ligand-receptor interaction, and expansion of the hormone signaling pathway were identified, implicating their roles of sex regulation inMauremys mutica. High-quality genome assembly may provide a valuable genomic resource for further research investigating gene-environment interactions in Mauremys mutica.

Effects of Simulated Heat Wave on Oxidative Physiology and Immunity in Asian Yellow Pond Turtle (Mauremys mutica)

Global warming has led to an increase in the frequency, duration, and intensity of heat waves in the summer, which can cause frequent and acute heat stress on ectotherms. Thus, determining how ectothermic animals respond to heat waves has been attracting growing interest among ecologists. However, the physiological and biochemical responses to heat waves in reptiles, especially aquatic reptiles, are still poorly understood. The current study investigated the oxidant physiology, immunity, and expression levels of heat shock proteins (HSP) mRNA after exposure to a simulated heat wave (1 week, 35 ± 4°C), followed by a recovery period (1 week, 28 ± 4°C) in juvenile Asian yellow pond turtle (Mauremys mutica), a widely farmed aquatic turtle in East Asia. The contents of malondialdehyde (MDA) in the liver and muscle were not significantly affected by the heat wave or recovery. Of all antioxidant enzymes, only the activity of glutathione peroxidase (GSH-Px) in muscles increased after heat wave, while the total superoxide dismutase (T-SOD), catalase activity (CAT), and total antioxidant capacity (T-AOC) did not change during the study. The organo-somatic index for the liver and spleen of M. mutica decreased after the heat wave but increased to the initial level after recovery. In contrast, plasma lysozyme activity and serum complement C4 levels increased after the heat wave, returning to the control level after recovery. In addition, heat waves did not alter the relative expression of HSP60, HSP70, and HSP90 mRNA in the liver. Eventually, heat wave slightly increased the IBR/n index. Therefore, our results suggested that heat waves did not lead to oxidative damage to lipids in M. mutica, but deleteriously affected the turtles’ immune organs. Meanwhile, the constitutive levels of most antioxidative enzyme activities, HSPs and enhanced blood immune functions might protect the turtles from the threat of heat waves under the current climate scenarios.