Comparison of Mitochondrial Genome Expression Differences among Four Skink Species Distributed at Different Latitudes under Low-Temperature Stress

Abstract

Continual climate change strongly influences temperature conditions worldwide, making ectothermic animals as suitable species for studying the potential impact of climate change on global biodiversity. However, the study of how lizards distributed at different latitudes respond to climate change at the transcriptome level is still insufficient. According to the Climatic Variability Hypothesis (CVH), the range of climate fluctuations experienced by terrestrial animals throughout the year increases with latitude, so individuals at higher latitudes should exhibit greater thermal plasticity to cope with fluctuating environments. Mitochondria, as the energy center of vertebrate cells, may indicate species' plasticity through the sensitivity of gene expression. In this study, we focused on the changes in transcript levels of liver mitochondrial protein-coding genes (PCGs) in skinks from the genus Plestiodon (P. capito and P. elegans) and the genus Scincella (S. modesta and S. reevesii) under low-temperature conditions of 8 °C, compared to the control group at 25 °C. Species within the same genus of skinks exhibit different latitudinal distribution patterns. We found that the two Plestiodon species, P. elegans and P. capito, employ a metabolic depression strategy (decreased transcript levels) to cope with low temperatures. In contrast, the two Scincella species show markedly different patterns: S. modesta exhibits significant increases in the transcript levels of six genes (metabolic compensation), while in S. reevesii, only two mitochondrial genes are downregulated (metabolic depression) compared to the control group. We also found that P. capito and S. modesta, which live at mid-to-high latitudes, exhibit stronger adaptive responses and plasticity at the mitochondrial gene level compared to P. elegans and S. reevesii, which live at lower latitudes. We suggest that this enhanced adaptability corresponds to more significant changes in a greater number of genes (plasticity genes).

Keywords: RT-qPCR; latitudinal pattern; low-temperature stress; mitochondrial genome expression; skink.

Figure 1

(A) Sampling sites and distribution areas of P. capito, P. elegans, S. modesta, and S. reevesii. Different colors represent different species. P. capito from Nanyang, Henan, is represented by blue (33°08′ N, 112°21′ E). P. elegans from Guilin, Guangxi, is represented by yellow (24°18′ N, 109°42′ E). S. modesta from Xianning, Hubei, is represented by red (29°34′ N, 114°29′ E). S. reevesii from Guangzhou, Guangdong, is represented by green (23°11′ N, 113°23′ E). (B) Temperature variation maps for January and July in China. The first row, from left to right, represents the mean temperature, minimum temperature, and maximum temperature in China for January, which is the coldest month of the year. The second row, from left to right, represents the mean temperature, maximum temperature, and minimum temperature in China for July, which is the hottest month of the year. The gradient colors on the map indicate temperature variations in the thermal environment.

Figure 2

Steady-state transcript levels of 13 PCGs under control (25 °C) and low-temperature (8 °C) stress in (A) Plestiodon elegans, (B) Plestiodon capito, (C) Scincella reevesii, and (D) Scincella modesta, where “*” indicates a significant difference (p < 0.05) and “**” indicates (p < 0.01). Gene names are displayed on the x-axis and gene steady-state transcript levels are shown on the y-axis. The y-axis represents mean ± SE. Relative expression levels were normalized using β-actin as the reference gene. Specific values can be found in Table S1.

Figure 3

Steady-state transcript levels of 13 PCGs of Scincella modesta in response to low-temperature stress. Gene names are displayed on the x-axis and gene steady-state transcript levels are shown on the y-axis. Asterisks indicate significantly different expression as compared with controls (*, p < 0.05) and (**, p < 0.01). The y-axis represents mean ± SE. Relative expression levels were normalized using β-actin as the reference gene. Specific values can be found in Table S1.