Differential Mitochondrial Genome Expression of Three Sympatric Lizards in Response to Low-Temperature Stress

Abstract

Ecological factors related to climate extremes have a significant influence on the adaptability of organisms, especially for ectotherms such as reptiles that are sensitive to temperature change. Climate extremes can seriously affect the survival and internal physiology of lizards, sometimes even resulting in the loss of local populations or even complete extinction. Indeed, studies have shown that the expression levels of the nuclear genes and mitochondrial genomes of reptiles change under low-temperature stress. At present, the temperature adaptability of reptiles has rarely been studied at the mitochondrial genome level. In the present study, the mitochondrial genomes of three species of lizards, Calotes versicolor, Ateuchosaurus chinensis, and Hemidactylus bowringii, which live in regions of sympatry, were sequenced. We used RT-qPCR to explore the level of mitochondrial gene expression under low-temperature stress, as compared to a control temperature. Among the 13 protein-coding genes (PCGs), the steady-state transcript levels of ND4L, ND1, ATP6, and COII were reduced to levels of 0.61 ± 0.06, 0.50 ± 0.08, 0.44 ± 0.16, and 0.41 ± 0.09 in C. versicolor, respectively, compared with controls. The transcript levels of the ND3 and ND6 genes fell to levels of just 0.72 ± 0.05 and 0.67 ± 0.05 in H. bowringii, compared with controls. However, the transcript levels of ND3, ND5, ND6, ATP6, ATP8, Cytb, and COIII genes increased to 1.97 ± 0.15, 2.94 ± 0.43, 1.66 ± 0.07, 1.59 ± 0.17, 1.46 ± 0.04, 1.70 ± 0.16, and 1.83 ± 0.07 in A. chinensis. Therefore, the differences in mitochondrial gene expression may be internally related to the adaptative strategy of the three species under low-temperature stress, indicating that low-temperature environments have a greater impact on A. chinensis, with a small distribution area. In extreme environments, the regulatory trend of mitochondrial gene expression in reptiles is associated with their ability to adapt to extreme climates, which means differential mitochondrial genome expression can be used to explore the response of different lizards in the same region to low temperatures. Our experiment aims to provide one new research method to evaluate the potential extinction of reptile species in warm winter climates.

Keywords: RT-qPCR; lizard; low-temperature stress; mitochondrial genome expression.

Figure 1

Main distribution areas of Calotes versicolor, Ateuchosaurus chinensis, and Hemidactylus bowringii in southeastern China, southwestern Asia, and southeastern Asia. A. chinensis is found mainly in southern China and Vietnam; H. bowringii is found mainly in southern China, Vietnam, Burma, and Japan; and C. versicolor is found widely across Asia.

Figure 2

The steady-state transcript levels of 13 PCGs in the three lizard species 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. The dashed line shows controls, standardized to 1.0, dark green columns show the experimental group for C. versicolor (at 4 °C), light yellow columns show the experimental group for H. bowringii (at 8 °C), and red columns show the experimental group for A. chinensis (at 8 °C), all after 24 h exposure to low temperatures. Asterisks indicate significantly different expressions as compared with controls (*, p < 0.05) and (**, p < 0.01).