# Terrestrial Adaptation in Chelonoidis vicina as Revealed Based on Analysis of the Complete Mitochondrial Genome

## TL;DR

This study analyzes the mitochondrial genome of Chelonoidis vicina to understand how it adapted to a terrestrial lifestyle.

## Contribution

The study identifies specific genes under positive selection in C. vicina that may be linked to terrestrial adaptation.

## Key findings

- The mitochondrial genome of C. vicina contains 13 protein-coding genes, 2 rRNAs, 22 tRNAs, and 1 noncoding control region.
- Positive selection sites were found in COX2, COX3, Cytb, ND3, ND4, ND4L, ND5, and ND6 genes.
- COX2 and ND3 genes showed faster evolutionary rates and are linked to changes in mitochondrial energy metabolism.

## Abstract

The mitochondrial genome has been widely used in biological phylogeny and evolutionary ecology due to its specific energy metabolism center and matrilineal inheritance. In this study, the mitochondrial genome of Chelonoidis vicina was assembled and annotated, and comparative mitochondrial genome, phylogenetic, and selection pressure analyses were used to examine the structure, phylogenetic status, and terrestrial adaptive evolution characteristics of C. vicina. These analyses can aid our understanding of the history of this ancient tortoise’s adaptive evolution to a terrestrial environment from a molecular evolution standpoint.

Background/Objectives: Mitochondrial genomes are widely used in phylogenetics and evolutionary and ecological research. Methods: In this study, the newest mitochondrial genome of Chelonoidis vicina was assembled and annotated. The comparative mitochondrial genome and selection pressure analyses were used to examine the terrestrial adaptive evolution characteristics of C. vicina and other terrestrial reptiles. Results: The results reveal that the mitochondrial genome of the tortoise C. vicina is consistent with that of other tortoise species, comprising 13 protein-coding genes (PCGs), 2 rRNAs, 22 tRNAs, and 1 noncoding control region (CR). The analysis of selection pressure reveals the presence of positive selection sites in the COX2, COX3, Cytb, ND3, ND4, ND4L, ND5, and ND6 genes of terrestrial reptiles. Of these, the COX2 and ND3 genes exhibited faster evolutionary rates. The mitochondrial genome structure of C. vicina is consistent with that of different terrestrial reptiles. The positive selection sites of COX2 and ND3 in terrestrial reptiles are closely related to a change in mitochondrial energy metabolism, which is possibly related to terrestrial adaptability. Conclusions: The results of this study provide new insights into the adaptive evolution of C. vicina to terrestrial niches from a mitogenomic perspective, as well as genetic resources for the protection of C. vicina.