Complete mitochondrial genome of the southern painted turtle (Chrysemys dorsalis, Testudines: Emydidae) in Korea

Abstract The complete mitochondrial genome of Chrysemys dorsalis in Korea was sequenced and characterized. The mitochondrial genome is 17,258 bp in length and the GC content is 39%. It is constituted of 37 genes, 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and a noncoding region. Phylogenetic analysis reveals that C. dorsalis forms a monophyletic group with C. picta turtles but is distinctly separated from them, aligning with previous findings. In Korea, C. dorsalis forms a discrete clade, separate from both native and invasive turtle species. No evidence of genetic disturbance or intermingling is observed. This is the first case of a complete mitochondrial genome from C. dorsalis and provides crucial data for understanding C. dorsalis and managing invasive species effectively, emphasizing the need for continued mitochondrial genome data accumulation.


Introduction
Chrysemys dorsalis (Agassiz 1857), commonly known as the southern painted turtle, belongs to the Emydidae family and is recognizable by a prominent red stripe running down the center of its carapace.Initially considered a subspecies of C. picta, subsequent studies argued for the recognition of C. dorsalis as a distinct species based on mitochondrial DNA sequences (Starkey et al. 2003).This conclusion was supported by the following study and accepted by other societies (Jensen et al. 2015).
The natural habitat of C. dorsalis extends across the southcentral United States, including regions from southern Illinois and Missouri to the Gulf coast of Louisiana and parts of Alabama (McAllister et al. 2007).In addition to the United States, C. dorsalis has also been found in other countries, including Korea (GBIF Secretariat 2022).
Most of the invasive species found in the wild result from release by humans (Oh and Hong 2007;Mun et al. 2013).This introduction causes serious damage to native ecosystems and threatens biodiversity (Nentwig et al. 2018).In Korea, the number of invasive species has been steadily increasing, particularly due to the pet trade (Koo et al. 2020).
Despite the importance of managing the invasive species C. dorsalis in Korea, there is few information available about this turtle, and its complete mitochondrial genome remains uncharacterized.This study aims to present the complete mitochondrial genome sequence of C. dorsalis and investigate its phylogenetic relationship with native and invasive turtle species in Korea.
extracted from the tail using the DNeasy Blood & Tissue kit (Qiagen, Valencia, CA) following the manufacturer's instructions.The extracted DNA sample was deposited at the Museum of Wildlife, located in Research Center of Ecomimetics, Chonnam National University, Korea (https://biology.jnu.ac.kr;Ha-Cheol Sung; shcol2002@jnu.ac.kr) under Specimen voucher number: 2023-RCE-CD001.Mitochondrial genome analysis was performed using Illumina NovaSeq X plus platform (Illumina, San Diego, CA) by Macrogen (Seoul, Korea).Raw sequence data were assessed using FastQC, and adaptor trimming and quality filtering were performed using Trimmomatic (Andrews 2010;Bolger et al. 2014).Subsequently, de novo assembly was conducted using SPAdes 3.15.0,and the filtered reads were aligned using BLAST (Altschul et al. 1990;Bankevich et al. 2012).Finally, the complete sequence was annotated using MITOS2 web server (Bernt et al. 2013).
To investigate the phylogenetic position of C. dorsalis, the complete mitochondrial genome sequences of 16 species in Testudines were obtained from GenBank, and the phylogenetic tree was constructed using MEGA X software (Kumar et al. 2018).The sequences were aligned using MUSCLE algorithm, and the phylogenetic tree was generated using maximum likelihood method with the GTR þ G model and 1000 bootstrap replicates (Waddell and Steel 1997;Edgar 2004).The GTR þ G substitution model was selected as the best-fit model by MEGA X.
To explore the mitogenomic relationship between C. dorsalis and both native and invasive species in Korea, we retrieved complete mitochondrial genome sequences of the respective species from GenBank.Subsequently, a phylogenetic tree was constructed.The analysis revealed that C. dorsalis forms a monophyletic group with other C. picta turtles, but is clearly separated from them with a high bootstrap score.Moreover, C. dorsalis in Korea is not clustered with other turtles found in Korea, regardless of whether they are native species (M.reevesii and P. sinensis) or the invasive species (P.peninsularis, P. concinna, and T. s. elegans) (Figure 2).

Discussion and conclusion
We sequenced the complete mitochondrial genome of C. dorsalis and revealed the phylogenetic relationship with other turtles by constructing a phylogenetic tree.In the phylogenetic tree, C. dorsalis makes a monophyletic group with the other C. picta turtles, but they are separated with a high bootstrap score, in line with findings from a prior study (Starkey et al. 2003).In contrast, C. dorsalis in Korea forms a distinct clade when compared to other turtles, including both the native species (M.reevesii and P. sinensis) and the invasive species (P.peninsularis, P. concinna, and T. s. elegans), aligning with results from other research resources (Fritz et al. 2011).There is currently no evidence of genetic disturbance or intermingling between invasive species and either other invasive species or native species.However, a comprehensive investigation into the impact of C. dorsalis on native species and their habitat requires the accumulation of mitochondrial genome data over an extended period.This study will provide previously unavailable information and offer new insights and crucial datas for understanding C. dorsalis and managing the invasive species including C. dorsalis effectively.

Figure 1 .
Figure 1.Mitochondrial genome map of Chrysemys dorsalis.Genes encoded on heavy strand are written outside the circle and genes on light chain inside the circle.

Figure 3 .
Figure 3. Reference image for Chrysemys dorsalis.This picture was taken by the authors..