# Unusual Patterns of Lateral Scutes in Two Olive Ridley Turtles and Their Genetic Assignment to the Thai Andaman Sea Populations of Lepidochelys olivacea Eschscholtz, 1829

## TL;DR

Two olive ridley turtles with unusual shell patterns were confirmed as the species using genetic testing, highlighting the need to study rare traits in sea turtle populations.

## Contribution

Identification of rare lateral scute patterns in olive ridley turtles in the Thai Andaman Sea using genetic markers.

## Key findings

- Both turtles with unusual lateral scute patterns were genetically confirmed as olive ridley turtles (Lepidochelys olivacea).
- The observed scute patterns (5/5 and 5/6) are rare in L. olivacea but resemble patterns more common in Kemp’s ridley turtles.
- Genetic analysis using mtDNA and RAG2 confirmed the turtles belong to the L. olivacea clade.

## Abstract

In this study, we used both morphology and molecular genetic tools, namely mitochondrial DNA (mtDNA) control region and nuclear DNA (nDNA) exon involving recombination activating gene 2 (RAG2), to confirm the species of two sea turtles found in the Thai Andaman Sea that possessed unusual lateral scute patterns from the original species. Both turtles were identified as the olive ridley turtle (Lepidochelys olivacea). This finding has raised awareness about the need for exploration of rare phenotypes of carapace scute patterns in the olive ridley turtle populations that reside in Thai Seas and the Indo-Pacific region.

Two stranded Lepidochelys-like sea turtles were rescued from the Thai Andaman Sea coastline by veterinarians of the Phuket Marine Biological Center (PMBC), one in May of 2019 and another in July of 2021. They were first identified as olive ridley turtles (Lepidochelys olivacea), as the external appearance of both turtles was closer to that species than the other four species found in the Thai Andaman Sea. In fact, when carefully examined, an unusual pattern of the lateral scutes on each turtle was observed, specifically symmetric 5/5 and asymmetric 5/6, both of which are considered rare for L. olivacea and had never been reported in the Thai Andaman Sea. In contrast, this characteristic was more common for the closely related species, Kemp’s ridley (L. kempii), although this species is not distributed in the Indo-Pacific Ocean. Thus, we further investigated their genetic information to confirm species identification using two molecular markers, namely the mtDNA control region and nDNA RAG2. The results from the mtDNA control region sequences using the Basic Local Alignment Search Tool (BLAST) indicated that both individuals exhibited a higher percent identity with L. olivacea (99.81–100.00%) rather than L. kempii (94.29–95.41%) or any other species. A phylogenetic tree confirmed that these two turtles belonged to the L. olivacea clade. Moreover, the results of RAG2 also supported the mtDNA result, as both individuals shared the same RAG2 haplotype with L. olivacea. Thus, we have concluded that the two turtles with unusual lateral scute patterns exhibited genetic consistency with their original species, L. olivacea, which has brought attention to the importance of exploring rare phenotypes in sea turtle populations residing in Thai Seas.