# Island vs. Mainland: Genetic Divergence of Calotes versicolor (Daudin, 1802) (Squamata: Agamidae) in Thailand

## TL;DR

This study examines how geographic isolation affects the genetic diversity of Oriental Garden lizards in Thailand, finding that both historical and current factors shape their genetic structure.

## Contribution

The study reveals that regional geography, not just island-mainland separation, influences genetic divergence in Calotes versicolor.

## Key findings

- Island and mainland populations show both shared and unique haplotypes, indicating mixed genetic relationships.
- Divergence-time analysis links lineage splits to late Pleistocene climatic changes and sea-level fluctuations.
- Three major genetic lineages were identified, including a clade restricted to specific regions like Trat Province and Phuket Island.

## Abstract

Islands provide unique opportunities to study how geographic isolation influences genetic diversity and evolutionary processes. The Oriental Garden lizard (Calotes versicolor) is a widespread reptile found across mainland and island habitats in Thailand. By analyzing mitochondrial CO1 sequences from populations in the Andaman Sea and Gulf of Thailand regions, we assessed their genetic diversity and population structure. The results revealed a mixture of shared and unique haplotypes, with some island and mainland populations being genetically similar, while others showed clear divergence. These patterns suggest that both historical connections and current geographic barriers have shaped the genetic landscape of C. versicolor. Our findings contribute to the understanding of reptile biogeography in Southeast Asia and provide valuable information for biodiversity conservation.

Geographic isolation can shape genetic variation and structure, leading to divergence between island and mainland populations. The Oriental Garden lizard (Calotes versicolor Daudin, 1802) is a widespread agamid reptile in Asia, occurring across diverse habitats from continental Southeast Asia to offshore islands. We examined mitochondrial cytochrome c oxidase subunit I (CO1) sequence variation in 143 individuals from 23 localities across the Andaman Sea and Gulf of Thailand to assess genetic diversity and structure between insular and mainland populations. Forty-six haplotypes (Cve1–Cve46) were identified, with haplotype diversity (Hd) ranging from 0.500 to 1.000 and nucleotide diversity (π) from 0.0057 to 0.0265. AMOVA revealed low to moderate differentiation between island and mainland groups in the Andaman Sea (FCT = 0.075, p > 0.05) and negligible differentiation in the Gulf of Thailand (FCT = 0.009, p > 0.05). Haplotype networks and PCoA showed clustering of most island and mainland populations within regions, with some localized divergence. Divergence-time analysis indicated that lineages split within the last 0.5 million years ago (Ma), coinciding with late Pleistocene climatic oscillations and sea-level changes. Species delimitation analyses supported three major lineages, including a geographically restricted clade confined to Trat Province and Phuket Island. These results suggest that C. versicolor populations are structured more by regional geography than strict island–mainland separation, reflecting historical connectivity and contemporary gene flow. The findings contribute to understanding reptile biogeography in Southeast Asia and highlight populations of conservation value.