A study on the origins, mitochondrial genome evolution and thermal adaptive strategies of marine copepods under global warming in Korean waters = 한국 연안 해역 해양 요각류의 기원, 미토콘드리아 유전체 진화 및 지구온난화에 따른 열 적응 전략 연구

다국어 초록 (Multilingual Abstract)

This dissertation investigates the origin and thermal adaptation mechanisms of copepods inhabiting the southern coastal waters of Korea, with a particular focus on the summer season when seawater temperatures reach their annual peak. As global warming accelerates, rising ocean temperatures are profoundly reshaping marine ecosystems, threatening the survival and distribution of thermally sensitive species such as copepods. In this context, understanding how these organisms respond to thermal stress at both ecological and genetic levels is critical. This dissertation comprises a series of integrative studies that trace species origins, uncover cryptic diversity, and explore genetic responses to heat stress through physiological experiments and transcriptomic analyses. In Chapter 2, I investigated the unexpected dominance of Calanus sinicus a cold-water indicator species of the Yellow Sea in Yeosu Bay during the high-temperature summer period. Despite elevated sea surface temperatures in the region, this species consistently appeared in large numbers. However, whether these individuals represent heat-adapted local populations or are recent immigrants from other water masses remained unexplored. To address this, I employed COX1 and ITS1 molecular markers for haplotype analysis, coupled with previously published ocean current data, to trace potential dispersal routes and identify the source populations of C. sinicus. Chapter 3 focuses on developing genomic resources necessary to advance the study of Tigriopus west, a harpacticoid copepod discovered in the intertidal zone of Mansung-ri, Yeosu. I isolated a genetically uniform population derived from a single egg sac and the complete mitochondrial genome. This newly reported mitogenome was used to confirm the species identity of the collected specimens and to evaluate their placement among described Tigriopus species using COX1-based phylogenetic analysis. My finding provides foundational genomic information for T. west and establishes a basis for future comparative studies on mitochondrial genome evolution and species-level divergence within the genus. In Chapter 4, I explore the molecular mechanisms underlying heat adaptation in T. west through transcriptome profiling under different temperature regimes. As noted in Chapter 3, molecular studies on T. west have been extremely limited. Unlike other Tigriopus species, T. west exhibits remarkable resilience to extreme heat, yet the underlying mechanisms remain poorly understood. Through differential gene expression analysis, I identify candidate genes and pathways associated with thermal tolerance, providing new insights into how this intertidal species adapts to episodic heat stress. In addition, these studies provide a comprehensive framework for understanding how copepods respond to thermal challenges at both ecological and molecular levels. By integrating field observations with genomic and transcriptomic tools, as well as phylogenetic analyses, this dissertation sheds light on the evolutionary processes and species origins that enable survival in fluctuating and extreme coastal environments.

목차 (Table of Contents)

• Contents ⅰ
• List of figures ⅴ
• List of tables ⅷ
• Abstract ⅹ
• Chapter 1. General introduction 1
• A. Background 1
• B. Thesis Objectives 6
• Chapter 2. Genetic insights into the population dynamics of Calanus sinicus
• (Calanidae, Copepoda) in Korean coastal waters 8
• A. Introduction 8
• B. Materials and methods 10
• 1) Study area and collection10
• 2)DNA amplification and sequencing 15
• 3) Haplotype analysis 16
• 4) Population structure analysis 17
• C. Results17
• 1) Population genetic structure 17
• 2) Minimum spanning network 18
• 3) Haplotype compositions and pairwise genetic distances 21
• D. Discussion 25
• 1) Genetic differentiation based on COX1 and ITS1 genes25
• 2) Connectivity of C. sinicus populations around the Korean peninsula 26
• 3) The C. sinicus population of YB27
• Chapter 3. Extreme thermal tolerance and the first complete mitochondrial
• genome of Tigriopus west 31
• A. Introduction 31
• B. Materials and methods 34
• 1) Sample collection and culture 34
• 2) DNA extraction and amplification 35
• 3) Library construction and whole genome sequencing 35
• 4) de novo mitochondrial genome assembly36
• 5) Phylogenetic analysis36
• 6) Lethal temperature 50 (LT50) test 38
• C. Results39
• 1) Sequencing information and characteristics of T. west mitochondrial genome39
• 2) Species identification and phylogenetic analysis 41
• 3) Environmental pressure on T. west mitochondrial genome 44
• D. Discussion 47
• Chapter 4. Molecular responses of Tigriopus west to high thermal stress in tide
• pool 50
• A. Introduction 50
• B. Materials and methods 53
• 1) Sample collection and sequencing 53
• 2) de novo transcriptome assembly 54
• C. Results55
• 1) Overview of RNA sequencing and differentially expressed genes (DEGs) 55
• 2) KEGG pathway enrichment of temperature-responsive core genes 60
• 3) KOG functional classification of heat-induced genes 60
• 4) Heat-induced expression of chaperone and co-chaperone genes60
• D. Discussion 66
• Chapter 5. General conclusion 70
• Overall finding 70
• Chapter 2 70
• Chapter 3 70
• Chapter 4 71
• References 72