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Primary process of speciation in marine lakes of Palau Islands: The case of the striped silverside, Atherinomorus endrachtensis (Atherinidae, Atheriniformes,

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Presentation on theme: "Primary process of speciation in marine lakes of Palau Islands: The case of the striped silverside, Atherinomorus endrachtensis (Atherinidae, Atheriniformes,"— Presentation transcript:

1 Primary process of speciation in marine lakes of Palau Islands: The case of the striped silverside, Atherinomorus endrachtensis (Atherinidae, Atheriniformes, Teleostei) Ryo Gotoh, N. Hanzawa Graduate School of Science and Engineering, Yamagata University Yamagata University

2 Terrestrial organisms Marine organisms Background Primary process of speciation of marine organisms caused by geographical isolation is unclear Ex) Darwin’s finch on Garapagos Islands ・ Ocean is connected in the world ・ Gene flow is occurring at the large scale Many study of geographical isolation have conducted. It is easy to set up geographical isolation models, such as oceanic islands. Ex) Speciation caused by formation of the Isthmus of Panama ・ This vicariant event had occurred several million years ago We focused on marine lakes on Palau Islands

3 ・ Palau Islands are located in the West Pacific ・ There are approximately 300 islands ・ The limestone islands called “Rock Islands” are in the central and south parts of Palau ・ There are approximately 70 marine lakes in Palau Islands Palau Islands and marine lakes ・ Several marine lakes have anoxic layer (meromictic lakes) ・ Toxic substances (ex. H 2 S) accumulate in anoxic layer ・ Organisms could not migrate between marine lake and lagoon in the present The formation procedure of marine lakes

4 Comparing genetic structures of lagoon populations and marine lake populations, we show primary process of speciation of marine organisms caused by geographical isolation. “Geographical isolation model for marine organisms” Organisms inhabiting marine lakes have been isolated since the lakes were formed

5 Biology Found in shallow coastal waters Atherinomorus endrachtensis (Atherinidae, Atheriniformes, Teleostei) Distribution Western Central Pacific: Philippines and Micronesia to northern Australia and the Solomon Islands. Materials & Methods We conducted population genetic analyses based on mt DNA cyt b gene (1141bp) and control region (877bp)

6 Ongael Island JFL MEC3 ONG Mecherchar Island Red letter shows marine lakes Bule letter shows lagoon 10km (20) (24) (26) KBB(23) JFOS NTOS(14) HLOS(15) (20) Palau Islands Sulawesi

7 Results & Discussion

8 JFOS KBB NTOS HLOS Genetic diversity JFL MEC ONG N H h π Cyt b N H h π Control region N: number of individuals, H: number of haplotypes, h: haplotype diversity π: nucletide diversity

9 0.5 h π Cyt bControl region Genetic diversity of marine lake populations is much lower than that of lagoon populations lagoon Marine lake π h

10 JFL MEC3 KBB JFOS NTOS HLOS ONG Marine lake Lagoon Statistical parsimony network based on cyt b gene Palau Gene flow occurs at large scale Palau-Sulawesi =1,200km The relationships among marine lake populations are unclear. Sulawesi

11 ONG JFL MEC3 Statistical parsimony network based on control region JFL MEC3 KBB JFOS NTOS HLOS ONG Marine lake Lagoon Sulawesi

12 ・ One major haplotype was found ・ The major haplotype was also found in lagoon population 24 1 1 Founder effect The ONG population

13 Isolation Genetic drift Founder effect Fixation

14 The ONG population ・ One major haplotype was found ・ The major haplotype was also found in lagoon population ・ Two endemic haplotypes were found 24 1 1

15 The JFL and MEC3 populations CT repeat 5⇔4 ・ The number of times of CT repeat found in the JFL and the MEC3 population differs from lagoon population ・ The minor haplotypes was endemic in each marine lake and the haplotypes were derived from the major haplotype ・ One major haplotype and several minor haplotypes were found 20 16 3 2 This strongly suggests that the minor haplotypes were emerged in marine lakes

16 JFL MEC3 Lagoon population has a large number of haplotypes It is unlikely that same haplotype was fixed in different marine lake populations by chance. However, the JFL and MEC3 population have the same major haplotype. We consider “stepwise formation hypothesis”, focusing on the facts that the two marine lakes are in the same island and differ in depth (JFL: 30m, MEC3: 20m)

17 Migration from lagoon to JFL Haplotype was fixed by founder effect Each marine lake population is isolated by anoxic layer Migration from JFL to MEC3 Fixation index  st (P<0.05) Slightly genetic differentiation has already occurred between the JFL and the MEC3 population Stepwise formation hypothesis

18 lagoon population Ancestral Colonized? JFL population MEC3 population ONG population Founder effct New mutation Accumulated ~12,000 years ago present Population growth Founder effct Population growth Population growth A schematic showing the primary process of speciation in marine lake populations

19 Conclusion Marine lakes are excellent model for geographical isolation of marine organisms ・ Genetic structure between lagoon and marine lake populations are obviously different ・ Genetic structure among marine lake populations are also different ・ Each marine lake population has endemic haplotypes

20 Thank you very for your attention!!

21 創始者効果 地理的分断 (海水湖形成) 地理的分断 (海水湖形成) 遺伝的分化 固定またはそれに近い状態 遺伝的浮動が 強く作用 遺伝的浮動が 強く作用 固定または それに近い状態 集団サイズの 拡大 集団サイズの 拡大 固有ハプロタイプの 出現 集団サイズの 拡大 集団サイズの 拡大 突然変異の 蓄積 突然変異の 蓄積

22 ラグーン ・一斉放散型のネットワークを示す ラグーン集団とは明確に異なる 遺伝的構造!! JFL MEC3 ONG 統計的最節約ネットワーク (control region)

23 KBB JFOS NTOS HLOS スラウエシ 統計的最節約ネットワーク (control region に基づいて構築 ) Control region では進化速度が速く ハプロタイプ間の関係性が不明瞭

24 カスミハゼ ホソスジマンジュウイシモチ ヤクシマイワシ属の一種 1.パラオ海水湖に生息する魚類3種の複合的解析


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