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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
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
・ 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. H2S) accumulate in anoxic layer
・ Organisms could not migrate between marine lake and lagoon in the present
The formation procedure of marine lakes
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
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) andcontrol region (877bp)
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
Results & DiscussionResults & Discussion
JFOS 20 6 0.737 0.089
KBB 23 9 0.688 0.140
NTOS 14 6 0.747 0.099
HLOS 15 4 0.371 0.035
33 17 0.936 0.335
23 21 0.988 0.642
13 13 1.000 0.680
16 12 0.967 0.519
Genetic diversity
JFL 20 4 0.284 0.026
MEC3 24 1 0.000 0.000
ONG 26 2 0.148 0.013
25 8 0.590 0.120
24 4 0.308 0.047
26 3 0.151 0.026
N H h π
Cyt b
N H h π
Control region
N: number of individuals, H: number of haplotypes, h: haplotype diversityπ: nucletide diversity
0.5
0.5
0.5
0.5
h
π
Cyt b Control region
Genetic diversity of marine lake populations is much lower than that of lagoon populations
lagoon
Marine lakeπ
h
JFLMEC3
KBBJFOSNTOSHLOS
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
ONGJFL
MEC3
Statistical parsimony network based on control region
JFLMEC3 KBB
JFOSNTOSHLOS
ONG
Marine lake Lagoon
Sulawesi
・ One major haplotype was found
・ The major haplotype was also found in lagoon population
24
11
Founder effect
The ONG population
Isolation Genetic drift
Founder effect
Fixation
The ONG population
・ One major haplotype was found
・ The major haplotype was also found in lagoon population
・ Two endemic haplotypes were found
24
11
The JFL and MEC3 populations
CT repeat5⇔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
2016
3
2
This strongly suggests that the minor haplotypes were emerged in marine lakes
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)
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
0.059 (P<0.05)
Slightly genetic differentiation has already occurred between the JFL and the MEC3 population
Stepwise formation hypothesis
lagoon population
Ancestral
Colonized?JFL population
MEC3 population
ONG population
Founder effct
New mutationAccumulated
~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
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
Thank you very for your attention!!
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