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Taiwanese minnows hybrids.

I studied the population structure and evolution of minnows, which are the most commonly harvested fish in rivers.

This is my second research projected advised by Professor Wang Hurng-Yi in National Taiwan University( NTU.)  It is partially sponsored by the Ministry of Science and Technology of Taiwan.

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The distribution of minnows in Taiwan

Three species of genus Opsariichthys and Zacco platypus can be found in the shallow water of rivers, especially in middle streams. While Zacco platypus is confirmed to be alien species introduced from Japan, Opsariichthys species are all native.

Opsariichthys and Zacco are closely related sister groups in Cyprinidae

O. pachycephalus was thought to residing in the whole island, but Chen I-Shiung separated the southern population as O. Kaopingensis according to morphology and mitochondrial D-loop sequences. [DOI: 10.1007/s10641-009-9499-y]

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Some individuals are morphologically ambiguous whose identities need investigation.

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We utilized multiple nuclear loci (from 25 to 39) and three mitochondrial sequences (cox-1, D-loop, cyt-b) to elucidate the population structures of minnows.

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The genetic structure of O. pachycephalus  & O. Kaopingensis.

This is inferred form 39 nuclear sequences (most of them are single-copied) with software STRUCTURE2. It shows there is clear population delimitation between the northern and southern populations.

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The genetic structure of native minnows.

O. evolans are distributed in northern Taiwan, sympatrically with O. pachycephalus. Our results indicate that there is no detectable gene flow between them, although their habitats are quite similar.

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The genetic structure of introduced Zacco platypus and native Opsariichthys species.

With multiple nuclear markers, we can prove significant hybridization among minnows, including O. pachycephalus × Z. platypus and O. evolans × Z. platypus. F1 dose exist. F2 or F3 exists as well. One sample was identified as Z. platypus according to morphology but turned out to be a hybrid.

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The phylogenetic relationship among minnows inferred from 3 mitochondrial loci.

From the mitochondrial sequences, we discover that the hybridization is bilateral, either Zacco or Opsariichthys can be the maternal part.

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tree comparison.png

The phylogenetic relationship among minnows inferred from mitochondrial loci (LEFT) or nuclear sequences (RIGHT).

This is the first phylogeny made according to nuclear sequences, which shows incongruity to mitochondrial tree. The minnows in SE Asia are involved. Candidia barbita is the out group.

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Inter-genera hybridization is confirmed among introduced Zacco and local Opsariichthys while there is remarkable reproductive barrier among native sympatric populations.

Reproductive barrier may be weakened or not well built in the history of speciation. If they meet each other again due to geological events or human translocation (such as here), the hybridization can occur again.

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  1. Photos of fish in this page are all from "The Fish Database of Taiwan." ​

  2. The names of the sequences and some information are masked because the data are going to be formally published.

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