Vol. 57, 2018 (update: 2018.06.19; 07.10) Variation in the Karyotype, Cytochrome b Gene, and 5S rDNA of Four Thunnus (Perciformes, Scombridae) TunasYan-Horn Lee1, Tsair-Bor Yen2, Chiu-Fen Chen3, and Mei-Chen Tseng3,* doi:10.6620/ZS.2018.57-34
1Tungkang
Biotechnology Research Center, Fisheries Research Institute, Council of
Agriculture, Pintung 928, Taiwan. E-mail: leeyh4331@hotmail.com (Received 23 October 2017; Accepted 1 June
2018; Communicated by Hin-Kiu Mok) Yan-Horn
Lee, Tsair-Bor Yen, Chiu-Fen Chen, and Mei-Chen Tseng (2018) Thunnus tunas in Scombridae are
divided into the temperate subgenus Thunnus
(bluefin group) and tropical subgenus Neothunnus
(yellowfin group) species based on anatomic traits and distributions.
The main purpose of this study was to examine the systematic status of T. obesus based on karyotype,
cytochrome (Cyt) b gene, and
5S ribosomal DNA sequences. All T.
obesus, T. albacares, T. alalunga, and T. orientalis
specimens were caught in southeastern coastal waters off the main
island of Taiwan. The karyotypical formula of T. obesus was 2 m + 2 st
+ 44 t, that of T. albacares was 2 m + 2 sm + 2 st + 42 t, that of T. alalunga was 2 m + 2 sm + 2 st +
42 t, and that of T. orientalis
was 2 m + 2 sm + 44 t (m: metacentric; sm: submetacentric; st:
subtelocentric; t: telocentric chromosome). According to a molecular
genetics analysis for these species using Cyt b gene sequences (1141 bp),
interspecific genetic distances ranged from 0.004 (T. orientalis vs. T. alalunga) to 0.038 (T. alalunga vs. T. obesus). The genealogy tree
exhibited these 4 species as being categorized into 4 monophyletic
groups with high bootstrapping values; T. alalunga and T. orientalis are sister species
This result suggests that the species currently allocated in Thunnus and Neothunnus
might need new taxonomic characters to redefine the monophyly of the
two subgenera. The sequence lengths of all cloned 5S genes from the 4
species ranged from 327-342 bp. Interspecific genetic distances ranged
from 0.016 (T. orientalis vs. T. alalunga) to 0.111 (T. orientalis vs. T. albacares). The phylogenetic
tree based on 5S rDNA shows T. obesus
divided into 2 groups: one similar to T.
albacares, and the other close to T. orientalis. These results imply
that Thunnus
tunas have a common synapomorphic character with Scombridae fish (2n =
48) and high numbers of telocentric chromosomes (42-44). Thunnus orientalis and T. alalunga are sister based on
molecular data. Thunnus
obesus may have been derived from a more-complicated speciation
processes. Key words: Thunnus albacares, T. alalunga, T. obesus, T. orientalis, synapomorphic
character. *Correspondence: Yan-Horn Lee and Tsair-Bor Yen
contributed equally to this work. E-mail: mctseng@mail.npust.edu.tw |