Abstract
Karyotype analysis was carried out on gill cells of three species of octopods using a conventional air-drying method. The karyotype results showed that all the three species have the same diploid chromosome number, 2n=60, but with different karyograms as 2n=38M+6SM+8ST+8T, FN (fundamental number)=104 (Cistopus chinensis Zheng et al., 2012), 2n=42M+6SM+4ST+8T, FN=108 (Octopus minor (Sasaki, 1920)) and 2n=32M+16SM+12T, FN=108 (Amphioctopus fangsiao (d’Orbigny, 1839–1841)). These findings were combined with data from earlier studies to infer the genetic relationships between nine species via cluster analysis using the karyotype evolutionary distance (De) and resemblance-near coefficient (λ). The resulting tree revealed a clear distinction between different families and orders which was substantially consistent with molecular phylogenies. The smallest intraspecific evolutionary distance (De=0.2013, 0.2399) and largest resemblance-near coefficient (λ=0.8184, 0.7871) appeared between O. minor and C. chinensis, and Sepia esculenta Hoyle, 1885 and S. lycidas Gray, 1849, respectively, indicating that these species have the closest relationship. The largest evolutionary gap appeared between species with complicated karyotypes and species with simple karyotypes. Cluster analysis of De and λ provides information to supplement traditional taxonomy and molecular systematics, and it would serve as an important auxiliary for routine phylogenetic study.
Highlights
Cephalopoda is an old and evolutionarily successful molluscan group with a worldwide distribution (Jazayeri et al 2011, Adachi et al 2014)
From the karyotype formulas, we found that A. fangsiao had no subtelocentric chromosomes, while O. minor and C. chinensis had quite close karyotypes, with differences only in themetacentric chromosomes
The chromosome number of the three species in the present study was 2n=60, which is consistent with previous karyotype studies of octopods (Gao and Natsukari 1990, Adachi et al 2014)
Summary
Cephalopoda is an old and evolutionarily successful molluscan group with a worldwide distribution (Jazayeri et al 2011, Adachi et al 2014). It includes several species that are precious marine resources but are difficult to manage due to their short life span and sensitivity to environmental conditions (Emery et al 2016). Extant cephalopods are divided into two subclasses: Nautiloidea and Coleoidea. 134 cephalopod species (Lu et al 2012), including commercially important marine species such as Octopus minor (Sasaki, 1920), Amphioctopus fangsiao (d’Orbigny, 1839–1841), Cistopus chinensis Zheng et al, 2012 and Sepia esculenta Hoyle, 1885, are found in Chinese waters. While significant genetic knowledge is required for effective breeding and aquaculture of octopods, modern cytogenetic studies of these species are scarce
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
