Comparison of the genetic relationship between nine Cephalopod species based on cluster analysis of karyotype evolutionary distance.

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 ( Zheng et al., 2012), 2n=42M+6SM+4ST+8T, FN=108 ( (Sasaki, 1920)) and 2n=32M+16SM+12T, FN=108 ( (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 ( ) and resemblance-near coefficient (). The resulting tree revealed a clear distinction between different families and orders which was substantially consistent with molecular phylogenies. The smallest intraspecific evolutionary distance ( =0.2013, 0.2399) and largest resemblance-near coefficient (=0.8184, 0.7871) appeared between and , and Hoyle, 1885 and 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 and provides information to supplement traditional taxonomy and molecular systematics, and it would serve as an important auxiliary for routine phylogenetic study.