Study On Morphology And Genetics Of Saurida Elongta

Saurida elongate, which belongs to Actinopterygii, Aulopiformes, Synodontidae, Saurida, is one of the most economical important warm-temperature and offshore demersal smaller fishes that can be caught in all year, especially in spring and winter. S. elongate can be found from north to south around coasts of China and is widely distributed in northwestern Pacific Ocean, including China, Japan and Korea. The management of S. elongate resources appeared to be more important under the influence of overfishing and environmental disruption in recent years. Our studies revealed the genetic diversity level and formation mechanism of S. elongate’s geographical pattern based on morphology and genetics. The taxonomic and phylogenetic relationships among 4 species of Saurida were also estimated in order to provide theoretical basis for rational utilization and support the further study of Saurida.1. Morphological analysis of S. elongate populationsThirty morphological indices (10 meristic characteristics and 20 measurement characteristics) of 144 individuals from 5 populations were measured by traditional morphological and landmark morphological methods and the data was analyzed by using oneway-ANOVA analysis, discriminant analysis, principal componnet analysis and cluster analysis. The results of meristic characteristics showed that there was no significant difference among populations; the results of principal component analysis showed that the first 8 principal components explained 85.8% of morphological difference, and the scatter plot on the first and second principal component indicated that apparent limit didn’t exist among populations; the result of cluster analysis showed that population Nantong and Qingdao were pooled in one group, then pooled with other populations; the results of discriminant analysis showed that the average classification ratio was 75.9%, and the scatter plot was bascial consistent with the results of principal component analysis apart from Rizhao and Beihai; the results of one way-ANOVA analysis showed that there was no significant difference between Nantong and Qingdao. These phenomena maybe related to the different environment around different populations.2. Otolith morphological analysis of S. elongate populationsShape index method and elliptic Fourier method were used in the Otolith morphological analysis of 5 S. elongate populations. The results of heterogeneity test indicated that there was no significant difference in left and right otoliths of S. elongate; the results of multivariate statistical analysis and traditional morphological analysis were different, because Rizhao population got the greatest differences with other populations in the former analysis, Beihai population got the greatest differences in the later. Otolith appearance changed with the growth of S. elongate, the smaller size of Rizhao population may lead to these results.3. Genetic analysis of S. elongate populationsIn order to reveal the genetic diversity level and population genetic structures of S. elongate, the mtDNA control region and Cyt b sequences of 118 individuals from 5 populations of S. elongate were sequenced and aligned. Results of the two sequences which showed the high haplotype diversities and low nucleartide diversities were accordant; the results of Fs, showed that there was significant genetic differentiation between Beihai population and other populations, the exact test also showed that the Beihai population and other populations are nonrandom mating, AMOVA revealed the genetic variation of S. elongala mainly comes from the internal populations; Minimum spanning tree and NJ phylogenetic tree showed us no obvious pedigree structure existed among the populations; the results of neutrality test and mismatch distribution analysis indicated that expansion has happened in S. elongate from small effective population size, which was the consequence of the late Pleistocene glacial event, and the expanding time might be 76300-254200 years before.4. Phylogenetic relationships of SauridaIn present study, we used COI gene sequences to investigate the phylogenetic relationships among 4 species of Saurida. The results showed that the nucleotide replacements of four Saurida species mainly occurred in the third amino acid codon, and mostly were synonymous mutation, rarely resulted in amino acid substitution. We used Neighbor joining method (NJ), Maximum parsimony (MP), Maximum likelihood (ML) and Bayesian inference method (BI) to construct the phylogenetic tree, at the same time we use 1.2% per million years as the COI gene nucleotide divergence rate to calculate four Saurida species differentiation time, we can see that 5. elongata firstly divided in about 8.9 million years ago, during the Miocene, later followed S. tumbil divided in about 6.43 million years ago, during the Pliocene the last two species S. umeyoshii and S. undosquamis generated differentiation in 4.28 millions of years ago.