Genetic Diversity Analysis of Mitochondrial D-loop Sequence of Ptychidio jordani in Xijiang River Basin

Abstract:

To study the genetic diversity and genetic differentiation of a Ptychidio jordani population in the Xijiang River Basin, Guangxi Province, China, mitochondrial D-loop sequences from six rivers were subjected to polymer chain reaction and DNA sequencing analysis. The A+T base composition was much higher (65.7%) than the C+G combination (34.3%) in 139 individuals, which have a D-loop sequence length of 725 bp, and a transversion ratio R of 11.5. Twenty-five polymorphic sites were defined. An NJ system tree of haplotypes and network structure diagram revealed two distinct branches among 23 haplotypes but no obvious geographic clusters, because the haplotypes from different geographic groups were mixed in two branches. Individuals from six different geographic populations had superior genetic diversity (Hd=0.71585~0.92063, Pi=0.00173~0.00668) and extremely significant genetic differentiation (Fst=0.36737, P<0.001). Analysis of molecular variance indicated that most of the variation was intragroup (63.26%). The results of a neutrality test (Tajima’s D= –0.50322, P-value=0.34600; Fu’s Fs= –5.05210, P-value=0.08800) and nucleotide mismatch distribution showed that the population of P. jordani in the Xijiang River Basin had not experienced a population expansion in recent years. The genetic diversity of the P. jordani in the Xijiang River Basin exhibited high haplotype and low nucleotide diversity. Various degrees of genetic differentiation intergroups indicate that a dam barrier and fishing factors may be contributing to their occurrence, and a cascade development of water resources may be the primary cause of population genetic differentiation of P. jordani.