Abstract:

Aims: Apple snails (Pomacea spp.) distribute widely in the Chinese provinces south of the Yangtze River, which are spreading to the northern regions every year. We aimed to determine the identities and distributions of Pomacea species in the lower reaches of the Yangtze River.

Methods: In this study, we collected apple snail samples from 11 populations in Shanghai and Jiangsu Province at the lower reaches of the Yangtze River. From these samples, we sequenced 270 mitochondrial COI sequences. We retrieved the published Pomacea sequences of other Chinese populations (in the China’s mainland and Hong Kong), Japanese populations, and the native populations in Argentina and Brazil to form a COI dataset of 972 sequences from GenBank. We first identified species based on genetic distance and phylogenetic analysis of haplotypes and then analyzed the population genetic structures based on the parsimony network under 95% parsimony limit using the COI dataset. To compare the genetic diversity of the populations from this study and other Chinese populations, we calculated the haplotype diversity (Hd), nucleotide diversity (π), and average number of nucleotide difference (k) for the populations of P. canaliculata and P. maculata. We conducted the hierarchical analysis of molecular variance (AMOVA) of the populations from the south and north of the Yangtze River for P. canaliculata, due to only this species distributed in both banks. Finally, we determined the introgression patterns by genotyping the nuclear EF1α using the primer-specific- multiplex polymerase chain reaction (PCR).

Results: We generated 10 haplotypes (Hap1-10) from the COI dataset, and identified Hap1-9 as P. canaliculata, and Hap10 as P. maculata. Pomacea canaliculata was found in all the surveyed populations, while P. maculata was only found in the Jiangsu populations north of the Yangtze River. The parsimony network of the populations of P. canaliculata split into three sub-networks, and each shared the haplotypes from Argentina. Notably, the sub-network containing Hap5 and Hap7 was firstly discovered in China. Both the parsimony network and the distribution frequencies of the haplotypes revealed that the population structures in this region were similar to the Japanese populations. Hap10 of P. maculata was identical with the dominant haplotype in other regions of China, which was shared with the haplotype from Brazil. The population diversity of P. canaliculata found in this study was the highest compared to other studies (Hd = 0.627), whereas the population diversity of P. maculata from the highest (Hd = 0.356) in Hong Kong. The populations of P. canaliculata across the Yangtze River were divided into three groups by AMOVA analysis, with the major source of molecular variance contributed from the groups. Genotyping the nuclear EF1α gene of the apple snails from this study revealed 52.6% hybrids, which was higher than that of the native populations.

Conclusion: The P. canaliculata populations in the lower reaches of the Yangtze River likely result from multiple introductions from Argentina, and provide a new history of introduction of P. canaliculata in Shanghai and Jiangsu Province. Pomacea maculata may be introduced from other existing populations in China mainly in Sichuan Basin and Zhejiang Province, which are derived originally from Brazil. The high proportion of hybrids suggest continuous introgressive hybridization during the invasion process. Our results provide important information for the monitoring and effective control of invasive apple snails.

Key words: biological invasion, molecular identification, population diversity, mitochondrial COI, introgressive hybridization, spread