Study Of Interspecific Introgressive Hybridization In Apple Snails With Morphological And Molecular Markers

The genus Pomacea belonged to the freshwater gastropod family Ampullariidae,which was native to South and Central America.When it introduced into the freshwater environment,this genus had a tenacious vitality and had a capable of fastly spread.P.canaliculata had been listedd as one of the 100 worst invasive species in the world.P.maculata is also an invasive species,causing serious damage to agriculture and wetland ecosystems in the United States,Japan,Philippines,Vietnam and other countries.Previous studies revealed four Pomacea species including P.canaliculata,P.maculata,P.diffusa,and P.scalaris)invaded Asia.Both P.canaliculata and P.maculata had invaded many countries of East and Southeast Asia from their native range in South America.Recent studies indicated that P.canaliculata and P.maculata and cryptic groups distributed in the mainland of P.R.China.P.canaliculata and P.maculata were sympatrically distributed in Chongqing.However,the possibility of hybridization between P.canaliculata and P.maculata in the sympatric area,the taxonomic status of the cryptic groups,and the relationship between cryptic groups and the two apple snails remained unclear.In this study,the two apple snails and cryptic groups were collected from China.Phylogenetic relationship of apple snails in China based on mitochondrial gene and nuclear gene were explained the introgressive hybridization between species.The external morphological characteristics and internal radula electron structure were analysed to reveal the morphological variation in these apple snails.Main results and conclusions were as follows:1)This study analysed the nuclear gene EF1α sequences of 61 apple snails from southern provinces and municipalities of the mainland China.Phylogenetic tree and haplotype Network were constructed based on the sequences of EF1α gene.There were two well-supported clades,P.canaliculata clade and P.maculata clade.The cryptic group did not form a separate lineage,which were clustered with both P.maculata and P.canaliculata clades.All haplotypes detected in the cryptic group were also found in P.canaliculata.These results showed the evidence of genetic exchange between P.canaliculata and P.maculata in China.2)The radular formula of the apple snails was 2·1·1·1·2.The main discrepancy between the two apple snails was the central teeth.The first cusp of the central tooth of P.canaliculata was shorter and wider,but not as sharp as P.maculata.There were significant differences in the ratio of the length of the first cusp,the width of the first cusp to the width of the central tooth between the two apple snails.The morphology of lateral tooth and marginal tooth for the two apple snails and cryptic group were similar.The first cusp of the central tooth was triangle,and three small cusps arranged symmetrically on both sides between the two apple snails and cryptic group.There were one small sharp cusp inside the big cusp of lateral teeth and two small cusps outside of that in the two apple snails and cryptic group.The inner and outer marginal teeth were similar in the two apple snails and cryptic group.The central cusp of the marginal tooth was sharp,with a small cusp near it.There were significant differences in the ratio of the width of the second cusp between female P.canaliculata and cryptic group,and the ratio of the length of the first cusp,the width of the first cusp,the width of the second cusp to the width of the central tooth between female P.maculata and cryptic group.There were significant differences in the ratio of the length of the first cusp,the length of the second cusp,as well as the width of the second cusp to the width of the central teeth between male P.canaliculata and cryptic group.There were significant differences in the ratio of the width of the first cusp,the length of the second cusp,and the width of the second cusp to the width of the central teeth between male P.maculata and cryptic group.The type of radula could reflect the phylogenetic relationships in molluscs,and the radula morphology had species specificity,we found a similarity between cryptic group and the two apple snails by judging from central tooth,which suggested that cryptic group was close to P.canaliculata and P.maculata.3)The shell characteristics of the two apple snails and cryptic group were compared,and based on 12 morphological parameters(BL,TW,SW,AL,AW,AP,PAL,IL,AL,APH,BL,ABW).Statistical results suggested that the female P.canaliculata and P.maculata had extremely significant difference in IL,female cryptic group and P.canaliculata had extremely significant difference in TW,AL,ABW.There were extremely significant difference in TW,IL,AL,ABW between female cryptic group and P.maculata;at the same time,had significant difference in AL,PAL.In the index of TW,both male P.canaliculata and male cryptic group had extremely significant difference with P maculata.There had so many differences in the morphological parameters between cryptic group and P.maculata,there might be more closed relationships between cryptic group and P.canaliculata.