Investigation of cryptic diversity and occurrence of echinostome metacercariae infection in Anentome helena (von dem Busch, 1847)

摘要

Objective: To investigate the parasitic infection of Anentome helena (A. helena) and determine the validity of species boundaries for A. helena by combining molecular phylogeny and morphological approaches. Methods: A total of 325 individuals of A. helena were collected throughout northern Thailand. Shells were measured and compared by t-test. Radulae were investigated by using light and scanning electron microscope. Two partial mitochondrial DNA sequences of COI and 16S rRNA from 36 specimens of A. helena and related species were used to test the validity of the morphospecies. Phylogenetic trees were constructed using neighbour joining, maximum likelihood and Bayesian inference. Infection of A. helena with trematode larva was examined and observed. Results: Morphological examination of A. helena revealed 2 distinct morphospecies. Genetic divergences supported the separation of the two morphotypes into two distinct groups. Both individual and combined analyses of the two nucleotide fragments revealed two phylogroups that corresponded with shell and radula characteristics. In addition, A. helena was found infected with 37-collar spined echinostome metacercariae. The prevalence and intensity of metacercariae was highest in the San Kamphaeng district, Chiang Mai province, with 7.5％ and 1.670±0.577, respectively. Conclusions: These findings suggest that comprehensive taxonomic revision of this unrecognised species complex is needed. This study represents the preliminary step to reveal new data on the recent distribution of trematode infection in A. helena. This information may be useful for developing conservation management of the snail and the practice of targeted regimes to reduce anthelmintic resistance in the future.