Population pairwise F_ST between 16 populations of <i>I</i>. <i>exustus</i> based on mitochondrial 16S rDNA sequences.

Population pairwise FST between 16 populations of I. exustus based on mitochondrial 16S rDNA sequences.</p

Maximum likelihood phylogenetic tree of <i>I</i>. <i>exustus</i> and trematode cercariae.

(A) ML phylogenetic tree of the haplotypes generated from 206 sequences of a partial COI sequence (569 bp) of I. exustus (162 sequences from Thailand and 44 sequences from other geographical regions). Samples in bold indicate infection with trematode cercariae. Biomphalaria pfeifferi was used as an out-group. (B) ML phylogenetic tree of the current furcocercous cercaria and related trematodes based on a partial 28S rDNA sequence (838 bp). (C) ML phylogenetic tree of the current xiphidiocercaria and related trematodes based on a partial ITS2 sequence (349 bp). The bold taxa represent the cercaria samples obtained from the current study. Support values (ML bootstrap/NJ bootstrap/Bayesian posterior probabilities) are shown above the branches of the phylogenetic tree. At the branches of the tree, a dash (-) indicates less than 50% support value or that a certain grouping was not observed via that method of analysis. The red color on the map represents the locations found to be I. exustus infected with trematode cercariae. Abbreviations: NSN, Nakhon Sawan province; SKA, Songkhla province. The map was created using MapChart software’s free version licence https://www.mapchart.net/terms.html#licensing-maps, under a CC BY license with permission of Minas Giannekas (owner and creator of the map-making website mapchart.net).</p

Pairwise genetic distances (%) among genetic markers of <i>I</i>. <i>exustus</i> samples.

Pairwise genetic distances (%) among genetic markers of I. exustus samples.</p

Diversity indices of the combined mtDNA in the <i>I</i>. <i>exustus</i> populations from Thailand and other geographical regions.

Diversity indices of the combined mtDNA in the I. exustus populations from Thailand and other geographical regions.</p

Diversity indices of COI and 16S rDNA sequences in the <i>I</i>. <i>exustus</i> populations from Thailand and other geographical regions.

Diversity indices of COI and 16S rDNA sequences in the I. exustus populations from Thailand and other geographical regions.</p

Distribution of the haplotype for <i>I</i>. <i>exustus</i> in Thailand.

(A) Median joining network of 162 I. exustus in Thailand based on COI, 16S rDNA, combined mtDNA, and ITS1 sequences. Each haplotype is represented by a circle, and circle sizes are proportional to haplotype frequency. Colors indicate the geographic origin of the haplotypes. Number on each branch represents the mutational step number, while the branch with no number represents one mutation step. Median vectors (small red dots) represent ancestral haplotypes that are either not sampled or missing haplotypes. (B) Distribution of COI haplotypes of I. exustus in Thailand. Colors represent different regions: North = pink; Northeast = orange; Central = red; West = green; East = blue; and South = yellow. The map was created using MapChart software’s free version licence https://www.mapchart.net/terms.html#licensing-maps, under a CC BY license with permission of Minas Giannekas (owner and creator of the map-making website mapchart.net).</p

Maximum likelihood tree of 16S rDNA sequences (381 bp) of 18 haplotypes generated from 206 sequences of <i>I</i>. <i>exustus</i> (162 sequences from Thailand and 44 sequences from other geographical regions).

Support values (ML bootstrap/NJ bootstrap/Bayesian posterior probabilities) are shown above the branches. At the branches of the tree, a dash (-) indicates less than 50% support value or that a certain grouping was not seen by that method of analysis. Samples in bold indicate infected with trematode cercariae. Biomphalaria pfeifferi was used as an out-group. Abbreviations: NSN, Nakhon Sawan Province; SKA, Songkhla Province. (TIF)</p

PCR primers and parameters used in this study.

Indoplanorbis exustus is a freshwater gastropod belonging to the family Planorbidae. This snail is widely distributed across the tropics and plays an important role as the intermediate host for trematodes. However, relatively little is understood regarding the genetic relationship between I. exustus and trematodes. The goals of this study were to investigate the current transmission status of trematode cercariae in I. exustus in Thailand and to examine the genetic diversity, genetic structure, and demographic history of I. exustus. We collected 575 I. exustus from 21 provinces across six regions of Thailand and investigated cercarial infections by using the shedding method. I. exustus from two provinces were infected with cercarial trematodes, and two types of cercarial stages were molecularly identified as furcocercous cercaria and xiphidiocercariae. Phylogenetic tree analysis based on 28S rDNA and ITS2 sequences demonstrated that furcocercous cercaria and xiphidiocercariae were closely clustered with a clade of Euclinostomum sp. and Xiphidiocercariae sp., respectively. Phylogenetic and network analyses of I. exustus haplotypes based on the COI, 16S rDNA, and ITS1 genes demonstrated four main clades. Only snails in clade A were distributed in all regions of Thailand and harbored trematode cercariae. The level of genetic diversity of I. exustus was relatively high, but most populations were not genetically different, thus suggesting the appearance of gene flow within the I. exustus populations. Overall, the haplotype network was star-shaped, thus suggesting the recent demographic expansion of populations. This result was also supported by the unimodal mode of the mismatch distribution graph and the large negative values of the neutrality tests. Therefore, the I. exustus snail was likely another freshwater snail of the invasive species in Thailand. This information will aid in monitoring the spread of the parasitic trematodes carried by I. exustus from different populations.</div

Number of nucleotide sequences of <i>I</i>. <i>exustus</i> used for genetic analyses.

Number of nucleotide sequences of I. exustus used for genetic analyses.</p

Estimates of genetic differences (%) within (bold) and among clades of <i>I</i>. <i>exustus</i> based on COI, 16S rDNA, combined mtDNA, and ITS1 sequences.

Estimates of genetic differences (%) within (bold) and among clades of I. exustus based on COI, 16S rDNA, combined mtDNA, and ITS1 sequences.</p