Low genetic diversity and the phylogeny of Achatina fulica, an intermediate host of Angiostrongylus cantonensis in Thailand, inferred from 16S mitochondrial sequences

Genetic diversity and population structure of Physella acuta (Gastropoda: Physidae) in Thailand using mitochondrial gene markers: COI and 16S rDNA

Physella acuta is a freshwater snail native to North America. Understanding the phylogeography and genetic structure of P. acuta will help elucidate its evolution. In this study, we used mitochondrial (COI and 16S rDNA) and nuclear (ITS1) markers to identify the species and examine its genetic diversity, population structure, and demographic history of P. acuta in Thailand. Phylogenetic and network analyses of P. acuta in Thailand pertained to clade A, which exhibits a global distribution. Analysis of the genetic structure of the population revealed that the majority of pairwise comparisons showed no genetic dissimilarity. An isolation-by-distance test indicates no significant correlation between genetic and geographical distances among P. acuta populations, suggesting that gene flow is not restricted by distance. Demographic history and haplotype network analyses suggest a population expansion of P. acuta, as evidenced by the star-like structure detected in the median-joining network. Based on these results, we concluded that P. acuta in Thailand showed gene flow and recent population expansion. Our findings provide fundamental insights into the genetic variation of P. acuta in Thailand.

Genetic analysis of a 66-kDa protein-encoding gene of Angiostrongylus cantonensis and Angiostrongylus malaysiensis

The rat lungworm Angiostrongylus cantonensis is globally known to be the cause of oeosinophilic meningitis in humans. Another congener, Angiostrongylus malaysiensis, is closely related to A. cantonensis and has been described as a potential human pathogenic parasite. These 2 worms are similar in terms of life cycle, host range and morphological and genetic information. However, there are limited studies about their genetic diversity based on the 66-kDa protein-encoding gene. The objective of this study was to explore the 66-kDa protein sequence variation of A. cantonensis and A. malaysiensis collected from Thailand. Two adult and 53 third-stage larval specimens of Angiostrongylus from 4 geographic locations in Thailand were molecularly identified using the 66-kDa protein gene. The phylogenetic trees (Bayesian inference tree and maximum-likelihood tree) showed that Angiostrongylus formed a monophyletic clade with a clear separation between A. cantonensis and A. malaysiensis. The genetic distance between A. cantonensis and A. malaysiensis varies from 0.82 to 2.86%, with a total of 16 variable sites. The analysis of genetic diversity revealed 1 and 5 new haplotypes of A. cantonensis and A. malaysiensis, respectively, and showed genetic differences between the populations of A. cantonensis and A. malaysiensis. The haplotype networks of A. cantonensis and A. malaysiensis populations in Thailand are similar to those of populations in some countries, indicating the range expansion of genomic origin between populations in different areas. In conclusion, the 66-kDa protein gene was a good genetic marker for studying genetic diversity and discriminating between A. cantonensis and A. malaysiensis.

Fine-scale geographical sampling and molecular characterization of the giant African land snail in its invasive range in Asia shows low genetic diversity, new haplotypes and the emergence of another haplotype from the Indian Ocean Islands

Native to East Africa, the giant African snail Lissachatina [=Achatina] fulica (Bowdich, 1822) is a tropical crop pest and one of the world’s top 100 invasive species. It is now present in at least 52 countries worldwide, with an actively expanding range. Lissachatina fulica was first introduced to India in 1847, but subsequent arrivals in India and local patterns of spread remain unclear. This study uses the 16S rRNA gene to identify the extent of genetic variation in India by sampling Indian populations and comparing them with published sequence data. A total of 307 snails were collected from 178 localities in India and from a single locality in the UAE, and the 16S rRNA gene was amplified and sequenced. Eight haplotypes were identified from India of which four are newly recognized. The new haplotypes identified in this study have increased the number of L. fulica 16S rRNA haplotypes from 19 to 23. Examination of haplotype and nucleotide diversities revealed that genetic variation is low in India, the UAE and across Asia as a whole. The number of haplotypes was higher in India when compared to other invasive regions but all of the Asian haplotypes appear to be closely related to the most common haplotypes in the Indian Ocean Islands. Heavy trade between the snail-infested and native-range countries suggests that the variation observed in India might be traced back to its native range, but the lack of sampling and paucity of sequences from East Africa currently prevents a comparison. Tracing back the emergent haplotypes by additional sampling could throw more light on the spread of L. fulica.