Reconstructing the invasion and demographic history of Lissachatina fulica (Mollusca, Gastropoda) in Brazil and South America based on genetic evidence

The snail Lissachatina fulica is currently widespread throughout Brazil; however, the timing of its introduction and the number of independent invasion events remain unclear. Although official records indicate its entry in the 1980s, residents report on commercial trade since the 1970s, suggesting at least three independent invasion events. Lissachatina fulica is currently considered the main intermediate host of Angiostrongylus cantonensis in Brazil, which causes cerebral angiostrongyliasis, an emerging zoonosis in the Americas. Given the rapid spread and medical importance of L. fulica , assessing its genetic diversity and population structure is essential to elucidate invasion pathways, demographic history, and public health implications. This information supports the identification of high-risk areas and informs, surveillance, control, and public health strategies. In this study, mitochondrial markers (MT-CO1 and 16S rRNA) were analyzed to assess the genetic composition of L. fulica populations in Brazil and to infer potential invasion and dispersal events. Sampling included 1–15 individuals per locality, depending on availability, from 37 localities encompassing all 26 Brazilian states and the Federal District. In addition, specimens from three localities in Indonesia were included for comparative purposes. We obtained MT-CO1 and 16S rRNA sequences from 331 and 338 individuals, respectively. A total of 11 haplotypes were identified for MT-CO1 and 10 for 16S rRNA, resulting in 17 haplotypes in the concatenated dataset. Haplotype C (16S rRNA) and H5 (MT-CO1) were predominant in Brazil and Indonesia ( n =228; n =225, respectively), followed by haplotype D (16S rRNA) also present in other countries, and Br1 (MT-CO1), which was found only in Brazil ( n =88; n =88). Two main haplotypes were observed for 16S rRNA and MT-CO1 and a concatenated dataset (Hc1=199; Hc2=79). Compared to other studies with 16S rRNA, both C and D haplotypes have been reported from other South American countries, including Ecuador and Bolivia, consistent with at least two independent introduction events. In addition, a third, less frequent haplotype (H) was detected in Brazil and Indonesia; this haplotype has also been reported in Mauritius and China, possibly indicating a third introduction event. Our results are consistent with at least two independent introduction events of L. fulica into Brazil, followed by demographic expansion. The detection of a rare additional haplotype suggests a possible third introduction, although this scenario requires confirmation with additional markers and denser sampling. Minas Gerais, one of the earliest documented localities of the species in Brazil, harbored three haplotypes, highlighting its importance for understanding early dispersal. Together, these findings provide the first nationwide genetic framework for reconstructing the invasion history of L. fulica in Brazil and provide a basis for future genomic studies aimed at refining invasion scenarios. Given that L. fulica is a major intermediate host of nematodes of medical and veterinary importance, these results also contribute to epidemiological surveillance and evidence-based control strategies.