Genetic differentiation
The differentiation index, Jost’s D (Jost, 2008), was calculated from the allele frequencies using SpadeR (Chao and Jost, 2015). Where Jost’s D between replicates was >0.01, the replicates were re-examined or eliminated (Silva et al., 2020). Differentiation of <0.05 was considered little differentiation, 0.05-0.25 moderate or great differentiation, and >0.25 as very great differentiation (Cormack et al., 1990).
The average differentiation among pairwise infrapopulations (parasite aggregated within one host) is designated the Di, between component populations the Dc (parasites aggregated within a group of hosts), and between an infrapopulation and a component population is the Dic. Genetic differences were analyzed the Dic with component populations based on place of birth (native-born vs immigrants); percentage of lifetime spent in Salvador (< 50 %, ≥ 50% to < 90%, ≥ 90%); age; sex; history of traveling outside of Salvador; contact with freshwater during traveling and contact with freshwater at five risk points within Pirajá (P1: Represa do Cobre; P2: Barragem Sete Quedas; P3: Córrego do Campo; P4: Vala da Baixa da Fonte; P5: Cachoeira de Nanã). Principal component analysis of the Dic was used to identify clustering based on the selected traits (Freeman and Jackson, 1992). To assess genetic relationship based on the Dic, we also conducted a network analysis (Kivelä et al., 2015). Principal component and network analyses were performed with an open-source statistical package PAST version 4.03 (Hammer et al., 2001).