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).