Female biased sex-ratio in Schistosoma mansoni after exposure to an allopatric intermediate host strain of Biomphalaria glabrata

Abstract

For parasites that require multiple hosts to complete their development, the interaction with the intermediate host may have an impact on parasite transmission and development in the definitive host. The human parasite Schistosoma mansoni needs two different hosts to complete its life cycle: the freshwater snail Biomphalaria glabrata (in South America) as intermediate host and a human or rodents as final host. To investigate the influence of the host environment on life history traits in the absence of selection, we performed experimental infections of two B. glabrata strains of different geographic origin with the same clonal population of S. mansoni. One B. glabrata strain is the sympatric host and the other one the allopatric host. We measured prevalence in the snail, the cercarial infectivity, sex-ratio, immunopathology in the final host and microsatellite frequencies of individual larvae in three successive generations. We show that, even if the parasite population is clonal based on neutral markers, S. mansoni keeps the capacity of generating phenotypic plasticity and/or variability for different life history traits when confront to an unusual environment, in this study the intermediate host. The most dramatic change was observed in sex-ratio: in average 1.7 times more female cercariae were produced when the parasite developed in an allopatric intermediate host.

Frequency and mitotic heritability of epimutations in Schistosoma mansoni

“…Parasites were used to infect sympatric and allopatric snail hosts for three generations as described in Lepesant et al . (). For RNA extraction, cDNA generation and sequencing, and comparative analysis with the tophat 2 and cufflinks , we followed Roquis et al .…”

“…We chose to work only with female parasites, as it was previously shown that there is an increase in female cercariae production when Sm Bre develops in Bg Gua hosts (Lepesant et al . ), and also to avoid possible bias caused by gender‐specific epialleles. We selected two infected snails with a large number of sporocysts to be donators for sporocyst grafts.…”

“…This shift in the environment does not represent a strong stress but has still measurable effects on the life history traits of the parasite (Lepesant et al . ). We sequenced the genomes of cercariae and adult parasites to search for somatic mutations, copy number variations (CNVs) and mobilization of transposable elements (TE).…”

“…Interactions between Sm Bre and the two mollusc strains have been previously characterized in great detail, and the differences in life traits are known (Lepesant et al . ; Theron et al . ).…”

Real-time PCR for sexing Schistosoma mansoni cercariae

“…Gender is genetically determined (ZZ males, ZW females) but males and females can be only distinguished morphologically when they are adults. However, no obvious morphological dimorphism is observable during the larval stages (miracidia and cercariae) [1,2], so efficient larval sexing methods are critical for experimental genetics and genomics [3–5], and for studies of sex ratio dynamics in different parasite populations and life-stages [6,7]. Several methods have been developed to sex cercariae.…”