Lack of trade-offs in host offspring produced during fecundity compensation

Comparative analysis of population genetics between Schistosoma japonicum-infected and uninfected Oncomelania hupensis snails using microsatellites

Schistosomiasis is now at a low prevalence in China, but schistosome infections in intermediate host Oncomelania hupensis have been constantly reported. Previous studies have revealed a behavioral modification of snails associated with infection. However, there is a lack of comparative population genetics between schistosome-infected and uninfected snails. This study aimed to investigate any differences in genetic diversity and/or structure in O. hupensis associated with Schistosoma japonicum infection, with the purpose of providing information on snail control. Snail survey was performed in Ding town in Shitai county in Anhui, China. Infected snails were identified and sampled. Then an equal number of uninfected snails from the same place where infected snails were sampled, were randomly sampled. Population genetic analyses were conducted for infected snails and uninfected snails based on nine microsatellites. The mean snail density was 0.71 snails/0.11 m2, and the mean infected snail density was 0.00275/0.11 m2. 31 infected and 30 uninfected snails were successfully genotyped. Both exhibited high genetic diversity, but no significant differences were observed between both in all diversity measures, with exception of Allele richness (Ar). No genetic differentiation or structure was observed between two groups. While snail density has significantly decreased, the density of infected snails has not decreased. Higher Ar in infected snails indicates the stronger long-term evolutionary potential in this part of snails. This, together with high diversity in both infected and uninfected snails, may complex the epidemiology and control of schistosomiasis, given wild rodents (and other possible infected mammals) as local reservoirs for S. japonicum.

Reproductive alterations of Biomphalaria glabrata (Say, 1818) infected with Angiostrongylus cantonensis (Chen, 1935) and exposed to Euphorbia milii var. hislopii latex

The natural phytochemical latex of Euphorbia milii var. hislopii is one of the most promising natural molluscicides for the control of Biomphalaria glabrata, and has been widely studied under laboratory conditions for selective control of schistosomiasis transmission. However, the effect of this product on B. glabrata infected by other helminths had not yet been investigated. The present study reports evaluation of the effect of E. milii var. hislopii latex on the survival and reproductive activity of B. glabrata infected by Angiostrongylus cantonensis. For this purpose, the following groups were formed: control (C), exposed (E), infected (I) and infected and exposed for different time intervals (1 day - I+E-1D, 7 days - I+E-7D, 14 days - I+E-14D, 21 days - I+E-21D and 28 days - I+E-28D). The experimental infection was performed with L1 larvae of A. cantonensis and exposure to 0.08 mg/L (LC50) of E. milii latex for a period of 24 hours. We analyzed the effects of E. milii latex on the survival of snails during four weeks, reproductive parameters and possible histophysiopathological changes in the gonad and albumen gland of the snails. Regarding survival, there was reduction of more than 50% in the groups exposed to latex (E and I + E) compared to the control group. As for the number of ovigerous masses, eggs, and average number of hatched snails, significant increases were observed in the I+E-1D group at the 4th week compared to the control group and the other weeks in the same group. Angiostrongylus cantonensis larvae were observed in the gonad and albumen gland from day 21 and 28 of infection in groups I and I+E, respectively, with granuloma-like formation. At these observation periods and in these groups, an increase in galactogen was observed in the albumen gland, which influenced egg laying, suggesting the existence of a fecundity compensation mechanism phenomenon. It was possible to conclude that both stressors - A. cantonensis infection and exposure to E. milii latex - directly influenced the survival and reproductive parameters of B. glabrata.