Climate change may affect the internal defense system (IDS) of freshwater snails, and as a result their capacity to transmit disease. We examined effects of short-term exposure to supra- and sub-optimal temperatures or starvation on 3 parameters of the IDS of the schistosome-resistant Salvador strain of Biomphalaria glabrata — hemocyte concentrations, cell division in the amebocyte-producing organ (APO), and resistance to infection with Schistosoma mansoni. Adult snails were exposed to 1 of 3 temperatures, 20 °C, 27 °C (controls), or 33 °C, for 1 or 2 weeks, with food. A fourth group was maintained at 27 °C, but without food. Compared to the controls, starved snails had significantly higher hemocyte counts at both 1 and 2 weeks, although mitotic activity in the APO was significantly lower at both time periods. Exposure to 20 °C or 33 °C for 1 or 2 weeks did not affect hemocyte numbers. However, APO mitotic activity in snails exposed to 20 °C was significantly higher at both 1 and 2 weeks, whereas mitotic activity in snails exposed to 33 °C was significantly lower at 1 week but normal at 2 weeks. None of the treatments altered the resistance phenotype of Salvador snails. In a follow-up experiment, exposure to 33 °C for 4–5 h, a treatment previously reported to both induce expression of heat shock proteins (Hsps) and abrogate resistance to infection, caused immediate upregulation of Hsp 70 and Hsp 90 expression, but did not alter resistance, and Hsp expression levels returned to baseline after 2 weeks at 33 °C. Results of this study indicate that abnormal environmental conditions can have both stimulatory and inhibitory effects on the IDS in adult B. glabrata, and that some degree of acclimation to abnormal temperatures may occur.
The anterior pericardial wall or amebocyte‐producing organ (APO) is a site of hemocyte formation in the schistosome‐transmitting snail Biomphalaria glabrata. Histological sections of the APOs of adult schistosome‐resistant Salvador strain snails, and two schistosome‐susceptible M‐line strains, BRI‐M and USF‐M, showed qualitatively differing amounts of hemopoietic tissue (HT), with Salvador>BRI‐M>USF‐M. Adult Salvador snails also had a significantly higher concentration of hemocytes in the hemolymph than the two M‐Line strains. In juvenile snails of the same three strains, measurements of total APO HT volume confirmed the qualitative differences seen in adults, and differences between the three strains were statistically significant. Crosses between Salvador (large HT volume) and USF‐M (small HT volume) show that a large HT volume is dominant in juvenile F1s. Analysis of the distribution of HT volume among F2s shows it to be a quantitative trait. Although USF‐M juvenile F0s had a significantly lower APO HT volume than that of BRI‐M F0s, they had a significantly higher mitotic index, possibly as a compensatory mechanism. Salvador APO allografts maintained HT volume and mitotic activity equally well in USF‐M and Salvador recipients after 2 weeks, suggesting that the low HT volume in USF‐M snails may result from a developmental defect rather than a lack of HT‐supportive plasma factors.
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