Complex environmental drivers of immunity and resistance in malaria mosquitoes - PubMed (original) (raw)

Complex environmental drivers of immunity and resistance in malaria mosquitoes

Courtney C Murdock et al. Proc Biol Sci. 2013.

Abstract

Considerable research effort has been directed at understanding the genetic and molecular basis of mosquito innate immune mechanisms. Whether environmental factors interact with these mechanisms to shape overall resistance remains largely unexplored. Here, we examine how changes in mean ambient temperature, diurnal temperature fluctuation and time of day of infection affected the immunity and resistance of Anopheles stephensi to infection with Escherichia coli. We used quantitative PCR to estimate the gene expression of three immune genes in response to challenge with heat-killed E. coli. We also infected mosquitoes with live E. coli and ran bacterial growth assays to quantify host resistance. Both mosquito immune parameters and resistance were directly affected by mean temperature, diurnal temperature fluctuation and time of day of infection. Furthermore, there was a suite of complex two- and three-way interactions yielding idiosyncratic phenotypic variation under different environmental conditions. The results demonstrate mosquito immunity and resistance to be strongly influenced by a complex interplay of environmental variables, challenging the interpretation of the very many mosquito immune studies conducted under standard laboratory conditions.

Keywords: circadian rhythm; innate immunity; mosquito; resistance; temperature.

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Figures

Figure 1.

The effects of temperature, diurnal fluctuation and time of day on defensin1 (DEF1) expression. (a) The expression of DEF1 in response to immune challenge varies depending on the time of day mosquitoes are challenged (06.00, black line; 18.00, red line). (b) DEF1 expression in response to immune challenge (unmanipulated, black line; injury, blue line; and heat-killed E. coli, red line) varies depending on the mean ambient temperature mosquitoes experience after immune challenge. (c) Independent of immune challenge, DEF1 expression differs depending on the time of day (06.00, black line; 18.00, red line) a mosquito is challenged, the ambient temperature a mosquito is housed in, and whether or not there is diurnal temperature fluctuation (±0°C, solid lines; ±6°C, dashed lines). Asterisks denote significant differences of p < 0.05, and bars around population means represent standard errors.

Figure 2.

The effects of temperature, diurnal fluctuation and time of day on cecropin1 (CEC1) expression. (a) The amount of CEC1 in response to immune challenge (unmanipulated, black line; injury, blue line and heat-killed E. coli, red line) varied significantly depending on the average temperature mosquitoes experienced and the time of day challenge occurred (06.00, solid lines; 18.00, dashed lines). (b) Independent of immune challenge, the expression of CEC1 varied significantly with the mean ambient temperature a mosquito experiences, the time of day mosquitoes were placed into their temperature treatments (06.00, black lines; 18.00, red lines), and whether or not there was diurnal fluctuation (±0°C, solid lines; ±6°C, dashed lines). Asterisks denote significant differences of p < 0.05, and bars around population means represent standard errors.

Figure 3.

The effects of temperature, diurnal fluctuation and time of day on NOS expression. NOS expression in response to immune challenge (unmanipulated, black lines; injury, blue lines; and heat-killed E. coli, red lines) varied significantly in response to the mean ambient temperature mosquitoes experience and the time of day of immune challenge (06.00, solid lines; 18.00, dashed lines). Asterisks denote significant differences of p < 0.05, and bars around population means represent standard errors.

Figure 4.

Bacterial growth in vivo and mosquito mortality are affected by ambient temperature, temperature fluctuation and time of day of infection. (a) Regardless of mean ambient temperature, bacterial growth (E. coli CFUs) within a mosquito was significantly affected by diurnal temperature fluctuation and time of day of infection (06.00, black line; 18.00, red line). The effect of mean ambient temperature on E. coli growth within the mosquito (b) and mosquito mortality (c) were also significantly shaped by the time of day of infection (06.00, black line; 18.00, red line). Asterisks denote significant differences (p < 0.05), and bars around population means represent standard errors.

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Complex environmental drivers of immunity and resistance in malaria mosquitoes - PubMed (original) (raw)