Comparing the thermal performance of mosquito immunity among species and life stages
LE3 .A278 2023
Master of Science
Climate change is affecting the global distribution of insect species and exposing them to new thermal environments. The immune system of insects is sensitive to temperature and is important for determining the outcome of infection. However, we have little understanding of how the immune system of different species and even life stages reacts to temperature. To help improve our baseline understanding of how temperature affects the insect immune system, my project objectives were: 1) to compare the immune performance of adult and juvenile life stages of lab-reared Aedes aegypti, and 2) to determine if temperature affects the immune system of different mosquito species in the same way, using wild-caught Culex territans, Culex pipiens, and Aedes japonicus as models. Melanization and encapsulation responses to Sephadex beads revealed high individual variation across species and life stages as well as robust responses mounted by larvae. Temperature had relatively little effect on the strength of responses by larvae, with most individuals mounting stronger responses relative to adults. Mortality rates in larvae following exposure to the fungus, Metarhizium brunneum, were significantly faster at 18°C. Higher temperatures (26°C and 32°C) increased the expression of the antimicrobial peptide defensin A in adults but did not impact expression in the larvae, potentially indicating different strategies mounted by different life stages when responding to pathogens. Of the three wild-caught species, temperature only significantly affected the performance of Cx. territans adults, but I observed differences in the strength of responses mounted by the different species, potentially due to varying life histories and investment strategies between the species. Differing responses mounted by different life stages and species indicate that we cannot make generalizable predictions about how the immune performance of different species or life stages will be impacted by changing thermal environments. This exemplifies the need to conduct further baseline studies to help understand the implications of shifting thermal environments for different insect species and how this will impact both terrestrial and aquatic ecosystems.
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