Jillian Dunbar, a student at the University of Alabama, worked with Ellen Martinson and Vincent Martinson in the lab of Dr. Michael Strand.
Reproduction and immunity are metabolically expensive systems; therefore, organisms with a limited amount of resources have to invest carefully (Schwenke et al. 2016). With the goal of producing offspring, organisms must invest resources into reproduction, yet also reserve resources for protecting themselves. In many cases reproduction and immunity are not directly linked. However, it has been shown in Aedes aegypti mosquitoes that, in addition to inducing egg production, a blood meal also increases the number of circulating immune cells called hemocytes (Castillo et all. 2011; Castillo et al. 2006). These findings elicit the question, does reproduction (blood-feeding) result in lower immunity for the mosquito? Through a variety of bacterial injections into blood-fed and non-blood-fed mosquitoes, this project worked to understand the possible tradeoffs between immunity and reproduction. We found an inverse relationship between immunity and reproduction, in that mosquitoes laid fewer and smaller eggs when injected with both live and heat-killed bacteria, but only for the more virulent species and higher doses. Interestingly, the results also showed that blood-fed mosquitoes were more successful in clearing or tolerating less virulent bacterial infections, suggesting resources gained from a blood meal are used to produce an anticipatory immune response. These preliminary findings are essential for continuing research and strengthening our understanding of the A. aegypti immune system with hopes of controlling or preventing diseases propagated by A. aegypti in the future.
J, Brown, MR and Strand, MR (2011) Blood feeding and insulin-like peptide 3
stimulate proliferation of hemocytes in the mosquito Aedes aegypti. PLoS pathogens 7: e1002274.
Castillo, J, Robertson, A and Strand, M (2006)
Characterization of hemocytes from the mosquitoes Anopheles gambiae and Aedes
aegypti. Insect biochemistry and
molecular biology 36: 891-903.
Schwenke, RA, Lazzaro, BP and Wolfner, MF (2016)
Reproduction–immunity trade-offs in insects. Annual Review of Entomology 61:
Robert Manuel, a junior from California State Polytechnic University, Pomona, worked with Ruby Harrison in the lab of Dr. Mike Strand to examine the relationship between mosquito gut biota and dengue infection.
Abstract: The mosquito Aedes aegypti is the primary vector of dengue virus (DENV). Prior studies report increased susceptibility of A. aegypti to DENV infection, and higher pathogen burden when adult females are treated with antibiotics. This suggests a role for the microorganisms that colonize the digestive tract of mosquitoes (gut microbiota) in susceptibility to DENV infection. We tested the hypothesis that microbe-depleted A. aegypti are more susceptible to DENV infection by comparing three treatments: axenic mosquitoes with no gut microbiota, gnotobiotic mosquitoes harboring only Escherichia coli, and conventional mosquitoes with a natural community of gut microbes. We validated the status of these mosquitoes using both culturing methods and PCR. We then assessed DENV presence/absence in each treatment fourteen days after feeding adult females an infected blood meal. Consistent with our working hypothesis, a larger proportion of axenic mosquitoes were infected with DENV than conventional mosquitoes. Proportions of axenic and gnotobiotic mosquitoes infected with DENV were nearly identical. However, our treatments had no effect on DENV dissemination among females that were infected. In summary, these results suggest A. aegypti with a more diverse gut microbiota are more resistant to DENV infection than axenic females but E. coli alone provides no increase in resilience.
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Molly Hancuh, a student from University of Minnesota-Morris, worked with Bret Boyd and Ruby Harrison in the lab of Dr. Mike Strand to examine the role of bacteria in mosquito larval development.
Abstract: The digestive tract of a mosquito is home to bacterial community that is essential for normal development (1). In the larval stages, bacteria stimulate molting and growth (1). Some members of the larval gut community persist into the adult mosquito where they influence reproduction and ability to vector pathogens (2,3). Previous studies on the role of gut- bacteria in development have focused on the genus Aedes, including Aedes aegypti, which transmits the pathogens that cause Dengue fever and Zika virus syndrome. It is unknown if findings from Aedes species apply to all mosquitoes. Here, we address two important findings from Aedes in distantly related genus Anopheles by studying the malaria vectors An. gambiae and An. stephensi. First, we asked if Anopheles need bacteria to develop and if so, can we rescue development with individual bacterial species? Second, we assessed whether bacterial abundance in the guts of adult Ae. aegypti and An. gambiae differ before and after females blood feed. Like Ae. aegpyti, we find that bacteria free larvae cannot develop, however unlike Ae. aegypti some bacterial species cannot fully rescue larval development in Anopheles. Additionally the results were not equivocal between An. gambiae and An. stephensi. In adult mosquitoes, the bacterial community in the digestive tracts of Ae. aegypti and An. gambiae also responded differently to blood feeding. Collectively we find that that are commonalities between Aedes and Anopheles, however there were significant differences as well.
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Sofia Bertoloni Meli, a student from Indiana University, worked with Dr. Michael Strand and Kerri Coon to studied the microbial community found in the gut of mosquitoes.
Abstract: Insects host many essential microbial symbionts. The bacteria in mosquito guts are important for development, nutrient acquisition, and reproduction. Developing mosquito larvae acquire their gut bacterial community (microbiota) from the aquatic environment they live in. However, little is known about the factors influencing the abundance of specific community members in the larval gut. Here, we investigated the contribution of host factors in shaping mosquito gut microbiota. We used experimental studies to manipulate the community present in the environment of individual and cohabitating mosquito species. Quantitative analysis of community structure in mosquito larvae identified species-specific bacterial associations that were robust to changes in the environment. Overall, our results indicate that both environmental and host factors affect bacterial community structure in mosquitoes, and reveal the potential importance of incorporating host phylogenetic history into our understanding of gut microbial diversity.
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Jacob Gafranek, a student at Xavier University, worked with Dr. Michael Strand and graduate student mentor Kerri Coon in the UGA Entomology Department, to look at the gut microbiota of a mosquito disease vector.
Jacob T. Gafranek1, Kerri L. Coon2, Michael R. Strand2
1 Xavier University
2 University of Georgia
Gut bacteria are ubiquitous among animals and are known to play important roles in the immunity, nutrition, and overall health of their hosts. The gut bacterial community of mosquitoes has received attention due to results showing that some bacterial community members in the mosquito midgut can alter competency of the mosquito to transmit a number of important infectious pathogens. More recently, we showed that axenic (i.e. bacteria-free) mosquito larvae do not molt past the first instar. However, axenic larvae colonized by a single bacterial species such as Escherichia coli develop normally. Subsequent work using Aedes aegypti mosquitoes indicates that a particular density of bacteria must be reached in the larval gut to initiate molting. Here, we extend these studies to the African malaria mosquito Anopheles gambiae. We report a robust protocol for colonizing axenic An. gambiae larvae and the number of bacteria required for normal development. We also show that colonization of the larval gut occurs within 8 hours after hatching. These results further demonstrate a fundamental dependence by mosquitoes on their gut bacteria for development. Furthermore, the reported protocol has important implications for future studies characterizing the mechanism by which gut community members modulate mosquito development.
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