Periodic Reporting for period 1 - IMMUNFUNC (Female immune function in compensation for polyandry)
Berichtszeitraum: 2017-09-01 bis 2019-08-31
Females of some species mate only once in their life, whereas others mate with more than one male (i.e. polyandry). Despite decades of research and recent progress, our understanding of why there is so much variation in the level of polyandry remarkably remains limited. During mating, male-derived materials are transferred to females. The physical contact can also involve potential risk of sexually transmitted infections. Thus, the more females mates, the higher the risk of potential infections. If costs of multiple mating outweigh the benefits, females will not mate polyandrously. The interaction between polyandry, pathogens, and immunity may therefore be key to understanding much of the unexplained variation in polyandry. To test the hypothesis that the level of polyandry positively correlates with the efficiency of female immune defence and may therefore compensate for the potential costs of multiple mating, I investigated the relationship between polyandry and female immune defence against pathogen challenge using multiple genotypes of the fruit fly Drosophila pseudoobscura that genetically differ profoundly in their predisposition to polyandry. The action of this research project revealed that there is no correlation between the level of polyandry and female immune defence. Instead, I found that there is genetic variation in female immune defence and that effects of mating on female immune defence are different among the female genotypes.
First of all, I gained experience in handling and rearing D. pseudoobscura and learned how to incubate bacteria, how to infect flies with bacteria, how to measure bacterial load, and how to quantify gene expression levels using RT-qPCR. I also determined which bacteria species and which concentration of bacteria are suitable to use for the following experiments. Then, to examine a relationship between the level of polyandry and female immune defence, I conducted survival assay using 10 gentypes of virgin females that genetically differ in the level of polyandry. I inoculated female flies with either Enterococcus faecalis (a Gram-positive bacteria) or Pseudomonas entomophila (a Gram-negative bacteria) and then checked the survival of female flies. Furthermore, to examine how mating affects female immune defence, I conducted survival assay, bacterial load assay and quantification of immune gene expression levels using virgin and one-mated females of 6 genotypes that genetically differ in the level of polyandry. I inoculated female flies with either E. faecalis or P. entomophila in the same manner as the above and checked their survival. For bacterial assay, I homogenized female flies in PBS at a certain time point after the inoculation and plated the homogenate on lysogeny broth plates to count colonies. For quantification of immune gene expression levels, I homogenized female flies in Trizol at a certain time point after the inoculation. After extracting RNA from all samples, I conducted reverse transcription and then performed qPCR for the all samples. I statistically analyzed the data obtained in this research project. Finally, I found that there is no correlation between the level of polyandry and female immune defence, which rejected my hypothesis that the level of polyandry positively correlates with the efficiency of female immune defence. Instead, I found that there is genetic variation in female immune defence and that effects of mating on female immune defence are different among the female genotypes. I have given poster presentations with these results at conferences for academics three times. I will give presentations on this research project whenever I have opportunities. I will also integrate the results into two original papers and publish them in peer-reviewed scientific journals.
My hypothesis that the level of polyandry positively correlates with the efficiency of female immune defence was rejected by the action of this research project. However, my findings would be the first evidence that the impact of mating on immunity is genetically variable within populations. This will contribute to deepen our understanding on relationships between immunity and life-history traits.