The role of diet and density on adult-egg cannibalism in red flour beetles

Background/Question/Methods

Red flour beetles (Tribolium castaneum) complete their entire life cycle in flour, which thus serves multiple functions: habitat, food, and a source of microbiomes, making it an ideal, tractable system. Moreover, these beetles are facultative cannibals in stressful conditions, so stress factors such as insufficient nutrition in diet and over-population were used to induce cannibalistic behavior. Cannibal-victim dynamics occur at various life stages, but adult-egg cannibalism was used to determine whether flour diet and population density alter the beetle gut microbiome and cannibalism rates. Two experiments were performed that manipulated different environmental stressors: host diet and population density. For the first experiment, the role of the host diet was isolated by rearing flour beetles on alternative flour diets varying in nutritional content: (1) whole wheat (high-nutrient), (2) high-gluten flour, (3) teff, and (4) oat (low-nutrient), with the same population size (n=20). For the second experiment, the role of population density was isolated by rearing flour beetles in a range of population sizes (n= 20, 40, 80, and 100) on whole wheat flour. For each experiment, adult-egg cannibalism rates were measured by counting the number of eggs in each sample every two days.

Results/Conclusions

For the first experiment examining the role of the host diet in terms of cannibalism, if a low-nutrient diet is more stressful than a high-nutrient diet, it was expected the lowest-nutrient diet (oat flour) would have the most egg victims over time. For the second experiment examining the role of population density in terms of cannibalism, if a high population density is more stressful, the population with the highest density (n=100) was expected to have the most egg victims over time. Our results indicate that stress type and cannibalistic behavior are correlated. For the diet experiment, oat flour has the highest rate of cannibalism. For the population density experiment, the cannibalism rate increased with adult density. Therefore, preliminary results supported the idea that varying stress types (nutrition and adult density) affect the rate of cannibalism. Future directions of this research include characterizing adult gut microbial communities, by surface-sterilizing adult beetles before dissecting and extracting DNA. I will use PCR to amplify DNA that will be sequenced using high-throughput Illumina sequencing.