Proximate mechanisms underlying plasticity in life history under variable dietary conditions in the milkweed bug, oncopeltus fasciatus
Duxbury, Ashley Emily
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Oncopeltus fasciatus males fed a diet of either milkweed seeds, the ancestral state, or sunflower seeds, the adapted state, have different reactions to their diet. Milkweed-fed males live a shorter life, while investing more in reproduction, while sunflower-fed males live longer, but at the expense of their fertility. To examine this trade-off further, I studied the fertility and fecundity of males on each diet as well as looked at the genes that were differentially expressed under each dietary condition. Males fed milkweed-seeds have more sperm than sunflower males at an older age, but not higher quality sperm, and older milkweed fed males are more likely to fertilize eggs than old sunflower-fed males. To determine if the change in fecundity and amount of sperm was due to a genetic factor, a transcriptome was completed on the testes of O. fasciatus males. The distal tip of the testis was separated from the proximal rest of the testis to try and separate the germline stem cell maintenance and activation genes from spermatogenesis genes. It was found that there were indeed differences in the distal tip and rest of the testes within as well as between the diets. Overall, there are candidates for further studies into the mechanisms behind life history plasticity that may lead to an answer as to what causes this trade-off between reproduction and longevity.