Differential parental investment in the face of pathogenic pressures: Manduca sexta as an insect model organism

Parents can invest in their offspring in a context-dependent manner. Parental nutrition, for example, can influence the size, weight and protein content of eggs and ultimately, their hatching success. Similarly, the pathogenic constraints under which parents develop may foster differential investment in their own offspring.  Parental investment theory predicts that parents exposed to pathogenic microbes may increase their fitness by provisioning their eggs with antimicrobial compounds, rendering them less susceptible to disease.  This study tests the hypothesis that maternal provisioning exists in the Tobacco Hornworm moth, Manduca sexta and that mothers invest in their progeny differently depending on their own pathogenic history. Female pupae were weighed and randomly assigned to four different treatments: naïve (not injected), controls (saline injected), immunized (injected with heat killed Serratia marcescens) and challenged (injected with a sublethal dose of active S. marcescens). Each treated female pupa was placed inside a flying cage with a naïve male pupa. Upon eclosion and copulation, the total number of eggs oviposited within the lifetime of the adult female was recorded.  Additionally, various physical attributes such as egg volume and weight were compared across treatments. The quantification of other raw materials conducive to survival, and immunity, such as glucose, yolk (vitellogenin), uric acid and triglycerides were measured and compared across eggs from the four treatments. Our initial results indicate a correlation between challenged females and certain egg attributes suggestive of maternal  contributions to their progeny which ultimately, could influence the offspring ‘s survival in a microbial-rich environment.