Transgenerational immunity in Manduca sexta

Insect parents are known to 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.  Theory predicts that parents exposed to pathogenic microbes may increase their fitness by provisioning their eggs with antimicrobial compounds, rendering less susceptible to disease. Here we tested trans-generational immunity in the Tobacco Hornworm moth, Manduca sexta.   Weighed female pupae were randomly assigned to four different treatments: naïve (not injected), controls (saline injected), immunized (injected with heat killed bacterium 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 emergence and copulation, the total number of eggs oviposited within the lifetime of the adult female was recorded.  Additionally, various physical (volume, weight) and immunological traits of eggs (protein profiles and antimicrobial assays) as well as the time to first hatch were compared across treatments. Eggs from challenged females were larger, heavier, contained higher amounts of protein than eggs from the other three treatments. Their protein profiles (evidenced by SDS-PAGE), however, did not differ.  Further research is ongoing, but these preliminary results are suggestive of maternal (non-genetic) effects being transferred to offspring which ultimately, could influence offspring survival in a microbial-rich environment.