21.6 Wednesday, Jan. 4 How do insect eggs avoid sunburns? POTTER, Kristen A.*; WOODS, H. Arthur; University of Montana, Missoula; University of Montana, Missoula email@example.com
Ultraviolet radiation (UVR) from the sun damages DNA and causes acute health problems in living organisms. In response, organisms have evolved a suite of defenses against the sun's harmful effects, including UV-screening compounds, UV-absorbing substances, efficient DNA-repair mechanisms, and behavioral strategies to avoid UVR. For most eggs (e.g., insect eggs, which have thinner shells than bird eggs), however, defending against UVR is particularly challenging: embryos are immobile and have poorly developed physiological systems. At the same time, their DNA divides rapidly during development, resulting in a high probability of DNA replication errors. In previous studies of the hawkmoth Manduca sexta, we noticed that females occasionally lay eggs on top of leaves (rather than underneath). These eggs turn dark yellow, instead of their typical green color. In a field experiment using UV filters, we showed that yellowing stemmed from UV exposure rather than other factors associated with the tops of leaves. We will discuss a series of laboratory experiments, currently underway, that are designed to distinguish whether (i) eggs are producing a sunscreen; or (ii) eggs are accumulating damage. The sunscreen hypothesis predicts that eggs with pre-exposure to natural levels of UVA and UVB will perform better during and after large UV doses delivered late in development. Egg performance is measured as hatching success, developmental time, and first-instar rates of growth.