First Analysis of Circadian Rhythms in the ERG, Compound Eye Pigment Migration, and Responses to Prey-like Stimuli in the Praying Mantis, Hierodula Multispina (Insecta:Mantodea)

The circadian (ca. 24 hr) oscillation of physiological parameters is ubiquitous among vertebrates and invertebrates. Recent neurophysiological and molecular data indicate that the underlying mechanisms modulating circadian rhythms are similar across these taxonomic groups. Multiple studies indicate that invertebrates display endogenous circadian rhythms in both compound eye sensitivity and behavior; one well-studied model is the cockroach (Insecta: Blattodea). However, with the exception of two brief papers published in 1979 and 1981, nothing is known about circadian rhythms in the Mantodea, the sister taxon to the Blattodea. Hence, we used the mantis, Hierodula multispina and Sphodromantis lineola to establish the presence of circadian rhythms in the compound eye electroretinogram (ERG), compound eye pigment migration, and behavioral responses in these mantises.  ERGs were recorded in response to 1000 ms light pulses every 15 minutes over 72 hours. These revealed rhythmic patterns in optic lobe sensitivity with an average period of 21.6 hours.  Compound eye pigment migration was monitored photographically every 30 minutes over 72 hours. Eye pigment did not oscillate under constant light, but did under alternating light/dark cycles. Finally, preliminary data indicate a circadian rhythmicity in responsiveness to prey-like visual stimuli. Taken together, these data reveal circadian rhythms in cellular activity in the compound eye of H. Multispina that appear to be independent of pigment migration, and effect visually elicited appetitive behavior.  These results represent novel findings. Hence, future studies are needed to understand the full impact of circadian rhythms on mantis behavior and physiology.