1. The effects of juvenile hormone modulation on development & stress-related behavior in Madagascar hissing cockroaches (Gromphadorhina portentosa) Clint Lexa, J.E. Davis Radford University
Radford University
Ecophysiology
Lab
Mortality
Both allostatin & methoprene significantly increased overall mortality of females
Fecundity
Methoprene treatment resulted in a complete cessation of hatching
Weight
Females weigh more than males, methoprene males weigh more, methoprene females had a larger range of weights.
Behavior
Hormonal alteration had no effect on in exploratory or photophobic behaviors
Females moved significantly less than males in tests of both exploration & photophobia
Background
Discussion I II
Growth, maturation, and stress are closely related systems in the physiology of insects as in vertebrates. Changes in these systems are regulated in part by juvenile hormone (JH); high levels of JH pre-maturation generally keep a nymphal individual from maturing into an adult state. Here we
Interpretation
Effects of juvenile hormone manipulations were visible in physiology, but dependent on sex. Both allostatin and methoprene negatively impacted female, but not male, mortality. Methoprene strongly inhibited reproduction. Delayed maturation or suppression of reproductive investment may also have allowed some methoprene-treated animals (particularly males) to invest more in growth.
Hormone treatment had no effect on exploratory or photophobic behavior. Sex differences in behavior are robust and persist despite reproductive inhibition. The role of juvenile hormone role in anxiety/stress reactivity remains unclear.
hypothesize that, due to it’s role in allocation of resources to individual survival, JH may also play a part in control of stress reactions, much as corticosteroids do in vertebrates. We specifically predicted that chronically increased JH would increase self-investment, impairing reproduction and improving health, while simultaneously increasing anxiety. Inversely, chronic reduction of JH would expedite reproduction at the cost of impaired fitness, and simultaneously reducing anxiety and self-preservatory behaviors.
I = p <.05
II = p <.01
III = p <.001
Methods
Housing
Housed in mixed male/female groups (~30 C). Hatchlings removed within two days of hatching.
Ad libitum food (grain cereal) and water
Mortality, fecundity and body condition tracked from 11/ to 11/2011
Hormone Modulation
116 nymphs of equivalent age were divided into 3 treatment groups: Control, agonist, and antagonist
Agonist group: .002% methoprene in water supply
Antagonist group: .002% allostatin in water supply
Behavioral Testing
Photophobia: distance travelled from a light source (n=7)
Exploration: distance spent in edge vs. center of open field (n=5)
Statistical Analysis
Survivorship & hatching were analyzed with Pearson’s chi-squared tests
Weight & behavioral results were analyzed with ANOVA and post-hoc Student’s T-tests
Female during nymph emergence
Deformation of shell observed in methoprene treatment group
Future Directions
Ongoing studies in our laboratory are directly exploring the role of chronic JH manipulation on metabolism and innate immunocompetence.
Future studies will also explore possible modulatory effects of both chronic and acute JH modulation on aggression and social interaction. We also plan to further explore the nature of sex-related differences in behavior and JH function.
Our results also suggest that Madagascar hissing cockroaches may be an ideal model for the study of individual variation in physiology and behavior.
III
III
III
Contact:
Thanks to:
Clint Lexa
Erin Dudley, Kristen Cale and other members of the Radford Ecophysiology lab.
The Ruth Bricker Painter Research Award and Radford University Honor’s College for funding in support of this project.
III
Exploration task
Photophobia task