|HELMS CAHAN, SARA - University Of Vermont|
|GRAVES, CHRISTOPHER - University Of Vermont|
Submitted to: Journal of Comparative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2011
Publication Date: 5/27/2011
Citation: Helms Cahan, S., Graves, C.J., Brent, C.S. 2011. Intergenerational effect of juvenile hormone on offspring in Pogonomyrmex harvester ants. Journal of Comparative Physiology. 181(8):991.
Interpretive Summary: Parents can influence the development of their offspring by various mechanisms. In harvester ants, whether daughters develop into workers or queens is influenced by the hormones a mother deposits into her eggs in response to her age and the temperature conditions she experiences. One maternal hormone that may be particularly important in regulating what goes into the eggs to influence offspring size and reproductive caste is juvenile hormone (JH). To test this hypothesis, we artificially increased or decreased maternal JH titers with methoprene, a JH analog, or precocene II, an inhibitor of JH synthesis, in laboratory colonies of two Pogonomyrmex populations. Increasing maternal JH resulted in a 50% increase in offspring body size and a reduction in offspring number, but did not alter offspring caste. JH manipulation also had no effect on the hormones being placed into the eggs, but evident changes to the nutrient environment may have affected offspring development. Additional evidence was found that the hormone content of the eggs can effect worker body size, suggesting that there are multiple independent routes by which queens can modify offspring development.
Technical Abstract: Parents can influence the phenotypes of their offspring via a number of mechanisms. In harvester ants, whether female progeny develop into workers or daughter queens is strongly influenced by the age and temperature conditions experienced by their mother, which is associated with variation in maternal ecdysteroid deposition in fertilized eggs. Ecdysteroid release can be inhibited by juvenile hormone (JH), suggesting that variation in maternal JH titers seasonally and as queens age may explain maternal effects on offspring size and reproductive caste. To test this hypothesis, we artificially increased or decreased maternal JH titers with methoprene, a JH analog, or precocene II, an inhibitor of the corpora allata where JH is synthesized, in laboratory colonies of two Pogonomyrmex populations exhibiting Genetic Caste Determination (GCD). Increasing maternal JH resulted in a 50% increase in worker body size, as well as a sharp reduction in total number of progeny reared, but did not alter the genotype of progeny reared to adulthood. The intergenerational effect of JH manipulation was not mediated by a reduction in ecdysteroid deposition into eggs; instead, changes in egg size, trophic egg availability or brood/worker ratio may have altered the nutritional environment of developing larvae. Egg ecdysteroid content was significantly negatively correlated with natural variation in worker body size, however, suggesting that there are multiple independent routes by which queens can modify offspring phenotypes.