PARENT SESSION
Symposium 9: Structural Equations, Path Analysis, and Other Causal Models
Organized by: S Scheiner
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Chatham Ballroom C.
Testing alternative models of social evolution.
Backus, Vickie*,1, Herbers, Joan2, 1 Middlebury College, Middlebury, VT2 Ohio State University, Columbus, OH
ABSTRACT- The decisions an organism makes when allocating energy will affect every aspect of its behavior. This process is especially complicated for eusocial species because the parties in the nest may disagree over the decisions. In ants hapliodiploid sex determination means that queens and workers have different optimum sex allocation ratios. Differences in life span for these two parties means they also differ in their optimum allocation ratios between growth and reproduction. Natural selection is superimposed on these conflicts which can lead to different sets of allocation rules as being optimal depending on the environment. Path analysis was used to determine the magnitude and direction of internal conflict over allocation decisions, and to determine the rules used by nests in making those decisions, for the small forest ant Leptothorax longispinosus. The data show that conflict over allocation decisions is common in this species; queens and workers frequently disagreed over the amount of energy to allocate to reproduction versus growth and how to package that allocation. Which party won the conflict varied both temporally and spatially. Path analysis also showed that selection would lead to different rules being used by nests while making these important decisions. Nests located in Vermont used a set of rules that operate at a proximate level; the parties in the nest first packaged resources into diploid or haploid offspring and then later decided how much of the diploid resources became growth versus reproduction. On the other hand nests in New York used rules that evolved under an ultimate level selection pattern where nests first decided how much to allocate to growth or reproduction and later decided how to package those resources.
Key words: sex ratio, allocation, path analysis, Leptothorax longispinosus