Meeting Abstract
P3.8 Wednesday, Jan. 6 Do the exaggerated eye stalks of stalk-eyed flies have a predation cost? HUSAK, J.F.*; WORTHINGTON, A.M.; SWALLOW, J.G.; Univ. of South Dakota jerry.husak@usd.edu
When opponents compete for access to an indivisible resource, signals can reduce costs associated with competition for that resource. Theory predicts that for signals to remain reliable in such situations there should be costs associated with the signal. These costs may be imposed when the signal is being developed, while it is being displayed to a receiver, or simply by bearing it when not using it. Stalk-eyed flies (Teleopsis dalmanni) have their eyes on the ends of large peduncles, with males having significantly greater eyespans than females. Males use the span of their eye stalks to reliably assess body size and fighting ability during agonistic interactions. To test whether there is a predation cost to the exaggerated eye stalks of stalk-eyed flies we conducted predation trials with flies and a generalist predator, a jumping spider (Phidippus audax). We determined whether male stalk-eyed flies suffered higher predation than females. We also examined, within each sex, whether individuals with greater eyespans suffered higher predation than those with smaller eyespans. We conducted experiments in a small enclosure with a single fly facing a predator, as well as in larger mesocosms that contained 20 flies and a predator. We found no support for the hypothesis that there is a predation cost to exaggerated eye stalks. Males did not have lower survival than females, and individuals with larger eyespans did not have lower survival in either sex. No other morphological variable differed between survivors and non-survivors within a sex. In the single-fly trials, anti-predator behavior was the best predictor of survival. Thus, we found no evidence for selection against greater eyespans in stalk-eyed flies. Our results suggest that the exaggerated eye stalks of stalk-eyed flies are a condition-dependent signal of individual quality or that other costs maintain reliability of the signal.
