Meeting Abstract

20.7  Saturday, Jan. 4 15:00  The games that flies play: laying eggs based on temperature and competition BORCHERT, JB*; ANGILLETTA, MJ; Arizona State University, Tempe jdborche@asu.edu

We used game theory to predict how fruit flies, Drosophila melanogaster, should compete for oviposition sites. Although flies prefer to lay their eggs within a particular range of temperatures, the potential for competition among offspring should cause females to accept warmer or cooler sites when preferred sites become crowded. To look at this problem, we observed where flies chose to lay eggs under various densities of competing females. In each trial, 4 or 15 flies were placed within a thermal arena containing a choice of two oviposition sites, one at a preferred temperature (25°C) and another at a lower temperature (20°C). In a concurrent trial, 100 eggs were added to the site with the optimal temperature and then 4 flies were added to see if behavior depended on the presence of other females or eggs. After 4 hours, we counted the eggs laid in each portion of the gradient and analyzed how the distribution of eggs was affected by the density of females. Flies at low density laid eggs almost exclusively at 25°C, but those at high density laid a significantly greater proportion of eggs at 20°C than did flies at low density. Surprisingly, flies did not avoid laying at 25°C when eggs were present, suggesting that flies responded to the presence of competing females rather than cues associated with eggs. By drawing on game theory to make quantitative predictions, this research builds on previous empirical studies of competition between thermoregulating animals.