PARENT SESSION
Poster Session 30: Invertebrate Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Spatial egg aggregation and the capacity to retain eggs in Drosophila.
Takahashi, Kazuo*,1, Kimura, Masahito1, 1 Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido, Japan
ABSTRACT- Spatial aggregation of eggs has been suggested to promote the coexistence of competing species on patchy, ephemeral resources. One of mechanisms underlying aggregated egg distributions is the production of clutches with several eggs. However, the production of a few large clutches yields a cost through sib competition, while the production of many small clutches yields a search and travel cost. An optimal clutch size strategy balances these competing costs, and therefore different clutch sizes would evolve if the pattern of resource distributions differs. For example, species that use sparsely distributed resources would evolve large clutches, while species that use densely distributed resources would evolve small clutches. Further, species with larger clutches would have larger capacities to retain eggs in their ovaries. It is therefore expected that the degree of spatial egg distribution is correlated with the capacity to retain eggs. Here we examined the spatial egg distribution and the capacity to retain eggs in the ovaries in three drosophilid species (D. simulans, D. auraria, and D. immigrans) by laboratory experiments. Oviposition pattern was investigated using an oviposition cage (180 cm×90 cm×45 cm) and artificial substrate. The capacity to retain eggs was investigated by leaving females in vials containing innutritious agar medium. In this experiment, time on agar medium was supposed to mimic spatial distance between resource patches. Results of cage experiments indicated that D. simulans tended to distribute eggs randomly while D. auraria and D. immigrans tended to distribute eggs in aggregated manner. It also appeared that the capacity to retain eggs was low in D. simulans.
Key words: spatial aggregation, clutch size, capacity to retain eggs, Drosophila