Indexed on: 01 Jun '76Published on: 01 Jun '76Published in: Oecologia
The number of eggs laid in aDrosophila culture and the survival of these eggs may depend on the number of larvae that are still inhabiting or that have already used the culture medium.A known average number ofD. simulans st larvae (designated original inhabitants) were introduced into culture vials by allowing adults to lay for 24 h (low density) or 48 h (high density). On each day for 14 days, adults of three competitor strains (D. melanogaster Or-R-C, D. melanogaster yw andD. simulans st) were added to different samples of these vials and allowed to lay for 24 h. The numbers of “effective eggs” (eggs expected to be laid less those withheld, cannibalised or buried) produced by competitor strains were estimated from adult emergences. Survival of original inhabitant larvae to the adult stage also was measured.At the lower density of original inhabitants, the mean proportions of effective eggs (number of effective eggs/number of eggs expected in an uninhabited culture) were not significantly different for the three competitor strains. The mean proportions were lower at the higher density (significantly so for the twoD. melanogaster competitors), and at this density, the mean proportion forD. melanogaster yw was significantly less than that forD. simulans st. These results are consistent with a simple egg destruction hypothesis, but suggest thatyw females were retaining more eggs at the higher density.Original inhabitants showed higher survival when at the higher density. Each of the three competitors caused a significantly different reduction in original inhabitant survival, which was directly related to competitor larval activity. Increasing larval activity probably reduced survival of original inhabitants by increasing pupal mortality due to drowning in the medium.Day of introduction of competitors influenced survival of original inhabitants and also the proportion of effective eggs from each competitor. The proportion of effective eggs decreased to the day 5 introduction. From day 5 to day 8, the proportion increased because the original inhabitants were pupating. After day 8, effective egg proportions again decreased, possibly due to inhibition of egg-laying or reduced survival of immature stages.