Are there genetically controlled habitat‐specific differences in spatial aggregation of drosophilids?

Variation in spatial patterns of competing organisms is of fundamental importance for community and population processes. Yet the mechanisms controlling subjects like the degree of spatial aggregation in competing insect larvae across fragmented resources have rarely been addressed. In the present study, we tested for systematic differences in the spatial distribution patterns of Drosophila subobscura in natural fly communities, and found significant differences in two habitats that differ in the availability of breeding substrate types (decaying fruits). Assuming that the spatial egg‐laying behaviour of drosophilids is under genetic control, and that different breeding substrates mediate different density‐dependent larval fitness consequences, we tested whether adaptive genotypic variability is involved in the local variation of egg distribution patterns. We extracted isofemale lines from both habitats and analysed the spatial distribution of eggs achieved by single female flies under controlled laboratory conditions. This is a reasonable first test, because spatial patterns at the fly population level can be attributed to individual egg‐laying behaviour. The degree of individual egg aggregation significantly depended on fly line identity, which indicates the existence of behavioural variants in natural populations. Based on habitat‐dependent differences in the degree of spatial aggregation, we discuss to what extent our findings may reflect a behavioural adaptation to local breeding conditions.