The Neuro-Ecology of <i>Drosophila</i> Pupation Behavior

<div><p>Many species of <i>Drosophila</i> form conspecific pupa aggregations across the breeding sites. These aggregations could result from species-specific larval odor recognition. To test this hypothesis we used larval odors of <i>D. melanogaster</i> and <i>D. pavani</i>, two species that coexist in the nature. When stimulated by those odors, wild type and <i>vestigial</i> (<i>vg</i>) third-instar larvae of <i>D. melanogaster</i> pupated on conspecific larval odors, but individuals deficient in the expression of the odor co-receptor <i>Orco</i> randomly pupated across the substrate, indicating that in this species, olfaction plays a role in pupation site selection. Larvae are unable to learn but can smell, the <i>Syn^97CS</i> and <i>rut</i> strains of <i>D. melanogaster</i>, did not respond to conspecific odors or <i>D. pavani</i> larval cues, and they randomly pupated across the substrate, suggesting that larval odor-based learning could influence the pupation site selection. Thus, <i>Orco</i>, <i>Syn^97CS</i> and <i>rut</i> loci participated in the pupation site selection. When stimulated by conspecific and <i>D. melanogaster</i> larval cues, <i>D. pavani</i> larvae also pupated on conspecific odors. The larvae of <i>D. gaucha</i>, a sibling species of <i>D. pavani</i>, did not respond to <i>D. melanogaster</i> larval cues, pupating randomly across the substrate. In nature, <i>D. gaucha</i> is isolated from <i>D. melanogaster</i>. Interspecific hybrids, which result from crossing <i>pavani</i> female with <i>gaucha</i> males clumped their pupae similarly to <i>D. pavani</i>, but the behavior of <i>gaucha</i> female x <i>pavani</i> male hybrids was similar to <i>D. gaucha</i> parent. The two sibling species show substantial evolutionary divergence in organization and functioning of larval nervous system. <i>D. melanogaster</i> and <i>D. pavani</i> larvae extracted information about odor identities and the spatial location of congener and alien larvae to select pupation sites. We hypothesize that larval recognition contributes to the cohabitation of species with similar ecologies, thus aiding the organization and persistence of <i>Drosophila</i> species guilds in the wild.</p>