Host plant-driven sensory specialization inDrosophila erecta

Jeanine Linz,Marcus C Stensmyr,Antonia Strutz,Bill S Hansson,Hany K M Dweck,Amelie Baschwitz,Silke Sachse

doi:10.1098/rspb.2013.0626

Jeanine Linz, Marcus C Stensmyr + Show 5 more

Open Access

https://doi.org/10.1098/rspb.2013.0626

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Abstract

Finding appropriate feeding and breeding sites is crucial for all insects. To fulfil this vital task, many insects rely on their sense of smell. Alterations in the habitat—or in lifestyle—should accordingly also be reflected in the olfactory system. Solid functional evidence for direct adaptations in the olfactory system is however scarce. We have, therefore, examined the sense of smell of Drosophila erecta, a close relative of Drosophila melanogaster and specialist on screw pine fruits (Pandanus spp.). In comparison with three sympatric sibling species, D. erecta shows specific alterations in its olfactory system towards detection and processing of a characteristic Pandanus volatile (3-methyl-2-butenyl acetate, 3M2BA). We show that D. erecta is more sensitive towards this substance, and that the increased sensitivity derives from a numerical increase of one olfactory sensory neuron (OSN) class. We also show that axons from these OSNs form a complex of enlarged glomeruli in the antennal lobe, the first olfactory brain centre, of D. erecta. Finally, we show that 3M2BA induces oviposition in D. erecta, but not in D. melanogaster. The presumed adaptations observed here follow to a remarkable degree those found in Drosophila sechellia, a specialist upon noni fruit, and suggest a general principle for how specialization affects the sense of smell.

Highlights

Because the sense of smell directly interfaces with the environment, it is an ideal system to study adaptive responses to altered environmental conditions and shifts in habitat preference
We show that D. erecta is more sensitive towards this substance, and that the increased sensitivity derives from a numerical increase of one olfactory sensory neuron (OSN) class
We show that axons from these OSNs form a complex of enlarged glomeruli in the antennal lobe, the first olfactory brain centre, of D. erecta

Summary

Introduction

Because the sense of smell directly interfaces with the environment, it is an ideal system to study adaptive responses to altered environmental conditions and shifts in habitat preference. In another study [15], a handful of D. erecta (but many D. melanogaster and Drosophila yakuba) were trapped in banana baits between two Pandanus fruiting events. We show that D. erecta, in contrast to its non-specialized sympatric relatives D. orena, D. yakuba and D. melanogaster, is more sensitive towards the Pandanus volatile 3-methyl-2-butenyl acetate (3M2BA; known as prenyl acetate). Gas chromatography coupled with electroantennographic detection (GC-EAD) and electroantennography (EAG) [25] were used to identify the antennal responses of the four sibling species to the collected Pandanus fruit volatiles. To test the activation of the Or22a receptor by different 3M2BA concentrations, dose– response experiments were performed on the large basiconic sensilla in D. erecta and D. melanogaster females. Prior to the analyses numbers of eggs were log-transformed

Results and Discussion

Dmel Dyak Dore Dere

Conclusion