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Animals may vary in their utilization of plants depending on plant availability, and also on the sex of the animal. Evolutionary adaptations may arise, particularly in specialist animals to the chemistry of the host plants, and these adaptations may differ between the sexes due to differences in their interactions with the plants. Drosophila mojavensis uses different host cacti across its range, and volatile chemicals emitted by the host are the primary cue for host plant identification. In this study, we measured responses of individual olfactory sensory neurons to a large suite of odorants across males and females of the two southern D. mojavensis populations. We show that a switch in host plant is accompanied by changes in the olfactory system, but the effect of this switch is minor compared to that of sex. That is, we observe differences in olfactory receptor neuron specificity and sensitivity to odorants between sexes, and to a lesser extent between populations. The majority of sensory differences are restricted to only three of the 17 sensory neurons measured. Further, we found numerous differences between sexes that only occur within one population, i.e., sex-by-population interactions., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Populations inhabiting habitats with different environmental conditions, such as climate, resource availability, predation, competition, can undergo selection for traits that are adaptive in one habitat and not the other, leading to divergence between populations. Changes in the olfactory systems of insects that rely on different host plants, for example, can occur in response to differences in sensory stimuli between habitats. In this study, we investigate the evolution of host preference by characterizing the coeloconic sensilla in Drosophila mojavensis, a species that breeds on different necrotic cacti across its geographic range. These cactus species differ in the volatile chemicals they emit, a primary sensory cue for host plant discrimination. Analysis of odor-evoked responses identified four coeloconic sensilla that were qualitatively similar to those of Drosophila melanogaster, but varied in the breadth and strength of their olfactory sensory neuron responses to some acids and amines. Variation in responses to certain odorants among D. mojavensis populations was also observed. Compared to D. melanogaster, there was a lack of sensitivity of antennal coeloconic type 3 (ac3) sensilla to primary ligands of OR35a across all populations. Consistent with this result was a lack of detectable Or35a gene expression. Using a comparative approach, we then examined odor specificity of ac3 sensilla for seven additional Drosophila species, and found that OR35a-like sensitivity may be limited to the melanogaster subgroup. The variation in specificity that was observed among species is not clearly attributable to the degree of ecological specialization, nor to the ecological niche., (Copyright © 2018 Elsevier Ltd. All rights reserved.)