Divergence in Olfactory Host Plant Preference in D. mojavensis in Response to Cactus Host Use

Abstract

Divergence in host adaptive traits has been well studied from an ecological and evolutionary perspective, but identification of the proximate mechanisms underlying such divergence is less well understood. Behavioral preferences for host plants are often mediated by olfaction and shifts in preference may be accompanied by changes in the olfactory system. In this study, we examine the evolution of host plant preferences in cactophilic Drosophila mojavensis that feeds and breeds on different cacti throughout its range. We show divergence in electrophysiological responses and olfactory behavior among populations with host plant shifts. Specifically, significant divergence was observed in the Mojave Desert population that specializes on barrel cactus. Differences were observed in electrophysiological responses of the olfactory organs and in behavioral responses to barrel cactus volatiles. Together our results suggest that the peripheral nervous system has changed in response to different ecological environments and that these changes likely contribute to divergence among D. mojavensis populations.

Population differences in olfaction accompany host shift in Drosophila mojavensis

“…Of the three ORNs with known receptor orthologues, ab9B and pb1B are highly responsive to aromatics in D. melanogaster and in D. mojavensis [27,29,30,38,41]. This is in line with previous work in D. mojavensis in which the Mojave population showed increased responses to aromatics and in which aromatics were found to be a dominant component of the headspace of barrel cactus, its host plant [25]. In D. melanogaster, the third neuron, ab7A, expresses Or98a and responds to several esters as well as aromatic esters such as ethyl and methyl benzoate [27].…”

“…This is not unexpected in the case of ab4B, because it has previously been shown in several species, including in D. mojavensis, to have a conserved and exclusive activation by geosmin, an indicator of harmful microbes ( [32], data not shown). Furthermore, D. melanogaster ab9A is responsive to citral, and pb2A to beta-ionone [40]-compounds not detected in characterizations of the volatile compositions of cacti in the D. mojavensis system [25]. Therefore, their function, as well as the function of ab3B, abXA and abYB, whose receptors are unknown in D. mojavensis [35], will require further study.…”

A major locus controls a biologically active pheromone component inHeliconius melpomene

“…) and Drosophila mojavensis (Date et al. ; Crowley‐Gall et al. ) despite much shorter divergence times than between H. melpomene and H. cydno (approximately 2.1 million years ago; Arias et al.…”

Physiological and behavioral responses in Drosophila melanogaster to odorants present at different plant maturation stages

“…The first species to colonize rotting fruit is D. simulans, which approaches fruit when few volatiles have been produced by fermentation, followed by D. melanogaster and D. immigrans, and then by the other species Drosophila hydei and Drosophila busckii [40,41]. Beside fermenting fruit, other parts of plants and maturation stages are attractive for certain Drosophila species and reflect different olfactory responses [36]: D. virilis [42] and D. pseudoobscura [43] are attracted by the tree sap, D. obscura and D. subobscura feed on leaves within the canopy [44,45], D. mojavensis is specialized on photosynthetic tissue of fermenting cactus [26], D. suzukii has evolved a segmented ovipositor that allows to cut the skin of small fruits and preferentially oviposits on ripening fruit [46]. Keesey et al [17] have compared three Drosophila species, finding that while D. suzukii, that oviposits on fresh fruit, responded to the leaf compound β-cyclocitral both at the electrophysiological (responses of the olfactory sensory neuron ab3A) and behavioral level (trap assays), D. melanogaster and D. biarmipes, that do not oviposit on fresh ripe fruit, did not.…”