Biology subjects

Alvarez-Ocana, R.

Publications and source records attributed to Alvarez-Ocana, R..

2 recordsLinked to original sources

bioRxiv2022

Odor-gated oviposition behavior in an ecological specialist

Colonization of a novel ecological niche can require, or be driven by, evolution of an animals behaviors promoting their reproductive success in the new environment. Little is known about the underlying mechanisms. We have exploited an emerging genetic model for behavioral neuroecology, Drosophila sechellia - a close relative of Drosophila melanogaster that exhibits extreme specialism for Morinda citrifolia noni fruit - to study the evolution and sensory basis of oviposition. D. sechellia produces fewer eggs compared to other drosophilids, but lays these almost exclusively on noni substrates, contrasting with avoidance or indifference of noni by generalist species. Visual, textural and social cues do not explain the species-specificity of this preference. By contrast, loss of olfactory input in D. sechellia, but not D. melanogaster, essentially abolishes egg-laying, suggesting that this sensory modality gates gustatory-driven noni preference. We find the noni bouquet is detected by redundant olfactory pathways. By parsing the fruits volatile chemicals and genetic perturbation of individual olfactory pathways in D. sechellia, we discover a key role for hexanoic acid and its cognate receptor, the Ionotropic receptor Ir75b, in odor-evoked oviposition. Through receptor exchange in D. melanogaster, we provide evidence for a causal contribution of odor-tuning changes in Ir75b to the evolution of oviposition behavior during D. sechellias host specialization.

animal behavior and cognition↗

bioRxiv2021

Odorant receptor copy number change, co-expression, and positive selection establish peripheral coding differences between fly species

1.Despite numerous examples of chemoreceptor gene family expansions and contractions, how these changes relate to modifications in the neural circuitry in which they are expressed remains unclear. Drosophilas Odorant receptor (Or) family is ideal for addressing this question because a large majority of Ors are uniquely expressed in single olfactory sensory neuron (OSN) types. Between-species changes in Or copy number, therefore, may indicate diversification/reduction of OSN populations. To test this, we investigated a rapidly duplicated/deleted subfamily (named Or67a) in Drosophila melanogaster and its sister species (D. simulans, D. sechellia, and D. mauritiana). We found that the common ancestor had three Or67a paralogs that had already diverged adaptively in their odor-evoked responses. Following their speciation, two Or67a paralogs were lost independently in D. melanogaster and D. sechellia, with ongoing positive selection acting on the intact genes. Instead of the expected singular expression of each diverged Ors, the three D. simulans Or67a paralogs are co-expressed. Thus, while neuroanatomy is conserved between these species, independent selection on co-expressed receptors has contributed to species-specific peripheral coding of olfactory information. This work reveals a model of adaptive change previously not considered for olfactory evolution and raises the possibility that similar processes may be operating among the largely uninvestigated cases of Or co-expression.

evolutionary biology↗