Disruption of the odorant receptor coreceptor (Orco) impairs foraging and host-seeking behaviors in the New World screwworm, Cochliomyia hominivorax

Authors: PAULO, DANIEL - Universidade De Campinas (UNICAMP); JUNQUEIRA, ANA - Universidade Federal Do Rio De Janeiro; Arp, Alex; VIERA, ANDRE - Universidade De Campinas (UNICAMP); CEBALLOS, JORGE - Smithsonian Tropical Research; Skoda, Steven; Perez De Leon, Adalberto - Beto; SAGEL, AGUSTIN - US Department Of State; MCMILLAN, WILLIAM - Smithsonian Tropical Research; SCOTT, MAXWELL - North Carolina State University; CONCHA, CAROLINA - Smithsonian Tropical Research; AZEREDO-ESPIN, ANA - Universidade De Campinas (UNICAMP)

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2021
Publication Date: 5/31/2021
Citation: Paulo, D.F., Junqueira, A.C., Arp, A.P., Viera, A.S., Ceballos, J., Skoda, S.R., Perez De Leon, A.A., Sagel, A., Mcmillan, W.O., Scott, M.J., Concha, C., Azeredo-Espin, A.M. 2021. Disruption of the odorant receptor coreceptor (Orco) impairs foraging and host-seeking behaviors in the New World screwworm, Cochliomyia hominivorax. Scientific Reports. 11. Article 11379. https://doi.org/10.1038/s41598-021-90649-x.
DOI: https://doi.org/10.1038/s41598-021-90649-x

Interpretive Summary: The driving factors involved in the evolution of parasitic lifestyles in some blow flies are not known. It is thought that smelling or olfaction is a primary driver, thus in this paper the gene olfactory receptor co-receptor (Orco) was characterized in the parasitic blow fly Chochliomyia hominivorax. Orco is needed for one of the three groups of olfactory genes, odorant receptors, to function. In other insects, knockout of Orco reduces food or mate seeking capability. In addition to characterizing this gene, functional knockouts were created using CRISPR-Cas9 to identify if food seeking or oviposition site selection were inhibited. These experiments found that Orco in C. hominivorax is similar to other flies, and is primarily present in young larvae and adults. In adults it is most present in sensory appendages and the abdomen. Knockout of Orco resulted in flies that could not find a food source and females unable to find oviposition sites. These results indicate that further investigation of the odorant receptor genes could identify specific genes involved in food seeking or oviposition behaviors as well as drivers of a parasitic lifestyle.

Technical Abstract: The evolution of obligatory ectoparasitism in blowflies (Diptera: Calliphoridae) has intrigued the scientific community for over a century, and surprisingly, the genetics underlying such lifestyle remain largely unknown. Blowflies rely on odors to find suitable oviposition sites, thus, we hypothesize that olfaction played a critical role in the adaptive transition from a free-living to a parasitic species within the group. In insects, the olfactory receptor co-receptor (Orco) is a required partner for all odorant receptors (ORs), a major gene family involved in olfactory-evoked behaviors. Aiming to rapidly expand our knowledge on the molecular pathways used by parasitic blowflies to find hosts for oviposition, we characterized and investigated the evolutionary and expression profiles of Orco in the New World screwworm fly, Cochliomyia hominivorax, the only obligatory ectoparasitic blowfly in the Neotropical region. The Orco orthologue of screwworm (ChomOrco) is highly conserved within Diptera, due a strong purifying selection. Expression of ChomOrco is particularly high in adults, broadly detectable in olfactory appendages, and is linked to morphological, developmental and behavioral aspects of the screwworm biology. We used CRISPR/Cas9 to knockout ChomOrco and evaluate the consequences of losing the ORs function on screwworm behavior. Two-choice assays revealed that Orco mutants display disrupted flight orientation towards host’s odors, suggesting that the OR-mediated olfaction is essential for host-seeking behavior in C. hominivorax. The data presented here offers the first genetic basis on which niche preferences in blowflies can be functionally interrogated, opening new routes for ecological and evolutionary studies in this diverse group of flies.