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1. Olfactory receptor gene evolution is unusually rapid across Tetrapoda and outpaces chemosensory phenotypic change

   https://doi.org/10.1093/cz/zoaa051  

   Yohe, Laurel R; Fabbri, Matteo; Hanson, Michael; Bhullar, Bhart-Anjan S (September 2020, Current Zoology)

   Muñoz, Martha (Ed.)

   Abstract Chemosensation is the most ubiquitous sense in animals, enacted by the products of complex gene families that detect environmental chemical cues and larger-scale sensory structures that process these cues. While there is a general conception that olfactory receptor (OR) genes evolve rapidly, the universality of this phenomenon across vertebrates, and its magnitude, are unclear. The supposed correlation between molecular rates of chemosensory evolution and phenotypic diversity of chemosensory systems is largely untested. We combine comparative genomics and sensory morphology to test whether OR genes and olfactory phenotypic traits evolve at faster rates than other genes or traits. Using published genomes, we identified ORs in 21 tetrapods, including amphibians, reptiles, birds, and mammals and compared their rates of evolution to those of orthologous non-OR protein-coding genes. We found that, for all clades investigated, most OR genes evolve nearly an order of magnitude faster than other protein-coding genes, with many OR genes showing signatures of diversifying selection across nearly all taxa in this study. This rapid rate of evolution suggests that chemoreceptor genes are in “evolutionary overdrive,” perhaps evolving in response to the ever-changing chemical space of the environment. To obtain complementary morphological data, we stained whole fixed specimens with iodine, µCT-scanned the specimens, and digitally segmented chemosensory and nonchemosensory brain regions. We then estimated phenotypic variation within traits and among tetrapods. While we found considerable variation in chemosensory structures, they were no more diverse than nonchemosensory regions. We suggest chemoreceptor genes evolve quickly in reflection of an ever-changing chemical space, whereas chemosensory phenotypes and processing regions are more conserved because they use a standardized or constrained architecture to receive and process a range of chemical cues. 

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2. HisCl1 regulates gustatory habituation in sweet taste neurons and mediates sugar ingestion in Drosophila

   https://doi.org/10.1101/2024.05.06.592591  

   Kim, Haein; Zhong, Ziqing; Cui, Xinyue; Sung, Hayeon; Agrawal, Naman; Jiang, Tianxing; Dus, Monica; Yapici, Nilay (May 2024, bioRxiv)

   SUMMARY Similar to other animals, the fly,Drosophila melanogaster, reduces its responsiveness to tastants with repeated exposure, a phenomenon called gustatory habituation. Previous studies have focused on the circuit basis of gustatory habituation in the fly chemosensory system^1,2. However, gustatory neurons reduce their firing rate during repeated stimulation³, suggesting that cell-autonomous mechanisms also contribute to habituation. Here, we used deep learning-based pose estimation and optogenetic stimulation to demonstrate that continuous activation of sweet taste neurons causes gustatory habituation in flies. We conducted a transgenic RNAi screen to identify genes involved in this process and found that knocking downHistamine-gated chloride channel subunit 1(HisCl1)in the sweet taste neurons significantly reduced gustatory habituation. Anatomical analysis showed thatHisCl1is expressed in the sweet taste neurons of various chemosensory organs. Using single sensilla electrophysiology, we showed that sweet taste neurons reduced their firing rate with prolonged exposure to sucrose. Knocking downHisCl1in sweet taste neurons suppressed gustatory habituation by reducing the spike frequency adaptation observed in these neurons during high-concentration sucrose stimulation. Finally, we showed that flies lackingHisCl1in sweet taste neurons increased their consumption of high-concentration sucrose solution at their first meal bout compared to control flies. Together, our results demonstrate that HisCl1 tunes spike frequency adaptation in sweet taste neurons and contributes to gustatory habituation and food intake regulation in flies. Since HisCl1 is highly conserved across many dipteran and hymenopteran species, our findings open a new direction in studying insect gustatory habituation. 

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3. Ecological constraints on highly evolvable olfactory receptor genes and morphology in neotropical bats

   https://doi.org/10.1111/evo.14591  

   Yohe, Laurel R.; Fabbri; Lee, Daniela; Davies, Kalina T.J.; Yohe, Thomas P.; Sánchez, Miluska K.R.; Rengifo, Edgardo M.; Hall, Ronald; Mutumi, Gregory; Hedrick, Brandon P.; et al (January 2022, Evolution)

   While evolvability of genes and traits may promote specialization during species diversification, how ecology subsequently restricts such variation remains unclear. Chemosensation requires animals to decipher a complex chemical background to locate fitness-related resources, and thus the underlying genomic architecture and morphology must cope with constant exposure to a changing odorant landscape; detecting adaptation amidst extensive chemosensory diversity is an open challenge. In phyllostomid bats, an ecologically diverse clade that evolved plant-visiting from an insectivorous ancestor, the evolution of novel food detection mechanisms is suggested to be a key innovation, as plant-visiting species rely strongly on olfaction, supplementarily using echolocation. If this is true, exceptional variation in underlying olfactory genes and phenotypes may have preceded dietary diversification. We compared olfactory receptor (OR) genes sequenced from olfactory epithelium transcriptomes and olfactory epithelium surface area of bats with differing diets. Surprisingly, although OR evolution rates were quite variable and generally high, they are largely independent of diet. Olfactory epithelial surface area, however, is relatively larger in plant-visiting bats and there is an inverse relationship between OR evolution rates and surface area. Relatively larger surface areas suggest greater reliance on olfactory detection and stronger constraint on maintaining an already diverse OR repertoire. Instead of the typical case in which specialization and elaboration are coupled with rapid diversification of associated genes, here the relevant genes are already evolving so quickly that increased reliance on smell has led to stabilizing selection, presumably to maintain the ability to consistently discriminate among specific odorants — a potential ecological constraint on sensory evolution. 

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4. Pheromone-Binding Proteins in Pest Control: From Molecular Insights to Real-World Applications

   https://doi.org/10.1021/acs.jafc.5c03663  

   Ray, Ishani; Mohanty, Smita (September 2025, Journal of Agricultural and Food Chemistry)

   Insects utilize sophisticated olfactory systems to detect chemical cues critical for behaviors such as mating, host selection, and predator avoidance. In lepidopteran moths, sex pheromone communication offers a well-established model where males detect female-emitted signals over long distances. Central to this process are pheromone-binding proteins (PBPs), which solubilize and transport hydrophobic pheromones through the sensillar lymph to olfactory receptors, enabling precise signal detection. Recent advances in molecular biology, structural biochemistry, and gene-editing technologies such as CRISPR/Cas9 have uncovered nuanced mechanisms underlying PBP function, including ligand-binding specificity, pH-dependent conformational dynamics, and molecular interactions. These discoveries have broad implications, extending beyond chemosensory biology to applications in reverse chemical ecology, biosensing, and environmentally conscious pest control. This review synthesizes insights from in vitro, in silico, and in vivo studies, highlighting the structural and functional diversity of PBPs across species and emphasizing their translational utility as molecular targets for sustainable agriculture and biodiversity conservation. 

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5. An updated synthesis of and outstanding questions in the olfactory and vomeronasal systems in bats: Genetics asks questions only anatomy can answer

   https://doi.org/10.1002/ar.25290  

   Yohe, Laurel R.; Krell, Nicholas T. (November 2023, The Anatomical Record)

   Abstract The extensive diversity observed in bat nasal chemosensory systems has been well‐documented at the histological level. Understanding how this diversity evolved and developing hypotheses as to why particular patterns exist require a phylogenetic perspective, which was first outlined in the work of anatomist Kunwar Bhatnagar. With the onset of genetics and genomics, it might be assumed that the puzzling patterns observed in the morphological data have been clarified. However, there is still a widespread mismatch of genetic and morphological correlations among bat chemosensory systems. Novel genomic evidence has set up new avenues to explore that demand more evidence from anatomical structures. Here, we outline the progress that has been made in both morphological and molecular studies on the olfactory and vomeronasal systems in bats since the work of Bhatnagar. Genomic data of olfactory and vomeronasal receptors demonstrate the strong need for further morphological sampling, with a particular focus on receiving brain regions, glands, and ducts. 

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