Biology subjects

Ferguson, S. T.

Publications and source records attributed to Ferguson, S. T..

5 recordsLinked to original sources

bioRxiv2025

Unveiling the Developmental Dynamics and Functional Role of Odorant Receptor Co-receptor (Orco) in Aedes albopictus: A Novel Mechanism for Regulating Tuning Odorant Receptor Expression

As one of the most aggressive disease vectors, the Asian tiger mosquito Aedes albopictus relies heavily on its olfactory system to search for food in the larval stage, locate hosts after eclosion, and identify suitable oviposition sites after blood feeding. In mosquitoes and other insects, the olfactory system detects environmental odors primarily through a diverse repertoire of tuning odorant receptors (ORs), which require the highly conserved odorant receptor co-receptor (Orco) to function. While Orcos role in enabling tuning receptor function is well established, its cellular localization patterns, developmental expression dynamics, and system-wide impact on olfactory physiology and behavior remain understudied in Ae. albopictus. To address this knowledge gap, we leveraged the Q-system to systematically characterize Orco-expressing neurons (ORNs) across embryonic, larval, pupal and adult stages of Ae. albopictus. We uncovered a dramatic reorganization of the olfactory system during metamorphosis: ORNs were observed as early as the embryonic stage and expanded during larval development before rapid degeneration and re-generation in the pupal stage resulting in the final population of adult ORNs. Orco expression in adults spanned the olfactory neurons of the antennae, labella, and maxillary palps in both male and female mosquitoes, consistent with its conserved peripheral distribution. To further investigate the functional implications of Orco, we generated Orco knockout mutants and strikingly discovered that Orco knockout mutants displayed significant widespread downregulation of tuning Ors, suggesting that Orco may influence OR expression or stability. Electrophysiological recordings confirmed significantly attenuated responses to human volatiles in Orco mutants, and behavioral assays demonstrated a marked decline in blood-feeding efficiency and elimination of host preference in females. Together, these findings reveal dynamic reorganization of ORNs during mosquito development and uncover the critical role of Orco in maintaining the integrity and function of the olfactory system, providing insights that may inform novel, next-generation vector control strategies.

neuroscience↗

bioRxiv2023

Age and Task Modulate Olfactory Sensitivity in the Florida Carpenter Ant Camponotus floridanus

Age-related changes in behavior and sensory perception have been observed in a wide variety of animal species. In ants and other eusocial insects, workers often progress through an ordered sequence of olfactory-driven behavioral tasks. Notably, these behaviors are plastic, and workers adapt and rapidly switch tasks in response to changing environmental conditions. In the Florida carpenter ant, smaller minors typically perform most of the work needed to maintain the colony while the larger majors are specialized for nest defense and rarely engage in these routine tasks. Here, we investigate the effects of age and task group on olfactory responses to a series of odorant blends in minor and major worker castes. Consistent with their respective roles within the colony, we observed significant age-associated shifts in the olfactory responses of minors as they transitioned between behavioral states, whereas the responses of majors remained consistently low regardless of age. Furthermore, we identified a unitary compound, 3-methylindole, which elicited significantly higher responses and behavioral aversion in minor nurses than in similarly aged foragers suggesting that this compound may play an important role in brood care. Taken together, our results suggest that age- and task-associated shifts in olfactory physiology may play a critical role in the social organization of ant colonies. Simple SummaryFlorida carpenter ants (Camponotus floridanus) live in colonies comprised of thousands of workers. The smallest workers, known as minors, engage in routine tasks such as nursing and foraging while the largest workers, known as majors, are thought to be soldiers specialized for defending the nest. How ant colonies allocate their workforce to address the dynamic and ever-changing needs of the colonies remains an open question in the field, but current evidence suggests that ant social behavior likely results from a combination of genetic/epigenetic, physiological, and systems-level processes. Here, we extend these studies by investigating the role of olfactory sensitivity in regulating ant behavior. Minor workers exhibited significant shifts in olfactory sensitivity and odor coding as they aged and switched tasks. The olfactory sensitivity of majors, however, remained relatively stable as they aged. From these studies, we also identified a single compound, 3-methylindole, which elicited significantly higher olfactory responses and aversive behavior in nurses compared to foragers, suggesting that this chemical may have a role in brood care. Overall, these studies support the hypothesis that changes in olfactory sensitivity play an important role in regulating social behavior in ants.

neuroscience↗

bioRxiv2022

Olfactory Sensitivity Aligns with Caste Revealing Multipotential Minors and Specialized Soldier Majors in Camponotus floridanus Ants

Camponotus floridanus ant colonies are comprised of a single reproductive queen and thousands of sterile female offspring that consist of two morphologically distinct castes: smaller minors and larger majors. Minors perform most of the tasks within the colony, including brood care and food collection, whereas majors have fewer clear roles and have been hypothesized to act as a specialized solider caste associated with colony defense. The allocation of workers to these different tasks depends on the detection and processing of local information including pheromones and other chemical blends such as cuticular hydrocarbons. We examined the electrophysiological responses to general odorants, cuticular extracts, and a trail pheromone in adult minor and major C. floridanus workers, revealing that the repertoire of social behaviors is positively correlated with olfactory sensitivity. Minors in particular display primarily excitatory responses to olfactory stimuli, whereas major workers respond primarily with inhibitory signals. The notable exception to this paradigm is that both minors and majors display robust, dose-dependent excitatory responses to conspecific, non-nestmate cuticular extracts. Moreover, while both minors and majors actively aggress non-nestmate foes, majors display significantly enhanced capabilities to rapidly subdue and kill opponents. Overall, our data suggest that C. floridanus majors do indeed represent a physiologically and behaviorally specialized soldier caste and support a model in which caste-specific olfactory sensitivity plays an important role in task allocation and the regulation of social behavior in ant colonies. Significance StatementThe detection and odor coding of chemical cues are essential components of the collective behavior observed in eusocial ants. To better understand the interdependent relationship between olfactory sensitivity and the allocation of worker castes to the various tasks critical for the success of the colony, a series of behavioral assessments and an electrophysiological survey of the antennae comprising general odorants, cuticular extracts, and a trail pheromone were undertaken. These studies reveal the behavioral repertoire of minors and majors aligned with profound shifts in olfactory sensitivity and odor coding. Our data support the hypothesis that minors are multipotential workers with broad excitatory sensitivity, and majors are dedicated soldiers with a highly specialized olfactory system for the detection of non-nestmate foes.

evolutionary biology↗

bioRxiv2021

Mutagenesis of the Ammonium Transporter AcAmt Reveals a Reproductive Role and a Novel Ammonia-Sensing Mechanism in the Malaria Vector Mosquito Anopheles coluzzii

Anopheline mosquitoes are the sole vectors of malaria and rely on olfactory cues for host seeking in which ammonia derived from human sweat plays an essential role. To investigate the function of the Anopheles coluzzii ammonium transporter (AcAmt) in the mosquito olfactory system, we generated an AcAmt null mutant line using CRISPR/Cas9. AcAmt-/- mutants displayed a series of novel phenotypes compared with wild-type mosquitoes including significantly lower insemination rates during mating and increased mortality during eclosion. Furthermore, AcAmt-/- males showed significantly lower sugar consumption while AcAmt-/- females and pupae displayed significantly higher ammonia levels than their wild-type counterparts. Surprisingly, in contrast to previous studies in Drosophila that revealed that the mutation of the ammonium transporter (DmAmt) induces a dramatic reduction of ammonia responses in antennal coeloconic sensilla, no significant differences were observed across a range of peripheral sensory neuron responses to ammonia and other odorants between wild-type and AcAmt-/- females. Taken together, these data support the existence of a unique ammonia-sensing mechanism in mosquitoes and that the ammonium transporter may be an important molecular target for vector control. Key MessagesO_LIMutagenesis of An. coluzzii ammonium transporter AcAmt followed by comprehensive electrophysiological investigation suggest a novel ammonia-sensing pathway in Anopheles mosquitoes. C_LIO_LIAcAmt-/- mutants displayed significant deficiencies in reproduction and eclosion, which are likely due to elevated ammonia levels and reduced ability of sugar feeding. C_LIO_LIAn. coluzzii coeloconic sensilla primarily detect amines and acids. C_LI

neuroscience↗

bioRxiv2019

The Molecular Basis for Nestmate Recognition in the Eusocial Ant Camponotus floridanus

BackgroundIn eusocial ants, aggressive behaviors require a sophisticated ability to detect and discriminate between chemical signatures such as cuticular hydrocarbons that distinguish nestmate friends from non-nestmate foes. It has been suggested that a mismatch between a chemical signature (label) and the internal, neuronal representation of the colony odor (template) leads to the recognition of and subsequent aggression between non-nestmates. While several studies have demonstrated that ant chemosensory systems, most notably olfaction, are largely responsible for the decoding of these chemical signatures, a definitive demonstration that odorant receptors are responsible for the detection and processing of the pheromonal signals that regulate nestmate recognition has thus far been lacking. To address this, we have developed an aggression-based bioassay incorporating a suite of highly selective odorant receptor modulators to characterize the role of olfaction in nestmate recognition in the formicine ant Camponotus floridanus.\n\nResultsValidation of our aggression-based behavioral assay was carried out by demonstrating an antennal requirement for nestmate recognition. In order to adapt this bioassay for the volatile delivery of Orco modulators, electroantennography was used to show that both a volatilized Orco antagonist (VUANT1) and an Orco agonist (VUAA4) eliminated or otherwise interfered with the electrophysiological responses to the hydrocarbon decane, respectively. Volatilize administration of these compounds to adult workers significantly reduced aggression between non-nestmates without altering aggression levels between nestmates but did not alter aggressive responses towards a mechanical stimulus.\n\nConclusionsOur studies provide direct evidence that the antennae (as olfactory appendages) and odorant receptors (at the molecular level) are necessary for mediating aggression towards non-nestmates. Furthermore, our observations support a hypothesis in which rejection of non-nestmates depends on the precise detection and decoding of chemical signatures present on non-nestmates as opposed to the absence of any information or the active acceptance of familiar signatures. In addition to describing a novel approach to assess olfactory signaling in genetically intractable insect systems, these studies contribute to a long-standing interest in odor coding and the molecular neuroethology of nestmate recognition.

ecology↗