Biology subjects

Knaden, M.

Publications and source records attributed to Knaden, M..

At least 19 recordsLinked to original sources

bioRxiv2026

Temporal niche partitioning through olfactory cell type evolution

Temporal niche partitioning enables species to use the same resource at different times, but the underlying mechanisms are unknown. We show that Drosophila sechellia, a specialist on Morinda citrifolia noni, exhibits narrow temporal preference for the most toxic, ripe fruit, reducing exposure to competition, parasitization and microbial infection that can occur on other stages. Chemical analysis highlighted ketones as signature odors of ripe noni. Comparative single-cell transcriptomic atlases revealed that D. sechellia has co-opted expression of a larval ketone receptor, Or45a, in an adult olfactory neuron population. The novel expression of Or45a can be ascribed solely to cis-regulatory changes and is sufficient to confer physiological sensitivity to ripe noni. Importantly, Or45a is required for D. sechellia's ripe noni preference, acting redundantly with a second ketone receptor, Or85c/b, whose neuron population has expanded in D. sechellia. Our results provide an unprecedented link between cell type evolution and ecologically-advantageous, temporal niche partitioning.

neuroscience↗

bioRxiv2026

Natural statistics of host odours predict species-specific olfactory behaviours in Drosophilids

Animals rely on olfaction to locate food, mates, and suitable habitats, yet natural odour environments contain thousands of volatile molecules, creating a high-dimensional sensory problem for both nervous systems and the researchers who study them 1-5. For example, a banana emits around 100 individual volatiles4,6. It remains unclear which components of complex odour blends animals have evolved to use as behavioural cues. Here, combining fieldwork, chemical and behavioural analyses, we show across multiple Drosophila species that behaviourally relevant cues can be predicted directly from the statistical structure of natural odour environments. Animals preferentially respond to components that are most distinctive within their natural host odour blends, and therefore most ecologically informative. These cues can be either major or minor blend components. Our results indicate that host-guided olfactory behaviours have evolved to exploit the statistical structure of natural odour environments by selectively targeting the most informative features of odour blends.

neuroscience↗

bioRxiv2024

Aggressive conflict impacts path integration in homing desert ants

Across many species of the animal kingdom, the ability to navigate long distances is important for securing food and other resources. For example, ants, bees, and rats have long been known to use path integration, a mechanism to integrate distance and direction travelled, to find their way back to their nest. However, path integration is imperfect, and errors accumulate over time as animals forage. There are several ways to counteract this uncertainty, for example by utilizing local olfactory or visual landmarks along a familiar route to infer an individuals position relative to its nest, i.e. its homing vector. Local landmarks are thought to be effective if they are constant, granting a strong association with the discrete location it is located at. Here we show that ants can utilize something much sparser and more distributed than an individual constant landmark to inform its homing vector. Our data suggests that Tunisian desert ants integrate intraspecific contact, or social cues, to augment navigation. We demonstrate that contact with foreign conspecifics at a position where the nest is expected diminishes path integration certainty, thereby expanding the nest search pattern. Furthermore, we show that ants form associations between intraspecific conflict and discrete locations to create so called local vectors, within which the homing path to the nest can be stored. Highlights- Contact with foreign ants reduces path integrator certainty and alters homing strategy - Pattern of systematic search could be altered by persistent adaptions of walking speed - Foraging ants can form local vector memories using intraspecific conflict as a landmark

animal behavior and cognition↗

bioRxiv2024

Quantitive variation of male and female-specific compounds in 99 drosophilid flies

Variation in sex pheromones is regarded as one of the causes of reproductive isolation and speciation. We recently identified 51 male- and female-specific compounds - many of which function as sex pheromones - in 99 drosophilid species1. Here, we report that despite many of these compounds being shared between species, their quantities differ significantly. For example, although 34 drosophilid species share the male-specific compound cis-vaccenyl acetate (cVA), which plays a critical role in regulating various social and sexual behaviors, the amount of cVA can differ by up to 600-fold between different species. Additionally, we found 7-tricosene, the cuticular hydrocarbon pheromone, present in 35 Drosophila species. Our findings indicate that 7-tricosene is equally present in both sexes of 14 species, more abundant in males of 14 species, and more abundant in females of 7 species. We provide raw data on the concentration of potential pheromone components in the 99 drosophilids, which can provide important insights for further research on the behavior and evolution of these species. Quantitative variations highlight species-specific patterns, suggesting an additional mechanism for reproductive isolation built on specific combinations of compounds at set concentrations.

evolutionary biology↗

bioRxiv2024

Preference for and resistance to a toxic sulfur volatile opens up a unique niche in Drosophila busckii

The ability to tolerate otherwise toxic compounds can open up unique niches in nature. Among drosophilid flies few examples of such adaptations are known and then typically from highly host specific species. Here we show that the human commensal Drosophila busckii uses dimethyldisulfide (DMDS) as a key mediator in its host selection. Despite DMDSs neurotoxic properties1, D. busckii has evolved tolerance towards high concentrations and uses the compound as an olfactory cue to pinpoint food and oviposition sites. This adaptability is likely linked to an insensitive cytochrome c oxidase (COX), a DMDS target in other insects. Our findings position D. busckii as a potential model for studying resistance to toxic gases affecting COX and offer valuable insights into evolutionary adaptations within specific ecological contexts.

ecology↗

bioRxiv2023

Male cuticular pheromones stimulate removal of the mating plug and promote re-mating through pC1 neurons in Drosophila females

In birds and insects, the female uptakes sperm for a specific duration post-copulation known as the ejaculate holding period (EHP) before expelling unused sperm and the mating plug through sperm ejection. In this study, we found that Drosophila melanogaster females shortens the EHP when incubated with males or mated females shortly after the first mating. This phenomenon, which we termed male-induced EHP shortening (MIES), requires Or47b+ olfactory and ppk23+ gustatory neurons, activated by 2-methyltetracosane and 7-tricosene, respectively. These odorants raise cAMP levels in pC1 neurons, responsible for processing male courtship cues and regulating female mating receptivity. Elevated cAMP levels in pC1 neurons reduce EHP and reinstate their responsiveness to male courtship cues, promoting re-mating with faster sperm ejection. This study established MIES as a genetically tractable model of sexual plasticity with a conserved neural mechanism. Significance StatementSexual plasticity, the adaptation of reproductive behavior to social changes, was explored in the fruit fly, a genetically tractable model insect. Our findings revealed that inseminated females, encountering another courting male post-mating, shorten the ejaculate holding period (EHP). Specific olfactory and gustatory pathways regulating this phenomenon were identified, converging on the pC1 neurons in the brain-a conserved neural circuit that regulates female mating activity. Odors associated with EHP shortening increased the second messenger cAMP. The transient elevation of cAMP heightened the excitability of pC1 neurons, facilitating the prompt removal of the male ejaculate and subsequent re-mating . This study established a behavioral model of sexual plasticity and provided a framework for understanding the neural circuit processes involved.

neuroscience↗

bioRxiv2023

Olfactory learning modulates a neural circuit mediating innate odor-guided behavior in Drosophila

Behavior is often categorized as being innate or learned, with the specific circuits being assigned to one of these categories. In Drosophila, neural circuits mediating an innate behavioral response are considered as being "hard-wired", as activation of these neuronal pathways leads to stereotyped behaviors. However, only a limited number of studies assessed whether innate behaviors and their underlying neural circuits are plastic or show experience-dependent modulation. Here, we show that experience modulates second-order olfactory neurons involved in innate behavioral responses. We focus on the neural circuit defined by multiglomerular projection neurons (mPNs) that target the lateral horn, a structure relevant in the genesis of innate behavior. We show that mPNs, coding for odor attraction, are bidirectionally modulated after olfactory associative learning: when an olfactory stimulus is paired with an aversive electric shock, the activity of these neurons is decreased, while when the odor is paired with a sucrose-reward they are potentiated. We further show that this modulation requires glutamate and serotonin signaling, and that downstream third-order neurons are consequently affected. The bidirectional nature of the plasticity in these neurons is reflected in behavior: silencing mPN activity leads to odor avoidance, while artificial activation induces approach. While output from the mPNs is not required in aversive olfactory conditioning, silencing these neurons during retrieval of appetitive memories leads to a significant memory impairment. Artificially activating these neurons during odor presentation is sufficient to generate a 3 h appetitive memory. Our study in flies shows that a neural circuit coding for innate odor attraction can contribute to learned behavior, is modulated by olfactory learning and can provide reward-like reinforcement.

neuroscience↗

bioRxiv2023

Temperature-dependent modulation of odor-dependent behavior in three drosophilid fly species of differing thermal preference

Rapid and ongoing climate change increases global temperature and impacts both feeding and reproduction in insects. The sense of smell plays an important underlying role in these behaviors in most insect species. Here, we aimed to investigate how changing temperatures affect odor detection and ensuing behavior in three drosophilid flies: Drosophila novamexicana, D. virilis and D. ezoana, species that have adapted to life in desert, global and subarctic climates, respectively. Using a series of thermal preference assays, we confirmed that the three species indeed exhibit distinct temperature preferences. Next, using single sensillum recording technique, we classified olfactory sensory neurons (OSNs) present in basiconic sensilla on the antenna of the three species and thereby identified ligands for each OSN type. In a series of trap assays we proceeded to establish the behavioral valence of the best ligands and chose guaiacol, methyl salicylate and isopropyl benzoate as representatives of a repellent, attractant and neutral odor. Next, we assessed the behavioral valence of these three odors in all three species across a thermal range (10-35 C), with flies reared at 18{degrees}C and 25{degrees}C. We found that both developmental and experimental temperatures affected the behavioral performance of the flies. Our study thus reveals temperature-dependent changes in odor-guided behavior in drosophilid flies.

ecology↗

bioRxiv2022

Increased ozone levels disrupt insect sexual communication

Insect sexual communication often relies upon sex pheromones1-3. Most insect pheromones, however, contain carbon-carbon double bonds and potentially degrade by oxidation4. Here, we show that already frequently reported increased levels of Anthropocenic ozone can oxidize all described male-specific pheromones of Drosophila melanogaster5-7, resulting in reduced amounts of e.g. cis-Vaccenyl Acetate and (Z)-7-Tricosene. At the same time female acceptance of ozone-exposed males is significantly delayed. Interestingly, groups of ozonized males also exhibit unnaturally high levels of male-male courtship behavior. When repeating similar experiments with nine other drosophilid species, we observe pheromone degradation and/or corrupted sex recognition in eight of them. Our data suggest that Anthropocenic levels of ozone can oxidize double bonds in a variety of insect pheromones extensively, thereby leading to deviations in sexual recognition.

animal behavior and cognition↗

bioRxiv2022

Aversive bimodal associations impact visual and olfactory memory performance in Drosophila

Insects rely heavily on sampling information from their environment for survival and fitness. Different sensory channels with dedicated downstream neural substrates are programmed to fine tune these signals and translate them into usable instructions to mediate complex behaviors. Sensory information can also be learned and stored as memories that influence decisions in the future. The learning of unimodal sensory signals, especially olfaction, has been studied extensively in different conditioning paradigms in different insects. Using the Drosophila melanogaster model in our work, we first investigated differences in the efficiencies of aversive associative visual and olfactory learning using sensory cues that are innately very attractive, such as blue or green light as well as food odors found in fruits or yeast. We then combined the presentation of visual and olfactory sensory stimuli during training to study the effect of bimodal integration on learning performance. When trained unimodally, flies did not easily learn visual stimuli, but when trained bimodally, they developed a significant short-term visual memory after a single learning trial. The bimodal training also suppressed the phototaxis response of the flies to near abolishment. However, a similar training did not enhance the short-term olfactory memory and in some cases, even caused reduction in strength. An enhancement after bimodal training was only seen with a weak long-term olfactory memory retrieved after 24h. Our study demonstrates that bimodal sensory integration is not always synergistic, but is conditional upon the training paradigm and inherent learning abilities of the sensory modalities involved.

animal behavior and cognition↗

bioRxiv2022

No functional contribution of the gustatory receptor, Gr64b, co-expressed in olfactory sensory neurons of Drosophila melanogaster

Chemosensation is essential for the survival of insects. Activities like searching for food, mating, and oviposition in the fruit fly, Drosophila melanogaster are to a great extent governed by chemical cues detected via olfaction and gustation. This chemical information is conveyed to higher brain centres via populations of diverse olfactory sensory neurons (OSNs) and gustatory sensory neurons (GSNs) expressing olfactory receptors (ORs) and gustatory receptors (GRs), respectively. ORs are exclusively expressed in the antenna and in the maxillary palps, while GRs are widely expressed in the labellum, tarsi, genitalia etc. Interestingly, 14 GRs were previously reported to be expressed in the antenna of D. melanogaster. However, the spatial expression pattern for all GRs and their functional role are still unclear. Recent data challenge the dogma that single OSNs express a single OR. In the present study, we studied the expression of 12 previously reported GRs among sensory structures on the fly antenna using the Gal4-UAS binary expression system. We observed antennal expression of nine out of the 12 reported. Out of these nine, consistent expression was only apparent for Gr64b, and we reconfirmed its presence in OSNs innervating three glomeruli in the antennal lobe. These glomeruli are known to be innervated by ab5A, ab5B and ab8A OSNs, respectively. Next, we generated double labelling crosses with Gr64b and observed co-expression of Gr64b with Or47a, which is expressed in the ab5B neuron. To elucidate the functional role of Gr64b co-expressed with Or47b, we challenged Or47a-expressing OSNs in wild type and Gr64b-/- mutant flies with odor stimulation using the single sensillum recording technique in two satiation states (fed and starved). Notably, we did not observe any significant odor sensitivity or specificity changes in Gr64b mutants as compared to wild type flies. Taken together, our results reveal co-expression of GRs with ORs in olfactory sensory neurons, while the functional contribution of the GR in this context remains obscure.

neuroscience↗

bioRxiv2022

Non-redundant odorant detection in a locust

Olfactory coding, from insects to humans, is canonically considered to involve considerable across-fiber coding already at the peripheral level, thereby allowing recognition of very large numbers of odor compounds. Here we show that the migratory locust, Locusta migratoria, has evolved an alternative strategy built on highly specific odorant receptors feeding into a complex primary processing center in the brain. By collecting odors from food and different life stages of the locust, we identified 208 ecologically relevant odorants, which we used to deorphanize 48 locust olfactory receptors via ectopic expression in Drosophila. Contrary to the often broadly tuned olfactory receptors of other insects, almost all locust receptors were found to be narrowly tuned to one ligand and most of these best ligands exclusively excited only one receptor. Knocking out a single receptor using CRISPR-Cas9 resulted in an abolished physiological and behavioral response to the corresponding ligand. We conclude that the locust olfactory system, with an apparent lack of redundancy among most olfactory receptors, differs from so-far described olfactory systems.

neuroscience↗

bioRxiv2022

Unique neural coding of crucial versus irrelevant plant odors in a hawkmoth

The sense of smell is pivotal for nocturnal moths to locate feeding and oviposition sites. However, these crucial resources are often rare and their bouquets are intermingled with volatiles emanating from surrounding background plants. Here we asked if the olfactory system of female hawkmoths, Manduca sexta, could differentiate between crucial and background cues. To answer this question, we collected nocturnal headspaces of numerous plants in a natural habitat of M. sexta. We analyzed the chemical composition of these headspaces, and used them as stimuli in physiological experiments at the antenna and in the brain. The intense odors of floral nectar sources evoked strong responses in virgin and mated female moths, most likely enabling the localization of profitable flowers at a distance. Bouquets of larval host plants and most background plants, in contrast, were subtle, thus potentially complicating host identification. However, despite being subtle, antennal responses and brain activation patterns evoked by the smell of larval host plants were clearly different from those evoked by other plants. Interestingly, this difference was even more pronounced in the antennal lobe of mated females, revealing a status-dependent tuning of their olfactory system towards oviposition sites. Our study suggests that female moths possess unique neural coding strategies to find not only conspicuous floral cues but also inconspicuous bouquets of larval host plants within a complex olfactory landscape.

neuroscience↗

bioRxiv2020

Large-scale characterization of sex pheromone communication systems in Drosophila

Insects use sex pheromones as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Despite the profound knowledge of sex pheromones, little is known about the coevolutionary mechanisms and constraints on their production and detection. Using whole-genome sequences to infer the kinship among 99 drosophilids, we investigate how phylogenetic and chemical traits have interacted at a wide evolutionary timescale. Through a series of chemical syntheses and electrophysiological recordings, we identify 51 sex-specific compounds, many of which are detected via olfaction. Behavioral analyses reveal that many of the 42 male-specific compounds are transferred to the female during copulation and mediate female receptivity and/or male courtship inhibition. Measurement of phylogenetic signals demonstrates that sex pheromones and their cognate olfactory channels evolve rapidly and independently over evolutionary time to guarantee efficient intra- and inter-specific communication systems. Our results show how sexual isolation barriers between species can be reinforced by species-specific olfactory signals.

evolutionary biology↗

bioRxiv2020

Alcohol boosts pheromone production in male flies and makes them sexier

The attraction of Drosophila melanogaster towards byproducts of alcoholic fermentation, especially ethanol, has been extensively studied 1-4. However, the adaptive value of this behavior has not been elucidated. Previous studies have suggested anthropomorphic interpretations of D. melanogaster behavior towards alcohols 5,6. Here, we instead assert that there exists a simple yet vital biological rationale for alcohol contact and consumption by these insects. We show that exposure to alcohols, especially methanol, results in an immediate amplification of fatty acid ester pheromone levels, which in turn elevates the probability that a male will successfully compete for a female during courtship. We proceed to identify three types of olfactory sensory neurons that detect ethanol and methanol. Moreover, we trace the ensuing neural circuits and reveal their role in controlling both attraction and aversion, where valence is balanced around mating status. Based on our results, we deduce that male flies associate with sources of alcohol as a biological imperative related to reproduction, and we provide an assessment of how and why D. melanogaster is associated with alcohol using a sound ecological and natural history approach to this previously enigmatic biological phenomenon. One sentence summaryFlies gain pheromone and courtship advantages with alcohol, but methanol is toxic, thus flies must balance risk versus reward.

neuroscience↗

bioRxiv2019

Mate discrimination among subspecies through a conserved olfactory pathway

Signaling mechanisms underlying the sexual isolation of species are poorly understood. Using four subspecies of Drosophila mojavensis as a model, we identify two behaviorally active male-specific pheromones. One functions as a conserved male anti-aphrodisiac in all subspecies and acts via gustation. The second induces female receptivity via olfaction exclusively in the two subspecies that produce it. Genetic analysis of the cognate receptor for the olfactory pheromone indicates an important role for this sensory pathway in promoting sexual isolation of subspecies, in collaboration with auditory signals. Surprisingly, the peripheral sensory pathway detecting this pheromone is conserved molecularly, physiologically and anatomically across subspecies. These observations imply that subspecies-specific behaviors arise from differential interpretation of the same peripheral cue, reminiscent of sexually conserved detection but dimorphic interpretation of male pheromones in D. melanogaster. Our results reveal that, during incipient speciation, pheromone production, detection and interpretation do not necessarily evolve in a coordinate manner.

neuroscience↗

bioRxiv2019

The olfactory co-receptor IR8a governs larval-frass mediated competition avoidance in a hawkmoth

Finding a suitable oviposition site is a challenging task for a gravid female moth. At the same time, it is of paramount importance considering the limited capability of most caterpillars to relocate to alternative host plants. The hawkmoth, Manduca sexta (Sphingidae), oviposits on solanaceous plants. Larvae hatching on a plant that is already attacked by conspecific caterpillars can face food competition, as well as an increased exposure to predators and induced plant defenses. Here, we show that frass from conspecific caterpillars is sufficient to deter a female M. sexta from ovipositing on a plant and that this deterrence is based on the frass-emitted carboxylic acids 3-methylpentanoic acid and hexanoic acid. Using a combination of genome editing (CRISPR/Cas9), electrophysiological recordings, calcium imaging and behavioral analyses we demonstrate that the ionotropic co-receptor IR8a is essential for acid-mediated frass avoidance in ovipositing hawkmoths.

neuroscience↗

bioRxiv2019

Evolution of a pest: towards the complete neuroethology of Drosophila suzukii and the subgenus Sophophora

Comparative analysis of multiple genomes has been used extensively to examine the evolution of chemosensory receptors across the genus Drosophila. However, few studies have delved into functional characteristics, as most have relied exclusively on genomic data alone, especially for non-model species. In order to increase our understanding of olfactory evolution, we have generated a comprehensive assessment of the olfactory functions associated with the antenna and palps for Drosophila suzukii as well as several other members of the subgenus Sophophora, thus creating a functional olfactory landscape across a total of 20 species. Here we identify and describe several common elements of evolution, including consistent changes in ligand spectra as well as relative receptor abundance, which appear heavily correlated with the known phylogeny. We also combine our functional ligand data with protein orthologue alignments to provide a high-throughput evolutionary assessment and predictive model, where we begin to examine the underlying mechanisms of evolutionary changes utilizing both genetics and odorant binding affinities. In addition, we document that only a few receptors frequently vary between species, and we evaluate the justifications for evolution to reoccur repeatedly within only this small subset of available olfactory sensory neurons.

evolutionary biology↗