Glial expression of a steroidogenic enzyme underlies natural variation in hitchhiking behavior.

Phoresy is an interspecies interaction that facilitates spatial dispersal by attaching to a more mobile species. Hitchhiking species have evolved specific traits for physical contact and successful phoresy, but the regulatory mechanisms involved in such traits and their evolution are largely unexplored. The nematode Caenorhabditis elegans displays a hitchhiking behavior known as nictation during its stress-induced developmental stage. Dauer-specific nictation behavior has an important role in natural C. elegans populations, which experience boom-and-bust population dynamics. In this study, we investigated the nictation behavior of 137 wild C. elegans strains sampled throughout the world. We identified species-wide natural variation in nictation and performed a genome-wide association mapping. We show that the variants in the promoter of nta-1, encoding a putative steroidogenic enzyme, underlie differences in nictation. This difference is due to the changes in nta-1 expression in glial cells, which implies that glial steroid metabolism regulates phoretic behavior. Population genetic analysis and geographic distribution patterns suggest that balancing selection maintained two nta-1 haplotypes that existed in ancestral C. elegans populations. Our findings contribute to further understanding of the molecular mechanism of species interaction and the maintenance of genetic diversity within natural populations.

Mass Spectrometry-Driven Discovery of Neuropeptides Mediating Nictation Behavior of Nematodes.

Neuropeptides regulate animal physiology and behavior, making them widely studied targets of functional genetics research. While the field often relies on differential -omics approaches to build hypotheses, no such method exists for neuropeptidomics. It would nonetheless be valuable for studying behaviors suspected to be regulated by neuropeptides, especially when little information is otherwise available. This includes nictation, a phoretic strategy of Caenorhabditis elegans dauers that parallels host-finding strategies of infective juveniles of many pathogenic nematodes. We here developed a targeted peptidomics method for the model organism C. elegans and show that 161 quantified neuropeptides are more abundant in its dauer stage compared with L3 juveniles. Many of these have orthologs in the commercially relevant pathogenic nematode Steinernema carpocapsae, in whose infective juveniles, we identified 126 neuropeptides in total. Through further behavioral genetics experiments, we identify flp-7 and flp-11 as novel regulators of nictation. Our work advances knowledge on the genetics of nictation behavior and adds comparative neuropeptidomics as a tool to functional genetics workflows.

The C. elegans regulatory factor X (RFX) DAF-19M module: A shift from general ciliogenesis to cell-specific ciliary and behavioral specialization.

Cilia are important for the interaction with environments and the proper function of tissues. While the basic structure of cilia is well conserved, ciliated cells have various functions. To understand the distinctive identities of ciliated cells, the identification of cell-specific proteins and its regulation is essential. Here, we report the mechanism that confers a specific identity on IL2 neurons in Caenorhabditis elegans, neurons important for the dauer larva-specific nictation behavior. We show that DAF-19M, an isoform of the sole C. elegans RFX transcription factor DAF-19, heads a regulatory subroutine, regulating target genes through an X-box motif variant under the control of terminal selector proteins UNC-86 and CFI-1 in IL2 neurons. Considering the conservation of DAF-19M module in IL2 neurons for nictation and in male-specific neurons for mating behavior, we propose the existence of an evolutionarily adaptable, hard-wired genetic module for distinct behaviors that share the feature "recognizing the environment."

Impact of virtual reality headset use on eye blinking and lipid layer thickness.

PURPOSE: Blinking plays an important role in protecting the eyes, and the use of computers has been associated with a reduction in the blink rate. The goal of this study was to evaluate the effect of a virtual reality headset on blinking and lipid layer thickness and to compare these data to those associated with a conventional desktop monitor. METHODS: Two experiments were performed to compare the effect of 20minutes of use of a virtual reality headset (FOVE) and 20minutes of use of a desktop monitor on the frequency and length of blinks (experiment 1, 15 participants) and on the thickness of the lipid layer as measured by Lipiview (experiment 2, 12 participants). RESULTS: In the first experiment, the blink rate [F(1.83)=4.3, P=0.04, ß=0.36] and duration [F(1.83)=13, P=0.001, ß=0.35] increased with time under both conditions, but no statistical difference was found between the two conditions (headset vs. desktop monitor) either for blink rate [rmANOVA F(1.11)=0.01, P=0.92; headset: 15.1 blinks, 95% CI: 12.6 to 17.6 blinks; desktop: 14.6 blinks, 95% CI: 13.6 to 15.7 blinks] or for blink duration [rmANOVA F(1.11)=4.534, P=0.06; headset: 205.75ms, 95% CI: 200.9 to 210.6ms; desktop: 202.82ms, 95% CI: 198.2 to 207.5ms]. However, strong individual variations were observed. Evaluation of simulator sickness and visual fatigue by questionnaire showed no significant differences between the two conditions (SSQ simulator sickness questionnaire: V=46, P=0.62; VFQ visual fatigue questionnaire: V=15.5, P=0.13). In the second experiment, the lipid layer thickness increased significantly after use of the VR headset [F(1.18)=11.03, P=0.004, headset: 76.2nm, desktop: 58.8nm]. CONCLUSION: In terms of recommendations, the effect of virtual reality headsets on blink duration and frequency during a moderate exposure (20minutes) is comparable to that of a conventional desktop monitor. However, the strong individual variations observed, the lack of reliable tests to evaluate this individual sensitivity, and the significant increase in lipid layer thickness in experiment 2 suggest the value of a more detailed investigation, in particular with consideration of a longer exposure time and other tear film parameters.

Nodding behavior observed in Japanese stiltgrass, Microstegium vimineum , seedlings from time-lapse observations.

Invasive species are the second main cause of biodiversity loss because of their exceptional ability to supplant native species by creating major upheavals in ecosystems. Inexpensive and prevalent time-lapse photography provides an exciting opportunity to better understand the aggressive behavior of invasive species including how they invade and conquer new territory. One of the most pervasive invasive species in the Eastern United States is Japanese stiltgrass, Microstegium vimineum (Trin.) A. Campus, which originated from Southeast Asia. Previous research has examined the conditions that enable Japanese stiltgrass to become invasive, but nothing is known regarding root and shoot behavior. Here time-lapse was used to examine Japanese stiltgrass seedlings, early in their development, as a first step to observe its behavior. Our results demonstrate that Japanese stiltgrass shoots appear to drop or collapse and then resurrect back to an upright stature - sometimes the same plant exhibits this behavior multiple times. We have shown, in addition, that emergent stilt root growth rate increases with increased root length. This and similar kinds of analyses may provide insight into how Japanese stiltgrass thrives aggressively in a non-native environment with the goal of developing better methods of controlling this noxious weed.

Neurogenetics of nictation, a dispersal strategy in nematodes.

Nictation is a behaviour in which a nematode stands on its tail and waves its head in three dimensions. This activity promotes dispersal of dauer larvae by allowing them to attach to other organisms and travel on them to a new niche. In this review, we describe our understanding of nictation, including its diversity in nematode species, how it is induced by environmental factors, and neurogenetic factors that regulate nictation. We also highlight the known cellular and signalling factors that affect nictation, for example, IL2 neurons, insulin/IGF-1 signalling, TGF-ß signalling, FLP neuropeptides and piRNAs. Elucidation of the mechanism of nictation will contribute to increased understanding of the conserved dispersal strategies in animals.

Regulation of a hitchhiking behavior by neuronal insulin and TGF-ß signaling in the nematode Caenorhabditis elegans.

Free-living nematode Caenorhabditis elegans exhibits various behaviors to adapt to the fluctuating environment. When early larvae of C. elegans experience the harsh environmental condition, they develop to an alternative developmental stage called dauer, which shows nictation, a stage-specific waving behavior. Nictation enables dauers to attach to more mobile animals, which helps them disperse to other habitats beyond physical barriers. However, underlying molecular mechanisms that regulate nictation behavior are largely unknown. In this study, we show that insulin signaling and transforming growth beta (TGF-ß) signaling, the two major parallel signaling pathways that mediate dauer development, are involved in the regulation of dauer-specific nictation behavior. Genetic analysis revealed that downregulation of insulin signaling enhanced nictation behavior. Heat-shock induced rescue experiments showed that the action period of the insulin signaling is before dauer formation. Surprisingly, lowering of TGF-ß signaling inhibited the normal performance of nictation, suggesting that TGF-ß signaling acts in an opposite way from that for dauer formation. Cell-specific rescue experiments revealed that two signaling pathways act in the nervous system and an epistasis experiment showed that TGF-ß signaling is epistatic to insulin signaling. Taken together, we propose that the neuroendocrinal insulin signaling and TGF-ß signaling regulate nictation behavior during development in response to environmental conditions.

Host orientation using volatiles in the phoretic nematode Caenorhabditis japonica.

Host orientation is the most important step in host-searching nematodes; however, information on direct cues from hosts to evoke this behaviour is limited. Caenorhabditis japonica establishes a species-specific phoresy with Parastrachia japonensis. Dauer larvae (DL), the non-feeding and phoretic stage of C. japonica, are predominantly found on female phoretic hosts, but the mechanisms underlying the establishment of this phoresy remain unknown. To determine whether C. japonica DL are able to recognize and orient themselves to a host using a volatile cue from the host, we developed a Y-tube olfactory assay system in which C. japonica DL were significantly attracted to the air from P. japonensis but not to the air from three other insects or to CO2. These results demonstrated that C. japonica DL utilize volatiles for host recognition and orientation and that the presence of a specific volatile kairomone released by the host attracts C. japonica DL.

Infection of the Entomopathogenic Nematode, Steinernema carpocapsae, as Affected by the Presence of Steinernema glaseri.

The infection behavior of Steinernema carpocapsae infective juveniles (IJ) was investigated in the presence and absence of S. glaseri. Mixed inoculation of S. carpocapsae with S. glaseri IJ significantly raised the nictation rates of S. carpocapsae IJ. Significantly more S. carpocapsae IJ migrated to the host insect in the mixed inoculation with S. glaseri IJ on agar plates. More S. carpocapsae IJ penetrated into the host insect placed 2 cm below the surface in the mixed inoculation with S. glaseri IJ. More S. glaseri than S. carpocapsae IJ penetrated into hosts placed 7 cm deep. Irrespective of host location, the male ratio of S. carpocapsae IJ established in the host body was always higher in the mixed inoculation with S. glaseri IJ.

Effects of Insecticides on Movement, Nictation, and Infectivity of Steinernema carpocapsae.

Movement, nictation, and infectivity of Steinernema carpocapsae strain All were compared for ensheathed (EnJ) and desheathed (DeJ) infective juveniles exposed to the insecticides acephate, dichlorvos, methomyl, oxamyl, or permethrin. Nematode response to various solutions included normal sinusoidal movement, uncoordinated motion, twitching, convulsion or formation of a pretzel shape, an inactive "S" posture with fine twitching, or a quiescent straight posture. The DeJ displayed these movements at lower concentrations of each insecticide than did EnJ. In petri dish bioassays, insecticide-treated EnJ caused generally lower mortality in the common cutworm, Spodoptera litura, than did EnJ alone but caused greater insect mortality than did insecticides alone. Nematode response to chemicals was more clearly demonstrated by nictating behavior than by the movement bioassay. Nictation of DeJ was suppressed by the test chemicals at low concentrations, except for acephate and permethrin. Nictating EnJ or DeJ, regardless of chemical treatment, killed host insects faster than did non-nictating juveniles. Insecticides that enhance nictating behavior at certain concentrations may be used for mixed applications with nematodes.