An easy and inexpensive method for determining the rate of individual phoretic events of nematodes.

Considering their limited locomotory capabilities, the cosmopolitan distribution of free-living nematodes may rely on phoretic dispersal. We describe a new, inexpensive device to investigate individual phoretic events of the nematode Caenorhabditis elegans using the pomace flies Drosophila melanogaster and Drosophila hydei over short time periods. Using our device, we replicated previous findings demonstrating that phoresis requires C. elegans to be in the dauer stage and capable of nictation. Additionally, we find that phoresis can happen on the order of seconds, and does not increase linearly with time of interaction. Using this approach can facilitate the investigation of nematode biogeography, which could provide useful insight into their, and their vector's, control.

The neuropeptide receptor npr-38 regulates avoidance and stress-induced sleep in Caenorhabditis elegans.

Although essential and conserved, sleep is not without its challenges that must be overcome; most notably, it renders animals vulnerable to threats in the environment. Infection and injury increase sleep demand, which dampens sensory responsiveness to stimuli, including those responsible for the initial insult. Stress-induced sleep in Caenorhabditis elegans occurs in response to cellular damage following noxious exposures the animals attempted to avoid. Here, we describe a G-protein-coupled receptor (GPCR) encoded by npr-38, which is required for stress-related responses including avoidance, sleep, and arousal. Overexpression of npr-38 shortens the avoidance phase and causes animals to initiate movement quiescence and arouse early. npr-38 functions in the ADL sensory neurons, which express neuropeptides encoded by nlp-50, also required for movement quiescence. npr-38 regulates arousal by acting on the DVA and RIS interneurons. Our work demonstrates that this single GPCR regulates multiple aspects of the stress response by functioning in sensory and sleep interneurons.

Epigenetic Plasticity Enables CNS-Trafficking of EBV-infected B Lymphocytes.

Subpopulations of B-lymphocytes traffic to different sites and organs to provide diverse and tissue-specific functions. Here, we provide evidence that epigenetic differences confer a neuroinvasive phenotype. An EBV+ B cell lymphoma cell line (M14) with low frequency trafficking to the CNS was neuroadapted to generate a highly neuroinvasive B-cell population (MUN14). MUN14 B cells efficiently infiltrated the CNS within one week and produced neurological pathologies. We compared the gene expression profiles of viral and cellular genes using RNA-Seq and identified one viral (EBNA1) and several cellular gene candidates, including secreted phosphoprotein 1/osteopontin (SPP1/OPN), neuron navigator 3 (NAV3), CXCR4, and germinal center-associated signaling and motility protein (GCSAM) that were selectively upregulated in MUN14. ATAC-Seq and ChIP-qPCR revealed that these gene expression changes correlated with epigenetic changes at gene regulatory elements. The neuroinvasive phenotype could be attenuated with a neutralizing antibody to OPN, confirming the functional role of this protein in trafficking EBV+ B cells to the CNS. These studies indicate that B-cell trafficking to the CNS can be acquired by epigenetic adaptations and provide a new model to study B-cell neuroinvasion associated CNS lymphoma and autoimmune disease of the CNS, including multiple sclerosis (MS).

Effects of larval size and hydrodynamics on the growth rates of the black fly Simulium tribulatum.

Black flies are ubiquitous and important members of lotic ecosystems. Size is known to affect many aspects of their life in the aquatic larval stage, including intraspecific competition for feeding sites. As filter feeders, flow affects their ability to feed and reach sufficiently fast flow. This, in turn, can lead to risky fluid-mediated dispersal behavior in search of better conditions. It is surprising, therefore, that little information is available regarding how physiological and environmental factors combine to affect larval growth rates. The present study determines the relative growth rates of small (0.6 mm) and large (approximately 4 mm) larvae in laboratory flumes designed to produce spatially homogeneous and temporally consistent flow regimes at ecologically relevant velocities (44 and 64 cm/s). Our results indicate that size and flow both influence growth rates and that the 2 interact significantly. Young larvae exhibit faster growth rates and a greater positive response to increased flow speed. This result might help explain why smaller larvae have a greater propensity to disperse than larger larvae: the benefit of increased growth rate that they receive from relocating to faster flow might balance the risks inherent in dispersal.

Internal movement of estuarine digenetic trematodes through their intermediate snail host Cerithidea californica.

The ability of free-swimming larval parasites to control emergence from their hosts can be critical in increasing the chances of successful infection transmission. For a group of estuarine trematodes, emergence of cercariae from their snail hosts is known to match favorable temperature, tidal activity, and light intensity. How the larvae time this behavior is not well understood, but the pathway that the larvae take through their host may play a role. Through video and histological analysis, we were able to identify the snail's anus as the emergence point and the peri-intestinal sinus dorsal to the intestines as the route by which they reach that point. By moving through this open sinus, the larvae have an energetically efficient pathway to reach their emergence point while minimizing damage to the host. Most importantly, it allows control over emergence to be maintained by the parasite, not the host, thus increasing the chances of the larva successfully reaching its intended destination.

Dispersal pathways, seed rains, and the dynamics of larval behavior.

Dispersing propagules (larvae, seeds, and spores) establish and maintain populations, which serve as templates for subsequent species interactions. Connectivity among demes derives, in large part, from connectivity between consecutive steps, release, transport, and settlement, in dispersal pathways. Concurrent measurements of individuals in each step are a necessary precursor to identifying governing mechanisms. Here we directly and definitively resolved the roles of physics and behavior in mediating dispersal pathways of an estuarine parasite between its intermediate hosts. Planktonic cercariae of Himasthla rhigedana, a parasitic flatworm, are functionally similar to lecithotrophic larvae of many free-living marine invertebrates. The combination of parasite life cycle characteristics and the relatively simple tidal flows in their habitat renders this system an effective model for dispersal studies. Simultaneous field measurements of larval release, transport, settlement, and the flow regime, together with mechanistic experiments, led to empirical understanding of host colonization. All dispersal steps were highly and significantly correlated over time and in space. This tight coupling resulted, unequivocally, from a suite of larval behaviors. Cercariae emerged from first intermediate host snails only during daytime flood tides, enhancing larval retention in the marsh. Daylight triggered downward swimming, and within seconds, cercariae overpowered turbulent mixing, landing in benthic habitat of second intermediate host snails and crabs. Larvae settled (encysted) on external regions of snails/crabs that, presumably, were most vulnerable to ingestion by definitive host shorebirds. In total, cercarial behaviors greatly foreshortened dispersal distances, magnified local parasite prevalence, and increased the likelihood of large-scale transmission by definitive hosts. Cracking open the black box of dispersal thus revealed mechanisms, connectivity, and ecological consequences of the larval stage.

Silk filaments enhance the settlement of stream insect larvae.

Many aquatic organisms need to settle in suitable benthic habitats while being transported via water currents. Such settlement is especially challenging for organisms that encounter complex benthic topography and lack the ability to move easily from the water column to the bed (e.g., via swimming). We conducted flume studies to examine whether the settlement of drifting stream insects is facilitated by adhesive filaments that extend from their bodies. Using a new tripwire visualization technique, we found that neonatal black flies (Simulium tribulatum) drifted with silk threads averaging six times their body length. These threads allowed larvae to contact or snag the bed from a greater height than would be possible through direct body-to-bed contact alone, and instantly arrested their downstream movement. Thus, silk increased their probability of settlement. We then performed an experiment to examine how settlement varied with bed topography and velocity. We tested whether settlement rate differed between a flat bed and an irregular bed that mimicked key aspects of their natural cobble-bed habitat. Velocities were similar for both bed treatments. Settlement on the irregular bed was 40 times greater than on the flat bed due to silk use. Settlement rate also exhibited a marginally significant decline with increasingly velocity on the flat bed, but not on the irregular bed. Silk threads should greatly increase the settlement rate of these nonswimming larvae on coarse-grained stream beds. Thus, silk snagging can potentially reduce the downstream distance that individuals are transported during a drift event, although the effects of silk on other phases of larval dispersal may differ.

Patterns and processes of larval emergence in an estuarine parasite system.

Trematode parasites in intertidal estuaries experience constantly varying conditions, with the presence or absence of water potentially limiting larval transport between hosts. Given the short life spans (< or =24 h) of cercariae, emergence timing should be optimized to enhance the probability of successful transmission. In the present study, field measurements and laboratory experiments identified processes that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclusively during daylight hours, and only when snails were submerged. The three factors operate over different temporal scales: temperature monthly, light diurnally (24-h period), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hierarchy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually reproduced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on subsequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Duration of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emergence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment.