High Larval Concentrations and Onshore Transport of Barnacle Cyprids Associated With Thermal Stratification

To better understand the hydrodynamic and hydrographic conditions experienced by larvae in the nearshore (within 1 km of shore), and the role that larval behavior plays in mediating shoreward transport to adult benthic habitats, we examined the vertical distribution and concentration of barnacle cyprids in a shallow, nearshore region in southern California, United States. We collected high-resolution physical measurements of currents and temperature at 3 stations (8, 5, and 4 m depths), and high-frequency measurements of barnacle larvae at a 4 m deep station ∼300 m from shore. Larvae were sampled from distinct 1 m depth intervals between the surface and the bottom (0–1 m, 1–2 m, 2–3 m, 3 m-bottom), each hour for overnight periods that ranged between 13 to 24 h in five cruises during the summers of 2017 and 2018. Barnacle cyprids of Chthamalus fissus predominated in all samples. Thermal stratification decreased closer to shore, but when the nearshore-most station remained stratified (Δ°C m–1 ≥ 0.1), C. fissus cyprid concentrations were high to extremely abundant (exceeding 200 and 4,000 individuals m–3, respectively). There were significant positive correlations between thermal stratification and the log-transformed C. fissus concentration at cruise-to-cruise scales, and between stratification and vertical variability in the high-frequency cross-shore currents at 2-day scales. Additionally, estimated larval transport was relatively high and shoreward when nearshore thermal stratification was greatest. Significant, albeit small, diel differences in cyprid distributions were also observed, with the proportion of cyprids increasing near the surface at night, and concentrations greater during the day than at night. Collectively, these results suggest that thermal stratification increases larval supply to the nearshore, and may enhance onshore larval transport to augment chances of successful settlement and recruitment to the intertidal adult habitat.

Assessing the bioactivity of cannabis extracts in larval zebrafish

Background Whole-plant cannabis extracts are consumed by the public for medical and non-medical (“recreational”) purposes but are poorly researched compared to pure cannabinoids. There is emerging evidence that cannabis extracts comprising complex mixtures of cannabinoids may have different biological effects from that of pure cannabinoids. In the current study, we sought to assess the effect of whole-plant cannabis extracts produced from different chemotypes of cannabis on the normal behavior of zebrafish larvae. Methods Three cannabis plant chemotypes were used in this study that contained either high amounts of THC, high amounts of CBD, high but equal amounts of THC and CBD, or low but equal amounts of THC and CBD. Following solvent extraction, liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) was performed for the detection and quantitation of target cannabinoids. Larval zebrafish behavioral models were subsequently used to assess the effect of the four different whole-plant cannabis extracts on the normal larval behavior using the DanioVision behavioral tracking systems and software. To compare, changes in the behavior activity levels for 30 min periods were compared to controls using 2-way ANOVA with multiple comparisons followed by a Bonferroni post hoc test. Results It was found that the whole-plant extracts that contained high levels of THC had similar effects on larval behavior, while the high CBD and low THC:CBD extracts produced distinct effects on normal larval behavior. Exposure of larvae to concentration-matched levels of THC and CBD found in the extracts revealed that a subset of the cannabis extracts tested had similar behavioral profiles to the pure cannabinoids while others did not. Conclusions To our knowledge, this is the first study to test and compare the bioactivity of different whole-plant cannabis extracts in larval zebrafish. This work will provide a framework for future studies of distinct cannabis extracts and will be useful for comparing the bioactivity of extracts from different cannabis chemotypes as well as extracts made through various heating processes. It will also act as the first stage of assessment before testing the extracts against zebrafish models of toxicity and disease.

Marine fish larvae consistently use external cues for orientation

The larval stage is the main dispersive mechanism of most marine teleost fish species. The degree to which larval behavior controls dispersal outcome has been a subject of debate in the past decades. Multiple studies demonstrated orientation mechanisms in several species separately, however a cross-species analysis examining fundamental orientation traits has not been carried out. Here, we apply a cross-species meta-analysis, focusing on the fundamental question of whether larval fish use external cues for directional movement. We compare the observed directional patterns to those expected under a strict use of internal cues. We find that the bulk of fish larvae use external cues for directional swimming, highlighting the contribution of larval orientation behavior to larval dispersal outcome. This finding is an essential step towards a proper implementation of larval behavior in biophysical dispersal models, improving our understanding of population connectivity, and facilitating sustainable management and conservation of marine resources.

Quantifying the Response of Grass Carp Larvae to Acoustic Stimuli Using Particle-Tracking Velocimetry

Acoustic deterrents are recognized as a promising method to prevent the spread of invasive grass carp, Ctenopharyngodon idella (Valenciennes, 1844) and the negative ecological impacts caused by them. As the efficacy of sound barriers depends on the hearing capabilities of carp, it is important to identify whether carps can recognize acoustic signals and alter their swimming behavior. Our study focuses on quantifying the response of grass carp larvae when exposed to out-of-water acoustic signals within the range of 100–1000 Hz, by capturing their movement using particle-tracking velocimetry (PTV), a quantitative imaging tool often used for hydrodynamic studies. The number of responsive larvae is counted to compute response ratio at each frequency, to quantify the influence of sound on larval behavior. While the highest response occurred at 700 Hz, we did not observe any clear functional relation between frequency of sound and response ratio. Overall, 20–30% of larvae were consistently reacting to sound stimuli regardless of the frequency. In this study, we emphasize that larval behaviors when exposed to acoustic signals vary by individual, and thus a sufficient number of larvae should be surveyed at the same time under identical conditions, to better quantify their sensitivity to sound rather than repeating the experiment with individual specimens. Since bulk quantification, such as mean or quantile velocities of multiple specimens, can misrepresent larval behavior, our study finds that including the response ratio can more effectively reflect the larval response.

Fasciola hepatica larval development within the intermediate host.

This book chapter focuses on host snail species and larval behavior forms in snails, and features of parasitic infections in naturally or experimentally infected snails, or in coinfected snails.

Aquatic larval of the genus Arrenurus (Trombidiformes: Parasitengonina: Arrenuridae) associated with Odonata species from Pampa Biome, Brazil

Many studies have reported that the interaction between water mite larvae and their Odonata hosts affects mating success, flight, and longevity. Males and females of Odonata species collected in the steppes and coastal plains (Pampa Biome) of Rio Grande do Sul were analyzed. Mites were removed when present and the prevalence and intensity of parasites was calculated. The aim of this study was to search and report new Odonata hosts species that are parasitized by water mite larvae and also to evaluate the prevalence and intensity rates; the differences in mite occurrence and frequency between males and females, and between thorax and abdomen of the dragonflies and damselflies in the southern Pampa biome located in Rio Grande do Sul. A total of 162 larval mites were found associated to two Odonata families: Coenagrionidae (Acanthagrion lancea Selys, 1876, Ischnura capreolus Hagen, 1861 and Ischnura fluviatilis Selys, 1876) and Libelullidae (Micrathyria ocellata Martin, 1897 and Perithemis mooma Kirby, 1889). All mites were identified as Arrenurus (Arrenurus) sp. (Arrenuridae) and showed high numbers when attached to I. capreolus (55.5%), I. fluviatilis (33.3%), followed by low numbers on M. ocellata (6.1%), A. lancea (3.7%), and P. mooma (1.2%). Mites were found on males and females of I. capreolus and I. fluviatilis, females of A. lancea and P. mooma and in M. ocellata only in males. As the parasitized Odonata species are generalist and abundant in all water body types, traits associated with mating and oviposition or larval behavior are believed to explain the frequency of parasitism in these species.

Departures from isotropy: the kinematics of a larval snail in response to food

The swimming behavior of invertebrate larvae can affect their dispersal, survival, and settlement in the ocean. Modelling this behavior accurately poses unique challenges as behavior is controlled both by physiology and environmental cues. Some larvae use cilia to both swim and create feeding currents, resulting in potential trade-offs between the two functions. Food availability is naturally patchy and often occurs in shallow horizontal layers in the ocean. Also, larval swimming motions generally differ in the horizontal and vertical. In order to investigate behavioral response to food by ciliated larvae, we measure their behavioral anisotropy by quantifying deviations from a model based in isotropic diffusion. We hypothesize that larvae will increase horizontal swimming and decrease vertical swimming after encountering food which could lead to aggregation at food layers. We consider Crepidula fornicata larvae which are specifically of interest as they exhibit unsteady and variable swimming behaviors that are difficult to categorize. We tracked the larvae in still water with and without food, with a portion of the larvae starved beforehand. On average, larvae in the presence of food were observed higher in the water column, with higher swimming speeds and higher horizontal swimming velocities when compared to larvae without food. Starved larvae also exhibited higher vertical velocities in food, suggesting no aggregation behavior. While most treatments showed strong anisotropy in larval behavior, we found that starved larvae without food exhibited approximately isotropic kinematics, indicating that behavioral anisotropy can vary with environmental history and conditions to enhance foraging success or mitigate food-poor environments.

THE EFFECT OF KAFFIR LIME (CITRUS HYSTRIX) ESSENTIAL OIL ON BEHAVIOR AND MORTALITY OF Aedes aegypti LARVAE

DHF vector control still uses chemicals. Long-term application can lead to target insect resistance and environmental pollution so that a better alternative is to use biological insecticides because it is environmentally friendly. The aim of the study is to identify the effect of kaffir lime peel essential oil on the behavior and mortality of Ae.aegypti larvae. The research method used was completely randomized design of three treatments and three replications. The results show that larval behavior after administration of kaffir lime peel essential oil at a concentration of 103 ppm decreased the frequency of movement, the larvae were unable to rise to the surface of the water after 1.5 hours. The results of the research were tested with probit analysis at a confidence level of 95% LD 263,552 ppm. The analysis result in one-way ANOVA for the number of differences in the number of dead larvaes, with the value obtained sig. = 0.000, which means that there is a significant influence on differences in doses of papaya seeds powder solution used against the death of Ae. aegypti larvaes. Kaffir lime peel contains essential oils that can be used as biological insecticides in DHF vector control.