Ecophysiology of the kleptoplastidic dinoflagellate Shimiella gracilenta: I. spatiotemporal distribution in Korean coastal waters and growth and ingestion rates

To explore the ecophysiological characteristics of the kleptoplastidic dinoflagellate Shimiella gracilenta, we determined its spatiotemporal distribution in Korean coastal waters and growth and ingestion rates as a function of prey concentration. The abundance of S. gracilenta at 28 stations from 2015 to 2018 was measured using quantitative realtime polymerase chain reaction. Cells of S. gracilenta were detected at least once at all the stations and in each season, when temperature and salinity were 1.7–26.4°C and 9.9–35.6, respectively. Moreover, among the 28 potential prey species tested, S. gracilenta SGJH1904 fed on diverse prey taxa. However, the highest abundance of S. gracilenta was only 3 cells mL-1 during the study period. The threshold Teleaulax amphioxeia concentration for S. gracilenta growth was 5,618 cells mL-1, which was much higher than the highest abundance of T. amphioxeia (667 cells mL-1). Thus, T. amphioxeia was not likely to support the growth of S. gracilenta in the field during the study period. However, the maximum specific growth and ingestion rates of S. gracilenta on T. amphioxeia, the optimal prey species, were 1.36 d-1 and 0.04 ng C predator- 1 d-1, respectively. Thus, if the abundance of T. amphioxeia was much higher than 5,618 cells mL-1, the abundance of S. gracilenta could be much higher than the highest abundance observed in this study. Eurythermal and euryhaline characteristics of S. gracilenta and its ability to feed on diverse prey species and conduct kleptoplastidy are likely to be responsible for its common spatiotemporal distribution.

Interactions Between the Kleptoplastidic Dinoflagellate Shimiella gracilenta and Several Common Heterotrophic Protists

The newly described dinoflagellate, Shimiella gracilenta, is known to survive for approximately 1 month on the plastids of ingested prey cells during starvation, indicating kleptoplastidy. To understand the population dynamics of this dinoflagellate in marine planktonic food webs, its growth and mortality rate due to predation should be assessed. Thus, we investigated the feeding occurrence of eight common heterotrophic protists on S. gracilenta. We also determined the growth and ingestion rates of Oxyrrhis marina and the naked ciliate, Rimostrombidium sp. on S. gracilenta as a function of the prey concentration. The common heterotrophic dinoflagellates (HTDs) Gyrodinium dominans, O. marina, and Pfiesteria piscicida and a naked ciliate Rimostrombidium sp. were able to feed on S. gracilenta; whereas the HTDs Aduncodinium glandula, Gyrodinium jinhaense, Oblea rotunda, and Polykrikos kofoidii were not. Shimiella gracilenta supported positive growth of O. marina and Rimostrombidium sp. but did not support that of G. dominans and P. piscicida. With increasing prey concentrations, the growth and ingestion rates of O. marina and Rimostrombidium sp. on S. gracilenta increased and became saturated. The maximum growth rates of O. marina and Rimostrombidium sp. on S. gracilenta were 0.645 and 0.903 day−1, respectively. Furthermore, the maximum ingestion rates of O. marina and Rimostrombidium sp. on S. gracilenta were 0.11 ng C predator day−1 (1.6 cells predator−1 day−1) and 35 ng C predator day−1 (500 cells predator−1 day−1), respectively. The maximum ingestion rate of O. marina on S. gracilenta was lower than that on any other algal prey reported to date, although its maximum growth rate was moderate. In conclusion, S. gracilenta had only a few common heterotrophic protist predators but could support moderate growth rates of the predators. Thus, S. gracilenta may not be a common prey species for diverse heterotrophic protists but may be a suitable prey for a few heterotrophic protists.

Diets and Seasonal Ingestion Rates of Aurelia coerulea (Cnidaria: Scyphozoa) Polyps by in situ Feeding Experiments in Jiaozhou Bay, China

The benthic scyphopolyp population is an important stage in the scyphozoan lifecycle. Nevertheless, few studies have detailed the natural feeding and quantified the energy flux of polyps based on field research. To better understand the scyphopolyp natural diet and seasonal variation patterns in the ingestion rate, in situ feeding experiments were conducted on Aurelia coerulea polyps in Jiaozhou Bay, China from August 2018 to April 2019. The diet of A. coerulea polyps was determined by gut content analysis. Digestion rates were also measured. Ingestion rates, based on the gut contents and digestion rates, were assessed monthly. Copepods, copepod nauplii, and ciliates were identified in the guts of A. coerulea polyps. Copepods with the bulk of total prey intake in number are an important source of nutrition for A. coerulea polyps in Jiaozhou Bay. Prey capture of A. coerulea polyps (prey polyp–1) varied among months, and was highly dependent upon the abundance of planktonic prey in the habitat. Copepods and copepod nauplii were digested more rapidly as temperature increased. Carbon weight-specific ingestion rate exhibited an obvious seasonal change, with the mean value of 0.13 ± 0.12 μg C μg C–1 d–1. More rapid digestion of prey at higher temperatures and larger prey availability would cause a higher ingestion rate in polyps. Scyphopolyps are widely distributed predators in littoral ecosystems and they may play an important role in plankton–benthos coupling by transferring energy from the water column to the benthos. Massive scyphopolyps blooms may influence pelagic ecosystems.

Metabolic Reliance on Photosynthesis Depends on Both Irradiance and Prey Availability in the Mixotrophic Ciliate, Strombidium cf. basimorphum

Many species of the ciliate genus Strombidium can acquire functional chloroplasts from a wide range of algal prey and are thus classified as generalist non-constitutive mixotrophs. Little, however, is known about the influence of irradiance and prey availability on their ability to exploit the photosynthetic potential of the chloroplasts, and how this may explain their spatial and temporal distribution in nature. In this study, inorganic carbon uptake, growth, and ingestion rates were measured for S. cf. basimorphum under three different irradiances (10, 40, and 120 μmol photons m–2 s–1) when acclimated to three different prey densities (5 × 103, 1 × 104, and 4 × 104 cells mL–1), as well as when allowed to deplete the prey. After prey depletion, cultures survived without prey longest (∼6 days) at the medium irradiance treatment (40 μmol photons m–2 s–1), while ciliate density, inorganic carbon uptake rates, and cellular chl-a content declined fastest at the highest irradiance treatment. This indicates that the ciliates may be unable to maintain the chloroplasts functionally without replacement at high irradiances. Ingestion rates were not shown to be significantly influenced by irradiance. The maximum gross growth efficiency (GGE) in this study (1.1) was measured in cultures exposed to the medium test irradiance and lowest prey density treatment (5 × 103 cells mL–1). The relative contribution of inorganic carbon uptake to the ciliate carbon budget was also highest in this treatment (42%). A secondary GGE peak (0.99) occurred when cultures were exposed to the highest test irradiance and the medium prey density. These and other results suggest that S. cf. basimorphum, and other generalist non-constitutive mixotrophs, can flexibly exploit many different environmental conditions across the globe.

Key considerations for assessing soil ingestion exposures among agricultural workers

Background Soil ingestion is a critical, yet poorly characterized route of exposure to contaminants, particularly for agricultural workers who have frequent, direct contact with soil. Objective This qualitative investigation aims to identify and characterize key considerations for translating agricultural workers’ soil ingestion experiences into recommendations to improve traditional exposure science tools for estimating soil ingestion. Methods We conducted qualitative in-depth interviews with 16 fruit and vegetable growers in Maryland to characterize their behaviors and concerns regarding soil contact in order to characterize the nature of soil ingestion in the agricultural context. Results We identified and discussed four emergent themes: (1) variability in growers’ descriptions of soil and dust, (2) variability in growers’ soil contact, (3) growers’ concerns regarding soil contact, (4) growers’ practices to modify soil contact. We also identified environmental and behavioral factors and six specific agricultural tasks that may impact soil ingestion rates. Significance Our investigation fills an important gap in occupational exposure science methodology by providing four key considerations that should be integrated into indirect measurement tools for estimating soil ingestion rates in the agricultural context. Specifically, a task-based framework may provide a structure for future investigations of soil contact that may be useful in other populations.

Characterization of activity behavior using a digital medicine system and comparison to medication ingestion in patients with serious mental illness

Activity patterns can be important indicators in patients with serious mental illness. Here, we utilized an accelerometer and electrocardiogram incorporated within a digital medicine system, which also provides objective medication ingestion records, to explore markers of patient activity and investigate whether these markers of behavioral change are related to medication adherence. We developed an activity rhythm score to measure the consistency of step count patterns across the treatment regimen and explored the intensity of activity during active intervals. We then compared these activity features to ingestion behavior, both on a daily basis, using daily features and single-day ingestion behavior, and at the patient-level, using aggregate features and overall ingestion rates. Higher values of the single-day features for both the activity rhythm and activity intensity scores were associated with higher rates of ingestion on the following day. Patients with a mean activity rhythm score greater than the patient-level median were also shown to have higher overall ingestion rates than patients with lower activity rhythm scores (p = 0.004). These initial insights demonstrate the ability of digital medicine to enable the development of digital behavioral markers that can be compared to previously unavailable objective ingestion information to improve medication adherence.

Mechanisms and fluid dynamics of foraging in heterotrophic nanoflagellates

ABSTRACTHeterotrophic nanoflagellates are the main consumers of bacteria and picophytoplankton in the ocean. In their micro-scale world, viscosity impedes predator-prey contact, and the mechanisms that allow flagellates to daily clear a volume of water for prey corresponding to 106 times their own volume is unclear. It is also unclear what limits observed maximum ingestion rates of about 104 bacterial prey per day. We used high-speed video-microscopy to describe feeding flows, flagellum kinematics, and prey searching, capture, and handling in four species with different foraging strategies. In three species, prey-handling times limit ingestion rates and account well for their reported maximum values. Similarly, observed feeding flows match reported clearance rates. Simple point-force models allowed us to estimate the forces required to generate the feeding flows, between 4-13 pN, and consistent with the force produced by the hairy (hispid) flagellum, as estimated using resistive force theory. Hispid flagella can produce a force that is much higher than the force produced by a naked flagellum with similar kinematics, and the hairy flagellum is therefore key to foraging in most nanoflagellates. Our findings provide a mechanistic underpinning of observed functional responses of prey ingestion rates in nanoflagellates.