Algal Toxins Alter Copepod Feeding Behavior

Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod’s feeding appendages–a “sampling beating” that has short durations (<100 ms) and involves little fluid entrainment and a longer duration “grazing beating” that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod’s grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod’s feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods

Anti-grazing properties of the toxic dinoflagellate Karlodinium veneficum during predator-prey interactions with the copepod Acartia tonsa

Karlodinium veneficum (syn. Karlodinium micrum, Bergholtz et al. 2006; J Phycol 42:170–193) is a small athecate dinoflagellate commonly present in low levels in temperate, coastal waters. Occasionally, K. veneficum forms ichthyotoxic blooms due to the presence of cytotoxic, hemolytic compounds, putatively named karlotoxins. To evaluate the anti-grazing properties of these karlotoxins, we conducted food removal experiments using the cosmopolitan copepod grazer Acartia tonsa. Wild-caught, adult female A. tonsa were exposed to 6 monoalgal or mixed algal diets made using bloom concentrations of toxic (CCMP 2064) and non-toxic (CSIC1) strains of K. veneficum. Ingestion and clearance rates were calculated using the equations of Frost (1972). Exposure to the toxic strain of K. veneficum did not contribute to an increased mortality of the copepods and no significant differences in copepod mortality were found among the experimental diets. However, A. tonsa had significantly greater clearance and ingestion rates when exposed to a monoalgal diet of the non-toxic strain CSIC1 than when exposed to the monoalgal diet of toxic strain CCMP 2064 and mixed diets dominated by this toxic strain. These results support the hypothesis that karlotoxins in certain strains of K. veneficum deter grazing by potential predators and contribute to the formation and continuation of blooms

Molecular Twister: A Game for Exploring Solution Chemistry

<p>pH is an essential biological concept with critical importance at various scales, from the molecular level, dealing with blood buffers, homeostasis, and proton gradients, all the way up to the ecosystem level, with soil chemistry and acid rain. However, pH is also a concept that spawns student misconceptions and misunderstanding in terms of what is happening in a solution on the atomic level. The Molecular Twister game, created for a Florida Department of Education funded professional development workshop for Florida high school teachers hosted at the University of Tampa  (Science Math Masters), seeks to model pH in such a way that students can visually and kinesthetically learn the concept in a few minutes. In addition, the basic design of the game pieces allow for teaching extensions to include more complex acid-base reactions. Challenge questions are provided to allow teachers to bring relevancy to the game, using examples of acid-base chemistry pulled from cases in human health and the environment.</p

Experimental setup for in-line digital holographic cinematography.

<p>Experimental setup for in-line digital holographic cinematography.</p

The time fraction and mean duration of feeding appendage beating, hopping and escape reaction.

★<p>The mean duration of a single beating event and its standard deviation.</p>♦<p>The total duration of a certain behavior divided by the observation time.</p

Sample holographic images and time series of <i>Acartia tonsa</i> behavior.

<p>Sample sequences of reconstructed images showing an <i>A. tonsa</i> performing: (a) feeding appendage beating, i.e. periodic movement of feeding appendages which include the 2^nd antennae, 1^st maxillae, 2^nd maxillae, mandibular palps and maxillipeds, shown at 4 millisecond (ms) interval, and (b) hopping involving a quick backward movement of both the 1^st antenna and pereiopods, shown at 8 ms interval. Escape reaction is characterized by repetitive motion of the pereiopods and retraction of the 1^st antennae, much like the last snapshot of the hopping sequence. (c) & (d) Samples of time series tracking the behaviors of a single <i>A. tonsa</i> when exposed to:(c) a mono-algal diet of <i>S. major</i>, and (d) a mono-algal diet of <i>K. brevis</i> 2228. For each event, the color and height of bars specifies the behavior and its duration respectively.</p

Sampling and grazing beating statistics.

★<p>The total duration of sampling/grazing divided by the observation time.</p>♦<p>Values corrected for differences in prey cell concentration.</p>•<p>For a normally-distributed variable, a domain consisting of ± standard deviation from the arithmetic mean contains 68.3% of the data. For a log-normally-distributed variable, 68.3% of the results fall within the range of the geometric mean ×/(multiply/divide) by the geometric standard deviation. Accordingly, represents a confidence interval of 68.3% <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036845#pone.0036845-Limpert1" target="_blank">[38]</a>.</p>◊<p>errors resulting from log-normal fits.</p