Approaches to Assess the Suitability of Zooplankton for Bioregenerative Life Support Systems

Future manned space exploration will send humans farther away from Earth than ever before (e.g., to Mars), leading to extended mission durations and thus to a higher demand for essentials such as food, water and oxygen. As resupplying these items from Earth is nearly impossible, aquatic bioregenerative life support systems (BLSS) appear to be a promising solution. Due to its central role in aquatic ecosystems, zooplankton could act as a key player in aquatic BLSS, linking oxygen liberating, autotrophic producers and higher trophic levels. However, prior to the utilization of BLSS in space, organisms proposed to inhabit these systems have to be studied thoroughly to evaluate any space-borne adverse traits, which may impede a proper function of the system. To investigate the impact of microgravity (μg), in particular, several platforms are available, providing μg periods ranging from seconds (Bremen drop tower and parabolic flights), to minutes (sounding rockets), up to even days and months (space flights and the International Space Station (ISS)). Furthermore, ground-based facilities, such as clinostats, enable the of candidate organisms to variable periods of simulated/functional μg. In this book chapter, research on zooplankton utilizing these methods is summarized

Inducible Defenses with a "Twist": Daphnia barbata Abandons Bilateral Symmetry in Response to an Ancient Predator

Predation is one of the most important drivers of natural selection. In consequence a huge variety of anti-predator defenses have evolved in prey species. Under unpredictable and temporally variable predation pressure, the evolution of phenotypically plastic defensive traits is favored. These "inducible defenses", range from changes in behavior, life history, physiology to morphology and can be found in almost all taxa from bacteria to vertebrates. An important group of model organisms in ecological, evolutionary and environmental research, water fleas of the genus Daphnia (Crustacea: Cladocera), are well known for their ability to respond to predators with an enormous variety of inducible morphological defenses. Here we report on the "twist", a body torsion, as a so far unrecognized inducible morphological defense in Daphnia, expressed by Daphnia barbata exposed to the predatory tadpole shrimp Triops cancriformis. This defense is realized by a twisted carapace with the helmet and the tail spine deviating from the body axis into opposing directions, resulting in a complete abolishment of bilateral symmetry. The twisted morphotype should considerably interfere with the feeding apparatus of the predator, contributing to the effectiveness of the array of defensive traits in D. barbata. As such this study does not only describe a completely novel inducible defense in the genus Daphnia but also presents the first report of a free living Bilateria to flexibly respond to predation risk by abandoning bilateral symmetry

Comparison of Gravisensing Organs in Different Planktonic Organism – From Evolution to Life Support Systems

Bioregenerative life support systems are critical components for long-term human space travel, as they provide processes for establishing the components for basic consumable biomass production, and therefore saving costs for transport and technical equipment otherwise necessary. The high reproductive output and the essential role in aquatic foodwebs suggest especially aquatic zooplankton species to be suitable for such bioregenerative life support systems. Considering the broad range of gravity-perception systems - from sensilla based structures up to statocyst systems - there is still a considerable lack of knowledge for zooplankton species in both marine and freshwater species regarding this aspect. Hence, the purpose of the current project is to develop a highly representative comparison of gravity-perception systems in selected zooplankton organisms with special emphasis on their evolutionary history. In addition, sensitive windows for graviperception in ontogeny as well as thresholds of graviperception will be analysed in selected organisms. Moreover, ground based studies will be performed to investigate the effects of reduced gravity on life history of the selected zooplankton species. The outcome will not only foster the selection of zooplankton species for future live support systems. Furthermore, it will significantly increase knowledge on the evolution of graviperception in aquatic ecosystems where gravity is often the only reliable cue for orientation, and may therefore elucidate general gravity-related mechanisms valid for other organisms as well

Comparison of the body torsion in non-predator-exposed (Control) and predator-exposed (Induced) primiparous <i>Daphnia barbata</i>.

<p>Body torsion is here defined as the sum of helmet and tail spine deviation from the body axis. The error bars show the standard error of Mean (SE), the asterisks indicate the significance level (*** <i>P</i> < 0.001) based on a F-Test (<i>F</i>(1, 22) = 264.09).</p

Scanning electron microscope images of the experimental animals.

<p>a) <i>Triops cancriformis</i>, ventral view with the arrow pinpointing to the narrow food groove. The ancient predator feeds on <i>Daphnia</i>, which are caught, subsequently placed into the food groove and transported towards the mandibles; b) Dorsal view of a <i>Triops</i>-exposed morph of <i>Daphnia barbata</i> showing the “twisted” appearance. The tips of helmet and tail spine deviate from the body axis in opposite directions, leading to an S-shaped dorsal ridge and thus abolishing bilateral symmetry of the individual. The twisted morphotype can be assumed to severely impede the transport through the food groove as it should cause the daphnid to wedge within the food groove of the predator. c) Dorsal view of <i>D</i>. <i>barbata</i> not exposed to the predator. The dorsal ridge aligns with the bilateral body axis, the tips of helmet and tail spine do not deviate from the body axis.</p

Inducible Defenses with a "Twist": <i>Daphnia barbata</i> Abandons Bilateral Symmetry in Response to an Ancient Predator

<div><p>Predation is one of the most important drivers of natural selection. In consequence a huge variety of anti-predator defenses have evolved in prey species. Under unpredictable and temporally variable predation pressure, the evolution of phenotypically plastic defensive traits is favored. These “inducible defenses”, range from changes in behavior, life history, physiology to morphology and can be found in almost all taxa from bacteria to vertebrates. An important group of model organisms in ecological, evolutionary and environmental research, water fleas of the genus <i>Daphnia</i> (Crustacea: Cladocera), are well known for their ability to respond to predators with an enormous variety of inducible morphological defenses. Here we report on the “twist”, a body torsion, as a so far unrecognized inducible morphological defense in <i>Daphnia</i>, expressed by <i>Daphnia barbata</i> exposed to the predatory tadpole shrimp <i>Triops cancriformis</i>. This defense is realized by a twisted carapace with the helmet and the tail spine deviating from the body axis into opposing directions, resulting in a complete abolishment of bilateral symmetry. The twisted morphotype should considerably interfere with the feeding apparatus of the predator, contributing to the effectiveness of the array of defensive traits in <i>D</i>. <i>barbata</i>. As such this study does not only describe a completely novel inducible defense in the genus <i>Daphnia</i> but also presents the first report of a free living Bilateria to flexibly respond to predation risk by abandoning bilateral symmetry.</p></div