Sponges sneeze mucus to shed particulate waste from their seawater inlet pores.

Sponges, among the oldest extant multicellular organisms on Earth,1 play a key role in the cycling of nutrients in many aquatic ecosystems.2-5 They need to employ strategies to prevent clogging of their internal filter system by solid wastes,6-8 but self-cleaning mechanisms are largely unknown. It is commonly assumed that sponges remove solid waste with the outflowing water through distinct outflow openings (oscula).3,9 Here, we present time-lapse video footage and analyses of sponge waste revealing a completely different mechanism of particle removal in the Caribbean tube sponge Aplysina archeri. This sponge actively moves particle-trapping mucus against the direction of its internal water flow and ejects it into the surrounding water from its seawater inlet pores (ostia) through periodic surface contractions that have been described earlier as "sneezing."10,11 Visually, it appears as if the sponge is continuously streaming mucus-embedded particles and sneezes to shed this particulate waste, resulting in a notable flux of detritus that is actively consumed by sponge-associated fauna. The new data are used to estimate production of detritus for this abundant sponge on Caribbean coral reefs. Last, we discuss why waste removal from the sponge inhalant pores may be a common feature among sponges and compare the process in sponges to equivalent mechanisms of mucus transport in other animals, including humans.

Pluripotency and the origin of animal multicellularity.

A widely held-but rarely tested-hypothesis for the origin of animals is that they evolved from a unicellular ancestor, with an apical cilium surrounded by a microvillar collar, that structurally resembled modern sponge choanocytes and choanoflagellates1-4. Here we test this view of animal origins by comparing the transcriptomes, fates and behaviours of the three primary sponge cell types-choanocytes, pluripotent mesenchymal archaeocytes and epithelial pinacocytes-with choanoflagellates and other unicellular holozoans. Unexpectedly, we find that the transcriptome of sponge choanocytes is the least similar to the transcriptomes of choanoflagellates and is significantly enriched in genes unique to either animals or sponges alone. By contrast, pluripotent archaeocytes upregulate genes that control cell proliferation and gene expression, as in other metazoan stem cells and in the proliferating stages of two unicellular holozoans, including a colonial choanoflagellate. Choanocytes in the sponge Amphimedon queenslandica exist in a transient metastable state and readily transdifferentiate into archaeocytes, which can differentiate into a range of other cell types. These sponge cell-type conversions are similar to the temporal cell-state changes that occur in unicellular holozoans5. Together, these analyses argue against homology of sponge choanocytes and choanoflagellates, and the view that the first multicellular animals were simple balls of cells with limited capacity to differentiate. Instead, our results are consistent with the first animal cell being able to transition between multiple states in a manner similar to modern transdifferentiating and stem cells.

Ciliates from ancient permafrost: Assessment of cold resistance of the resting cysts.

There is evidence that resting cysts of soil ciliates and numerous taxa of other protists can survive in permafrost for thousands of years at subzero temperatures; however, our knowledge about mechanisms of long term cryobiosis remains incomplete. In order to better understand the means by which ancient cysts survive, we investigated resistance to cyclical supercooling stress of resting cysts of the soil ciliate Colpoda steinii (Colpodida, Ciliophora). Three clonal strains were used for comparison, isolated from Siberian tundra soil, ancient Holocene (5-7,000 y) and late Pleistocene (32-35,000 y) permafrost sediments. To determine the viability of the ancient and contemporary ciliate cysts we improved and validated a cultivation-independent method of vital fluorescent staining with a combination of two nucleic acid binding dyes, acridine orange and propidium iodide. The viability of Colpoda steinii cysts during low-temperature experiments was measured using both the proposed vital fluorescent staining method and standard germination test. Our results indicate that the dual-fluorescence technique is a more accurate, rapid, and efficient method for estimating cyst viability. We found that cysts of ancient ciliates display lower tolerance to the impact of cyclical cold compared to cysts of contemporary ciliates from Siberian permafrost affected soils.

Sensory Flask Cells in Sponge Larvae Regulate Metamorphosis via Calcium Signaling.

The Porifera (sponges) is one of the earliest phyletic lineages to branch off the metazoan tree. Although the body-plan of sponges is among the simplest in the animal kingdom and sponges lack nervous systems that communicate environmental signals to other cells, their larvae have sensory systems that generate coordinated responses to environmental cues. In eumetazoans (Cnidaria and Bilateria), the nervous systems of larvae often regulate metamorphosis through Ca(2+)-dependent signal transduction. In sponges, neither the identity of the receptor system that detects an inductive environmental cue (hereafter "metamorphic cues") nor the signaling system that mediates settlement and metamorphosis are known. Using a combination of behavioral assays and surgical manipulations, we show here that specialized epithelial cells-referred to as flask cells-enriched in the anterior third of the Amphimedon queenslandica larva are most likely to be the sensory cells that detect the metamorphic cues. Surgical removal of the region enriched in flask cells in a larva inhibits the initiation of metamorphosis. The flask cell has an apical sensory apparatus with a cilium surrounded by an apical F-actin-rich protrusion, and numerous vesicles, hallmarks of eumetazoan sensory-neurosecretory cells. We demonstrate that these flask cells respond to metamorphic cues by elevating intracellular Ca(2+) levels, and that this elevation is necessary for the initiation of metamorphosis. Taken together, these analyses suggest that sponge larvae have sensory-secretory epithelial cells capable of converting exogenous cues into internal signals via Ca(2+)-mediated signaling, which is necessary for the initiation of metamorphosis. Similarities in the morphology, physiology, and function of the sensory flask cells in sponge larvae with the sensory/neurosecretory cells in eumetazoan larvae suggest this sensory system predates the divergence of Porifera and Eumetazoa.

Life, the universe, and everything: an education outreach proposal to build a traveling astrobiology exhibit.

Astrobiology is a transdisciplinary field with extraordinary potential for the scientific community. As such, it is important to educate the community at large about the growing importance of this field to increase awareness and scientific content learning and expose potential future scientists. To this end, we propose the creation of a traveling museum exhibit that focuses exclusively on astrobiology and utilizes modern museum exhibit technology and design. This exhibit (the "Astrobiology Road Show"), organized and evaluated by an international group of astrobiology students and postdocs, is planned to tour throughout the Americas.

Cryptic diversity within the choanoflagellate morphospecies complex Codosiga botrytis - phylogeny and morphology of ancient and modern isolates.

Choanoflagellates are closely related to metazoans and fungi according to recent phylogenetic studies; therefore the systematics of these organisms is of particular interest. The choanoflagellate morphospecies Codosiga botrytis is the first described choanoflagellate, and is one of the most frequently reported choanoflagellate species. In this study we present phylogenetic and morphological data on eight different strains of Codosiga botrytis. Among these there are five ancient strains; these cultures have been established from up to 43,000 years old cysts from Siberian permafrost. We found that based on the variable V4 region of the small subunit (SSU) of the rDNA, all the investigated freshwater isolates of Codosiga botrytis, together with Sphaeroeca volvox, form a cluster at the base of all other choanoflagellate species. Moreover, the morphospecies described classically as Codosiga botrytis contains at least four different genotypes separated by considerably high genetic distance. All these 'cryptic species' have identical general morphology and cell structure. Strains have a similar life cycle with several different life forms and large morphological plasticity. For the first time we were able to establish cultures from cryo-conserved cysts of choanoflagellates. The ancient strains did not differ significantly in partial SSU rDNA from the modern ones. Besides, no biogeographically pattern could be established. This fact and the low genetic distances of some strains from remote locations support the distribution of dormant stages via air.