Sensory organ discovered in sponges helps them respond to their environment despite having no nervous system

by Amanda Kahn

Sponges are animals, but they do not have the features we’re used to seeing when we think of animals: no gut, no head or tail, no nerves, and no stomachs or other organs.  And yet despite not having a nervous system, sponges are able to respond to their environment by changing the canal sizes in their filter-feeding system, in an action called the “inflation-contraction response.”  It’s basically akin to what we do when we sneeze.  This was observed in the mid-1900’s, but scientists have only been able to speculate what could be helping the sponges sense and coordinate various cells in their body when there are no nerves or sensory organs observed.  Danielle Ludeman, one of the authors here at the Madreporite, has just published an article describing the sensory organ that she and her coauthors, Nathan Farrar, Ana Riesgo, Jordi Paps, and Sally Leys, discovered in many different species of sponges: primary cilia used to detect changes in water flow.  Check out the time-lapse video below to see how responsive sponges are to irritants (in this case sediments) in the water.

Danielle tested if those cilia are used to detect changes in water flow by using drugs that target and knock out the cilia.  When the cilia were knocked out or knocked down, the “sneeze” response couldn’t be initiated.  If cilia were permitted to grow back following treatment, the “sneeze” response could be initiated.  In our kidneys, primary cilia are used to detect water flow.  The structure of the paired cilia Danielle found aligns well with those of primary cilia in other animals, further supporting that these are sensory cilia that allow the sponges to detect their environment.

The cilia line the osculum, the chimney-like opening of the sponge.  If that osculum is removed, the sponge also is not able to initiate a sneeze response.  This led Danielle and co-authors to determine that the osculum can be thought of as a sensory organ, and not just a giant chimney.

Figure 4 from Ludeman et al. 2014

The “sneeze” response is shown by an increase in canal diameter followed by a rapid decrease (the black lines in the graphs). Various drugs that affect the cilia also affected that inflation/contraction. Source: Ludeman et al. (2014).

Why does this matter to us, and how does it apply to evolutionary theory?  Sponges are one of the earliest branches off of the animal tree of life (the Metazoa).  While they are animals, their distant relation to us and to all other animals (collectively called the Eumetazoa) means they diverged from whatever last common ancestor the Metazoa shared and evolved into something quite different and independent of what other animals have evolved into.  This isn’t unique–every animal phylum is very different from every other.  What is unique is their placement at the base of our collective “family tree.”  If a sponge shares a feature that we also have, it’s likely that the proto-animal–the last common ancestor that all animals shared–had that feature as well.  It brings us a little bit closer toward understanding how we evolved from single-celled organisms to the multicellular, fantastically complex and coordinated animals we are today.

Still think sponges are boring?
(Hint: they are, but only in one way that word is defined!).

Citation:

Ludeman, D.A., N. Farrar, A. Riesgo, J. Paps, and S.P. Leys (2014).  Evolutionary origins of sensation in metazoans: evidence for a new sensory organ in sponges.  BMC Evolutionary Biology, 14(3).  doi:10.1186/1471-2148-14-3.

To learn more about sponges and research on the origin of animal body plans, check out the Leys lab website.

Glass sponge videos: Animals of the reefs

by Amanda Kahn

Did you know that glass sponges form reefs the size of cities here in BC?  If we were to drain the water from the Strait of Georgia (between the mainland and Vancouver Island, where Bamfield sits), you’d be able to see huge structures built by generations of glass sponges as they grew higher and higher to get into strong water flow.  Among other things, the Leys lab–headed by Dr. Sally Leys at the University of Alberta–studies the glass sponge reefs.  Student Sameena Sherman put together two videos to introduce the reefs and the animals that live in them.  If you haven’t seen the first video, you can find it here.  Check out the latest video, Animals of the Reefs, below!

Could sponges affect mean global sea level?

by Amanda Kahn

In case you don’t know about it, xkcd.com has a fabulous blog section called What-If.  In it, the author responds to readers’ questions, and one from a few weeks ago caught my eye because the last paragraph talked about sponges.  The question was, “How much would the sea level fall if every ship were removed all at once from the Earth’s waters?”  The answer to that was six micrometers, but at the end, the author brought up another sea-level question (often used as a joke): how much deeper would the ocean be if it didn’t have sponges in it?

Image credit: xkcd.com

Imagining that a single group of animals can affect sea level that much seems preposterous at first.  After all, I imagine that even though there are very few blue whales left in the ocean, in terms of biomass there is surely more displacement caused by whales, sharks, and fish than by sponges, which appear lower on the food pyramid.  In the ocean, food pyramids are inverted, meaning there is more biomass at higher food levels (called “trophic levels”) than at lower ones.  This is opposite than what we often see in ecosystems on land.  By some quick back-of-the-envelope calculations, blue whales don’t even occupy 0.000000001% of the volume of the ocean (it’s somewhere around 10e11%, if you really wanted to know).

Inverted trophic pyramid of the open ocean

In terms of biomass, there is WAY more displacement occurring from fish, whales, and sharks than from sponges, which feed at a lower trophic level (closer to the bottom in this pyramid). Image credit: studyblue.com

Sponges do, however, cover large portions of the ocean and can dramatically affect the water they live in.  Sponges and other filter feeders can process vast volumes of water during the filtering process, resulting in major changes in water clarity and plankton concentrations.  So while these animals do not take up a lot of space in the ocean, they are still very important and have a strong impact in some regions.  In case you don’t have time to watch the whole video below (it’s super interesting!  I highly recommend watching it from the beginning, if you’ve got time), skip to 4:22 to see the filtering ability of oysters.

I didn’t think a single species could have a large impact on sea level until I remembered the elephant in the room: Homo sapiens.  With mounting evidence that global temperature is rising and local climates are changing around the world, humans are already causing a much greater change in sea level than removing any one particular species, all the ships in the ocean, or even removing some islands.

As written in the What-If post, since sea level is already rising from human activities, the sea level drop incurred by removing all ships from the ocean at once would disappear after only 16 hours. Credit: xkcd.com

An introduction to glass sponge reefs

by Amanda Kahn

Okay, as far as we know, glass sponges do not form reefs offshore of Barkley Sound, but the same species that form the reefs in these videos do appear as solitary individuals near Bamfield, and in any case, the idea that sponges form reefs is so awesome that this video should be posted here anyway.  Check out the first installment of a series of short videos about glass sponge reefs, put together by Sameena Sherman from the Leys lab at the University of Alberta.  A transcript of the video can be found below.

Transcript of the video:

Fossils suggest that glass sponges were established by the Late Proterozoic era. In the Jurassic, there were large reefs formed of glass sponges that covered the Northern shore of the Tethys Sea, which is now the area representing Europe and Eastern Canada. Sponge reefs, as a biogenic structure, were initially thought to be extinct until the discovery of the reefs in the Pacific Northwest.

Most glass sponges live in depths greater than 500 metres. Off the coast of British Columbia in the North Pacific, vast reefs spanning hundreds of square kilometres live in shallower depths of approximately 200 metres. This depth is speculated to be favourable for sponge reefs because of high silica content, high food content, high water flow, and cold temperatures reminiscent of the deep sea.

Glass sponges possess a unique silicon dioxide skeleton and syncytial tissue formed by fused embryonic cells. They are typically vase, plate, or tube-shaped.

There are two structural types of glass sponges. Lyssacine sponges have a loose spicule skeleton and are non-reef-forming. Dictyonine, on the other hand, can form reefs due to a fused spicule skeleton. Only 3 species make up reefs; they are Aphrocallistes vastus, Heterochone calyx, and Farrea occa. These species are found throughout the Pacific as individuals; it is only in the northeast Pacific that they form reefs.

You can learn more about glass sponges and see more videos at our website: http://www.biology.ualberta.ca/leys_lab/.

The Octopus of Saanich

By Jackson Chu and Danielle Ludeman

As part of the Oceans Network Canada observatory, the Victoria Experimental Network Under the Sea (VENUS) provides real-time measurements, images, and sound to researchers and observers on-shore.

Anyone, from scientists to the general public, can access the network’s data and monitor environmental changes as they happen (see here for a previous post on accessing and graphing VENUS using R). The VENUS instrumentation is found in the coastal waters of the Salish Sea and is the sister network to the offshore NEPTUNE Canada regional cabled ocean network

Video and data provided by Jackson Chu

Captured in this time-lapse video from Saanich Inlet is a juvenile, ~10 cm long, Pacific Red Octopus (Octopus rubescens), which had temporarily moved underneath the VENUS Camera Array for a month. When the oxygen levels drop to near zero, it decides to pack up and move somewhere more hospitable. You would to if you had a dozen squatters (Munida quadrispina) hanging around your neighborhood all day!
Note: You can see the white ball sponges (Suberites sp.) contracting in the video – the first time this behavior has been captured in situ on the bottom of the ocean. You can check out another time lapse of a contracting sponge done in the lab, Tethya wilhelma, and one of a freshwater sponge Ephydatia muelleri.

Metadata:
Location: Saanich Inlet, 96 m depth
Camera: Olympus C8080WZ
Exposure Settings: 7mm @ F5.6, 1/30s, ISO100, with offcamera strobe in custom housing
Time start: Sept. 14, 2012 @ 07:47:42 UTC
Time end: Oct. 09, 2012 @ 14:47:28 UTC
Total # of images: 1691 8MP still images (3264p x 2448p) taken in doublets (10 s interval) every 30 mins
Workflow:
Images were batched processed to 1440p x 1080p dimensions (Adobe Photoshop) and made into a 15 frames per second (fps) time lapse movie (Avidemux). The time lapse video was then stabilized and re-rendered (Adobe After Effects) because the images did not perfectly overlay on top of one another which resulted in shakey raw footage. Oxygen data profile for the time sequence was downloaded from the VENUS website, processed (Matlab), and plotted (Adobe Illustrator, Adobe Photoshop). The Oxygen profile was then overlaid onto the time lapse video (Adobe After Effects), and an animated time marker was added using keyframes before finalizing the video by pillarboxing into a 1080p HD-video with audio accompaniment (Adobe Premiere Pro).

The hunt for glass sponge larvae

Amanda loves tide poolsby Amanda Kahn

This past week, I left frozen Edmonton, Alberta for some field work on the coast.  My supervisor (Sally Leys) and I went on the hunt for larvae of glass sponges.  Several years ago, a single larva was spotted in a sponge collected in November or December.  We then found sperm and eggs in sponges this past year, so we decided to go investigate.  This is important because this species of glass sponges forms the foundation of the sponge reefs that populate the straits of western Canada (and so far, form reefs nowhere else in the world), so learning about how and when they reproduce will help us determine what factors might positively or negatively affect their breeding success, and therefore the successful growth of the reefs.

Check out the post documenting our trip at the Leys lab website.

Credit: A Kahn 2012

Also, to see what the reefs look like that these sponges form,  check out the video at this link, compiled by Sameena Sherman of the Leys lab, showing reefs in Hecate Strait.

 

A spongy habitat

By Danielle Ludeman

The world is full of organisms, living on organisms, that are living on other organisms.  You just have to take a moment to think about the complexity of life that can occur to start to appreciate all of the life around us.  Take a tree in your front yard – at first glance you may just see a tree, but when you start to look closer you notice the bird nest that will be home to baby chicks in the spring, and the squirrel that runs up and down the branches.  Then you notice all the different types of moss, lichen, and mushrooms that are growing on the tree.  And upon closer inspection you realize that this creates even more space for a variety of spiders and insects to thrive.  And we can keep going on and on to include all of the life that we need a microscope to see. And this is just on a single tree!

This summer, while doing some field studies at Bamfield, I began to appreciate all of the life that can be found on a single sponge.  Now it is well known that sponges can be very important habitat for many organisms, with some species being obligate commensals of sponges, meaning they can ONLY live on a sponge to survive.  But when I started to look closer at some of the sponges in my studies, I began to realize just how many other organisms call a sponge its home!  One species of sponge in particular – Suberites sp.  that I collected off of Brady’s beach – seemed to have a surprise guest visiting every time I looked at it!  I managed to photograph a few of these, and thought I would share these with you in the slideshow below!

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