Symbion pandora is a microscopic animal that lives exclusively on the mouth-parts of lobsters. When we think of a life-cycle, we usually think of a baby growing into an adult, a female mating with a male, and then the female giving birth to a baby. But as Symbion pandora demonstrates, this isn’t always the case. Symbion pandora undergoes both asexual and sexual reproduction. Its life cycle is especially interesting because the timing of its sexual reproduction matches the moulting of its lobster host. This allows Symbion pandora to move from the lobster’s old shell to its new one, a remarkable solution to the problem of a temporary home. First described in 1995 by Peter Funch and Reinhardt Kristensen, Symbion pandora’s life-cycle provides insight on the incredible diversity and range in the ways organisms grow and reproduce.
Here is a video from Robert Sandler, an undergraduate in Casey Dunn’s Biology0410 Invertebrate Zoology class. In this video Robert introduces gyrodactylids, a group of flatworms that live attached to fish.
In the vast ocean, without walls and far from the floor, jellyfish can become drifting islands of activity. Creatures from far and wide will congregate on them to act out the ups and downs of life and death. Jellyfish have symbiotic relationships with living things of all sizes, from fish and shrimp that feed off them or off the pieces of food left between their tentacles, to single-celled photosynthesizing organisms that take shelter inside the cytoplasm of the jellyfish’s cells.
In this video, Trisha Towanda talks about one particular jellyfish, the fried egg jelly, and some of the other creatures that hang around it. There are moon jellies that the fried egg jelly eats. These moon jellies have little parasitic crustaceans on them called amphipods, which jump to the fried egg jelly while the moon jelly is being eaten. There are also crabs that ride around on the fried egg jelly, that are parasitic in their youth, but then grow to be helpful symbionts by eating off the little amphipods. This sort of coming of age story, where a symbiont’s relationship changes over its lifespan is an unusual one. Trisha put the pieces together by staring at them for hours and days and weeks when she was in Erik Thuessen‘s lab at Evergreen State College.
Many thanks to Trisha Towanda, who is now stationed in the Seibel lab at the University of Rhode Island. This video was edited and animated by Sophia Tintori, with an original score by local pop hero Amil Byleckie. It is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license. Here is the paper Trisha wrote about the story.
When collecting bugs out in the field, it can be easy to get more than one bargained for. Many flies, beetles, and other mobile beasties such as the harvestman shown above (Megalopsalis sp. from New Zealand) find themselves regular host to hitchhikers of arachnid origin: the five orangish globules nestled among the bases of this unfortunate individual’s limbs are parasitic mites hunkered down for the long haul.
Indeed, many tens of thousands of mite species spend their early lives attached to a host, slowly drawing nutrition from its internal fluids until they become large enough to drop off wherever their hosts have carried them, where they begin life as free-living adults. However, these parasitic freeloaders aren’t the only kind of tenants one will find on harvestmen; there are also diverse sorts of more benign bedfellows who climb aboard with no appreciable harm to their unwitting ride.
One group of these tag-alongs is the pseudoscorpions – distant relatives of true scorpions, living secretive lives in forest soil and tree bark – which many would doubtless find abjectly terrifying… if they ever got larger than a few millimeters. Below, you can see a pseudoscorpion hanging for dear life onto the leg of another Megalopsalis. There are reports of pseudoscorpions waiting eagerly around a flower for a bee pollinator to grab onto, or clustering around the pupal bores of flies just before the airborne adult emerges. The traditional interpretation of this behavior suggests that climbing aboard larger, more mobile animals is an adaptation meant to transport these tinier critters to a wider range of habitats. Others, however, have suggested that perhaps pseudoscorpions simply grab onto whatever passes by them in the hopes that they might be able to eat it.
Strangely enough, even pseudoscorpions can bear hitchhikers, as the parasitic mites on this neobisiid I collected during field work in Alabama attest (gray bugs next to the greenish dots). It’s hard not to be reminded of the poet Jonathan Swift’s famous verses:
“The vermin only teaze and pinch
Their foes superior by an inch.
So, naturalists observe, a flea
Has smaller fleas that on him prey,
And these have smaller still to bite ‘em,
And so proceed ad infinitum.”
First three photographs by Gonzalo Giribet. Last photograph by Christopher Laumer.
The slug pictured above, Elysia chlorotica, is a symbiont thief.
Elysia chlorotica eats the alga Vaucheria litorea but does not digest it. The slug cuts open algal filaments and sucks out the contents, transferring the living chloroplasts to its own tissue. Chloroplasts are organisms that have lived symbiotically within plant cells for many millions of years. They harness energy from the sun, which they give to the plant or alga cell they live within. Most animals digest the chloroplasts entirely when they eat plants, but not Elysia. By keeping the chloroplasts intact and transferring them to its own tissue, Elysia allows them to continue photosynthesizing, producing energy for the slug. The slug can then live for months without eating as long as sunlight is available, and can maintain the same chloroplasts for its entire adult life. This is an extremely unique relationship between an animal and plant symbionts.
Many other animals form associations with photosynthetic organisms. Corals such as the one depicted below have a symbiosis with multiple single-celled organisms called zooxanthellae. This is a multiple-level symbiosis because corals house the entire chloroplast-containing zooxanthellae cells within their tissue. This is different from Elysia chlorotica, who has cut out the middleman — instead of incorporating entire cells, it only retains the chloroplasts.
The upper photograph (of Elysia chowing down) was taken by Nicholas E. Curtis and Ray Martinez. The second photograph is courtesy of Mary S. Tyler, and was the cover of PNAS when this paper was published. The lower picture is the coral Porites as photographed by Casey Dunn. You can watch two amazing videos of the slugs in action, here and here, both of which were included in the PNAS paper.