Symbiosis

Definition: “To live together”… the intimate living together of two different species…

Subdivisions of symbiosis:

1. Commensalism - A symbiotic condition where one of the partners benefits from the interaction, while the other member is not harmed, but does not necessarily gain any advantage either…

2. Mutualism -

A symbiotic condition where both partners benefit from the interaction.

Inquilinism is a special type of commensalism where one animal lives in the home or digestive tract of another…

In commensalistic relationships the partner gaining the advantage is called the commensal, and the other partner is called the host.

In such mutualistic relationships, the two partners are often referred to as the symbionts.

Symbiosis

Subdivisions of symbiosis (cont.):

3. Parasitism -

An extreme case of symbiosis, parasitism is a condition when one partner,the parasite, benefits from the interaction at the expense of the othersymbiotic partner, sometimes referred to as the host.

Symbiosis of Algae and Animals

Symbiotic relationships between algae and animals are typically found between unicellular algae and their invertebrate symbiont hosts.

These relationships are most commonly seen between the algae and members ofPorifera, Cnidaria, Platyhelminthes, Mullusca, and even Protista…

The most common of these interactions is that between symbiotic dinoflagellates (Zooxanthellae) or symbiotic chlorella (zoochlorellae), and cnidarians.

Note that the green color of the local sea anemoneAnthopleura elegantissima and A. xanthogrammicais because of their symbiotic algae.

These individuals may have either one or bothtypes of the symbiotic algae (i.e. zooxanthellaeand zoochlorellae).

Symbiosis of Algae and Animals

Algal-cnidarian symbiosis are considered to be mutualistic…So what benefitdoes each symbiotic partner get from this interaction?

The cnidarian receives nutrients from the algae in form of sugars and other basic photosynthates… in fact, some studies suggest that certain species of cnidarians can fulfill their entire energetic requirement fromthe sugars they get from their symbiotic partners...

The algae on the other hand receive cnidarian metabolic bi-products in form of nitrates and phosphates…

This mutualistically beneficial interactionis probably the basis for the success of coralreefs in otherwise nutrient poor waters oftropical oceans.

Symbiosis of Algae and Animals

The algal-cnidarian symbiosis is a very tight relationship… The algae reside withinthe endodermal cells of the cnidarians, and typically, individual cnidarians will be associated with a million or more algae per square centimeter of tentacle tissue...

Also, the symbiotic relationship is tightly regulated, such that neither partnerOutgrows the other… in fact the entire physiology and anatomy of the symbiontsCan change following the establishment of symbiosis…

Symbiosis of Algae and Animals

Algal cnidarian symbioses are found in a range of animals including sponges, flatworms, and even molluscs like this giant clam…

Not all algal-animal symbioses are alike though. In some cases, the algae residewithin the cells of their hosts, whereas in other cases, they are extra-cellular.Yet in other cases, the host individual retains only the chloroplasts of the symbiont.

Symbiosis of Algae and AnimalsFinal Notes

In most cases, the symbiont partners of algal-animal relationships can live withouteach other (aposymbiotic); however, in nature, this is a rarity, as the symbiotic relationship is the only way these organisms are capable of remaining “competitive” within their environments… this is typically more vital to the animal symbiont…

Algal-animal symbioses are very tight and well regulated interactions… it is hypothesizedthat similar symbiotic interactions are what gave rise to chloroplasts within plant cells…

Algal-animal symbioses are transmitted to offspring through both open and closed systems:

Open - the juvenile animals do not have any symbions, and they get their symbiotic partners from the environment.

Closed – algal symbionts are passes to the next generation along with the fertilizedeggs of the reproductive individuals.

Symbiosis Between Animals

Symbiotic relationships between animals are found throughout marine systems,but typically, these systems are not as tightly regulated as animal-algal systems.

Also, animal-animal symbioses are in many cases commensal, and in some casesonly partially mutualistic for both partners…

Types of commensal associations:

Epizoits – commensals that live on other organisms e.g. barnacles and small snails living on larger snails…

Endozoites – commensals that live inside other animals but are not parasites e.g. turbellarian flatworms live in the digestive tracts of larger invertebrates and in the mantle cavity of mollusks.

Symbiosis Between Animalsother examples

On the California coast, the echiurid worm Urechis caupo builds burrows whichIt “shares” with other organisms including annelid worms, shrimps, and crabs…

Symbiosis Between Animalsother examples

Crab - sea anemone interactions seem to be common in marine systems… Can you think of the advantages to the crabs?

Another common association is thatbetween anemone fish (Amphiprion sp.)and sea anemones… Do you think thisis an example of a commensal or mutualistic interaction?

Symbiosis Between Animalsother examples

Another type of association is that between various fish and sea urchins…

Symbiosis Between Animalsother well known examples…

Pearl fish living within the cloaca of sea cucumbers…

Fish living within tentaclesof a Portuguese man of war

Remora living attachedto other larger fish…

For each of these cases, try to consider what the advantages (or disadvantages)may be for each symbiotic partner…

Symbiosis of Animals and Bacteria

In many animal-bacterial symbioses, the bacteria can provide nutrients for theiranimal symbiotic partners… this is perhaps most evident in case of chemoautotrophicbacteria living in symbioses with vestimentiferan tube worms found around hydro-thermal vents in the deep oceans…

This symbiotic relationshipis the basis for many of thesedeep ocean communities.

Other organisms rely either directly or indirectly on the nutrients assimilated into the system through the symbioticinteraction.

Symbiosis of Animals and Bacteriaanother example…

The squid Eupryman scolopes is symbiotic with the bioluminescent bacteriaVibrio fischeri.

The squid provides the bacteria an ideal growth environment, and in return it usesthe light generated by the bacteria (controlling light levels) to establish a form of“counter lighting”. How do you think this may be advantageous to the squid?

These squids are not the only organisms symbiotic with bioluminescent bacteria.This type of symbiosis is common in a number of fish species…

Symbiosis – try this one…

This is a female angler fish (Linophyryne argyresca) with a male attached to it…What is going on? Is this symbiosis? If so, what kind???

Symbiosis - Parasitism

We have not discussed details of parasitic symbiosis, but parasitism is very widespreadthroughout marine systems…

A close study of many invertebrates and almost all ocean fish will reveal both externalas well as internal parasites…

Typically parasites include (but are not limited to) various nematodes, annelids (leaches), and parasitic isopods.

Symbiosis – one final example…