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
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“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…
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.
2. Mutualism -
A symbiotic condition where both partners benefit from the interaction.
In such mutualistic relationships, the two partners are often referred
to as the symbionts.
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 other
symbiotic partner, sometimes referred to as the host.
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 of
Porifera, 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 anemone
Anthopleura elegantissima and A. xanthogrammica
is because of their symbiotic algae.
These individuals may have either one or both
types of the symbiotic algae (i.e. zooxanthellae
Algal-cnidarian symbiosis are considered to be mutualistic…So what benefit
does 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 from
the 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 interaction
is probably the basis for the success of coral
reefs in otherwise nutrient poor waters of
The algal-cnidarian symbiosis is a very tight relationship… The algae reside within
the 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 partner
Outgrows the other… in fact the entire physiology and anatomy of the symbionts
Can change following the establishment of symbiosis…
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 reside
within 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
In most cases, the symbiont partners of algal-animal relationships can live without
each 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 hypothesized
that similar symbiotic interactions are what gave rise to chloroplasts within plant cells…
Algal-animal symbioses are transmitted to offspring through both open and closed
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 fertilized
eggs of the reproductive individuals.
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 cases
only 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.
On the California coast, the echiurid worm Urechis caupo builds burrows which
It “shares” with other organisms including annelid worms, shrimps, and crabs…
Crab - sea anemone interactions seem to be common in marine systems… Can you
think of the advantages to the crabs?
Another common association is that
between anemone fish (Amphiprion sp.)
and sea anemones… Do you think this
is an example of a commensal or
Another type of association is that between various fish and sea urchins…
Pearl fish living within the
cloaca of sea cucumbers…
Fish living within tentacles
of a Portuguese man of war
Remora living attached
to other larger fish…
For each of these cases, try to consider what the advantages (or disadvantages)
may be for each symbiotic partner…
In many animal-bacterial symbioses, the bacteria can provide nutrients for their
animal symbiotic partners… this is perhaps most evident in case of chemoautotrophic
bacteria living in symbioses with vestimentiferan tube worms found around hydro-
thermal vents in the deep oceans…
This symbiotic relationship
is the basis for many of these
deep ocean communities.
Other organisms rely either
directly or indirectly on the
nutrients assimilated into the
system through the symbiotic
The squid Eupryman scolopes is symbiotic with the bioluminescent bacteria
The squid provides the bacteria an ideal growth environment, and in return it uses
the 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…
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???
We have not discussed details of parasitic symbiosis, but parasitism is very widespread
throughout marine systems…
A close study of many invertebrates and almost all ocean fish will reveal both external
as well as internal parasites…
Typically parasites include (but are not limited to) various nematodes, annelids (leaches),
and parasitic isopods.