Symbiosis
[3] Symbiosis can be obligatory, which means that one, or both of the organisms depend on each other for survival, or facultative (optional), when they can also subsist independently.
[8][9] In 1878, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms".
[13] In 1949, Edward Haskell proposed an integrative approach with a classification of "co-actions",[14] later adopted by biologists as "interactions".
[11][19][20][21] The algal or cyanobacterial symbionts in lichens, such as Trentepohlia, can generally live independently, and their part of the relationship is therefore described as facultative (optional), or non-obligate.
Species that are naturally evolving and contain reduced sizes of genes can be accounted for an increased number of noticeable differences between them, thereby leading to changes in their evolutionary rates.
The incapability of the endosymbiotic bacteria to reinstate their wild type phenotype via a recombination process is called Muller's ratchet phenomenon.
Muller's ratchet phenomenon, together with less effective population sizes, leads to an accretion of deleterious mutations in the non-essential genes of the intracellular bacteria.
An example of antagonism is Juglans nigra (black walnut), secreting juglone, a substance which destroys many herbaceous plants within its root zone.
[37] The term amensalism is often used to describe strongly asymmetrical competitive interactions, such as between the Spanish ibex and weevils of the genus Timarcha which feed upon the same type of shrub.
It derives from a medieval Latin word meaning sharing food, formed from com- (with) and mensa (table).
Examples of metabiosis are hermit crabs using gastropod shells to protect their bodies, and spiders building their webs on plants.
[46] A spectacular example of obligate mutualism is the relationship between the siboglinid tube worms and symbiotic bacteria that live at hydrothermal vents and cold seeps.
The bryozoan colony (Acanthodesia commensale) develops a cirumrotatory growth and offers the crab (Pseudopagurus granulimanus) a helicospiral-tubular extension of its living chamber that initially was situated within a gastropod shell.
Among the many types of mimicry are Batesian and Müllerian, the first involving one-sided exploitation, the second providing mutual benefit.
This is to the advantage of the mimic but to the detriment of both the model, whose protective signals are effectively weakened, and of the dupe, which is deprived of an edible prey.
[54][55] For example, different species of bumblebee mimic each other, with similar warning coloration in combinations of black, white, red, and yellow, and all of them benefit from the relationship.
[56] Cleaning symbiosis is an association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client).
[60] A study by Raymond Keyes addresses the atypical behavior of a few shark species when exposed to cleaner fish.
For example, Atlantic and Pacific lemon sharks consistently react to the wrasse fish in a fascinating way.
Then, the fish passes further into the mouth to examine the gills, specifically the buccopharyngeal area, which typically holds the most parasites.
[60] Symbiosis is increasingly recognized as an important selective force behind evolution;[5][61] many species have a long history of interdependent co-evolution.
[62] Although symbiosis was once discounted as an anecdotal evolutionary phenomenon, evidence is now overwhelming that obligate or facultative associations among microorganisms and between microorganisms and multicellular hosts had crucial consequences in many landmark events in evolution and in the generation of phenotypic diversity and complex phenotypes able to colonise new environments.
Under certain conditions species of fungi previously in a state of mutualism can turn parasitic on weak or dying plants.
[68] One hypothesis for the origin of the nucleus in eukaryotes (plants, animals, fungi, and protists) is that it developed from a symbiogenesis between bacteria and archaea.
[74] The biologist Lynn Margulis, famous for her work on endosymbiosis, contended that symbiosis is a major driving force behind evolution.
Some groups of plants developed nectar and large sticky pollen, while insects evolved more specialized morphologies to access and collect these rich food sources.
In order to attract animals, these plants evolved a set of morphological characters such as fruit colour, mass, and persistence correlated to particular seed dispersal agents.
