Mutualistic symbiosis

Intracellular symbiosis is extremely widespread in invertebrates. For example, mutualistic symbioses with intracellular bacteria can be found in almost all animal phyla, including sponges, cnidaria, nematodes, anellids, mollusca and arthropoda. Buchner (1965) thoroughly reviews most information published on bacterial symbiosis in animals up to 1964. After this monumental work, various reviews on more specific subjects have been published (e.g. Baumann, 1998, and references therein) including some recent reviews on Wolbachia (O Neill et al., 1997 Werren, 1997). In most of these papers, the term symbiosis is apparently used with a broad meaning the intracellular bacterium is usually referred to as an endosymbiont even in the absence of data on effects on host fitness. Here only key points on intracellular symbiosis and Wolbachia will be summarized, so as to put the information available on symbiosis in filarial nematodes into a broader context. 

Wolbachia, vertical transmission, mutualistic symbiosis and reproductive parasitism... 

It is also possible that polydnaviruses were originally virulent in C. sonorensis, but the virus-wasp relationship has evolved toward mutualism (103). Obligate symbiosis enables the host to acquire functions that improve its chances for survival the mutualist also benefits by securing its passage to the host progeny. Polydnaviruses may be optimal mutual-... 

Tanaka A et al., A symbiosis expressed non-ribosomal peptide synthetase from a mutualistic fungal endophyte of perennial ryegrass confers protection to the symbiotum from insect herbivory, Mol Microbiol 57 1036—1050, 2005. 

Muscatine L, Porter JW. Reef corals mutualistic symbiosis adapted to nutrient poor environments. Bioscience 1977 27 454-460. 

Many species of fungus grow in a close association with the roots of higher plants, in a mutualistic symbiosis known as a mycorrhiza. The mycorrhizal mutualism is very important to the uutritiou of the plant, because of the greatly enhanced access to uutrieuts that is provided, particularly to phosphate. 

Most of our knowledge on the interaction between UVR and mutualistic associations is based on studies on algal-invertebrate symbiosis, particularly on scleractinian corals and their endosymbiotic dinoflagellates, the so-called zooxanthellae from the genus Symbiodinium. Recently, the scientific literature on this topic has been extensively reviewed [33,62,63]. Here, I will only briefly highlight the most important aspects regarding potential population changes in this association as affected by UVR and review the information for other symbiotic relationships. 

There is considerable variation in the life cycles of different Epichloe species and in different host populations (White, 1988 Leuchtmann and Clay, 1997). In some species, stromata are formed invariably on all tillers of infected grass hosts, so that seed production is completely suppressed. This type of symbiosis represents the antagonistic extreme. Other species display both sexual and asexual cycles (balanced transmission) on different tillers of an infected plant, or on different subsets of individuals of a host population where seed transmission is often predominant. These associations are considered to be more mutualistic. In a third category, no stromata are formed on any of the infected plants, and seed transmission is the only means of dispersal. The latter group includes genetically distinct strains derived from sexual Epichloe spp. and all Neotyphodium species. 

Lewis DH. The relevance of symbiosis to taxonomy and ecology, with particular reference to mutualistic symbioses and the exploitation of marginal habitats. In Heywood VH, ed. Taxonomy and Ecology. London and New York Academic Press,... 

Plants and fungi often co-operates. The most well known example of such cooperation is the lichens where an algae and a fungus cooperates and build up the lichen body. Most land plants are also dependent on co-operation with plants. The cooperation takes place between the plant roots and the fungus growing out into the soil. In most cases the symbiosis is mutualistic in that both partners gain on the relationship but it is not necessary (as with the orchid mycorrhiza. 

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