Mutualists

Associations between endosymbiotic bacteria and the Homoptera, Blattaria, and Coleoptera are common. One of the best known is that between Biicli-nera and the aphids (149,150). Both partners are obligate and mutualistic symbionts, and the aphids cannot survive without the bacteria (150). Buclmera, in fact. 

Tyagi RD, Tran FT, Polprasert C. 1988. Bioconversion of lignosulphonate into lignin and hydrogen sulfide by mutualistic bacterial system. Journal of Microbial Biotechnology 3 90-98. 

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... 

Martens EC, Heungens K, Goodrich-Blair H. Early colonization events in the mutualistic association between Steinemema carpocapsae nematodes and Xenorhabdus nematophila bacteria. J Bacteriol. 2003 185 3147-3154. 

Sicard M, Ramone H, Bran N-le, Pages S, Moulia C. Specialization of the entomopathogenic nematode Steinernema scapterisci with its mutualistic Xenorhabdus symbiont. Naturwissenschaften. 2005 92 472-476. 

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-... 

Stachowicz JJ, Hay ME (1996) Facultative mutualism between an herbivorous crab and a coralline alga advantages of eating noxious seaweeds. Oecologia 105 377-387 Stachowicz JJ, Whitlatch RB (2005) Multiple mutualists provide complementary benefits to their seaweed host. Ecology 86 2418-2427... 

Schardl CL, Epichlo efestucae and related mutualistic symbionts of grasses, Eungal... 

Faeth SFi, Are endophytic fungi defensive plant mutualists , Oikos 98 25—36,... 

Tudzynski B, Fungal phytohotmones in pathogenic and mutualistic associations, in Carroll GC, Tudzynski B (eds.). The Mycota. A Comprehensive Treatise on Fungi as Experimental Systems for Basic and AppHed Research. V. Plant Relationships. Part A., Springer-Verlag, Berlin, Germany, pp. 167—184, 1997. 

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. 

We also need a better understanding of mutualism. Undoubtedly, many mutualistic associations exist of which we are not aware. For example, might associated microbes produce chemicals that help plants defend their space ... 

Essential oils are especially important in mutualistic relationships between plants and insects such as pollination and seed and fruit dissemination (37,45,77-79). In these instances essential oil components serve as attractive substances for the plant. These compounds vary widely in composition but contain most of the chemical types described above. In some cases even volatile amines and skatole are involved, as in the pollination of Sauronatum guttatum (Araceae) (80). 

Defense is a further category in which plants employ food rewards to acquire protection by arthropod mutualists. The provision of food sources allows plants to recruit or sustain predators or parasitoids, which, in turn, can provide protection against herbivory. The plant-derived food structures involved in indirect defensive interaction can be divided in two main groups food bodies and extrafloral nectaries. 

In the case of food bodies, the primary mechanism of induction might be food body removal. Risch and Rickson (1981) showed that the production of unicellular food bodies by Piper cenocladum is stimulated by the presence of the mutualist ant Pheidole bicornis. When ants are present, the plant produces 30 times as many food bodies as control plants. Similar effects had previously been reported for other types of food bodies (Carroll and Janzen, 1973). In P. cenocladum, a clerid beetle exploits this relationship. Their larvae are also able to stimulate food body production in the absence of the ants (Letoumeau, 1990). 

In addition to these empirical studies, there is indirect ecological evidence for the defensive function of extrafloral nectaries. Several studies have reported correlations between the abundance of plants with extrafloral nectaries and ant abundance (Pemberton, 1998 Rico-Gray et al, 1998). Bentley (1977) and Rickson (1977) showed that plants may lose extrafloral nectaries in ecosystems void of mutualist ant species. 

Plant bodyguards mutualistic interactions between plants and the third trophic level. In Functional Dynamics of Phytophagous Insects, ed. T. N. Ananthakrishan, pp. 207-248. New Dehli Oxford and IBH Publishing. 

Bronstein, J. L. (1994). Conditional outcomes in mutualistic interactions. Trends in Ecology and Evolution 9 214-217. 

As an adjunct to the concept of co-evolution, the New Function Hypothesis proposed by Clay (1988) suggests that pathogens may evolve towards a mutualistic relationship with their hosts through the appearance of pathogen strains with beneficial... 

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