Drosophila- cactus-yeast

Glycosides are elaborated by a large number of plants, and within families are often diversified in structure considerably. This diversification seems correlated with the coevolution of groups of plants with specialist herbivores. Examples are found In the Passiflora-Heliconius interaction and in the association of Pieris and Brasslca The same phenomenon has recently been determined to occur in the Drosophila-cactus-yeast coevolved system (5,6) and may be present In the Danaiid-AscIepias and other systems (7). 

Gibson, A.C. (1982). Phylogenetic relationships of Pachycereeae. In Barker, J.S.F., Starmer, W.T. (eds.). Ecological Genetics and Evolution the Cactus-Yeast-Drosophila Model System, pp. 3-16. Sydney Academic Press. 

Fly adults and larvae prefer yeast to bacteria as food (Vacek et al., 1985). There are numerous benefits to Drosophila from the presence ofyeast. Some cactus tissue does not provide a complete diet for the Drosophila that breed in it (Starmer, 1982). This is usually because the cactus tissue is deficient in nitrogen resources. Yeast are protein-rich and complete the fly s diet. Some yeast reduce the toxicity of the host tissue for the fly by metabolising toxins. Experiments that demonstrate a biculture effect have demonstrated that, except for the metabolism of specific toxins by specific yeast, the benefits supplied by yeast can usually be supplied by any of several yeast species. A biculture effect is an increase in some fitness component (larval or pupal viability, reduction in development time, increase in size at eclosion) for flies reared with two yeast species compared with the midpoint performance of the flies on the relevant monocultures (Starmer and Aberdeen, 1990). The reason for the effect is not known but is probably the result of amino acid, lipid or vitamin complementarity. Ganter (2006) reviews a number of cactophilic Drosophila-yeast... 

This effect is tested more explicitly in a second data set of yeast from cactus rots and the flies found on the same rots. In this set, the yeast from individual rots and individual adult flies are compared for two different species of Drosophila from different host cacti and different locales in the Sonoran Desert (Table 8.9). Also... 

Phytosterols in the various cactus species exist as glycosides or saponins. Yeasts found in the rotting cactus plants hydrolyze these saponins and make the phytosterol agly-cones available to the insects (Spencer, 1987). Both 24/ -and 24S-methyl groups occur in phytosterols. Individuals of Drosophila melanogaster utilize both 24/ - and 24S-meth-ylcholest-5,7-dien-3p-ol (37), whereas those of D. pachea prefer the 24S-isomers and those of >. mojavensis prefer the 24/ -isomers (Rees, 1983). 

Interactions of Cactus Species, Yeasts, and Drosophila Benzylisoquinoline Alkaloids... 

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