714 



ECOLOGY AND EVOLUTION 



chewed up and inserted in the fungus gar- 

 den. Manuring ceases, and the fungus is 

 now entirely cultivated by the workers. The 

 spherical bromatia are harvested and used 

 for food by the entire colony. The larvae 

 are fed with the bromatia, and the ants 

 eat little food other than the fungus. 



The knowledge of the taxonomy and 

 phylogeny of the fungi cultivated by the 



transported and "planted" by the repro- 

 ductive pair is not known. The fungus spe- 

 cies are usually not specific for the termite 

 species or genera, and are also free-living, 

 so that it is doubtful whether the fungus 

 has evolved any mutualistic adaptations. 

 Heim (1940) says that some species of 

 fungi {Collybia albuminosa) are found only 

 in termite nests and are dependent upon 



Fig. 253. Leaf-cutting ants (Atta) carrying portions of leaves to their subterranean nest, 

 where fungus is cultivated on a substrate of chewed leaves. Note the individual at the left, 

 riding back to the nest on the leaf carried by another worker. (Photograph by Ralph Buchs- 

 baum. ) 



attine ants is not sufiicient to establish their 

 reciprocal evolution with the ants. 



The fungus-growing termites (Macro- 

 termitinae) cultivate fungi on the excre- 

 ment of the workers. The clay like excre- 

 ment is built into rather elaborate struc- 

 tures or gardens with involutions that pro- 

 vide a large surface with abundant aera- 

 tion. Ventilation tunnels often connect the 

 fungus gardens with the surface wall of the 

 mound, but do not penetrate into the open 

 air (Grasse, 1937). Small spherical bodies 

 develop from the myceHum and are har- 

 vested and fed to the reproductive pair and 

 to the nymphs by the workers. Adult work- 

 ers and soldiers feed almost exclusively on 

 cellulose contained in grass, leaves, and 

 wood. The means by which the fungus is 



termites for their existence. If this be true, 

 some degree of mutualism has evolved in 

 both fungus and termite species. 



Many plants, for example, the burdock 

 (Arctium minus), have evolved adapta- 

 tions whereby the seeds cling to the fur 

 of mammals and are thus dispersed (p. 

 251). Both hooks and adhesive surfaces 

 have evolved (Ridley, 1930). These adap- 

 tations are as distinct as the numerous ad- 

 justments for seed dispersal by wind and 

 by water. There is no indication, however, 

 that the mammal in any way benefits by 

 the clinging seed in its fur. 



On the other hand, fruits, by their edi- 

 biUty, fragrance, changing color, and posi- 

 tion, induce birds and other animals to 

 transport mature seeds (Ridley, 1930; 



