718 



ECOLOGY AND EVOLUTION 



interspecies supraorganism about as well 

 integrated as parts of an individual organ- 

 ism, with selection operating on the system 

 as a functional whole, and favoring greater 

 living efficiency for the mutualistic partners 

 (Emerson, 1947; see also p. 721). 



It is noteworthy that this mutualism, at- 

 tained and evolved over great periods of 

 time, has nevertheless been lost in the evo- 

 lution of the most advanced termites (Ter- 

 mitidae). Circumstantial evidence, partic- 

 ularly from zoogeography, points to the 

 origin of the family Termitidae by Creta- 

 ceous times. These higher termites have 

 not only diverged into the largest number 

 of species (1333 described by 1947), but 

 they are without question the most success- 

 ful termites in tropical regions the world 

 over and have advanced far beyond their 

 primitive relatives in the integration of 

 their social systems and in their remark- 

 able nest-building instincts. Although many 

 feed on leaves, grass, fungi, and animal 

 excrement, they also feed on cellulose in 

 the same hard wood that may also be oc- 

 cupied by the flagellate-harboring termites. 



The physiology of digestion has not been 

 studied in these advanced termites, but 

 they must have some ability to digest cel- 

 lulose without the assistance of intestinal 

 flagellates, which are lacking in their intes- 

 tines. Hungate (1938) reports that the ter- 

 mite, Zootermopsis angusticollis (Hodoter- 

 mitidae), digests one-third of the total 

 amount of wood digested without the aid 

 of its protozoa. Possibly this ability has 

 been expanded in the Termitidae. 



Thus, the flagellate-termite mutualism 

 may have been an inhibiting factor in the 

 evolution of higher social functions, and 

 once rid of it, a great advance and fur- 

 ther adaptive radiation of the social sys- 

 tem could take place. Further progressive 

 evolution is more in the direction of con- 

 trolling the intrasocial environment (p. 

 672) than an adaptation toward diverse 

 external habitats. Much more information 

 is needed before valid conclusions may be 

 drawn, but it appears that in this instance 

 interspecies mutualism is less efficient than 

 intraspecies internal organic adaptation and 

 social adjustment. 



It may be possible that evolutionary 

 mechanisms leading to adaptive modifica- 

 tion may be speeded up when operating 

 through a single germ plasm, rather than 



through the two or more germ plasms in 

 volved in a mutualistic association. If this 

 be true, it may help to explain the general- 

 ization that the integration of the individ- 

 ual organism and of the intraspecies popu- 

 lation is far more advanced than the in- 

 tegration of interspecies systems in the 

 community. 



The evolution of the ants, remarkably 

 convergent to that of the termites, had no 



Fig. 255. Perinthus vestitus, a staphylinid 

 synoekete in the nest of the termite, Nasuti- 

 termes octopilis, in British Guiana. 



interspecies mutualism to start with, but 

 evolved extreme intraspecies population 

 integration. Both the more advanced ant 

 and termite populations, with a degree of 

 social control of their habitats, have set the 

 stage for the evolution of a mutualistic re- 

 lation between the social insects and many 

 other organisms (p. 253). The cultivation 

 of fungi has already been discussed (pp. 

 713, 714). The relations of the myrmeco- 

 philes and termitophiles** to their hosts af- 

 ford another illuminating example of 

 mutualism. 



* We here refer to organisms living in the 

 galleries with ants and termites by the estab- 

 lished terms, myrmecophiles and termitophiles, 

 though regretting the anthropomorphism (p. 

 8). Organisms occupying the nests of these 

 social insects are called myrmecocoles or ter- 

 mitocoles, including those forms not living in 

 the galleries of the hosts (O. Park, 1929). 



