Succession itself may be, to a significant extent, a result of 

 dynamic integration (inhibition of neighbors or self-inhibition) of the 

 community, mediated by exocrines. This aspect of the significance of 

 free metabolites facilitates the development of new connections between 

 species and the occupation of new habitats. The exocrines indirectly 

 regulate the populations, marking out the path of migrants, facilitating 

 encounters between the sexes, unmasking prey, marking spots for settling 

 of larvae, etc. This indicator role of external metabolites is no less 

 significant than the "plus-minus interaction" reactions mentioned above. 



3.2 Pheromone Regulation 



The steroid compounds, the derivatives of which usually serve as 

 moulting and juvenile hormones, as well as sexual pheromones, are inherent 

 in all types of invertebrates. Pheromone regulation, in particular, is one 

 type of exocrine regulation. When in the process of evolution specialized 

 receptors developed on the one hand and, on the other hand, the hormones 

 of the donor began to be liberated into the environment, communication by 

 means of pheromones became possible (Kittredge, Takahashi, 1972). The 

 sexual pheromones have been most thoroughly studied to date. It is 

 possible that they appeared earliest in the course of evolution. Usually, 

 a sexual pheromone is a relatively species-nonspecific substance liberated 

 into the water, causing swarming of individuals of both sexes and subsequent 

 emission of reproductive products, e.g., in the polychete Platynereis 

 dumeril ii (Boilly-Marer , 1959). In the polychete Ophryotrocha puerilis , 

 sexually mature females liberate into the water a substance which stimulates 

 the development of male sexual characteristics in immature individuals. 

 The females of many nereids excrete species-specific substances which 

 accelerate the discarding of sperm by the males. The males of the polychete 

 Grubea c lavata produce a substance which facilitates emission of eggs; 

 without this substance, the eggs are resorbed in the bodies of the females. 

 The ability to attract males or females, preferably of only the same species, 

 is evolutionarily more progressive; this occurs, for example, in the 

 gastropod Littorina littorea (Dinter, 1974). 



The species specificity of sexual pheromones is relative and does 

 not assure complete reproductive isolation. For example, males of the 

 copepod Eurytemora aff inis demonstrate searching sexual behavior and 

 "chase" not only females of their own species, but also females of E. 

 herdmani and P seudodiaptomus c oronatus . However, the males of the latter 

 two species demonstrate sexual behavior only toward females of their own 

 species (Katona, 1973). The searching behavior of Calanus and Pseudocalanus 

 is equally expedient (Griffiths, Frost, 1976). 



Even in the decapods, the larval hormones and sexual pheromones have 

 still not completely biochemically diverged. The crustecdyson of the 

 decapods usually acts as a pheromone in combination with any other pheromone, 

 causing onset of the stage of maturation of the female. The females of 

 Homarus a mericanus , just after ecdysis, liberate a pheromone which suppresses 

 the aggressiveness of the males and provokes sexual behavior in them. 

 However, if females are forced to moult by removal of the eye stalks, the 



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