FISHERY BULLETIN: VOL 72. NO 1 



cannot exhibit chemotactic behavior. This 

 reasoning has been applied to all small marine 

 Crustacea including copepods. From the above 

 observations it is apparent that the reasoning 

 of Crisp and Meadows is invalid for Labidocera 

 and probably for other small Crustacea. The 

 critical dimension is the diameter of the circular 

 course, not the dimensions of the organism. A 

 circular swimming i)attern in a concentration 

 gradient of a stimulant would result in a sinus- 

 oidal variation in the signal intensity. Altera- 

 tion of the radius of curvature of the swimming 

 course in response to this sinusoidal input 

 would result in cycloidal progression in the 

 gradient. It appears from the observations 

 of the behavior of male L. jollae in the feeding 

 experiment that a threshold level of stimulant 

 will trigger a circular swimming pattern, if this 

 circular course results in the detection of a 

 gradient, the circular course will become a 

 curtate cycloid with the ratio of the major to the 

 minor radius being a function of the intensity 

 of the gradient. A frequent observation is a 

 doubling back. If several progressions of the 

 cycloid result in loss of the gradient signal (as 

 must frequently occur in a medium in which the 

 dimensions of the turbulent flow are of the 

 same scale as the swimming pattern), the 

 swimming plots indicate that the male Labido- 

 cera can effectively loop back through the area 

 where the signal was initially detected (Figure 

 3). These observations indicate some power of 

 spatial orientation and short term memory in 

 Labidocera. 



In crabs the male is attracted to the premolt 

 female. During this attraction phase he may 

 display a stance characterized by standing on 

 the tips of his dactyls and elevating his body. He 

 will seize the premolt female and place her 

 below his body. He will protect her during the 

 vulnerable molting period and they copulate 

 immediately after molting. Ryan (1966) demon- 

 strated pheromone communication in this inter- 

 action. Water from a tank containing a premolt 

 female Portunus sanguinolentus, when added to 

 a tank containing a male of this species, elicited 

 the premolt stance. Evidence that the pheromone 

 is released from the antennule glands was 

 provided by sealing these glands and noting the 

 absence of the stimulating factor. 



We have examined this pheromone com- 

 munication in the lined shore crab, Pachygrap- 

 sus crassipes. We isolated an active substance 



and found that it behaved chromatographically 

 like the molting hormone, crustecdysone. Pure 

 crustecdysone is active in stimulating all of the 

 precopulatory behavior of male lined shore crabs 

 from an early search behavior through the 

 display stance to seizing the female. The thresh- 

 old for stimulating the stance is 10''^ M 

 (Kittredge, Terry, and Takahashi, 1971). Con- 

 firmation of the identification has been obtained 

 by injecting tritiated crustecdysone into inter- 

 molt female Dungeness crabs (Cancer niagister) 

 and detecting its release as the females entered 

 premolt. Recently we have detected the presence 

 of two additional pheromones released by the 

 female lined shore crabs. Compound A is released 

 in addition to crustecdysone prior to molt. After 

 molting compound A is no longer released into 

 the water, but, if the female is held in isolation 

 from male crabs, a second compound, B, is re- 

 leased. It is likely that the postmolt female has a 

 different message to transmit. 



Evolutionary biologists concerned with the 

 inception of pheromone communication have 

 long been puzzled by a dilemma. This chemical 

 communication implies two new capabilities, 

 that to synthesize a messenger compound and 

 the ability to receive the message and trans- 

 late it into a behavioral response. The improb- 

 ability of the simultaneous occurrence of these 

 two de novo events suggests a stepwise sequence. 

 The observation that the molting hormone of 

 Crustacea can function as a sex pheromone 

 indicates that the primordial Arthropoda, 

 through an evolutionary sequence that resulted 

 in structuring the receptor site for the hormones 

 on chemosensory membranes, were able to 

 initiate pheromonal communication (Kittredge 

 and Takahashi, 1972). 



SUMMARY 



Evidence from the literature supports 

 Haldane's premise that chemical communica- 

 tion is the most primitive form of communica- 

 tion and thus the lineal predecessor of synaptic 

 transmission and hormone function. Trans- 

 ducers of environmental chemical information 

 have likely evolved in response to the metabolic 

 products released by their prey and by competi- 

 tive organisms. This coevolution of "natural 

 products" and the respective transducers has 

 existed from the earliest metabolic product that 

 happened to be a membrane irritant to the 



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