FISHERY BULLETIN: VOL. 72. NO. 1 



the presence of a large number of agents chemo- 

 tropic for male gametes exists (Machlis and 

 Rawitscher-Kunkel, 1963). only two have 

 been chemically characterized. Sirenin. the 

 active compound produced by the female 

 gametes of the water mold Allomyces, has been 

 isolated and characterized as an oxygenated 

 sesquiterpene (Machlis et al., 1966), and its 

 structure has been uniquely established 

 (Machlis, Nutting, and Rapoport, 1968). It is 

 active in attracting male gametes at 10"'"M. 

 The corresponding work from the marine field 

 resulted in the characterization of the active 

 substance released by the female gametes of 

 the brown alga Ectocarptis siUckIosk.'^ as allo- 

 cis-l-(cycloheptadien -2', 5'-yl)-butene-l (Miiller 

 et al.. 1971). The receptor sites on the male 

 algal gametes evidence a low level of specificity. 

 Many lower hydrocarbons, esters, alcohols, 

 and aldehydes, at higher concentrations, will 

 mimic the natural compounds in attracting 

 male gametes (Cook, Elvidge, and Bentley, 

 1951; Miiller, 1968; Hlubucek et al., 1970). 



Though many efforts to demonstrate a chemo- 

 tactic response by mammalian sperm to sub- 

 stances from eggs have yielded negative results, 

 such attraction does occur in marine forms. 

 Sperm of the thecate hydroids Cai)ipanularia 

 flexuosa and C. calceolifera respond to a sub- 

 stance issuing from the aperture of the female 

 gonangium. The response is species specific 

 (Miller, 1966). Observations by Dan (1950) 

 suggest the activity of a similar substance from 

 the eggs of the medusa Spirocodan saltatrix 

 on the sperm of this species. The first examples 

 of sperm chemotaxis in vertebrates are described 

 in pai)ers on fertilization in the herring Clnpea 

 by Yanagimachi (1957) and in the bitterling 

 Acheilognathus by Suzuki (1961). 



The attraction of the amoeboid form of the 

 slime mold Dictyostelium discoideum during 

 the aggregation phase which results in the 

 formation of a multicellular "slug" represents 

 the best studied protistan communication. The 

 attractant is cyclic adenosine monophosphate 

 (Konijn et al., 1968; Barkley, 1969). Pulses of 

 cyclic AMP radiate out through the soil 

 moisture at 5 min intervals from the center of a 

 growing aggregation. The gradient and the 

 pulse nature of the signal are maintained by 

 each inward streaming amoeba. Each amoeba 

 secretes a phosphodiesterase to break down the 

 cyclic AMP and, on sensing a pulse of cyclic 



AMP, emits its own pulse of cyclic AMP about 

 15 sec after receiving a signal (Cohen and 

 Robertson, 1971; Robertson, Drage, and Cohen, 

 1972). Bonner (1969) has indicated the likely 

 course of the evolution of this communication 

 in the social slime molds. Soil bacteria, the food 

 of the solitary predecessors of the slime mold 

 amoeba, secrete cyclic AMP. It is reasonable 

 to assume that a mechanism which initially 

 increased the feeding success of these amoebas 

 developed, due to selective pressure, the requi- 

 site high sensitivity of response to a chemical 

 signal necessary for aggregation. This capacity 

 then facilitated the evolution of the social 

 species. This is very close to Haldane's premise 

 of the evolution of chemical communication 

 prior to the evolution of metazoans. In further 

 support of Haldane's premise of the lineage of 

 hormones, after aggregation is complete 

 the "metazoan" slug phase migrates to the soil 

 surface and then certain cells differentiate into 

 stalk cells which will eventually support the 

 spore head. Cyclic AMP is apparently the 

 chemical signal for the developmental differ- 

 entiation of some cells into stalk cells (Bonner, 

 1970). 



The recent rapid growth of our understanding 

 of pheromone communication in insects was 

 founded on half a century of acute biological 

 observations which implicated the existence of 

 chemical messengers. The isolation and 

 chemical characterizations of a growing number 

 of pheromones, and the concomitant behavioral 

 studies, have provided the basis for our 

 appreciation of the role of chemical communica- 

 tion in the life cycle of many species. Among the 

 many recent reviews are those of Beroza (1970) 

 and Jacobson (1972). Electrophysiological 

 investigations of chemoreception in insects 

 have demonstrated that the receptor cells may 

 be divided into two groups, either "specialists" 

 or "generalists" (Yamada, 1970). Among the 

 "specialists" are the pheromone receptors and 

 the receptors for specific secondary plant sub- 

 stances that act as phagostimulants (Schoon- 

 aoven, 1968). While remarkable success has 

 been achieved in recording the response of 

 single receptor cells as well as the summed 

 receptor potential of all the antennal chemore- 

 ceptors (electroantennogram) these workers 

 have had to contend with a technical problem 

 inherent in studies with this material. Evalua- 

 tion of the response of a chemosensory organ 



