MULTIPLE-FACTOR AND SYNERGISTIC STRESSES 737 



REPRODUCTIOIM 



Asexual reproduction in an intertidal zone sea anemone, Hali- 

 planella luciae, was influenced by exposure to both fluctuating 

 temperature and immersion (Johnson and Shick, 1977). Significantly 

 different numbers of fissions were observed under these various test 

 conditions. 



Other reproductive phenomena can be influenced by 

 environmental-factor interactions. De Vlaming (1975) reported that 

 at any time during the year a long-photoperiod warm -temperature 

 regime stimulated gonadal development to the prespawning condi- 

 tion or induced spawning in the cyprinid fish Notemigonus 

 crysoleucas. Neither photoperiod nor temperature acting alone 

 would stimulate final gonadal maturation. Although spermatocyte 

 formation, proliferation, and the early stages of vitellogenesis 

 occurred independently with respect to imposed conditions, final 

 gonadal maturation and the rate of gametogenesis depend on specific 

 environmental conditions. Rouquette (1976) reported that tempera- 

 ture and light influenced ovary development, formation of periodic 

 sexual characteristics, and egg laying of the crab Pachygrapsus 

 marmoratus. 



BEHAVIOR 



Environmental-factor interactions also influence the behavior of 

 many species of organisms. Both the haird-shell clam Mercenaria 

 mercenaria and the Atlantic surf clam Spisiila solidissima experience 

 extremes of temperature and dissolved oxygen during their bur- 

 rowing activity. For each species a thermal zone of optimum activity 

 was determined; above and below this zone burrowing declined with 

 changing temperature. Exposing Mercenaria to low oxygen condi- 

 tions (<1 mg/liter) for 3 weeks did not severely impair burrowing 

 (Savage, 1976). Gallepp (1977) observed the behavior patterns 

 (filtering, withdrawal, and case building) of larvae of the caddisfly 

 Brachy centrus under different combinations of temperature, food 

 availability, and water velocity. He demonstrated that temperature 

 and food availability were more important than water velocity in 

 influencing behavior. The interaction of these three factors largely 

 controls the bioenergetic state of the larvae and thus influences the 

 behavior of this species. 



Another behavioral response, thermal preference, has been 

 studied in relation to thermal acclimation and salinity in the fishes 



