196 VISION 



BRAIN-BEHAVIOR RELATIONSHIPS 

 A Systematic Approach to Shark Behavior 



The design of an animal's central nervous sytem is highly correlated with the 

 characteristics of its sensory input and behavioral output. The specific 

 strengths and limitations of these two variables are reflected in the structure 

 and organization of the brain that processes them. Thus, information regard- 

 ing the sensory and behavioral capabilities of a particular species or class of 

 animals can be a helpful guide to its brain function. Similarly, detailed know- 

 ledge about an animal's brain structure can provide clues to its general 

 behavioral repertoire. 



Aronson (1963), in his review of the elasmobranch central nervous system, 

 underscored the potential usefulness of this inferential approach, suggesting 

 that it would hasten our understanding of shark behavior by providing a 

 theoretical framework for experimentation. Several years later Masai (1969) 

 became the first investigator to heed Aronson's advice. Starting with gross 

 neuroanatomical descriptions of 12 Pacific and Indian Ocean shark species, 

 he demonstrated correlations between their external brain morphology and 

 known behavioral characteristics. Masai's macroanalysis was limited, however, 

 by the generality of the neuroanatomical and behavioral data available to 

 him, and it must therefore be considered more intriguing than useful for pre- 

 cise prediction of either behavior or morphology. 



The opportunity now exists for a much more detailed and productive 

 analysis. The recent resurgence of elasmobranch research has produced a 

 wealth of sensory and behavioral information about sharks. In general, the 

 recent findings of sensory biology indicate that their sensory systems are 

 remarkably diverse and sensitive, compared to those of most other extant 

 animal species. For instance, we now know that a great many sharks have a 

 duplex retina, which is at least as sensitive as man's and can detect light from 

 all parts of our visible spectrum (Gruber 1975). Kalmijn (1966) has demon- 

 strated the presence of electroreceptors that are probably the most sensitive 

 in the animal kingdom. Similar examples of sharks' unusual sensory capabili- 

 ties can be found throughout this book. 



From a behavioral perspective, other studies have shown that sharks can 

 modify their responses in reaction to specific environmental stimuli. Al- 

 though the precise extent of this behavioral flexibility has not yet been de- 

 fined, substantial evidence indicates that sharks can learn certain types of 

 instrumental discrimination tasks as rapidly as most mammals (Aronson et 

 al. 1967, Graeber 1972, Graeber and Ebbesson 1972a, Kelly and Nelson 



Note: The opinions or assertions contained herein are the private views of the author 

 and are not to be construed as official or as reflecting the views of the Depart- 

 ment of the Army or the Department of Defense. The experimental work was 

 conducted at the University of Virginia and the Lerner Marine Laboratory 

 during 1970-1972. It was supported by National Eye Institute Grant 1 R01 

 EY00154, Career Development Award 1 K04 NS46292 to S.O.E. Ebbesson, and 

 the Stephen Hagan Research Fund. 



