6. EARLY BEHAVIOR PATTERNS IN THE 



AMPHIBIA 



PURPOSE: To determine the time of onset of various t jjes of response to external stim- 

 uli in amphibian embryos, and the succeeding appearance of integrated reactions. 



MATERIALS: 



Biological: Amblystoma, Hyla, Rana, and Bufo embryos from tailbud stages onward. 



Technical : Detwiler racing ring (see diagram) 



METHOD: 



Precautions : 



1. The staging of the embryos to be tested must be exact. Even within a single 

 stage there may appear individual differences in behavior. 



2. Repeated stimulation may lead to fatigue, particularly in the first phases of 

 response. Ample time must be allowed for recovery. In later stages the 

 stimulus (hair loop) must be applied to the same region of the body of all 

 larvae, preferably the dor so-lateral body wall, near the myotomes. 



3. The hair loop is the most satisfactory instrument for stimulation, being 

 pliable and least likely to damage the surface cells. A ball tip or flexible 

 glass needle may be used with caution. 



4. Eliminate any extraneous stimuli such as excessive heat, light, or anisotonic 

 media. 



Controls : The response of earlier and later stages will constitute one type of control, 

 but the embryos without any external (tactile) stimulation may be considered as 

 controls. 



Procedure : 



1. To become acquainted with the various types of response, select a group of 

 embryos such as Amblystoma stages #20 - #46 or Rana stages #16 - #33. 

 Place individuals in Syracuse dishes with the appropriate medium and allow 

 them to become adjusted to the new environment for several minutes. Under 

 low power magnification (binocular microscope) gently stimulate the various 

 embryos with the hair loop to elicite a response. Immediately classify the 

 response as one of the following: 



The chronological onset of behavior patterns in the amphibian larvae has 

 been studied by Coghill (1929) by DuShane and Hutchinson (1941). The 

 latter authors describe eight steps as follows: 



a. Premotile stage: no response to tactile stimulation. 



b. Myotomic response: a non-nervous response of myotomes as a 

 result of direct stimulation. Both response and recovery are slow. 



c. Early flexure: bending of the body away from the point of stimula- 

 tion, with rapid recovery. The initial evidence of this response 

 will be at the anterior end, but eventually the tail response will 

 bring it close to the head. 



d. Coil: the early flexure response when extended so that the tail 

 passes the head. The reaction is away from the point of stimula- 

 tion. There may appear a compensatory coil in the opposite di- 

 rection in later stages. 



e. S-reaction: undulatory contraction wave passing down the stimula- 

 ted side, but not vigorous enough to result in swimming progression. 



f. Early swiinming: forward progress as a result of the integration of 

 the S-reactions. The progression is never more than 3 body lengths. 



-111. 



