KREKORIAN, SOMMERVILLE, and FORD: LOBSTER BEHAVIORAL INTERACTIONS 



Table 1. — Experimental paradigm for social interaction study between Homarus americanus, Panulirus interruptus, and 



Cancer antennarius 



responding to the stimuli) were both recorded in 

 the predetermined categories described below. In 

 addition, the amount of locomotion displayed by 

 subjects, their location in the tank with respect 

 to the wall, and the number of individuals in 

 shelters, when present, were recorded. The 

 behavioral action patterns of P. interruptus, H. 

 americanus, and C. antennarius described 

 by previous workers were employed in this study 

 where possible. 



I. The following categories were employed for 

 the actor: A) Approach, B) Threat, C) Attack, 

 and D) Social contact. These terms are 

 defined, in most cases, separately for each 

 of the three species considered. 



A) Approach — Movement of the actor 

 directly toward a moving or stationary 

 heterospecific. During approach, the 

 actor compensates for changes in the 

 direction of movement of a moving 

 heterospecific so that the actor is always 

 moving directly toward the heterospeci- 

 fic. No implication of function is 

 intended in our use of the term 

 approach. 



B) Threat 



1) Homarus americanus 



Meral spread — In this study only 

 the display described by Schrivener 

 (1971) as meral spread was re- 

 corded as threat. Schrivener's 

 description of this behavior is as 

 follows: "During meral spread, the 

 lobster stands on its walking legs 

 with its body raised from 4 to 5 

 cm off the bottom. The abdomen is 



usually fully extended, with the 

 cephalothorax angled slightly up- 

 wards from the horizontal. The 

 chelae are held about 5 cm off the 

 bottom spread wide apart with 

 their long axes pointing directly at 

 the opponent. Some animals hold 

 the claws fully extended, wide 

 apart, and as high off the bottom 

 as possible." 

 2) Cancer antennarius 



Lateral Merus Display — The 

 merus of the chelipeds is extended 

 laterally, with the distal end of the 

 meri raised and extended some- 

 what anteriorad. The higher the 

 intensity of the display, the greater 

 is the lateral spreading of the 

 chelipeds (Schone, 1968; Wright, 

 1968). Wright (1968) subdivides 

 the Lateral Merus Display into 

 three subtypes based on the 

 position of the chelae. These are: 

 1) the High-Intensity Merus Dis- 

 play in which the chelae are un- 

 flexed (maximum adduction) with 

 the tips held laterally; 2) the Mid- 

 Intensity Merus Display in which 

 the chelae are half flexed so that 

 the tips point forward; and 3) the 

 Low-Intensity Merus Display 

 in which the chelae are flexed, with 

 their tips medial. All intensities of 

 the meral spread were observed, 

 but these were simply recorded to- 

 gether as threat in our study. 



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