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Pacifists

 

The intention generator of a pacifist differs from that of a prey in that intention mate is enabled and the intentions escape and school are disabled. Piscatorial mating behaviors show great interspecies and intra-species diversity [Thresher1984]. However, two behaviors are prevalent: (i) nuzzling, where typically the male approaches the female from underneath and nudges her abdomen repeatedly until she is ready to spawn, and (ii) spawning ascent, where in its simplest form, the female rapidly swims towards the surface pursued by the male and releases gametes at the peak of her ascent. Moreover, courtship dancing is common in many species, albeit with substantial variation. Two frequently observed patterns are looping, in which the male swims vigorously up and down in a loop slightly above and in front of the female, and circling, in which the male and female circle, seemingly chasing each other's tail. Fig. gif shows photographs of natural fish displaying various mating behaviors [Thresher1984].

  figure1764

The complex mating rituals observed in the majority of animals are composed of a sequence of sub-behaviors (e.g. courting, spawning ascent) performed in a unique order. This is referred to as fixed action patterns by ethologists [Tinbergen1951]. We have implemented a mating behavior routine which simulates courtship looping, circling, spawning ascent, and nuzzling in sequence (see Fig. gif and Fig. gif(a)-(f)). This sequence is represented as a finite-state machine where each state is linked with a component behavior and has a boolean transition function. The transition function evaluates the associated behavior to see if it is completed, if positive, a transition is performed and the next component behavior is activated.

A male fish selects a mating partner based on the following criteria: A female of the same species is more attractive than one of different species, and closer females are more attractive than ones further away. A female selects a partner similarly, but shows preference to male fish size (stronger, more protective) rather than proximity. Suppose some fish i has selected a potential partner j then one of three things may happen:

Fish j's intention is not to mate:
Fish i approaches j and follows it around by performing the chasing-target behavior.

Fish j's intention is to mate but not with fish i:
If i is female it will choose another potential mate. Otherwise i is male and it will perform looping behavior in front of j for a certain amount of time. If j is suitably impressed during this time period then she will select i and the courtship sequence continues, otherwise i will discontinue looping and leave j to find a new potential partner. Fig. gif shows two examples where two male poker fish vying for the attention of a female by performing elaborate looping behavior.

Fish j's intention is to mate with fish i:
Courtship behavior starts with the male looping in front of the female while she hovers and bobs her head. The female's hovering and head bobbing is accomplished through motor control of her pectoral fins.

The male looping behavior is simulated by invoking chasing-target, with the `target' being a point in front of the female's head which moves up and down at a certain frequency. When the number of times that the male reaches the moving point exceeds a certain threshold he makes a transition from looping to circling behavior. Although the threshold is fixed, in practice the actual motions and duration of looping is highly unpredictable due to any number of reasons, such as looping being temporarily suspended to avoid a collision. If a new larger male joins in the looping display before the transition to circling, then the female may reject her initial partner and turn to the new fish. The rejected male will then turn away as described in the second case, above.

The circling behavior is implemented using chasing-target, where the target is the other fishes tail and is completed after the female has made a fixed number of turns. Next the spawning ascending routine is invoked whereby the female fish ascends quickly upwards and then hovers. She is followed by the male who uses chasing-target to follow her abdomen. In the nuzzling behavior routine, the male approaches her abdomen from below until he successfully touches it with his mouth. He then retreats, waits, and repeats the process. For such close contact to occur both fish's collision sensitivity region is set very close to their bodies.

   figure1800
Figure: Two males (larger) vying for the attention of a female.

  figure1806


next up previous contents
Next: Discussion Up: Artificial Fish Types Previous: Prey
Xiaoyuan TuJanuary 1996