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stepping patterns of tarantula

# stepping patterns of tarantula - J Exp Biol(1967 47 133-iSi...

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J. Exp. Biol. (1967), 47. 133-iSi 133 With 8 text-figures Printed in Great Britain STEPPING PATTERNS IN TARANTULA SPIDERS BY DONALD M. WILSON* Department of Molecular Biology, University of California, Berkeley (Received 6 March 1967) INTRODUCTION The limb movements of many multilegged animals occur in metachronal sequences, often sequences running from posterior to anterior. Such sequences are not so con- spicuous in animals with few legs. However, for the walking of certain insects with variable gaits it has been possible to produce a descriptive model based on meta- chronal rhythms with stepping pattern varying with frequency (Wilson, 1966 a). This same model can be extended to animals with four (or more) pairs of legs. For simplicity one can assume that legs on opposite sides of the animal always alternate and then make the following formulation for legs of one side. Number the legs 1, 2, 3, and 4, from front to back. Then the basic stepping sequence in the model is 4321. Again for simplicity, hold the interval between 4 and 3, 3 and 2, and 2 and 1 constant. Vary the repetition rate of the whole set. At low repetition rates the stepping pattern is (a) 4 3 2 1 4 3 2 1. The wavelength, or number of segments between legs having the same posture, is greater than three segments and no two legs step at the same time. If the cycle interval is decreased a state is reached in which legs 1 and 4 step synchronously. (6) 4 3 2 1 4 3 3 2 (14) 3 2 (14) 3 The length of the metachronal wave is three segments. Greater reduction of the cycle interval produces further overlap of the basic sequences. (c) 4 3 2 1 4 3 2 i 4 3 2 3 241 3 3 2 Th e next stage of overlap produces («*) 4 3 2 1 4 3 4 3 2 1 (24) (13) (13) in which the wavelength is two segments and even-numbered legs alternate exactly with odd-numbered legs. If legs on the other side are just in antiphase then the animal • Address after July 1967: Department of Biological Sciences, Stanford University, California.

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134 DONALD M. WILSON moves on alternating tetrapodal diagonal sets of legs (see later). Further compression of the sequences gives a new pattern: (e) 4 3 2 i 4 3 ? I 4 2 31 42 31 and yet others: (/) 4 3 2 1 2 3 (14) 2 3 (14) 2 3 (g) 4 3 2 1 23 4 123 4 4 12 3 and finally the absurd pattern of one wavelength one segment is achieved: (A) 4 3 2 1 (1234) ("34) A gait may be denned for one side as any pattern arising from the repetitive or cyclic use of legs in which each leg is used exactly once per cycle. Then if one excludes cases with synchronous leg movements, the six possible gaits for four legs are 1 412 3 2 431 2 3 4 1 3 2 4 421 3 5 423 1 6 432 1 where 4321 equals 3214,2143, and 143 2, since a cycle has no especially significant starting point. The model presented above thus generates four of the six possible orders, namely 4321 = (a), 4132 = (c), 4231 = (e), and 4123 = (g). Only the orders 4312 and 4213 cannot be generated in this way. In addition the model generates the patterns with some synchronies— (b), (d) and (J) —which are possible real gaits, but since perfect synchrony between legs seldom occurs in the data from the animals used in the present study we can dispense with these patterns for most of the discussion.
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stepping patterns of tarantula - J Exp Biol(1967 47 133-iSi...

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