Imprecision in the behavior ofLeptomorphus sp. (Diptera, Mycetophilidae) and the evolutionary origin of new behavior patterns

Abstract

The hypothesis is advanced that nervous control of behavior is imprecise and that some behavioral evolution involves a selective pruning of variants similar to that which occurs in embryological canalization. Variations documented in many previous behavioral studies may have been selectively advantageous and therefore do not provide appropriate tests for the imprecision hypothesis. The spinning behavior of individual larvae of the fly Leptomorphussp. satisfies the conditions for a sufficient test. As predicted by the hypothesis, the behavior is extremely variable at several levels of organization (attachment sites, movements between sites, sequences of up to four movements, pairs of sequences, and entire trains of spinning behavior between movements forward), even when the larva is on a relatively uniform substrate. The temporal clumping of different variations, the combination of responses to large discontinuities and lack of responses to smaller discontinuities, and the improbability of selection favoring such a wide variety of responses all suggest that some of the variation in high as well as low levels of organization of behavior does not represent adjustments to irregularities in the substrate. Larvae can reduce or repress this behavioral variability, as stereotypy increased at several levels of organization when larvae encountered large irregularities in their environments. Variation in spinning by Leptomorphussp. larvae may thus be due to “imprecision” in the nervous control of their behavior.