Morphometric description of the wandering behavior in Drosophila larvae: a phenotypic analysis of K+ channel mutants.

Genetic dissection in Drosophila has provided insights into the molecular mechanisms of K+ channel subunits that underlie various physiological functions. The involvement of these subunits in animal behavior, however, is not well understood. Mutations of the Shaker (Sh), Hyperkinetic (Hk), ether a go-go (eag) and quiver (qvr) genes have been found to affect the IAK+ channel in different ways. The influence of individual K+ channel subunits on complex larval locomotion behavior can be quantified utilizing the computer-assisted Dynamic Image Analysis System (DIAS), a motion analysis system that allows morphometric assessments. Different aspects of larval locomotion in mutants of these four genes were contrasted to those modified by the Na+ channel mutations paralytic(ts) (para(ts)) and no-action-potential(ts) (nap(ts)). Genetic interactions among these K+ channel mutations and the counter-balancing effects of nap(ts) were studied in double and triple mutant combinations. An animal at the wandering stage was allowed to crawl spontaneously on an agar substrate to extract features of the crawling pattern by DIAS. To quantify locomotion, characteristic parameters, including time spent in forward locomotion and direction change, and stride length and frequency, were computed by DIAS. Sh, Hk, and qvr mutant larvae were found to spend more than 80% of their crawling time on forward locomotion (i.e., less than 20% in direction change), in contrast to 70-74% in wild-type larvae, and less than 60% in eag mutant larvae. The synergistic effects of double and triple K+ channel mutations on these parameters of locomotion suggest that each K+ channel subunit contributes in a specific manner to the efficiency of locomotion.