Strength of forelimb lateralization predicts motor errors in an insect

Abstract

Lateralized behaviours are widespread in both vertebrates and invertebrates, suggesting that lateralization is advantageous. Yet evidence demonstrating proximate or ultimate advantages remains scarce, particularly in invertebrates or in species with individual-level lateralization. Desert locusts (Schistocerca gregaria) are biased in the forelimb they use to perform targeted reaching across a gap. The forelimb and strength of this bias differed among individuals, indicative of individual-level lateralization. Here we show that strongly biased locusts perform better during gap-crossing, making fewer errors with their preferred forelimb. The number of targeting errors locusts make negatively correlates with the strength of forelimb lateralization. This provides evidence that stronger lateralization confers an advantage in terms of improved motor control in an invertebrate with individual-level lateralization.

Keywords: handedness; limb control; locust; motor control; reaching.

Figure 1.

(a). Frequency distributions of movements initiated by the right forelimb (red) compared with the expected binomial distribution (p = 0.5) (blue). Asterisks indicate significant deviations from the binomial distribution determined by exact binomial tests. (b) Frequency distribution of reaching errors made by locusts (red) compared with the expected Poisson distribution (blue) (N = 80, n = 20).

Figure 2.

Strong forelimb preference is advantageous while gap-crossing. (a). Strongly biased individuals make fewer reaching errors than weakly biased individuals while gap-crossing. Error bars indicate the standard error (N = 80, n = 20). (b). The strength of an individual's bias is inversely related to the number of reaching errors (N = 80, n = 20). (c). There is no relationship between strength of bias and error rate in the non-preferred forelimb (N = 72, n = 20).