, Volume 158, Issue 3, pp 405-411

Mechanosensory cues control chasing behaviour of whirligig beetles (Coleoptera, Gyrinidae)

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Summary

  1. Male whirligig beetles,Gyrinus substriatus, G. marinus, chasing other beetles of the same species on the water surface were filmed from above. Their movements were reconstructed frame by frame.

  2. The pursuer's angular velocity (the turning response) is linearly related to the error angle between the pursuer's long axis and the target (Fig. 2c), with slopes varying between 5 and 15 [1/s]. The latencyT o of the turning response depends on the distance between target and pursuer. At short distances (1–2 cm)T o amounts to about 40 ms; with increasing distanceT o increases to up to 120 ms (Fig. 5).

  3. When the distance between the beetles is shorter than 4 cm, the forward velocity of the pursuer tends to increase with decreasing distance — presumably in a nonlinear manner (Fig. 4a).

  4. The leading beetle — usually a female — accelerates when the distance to the pursuer decreases. Its forward velocity is a nonlinear function of the distance (Fig. 4b).

  5. Evidence that chasing is guided by surface waves and not by visual cues comes from three observations: a) delays are distance dependent (Fig. 5); b) normal chases can be observed under infrared illumination (Fig. 6), and c) when the water surface is randomly disturbed, the animals do not chase.

  6. The function of chasing seems to be for males to catch females in order to mate. The distance dependent acceleration of leading females in a chase suggests that females might select males according to their manoeuvrability and swimming speed.