Head-Arresting System

Recent Study:

Scientists have general interest in the arrester system because of the microtrichia-covered surfaces which provide fixation via high friction contact between the interlocked structures.

Four sets of correlating microtrichia types occur in various head-arresting systems (Fig. 1) (Gorb, 1999):

• (a) Hook-like or cone-shaped microtrichia and mushroom-like microtrichia. (Sympecma, Libellulidae)

• (b) Cone-shaped microtrichia and thin seta-like microtrichia. (Aeshnidae)

• (c) Mace-like microtrichia on both surfaces presumably acting like an elastic snap. (Lestinae)

• (d) Smooth surface and compressed microtrichia. (Gomphidae, Petaluridae)

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There are many behavioral instances in which the arrester system is involved. Electrophysiological recordings of fight muscle activity with simultaneous photodiode registrations of microtrichia movements showed that the release of the head was synchronized with the initiation of wing muscle activity, but only when the fight was elicited by substrate removal or a wind pulse (Gorb, 1999). In contrast, the head-arrester system can work independently of the wing apparatus in at least two behavioral situations: while eating or while flying in tandem, when a dragonfly shows wing muscle activity even while the head is arrested.

Figure 1. Schemes of corresponding frictional surfaces occurring in odonate head-arrester systems (Gorb, 1999).

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As depicted in Figure 2...

The head typically arrested during the following activities:

• Tandem sitting (1)

• Perching (2)

• Feeding (4)

• Flying with captured prey (5)

• Tandem flight (female only) (7)

The head is typically free during the following activities:

• Saccadic head movements during ambushing (3)

• Patrolling/High-speed maneuvering flight (6)

• Tandem flight (male only) (7)

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Figure 2. Scheme of diverse behavioral situations when the head is free or fixed by the arrester system. Shaded quadrants indicate that the head is fixed. Clear quadrants indicate that the head is free (Gorb, 1999).

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Conclusion:

It is believed that the evolution of the arrester system was connected to the evolution of the dragonfly reproduction process, which is one of the most unusual among insects due to specialized male copulative organs and tandem postures during copulation. An additional selective pressure might have been the evolution of dragonflies as active flying predators that often feed on the wing. The arrestor would prevent head disturbances and stabilize gaze while in flight.