Circuits for escape II. Giant axons and the %22rare enemy%22

Circuits for escape II. Giant axons and the %22rare...

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Circuits for escape II: giant axons and the “rare enemy” effect.
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2 Tipulidae Syrphidae Sarcophagidae Tabanidae
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3 no giant axons giant axons
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“a predator with a comparatively small impact on prey relative to more common predators may develop and maintain a strategy that exploits the prey's behavior - and by extension its nervous system.” “Rare” predator effect
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Painted Redstart ( Myiborus picta ) (family Parulidae) USA Willie Wagtail ( Rhipidura leucophrys ) (family Rhipiduridae) Australia Some birds have convergently evolved the strategy of “flushing” insects by exploiting their giant axon- mediated escape behavior.
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Nematoceran (no giant fibers) = 21% Brachyceran (giant fibers) = 71% The type of insects that redstarts caught when forging were sampled when they returned to their nests. The majority were those with giant fibers!! Note: they did not report on the abundance of each type of insect in the local habitat to test whether the birds were actually taking more of one type than another or sampling randomly.
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Redstarts flush insects by flashing high contrasting tail and wing patches and pivoting about. Jablonski & Strausfeld, 2000
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Pivoting movements and bright patches are more effective at flushing insects Flies jump farther when suddenly exposed to models of birds that pivot and/or that have high contrast patches on the tail or wings. Jablonski & Strausfeld, 2000
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“We propose that redstarts have evolved visual displays that specifically exploit the tuning properties of brachyceran giant fiber escape circuits - neuronal pathways that evolved some 100–70 million years before the appearance of flush-pursuing birds. We also propose that escape responses might have shaped the evolution of plumage and motor actions typical of flush-pursuers.”
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This same strategy of co-opting a prey’s stereotyped (and therefore predictable) giant axon-based escape strategy against it has evolved in a fish-eating snake!!
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Parallel Evolution of co-option of giant neuron-mediated escape by a snake The tentacled water snake waits until a fish swims into the U” shaped space between its body and head (0.0 ms). It makes a slight movement of its body toward the fish (red arrow) thereby “faking” a lunge toward the fish which triggers a Mauthner cell-mediated escape response (15 ms), and meanwhile rapidly places its open mouth where it “anticipates” the escape reflex will move the fish (24 ms), and gobbles him up!
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