In the Light of Evolution Volume VI: Brain and Behavior (2013) / Chapter Skim
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13 Evolution of Brains and Behavior for Optimal Foraging: A Tale of Two Predators--Kenneth C. Catania
13 Evolution of Brains and Behavior for Optimal Foraging: A Tale of Two Predators--Kenneth C. Catania
Pages 229-250
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From page 229... ...
Optimal foraging theory suggests that the star evolved for profitably exploiting small invertebrates in a competitive wetland environment. The tentacled snake's facial append ages are superficially similar to the mole's nasal rays, but they have a very different function.
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However, the most interesting finding from the tentacled snake is its remarkable ability to use fish escape responses to its advantage (Catania, 2009, 2010)
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In each case, an integrative approach combining neurobiological, behavioral, and ecological facets is necessary to best understand the sensory system. In the spirit of such an approach, it is hoped that the reader will view Movies S1, S2, S3, S4, S5, and S6 of Supporting Information in Catania (2012)
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(F) Frames from high-speed video illustrate a saccadic star movement to a small prey item (outlined in red)
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. STAR REPRESENTATION IN THE CNS The segregated nature of the mole's sensory rays suggested that there could be a corresponding modular representation within cortical and subcortical areas, which was found for the whiskers of rodents (Woolsey and Van der Loos, 1970; Van Der Loos, 1976; Ma, 1991)
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(B) Anatomically visible star representation at the trigeminal level with each ray representation labeled.
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What can star-nosed moles do that other moles cannot? A likely answer comes from considering the star-nosed mole's behavior and environment in the context of optimal foraging theory.
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is equivalent to E/(Ts + Th) , where E is the energy gained from a prey item, Ts is the time spent searching for prey, and Th is the time spent handling prey (handling time includes pursuit, capture, and consumption of prey)
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. For most handling times, small prey items are minimally profitable.
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, suggesting that nervous system processing of touch lags behind the rapid star movements. To put short handling time in context, it is important to consider profitability for larger prey items.
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clearly show that star-nosed moles are more efficient at exploiting this resource. Thus, numerous small Eimer's organs, modified teeth integrated with the star, and many CNS specializations seem to be adaptations that help to reduce handling time (Th)
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(E) An early embryonic star-nosed mole nose looks strikingly similar to an adult coast mole nose.
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The adult coast mole nose has a striking resemblance to an early embryonic star-nosed mole nose (Fig.
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This idea and others have been suggested for over a century, but only recently, experiments have been conducted to investigate various possibilities. The function of the tentacles was explored using a multifaceted approach that included anatomical investigation of their internal and external anatomy, electrophysiological recordings from the trigeminal afferents and the optic tectum, and behavioral observation based on slow motion analysis of high-speed video recordings under visible or infrared lighting (Catania et al., 2010)
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. Receptive fields for neurons in the superficial layers of the tectum form a visuotopic map of the contralateral eye, with superior fields represented dorsally, inferior fields represented laterally, nasal fields represented rostrally, and temporal fields represented caudally.
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However, a number of observations suggest that tentacled snakes rely most heavily on visual cues to guide their strikes when possible (Catania, 2009, 2010; Catania et al., 2010)
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(A) A striking tentacled snake takes roughly 25 ms to reach a nearby fish (Catania, 2012, Supporting Information, Movie S4)
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that fish are partially swallowed during strikes and the later observation in the work by Murphy (2007) that some fish disappeared completely in a single video frame when strikes were filmed at 30 frames/s, suggesting minimal or even nonexistent handling times (Murphy, 2007)
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[Note: Figure can be viewed in color in the PDF version of this volume on the National Academies Press website, www.nap.edu.] BORN KNOWING The observation that tentacled snakes can startle fish and predict their future movements raises the question of whether this strategy is an innate ability or learned through a lifetime of striking at escaping fish.
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From page 248... ...
However, the most surprising finding for this species is their ability to startle fish toward strikes, thus taking advantage of the neural circuitry that mediates obligatory fish escape responses. Tentacled snakes provide a concrete example of the
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From page 249... ...
Evolution of Brains and Behavior for Optimal Foraging / 249 rare enemy effect, which suggests that uncommon predators may tap into prey behavior that is usually adaptive. These various discoveries in two divergent species illustrate the necessity of integrating neurobiological, behavioral, and ecological approaches to best understand adaptations.
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