NS

Neural Basis of Behavior & Phenotypic Plasticity – Key Vocabulary

Phenotypic Plasticity & Polyphenism

  • Definition: Phenotypic plasticity = capacity of one genotype to express >1 phenotype depending on environmental cues.
    • Graphical variants (Fig. 3.28)
    • Lots of variation around a single mean
    • Minimal variation around a single mean
    • Discontinuous variation with two or more means
  • Relationship hierarchy
    • Polyphenism = special case of phenotypic plasticity (discrete morphs)
    • May or may not underlie observed phenotypic variation; some variation is non-plastic.
  • Zero plasticity condition: genotype → one phenotype regardless of environment.

Categories & Examples of Polyphenism

  • Density-dependent polyphenism
  • Socially-induced polyphenisms (common in fish)
  • Food-induced polyphenisms
  • Predator-induced polyphenisms
    • Triggered by predator kairomones (chemical cues released by predator)
    • Empirical data
    • Rotifer spines: \frac{18}{59} spined morphs vs typical
    • Barnacle aperture rotation: \frac{11}{43} rotated vs typical
    • Mollusc thickened, “toothed” shell requires ≥50\% loss of typical morphs before predation stops
    • Carp body depth expanded: \frac{30}{100} deep-bodied under predation

Behavioral Polymorphism & Supergenes

  • Behavioral polymorphism
    • Loss of ability to plastically regulate behavioral roles according to environment.
    • Leads to fixed behavioral morphs within same species.
    • Frequently controlled by supergenes.
  • Supergene (review)
    • Region of DNA containing many linked genes that collectively influence a complex trait (e.g., behavioral phenotype).
    • Tight linkage prevents recombination → preserves adaptive gene combinations.

Interactive Poll Prompts (lecture engagement cues)

  • Spectrum of foraging behaviors in rodents → ask students “What type of phenotypic plasticity is this?” (continuous/gradient type)
  • “Describe a supergene.”
  • “Give an example of other instincts.”
  • “Write a type of stimulus an organism may detect.”
  • Emotional check-in (“In one word describe how you feel about week 1”).

Neural Basis of Behavior (Chapter 4)

  • Learning Objectives
    • Describe neurological processes responding to external stimuli.
    • Relate neural mechanisms to major hypotheses in Animal Behavior.

Basic Neuroanatomy

  • Neuron = main cell of nervous system
    • Dendrite → receives signals
    • Axon → transmits signals away from cell body
    • Cell body → nucleus & organelles; metabolic control
    • Synapse → junction transmitting electrical impulses & neurotransmitters
    • Neural circuit → interconnected group of neurons
  • Signaling process
    1. Dendrites receive input (from other neurons or sensory receptors).
    2. If input exceeds threshold, action potential (AP) propagates down axon.
    3. At synapse, electrical AP converted to neurotransmitter release → continues signal in next cell.
  • Key reminders
    • Neurons send & receive; detect stimuli & mediate responses.
    • Morphology & neurotransmitter type vary by location & function.
    • Neuronal architecture is highly conserved among mammals.

Stimulus–Response Foundations (Tinbergen & Lorenz)

  • Research questions: “What sensory input stimulates pecking?” (herring gull chicks – Tinbergen)
  • Innate behavior (instinct)
    • Fully formed on first performance; no learning required.
  • Fixed Action Pattern (FAP)
    • Once triggered by releaser (sign stimulus), sequence runs to completion.
    • Mediated by Innate Releasing Mechanism (IRM) – dedicated neural circuit.
  • Classic examples
    • Egg-rolling in greylag geese (Lorenz)
    • Male stickleback attack behavior triggered by red belly.
  • Data snippet (Fig. 4.4)
    • Relative pecking responses: 100, 92, 35, 126 across model variants.

Are Instincts Always Beneficial?

  • Exploitation scenarios
    • Blister beetle larvae aggregate to mimic female bee → male bee attempts mating, transports larvae to hive → larvae consume provisions.
    • Avian brood parasitism (cuckoo vs reed warbler).
    • Stimulus = gaping mouth markings & begging calls.
    • Coevolutionary arms race in estrildid vs vidua finches (Fig. 4.6)
    • Parasite chicks evolve host-like mouth markings.
    • Hosts evolve finer discrimination of markings.

Sensory Modalities & Stimulus Filtering Overview

  • Acoustic: moths vs bats
  • Visual: monarch butterfly migration
  • Tactile: star-nosed mole foraging
  • Olfactory/Chemical: predator-induced plasticity, kairomones
  • Stimulus filtering = neural capacity to ignore irrelevant data & prioritize biologically relevant cues; species-specific and can be automatic or modulated.

Acoustic Case Study: How Moths Avoid Bats

  • Bats use ultrasonic echolocation pulses; moths evolved counter-measures.
  • Moth ear anatomy (Noctuids)
    • Tympanum on body surface; two receptor neurons: A1 (sensitive) & A2 (responds only to loud, close bats).
  • Signal transduction (Fig. 4.7–4.9)
    1. Sound → tympanum vibration.
    2. Vibration → receptor neuron depolarization.
    3. Receptor AP frequency proportional to sound intensity (distance) and lateral differences (direction).
    4. Interneurons relay to motor neurons → wing muscle adjustments: dives/swerves.
  • Direction coding (Fig. 4.10)
    • \text{Left\,vs.\,Right A1 rate} \Rightarrow source direction.
  • Tiger moth ultrasonic clicks
    • Hypotheses tested (Corcoran et al. 2009):
    1. Startle effect
    2. Aposematic “I taste bad” warning
    3. Sonar jamming (strongly supported)
    • Experiment: bats given silent vs clicking moths; measured attack success.

Visual Case Study: Monarch Butterfly Migration

  • Migration map (Fig. 4.15): breeding range \approx 20^{\circ}N-50^{\circ}N; overwinter in Sierra Madre, Mexico.
  • Sun compass navigation
    • Day-flying migrants use sun azimuth; must compensate for sun’s movement using circadian clock.
  • Circadian Clock Integration (Froy et al. 2003)
    • Flight simulator experiments
    • Normal LD cycle → correct south-westerly orientation (“Mexico!”).
    • Clock advanced +6\,\text{h} → mis-oriented (east, over Atlantic).
    • Conclusion: navigation = sun position × internal time reference.
  • UV & Polarized Light Cues
    • UV light required to initiate correct orientation.
    • UV-filter in simulator → moths stop or orient randomly; removal restores direction.
    • Polarized light patterns (sky polarization rotated 90^{\circ}) dictate heading corrections as sun moves.
  • Neural mechanism (Fig. 4.15, 4.16)
    • UV-sensitive receptors in antennae activate “clock” genes → brain → directional flight commands.
    • Ocular photoreceptors detect sun angle; combined with clock outputs.

Tactile Case Study: Star-Nosed Mole Foraging

  • Sensory organ: nose with 22 highly mobile rays containing ≈25\,000 Eimer’s organs (mechanoreceptors).
  • Behavioral performance (Fig. 4.26)
    • Contact to prey capture in 300–400\,\text{ms}; rays move independently.
  • Neural representation (Catania & Kaas 1997)
    • Somatosensory cortex has spatially distinct neuron clusters per ray.
    • Cortical magnification: ray 11 (“tactile fovea”) occupies disproportionate cortical area.
    • Comparative magnification across insectivores (Fig. 4.27).

Stimulus Filtering: Parasitoid Fly (Ormia ochracea)

  • Life history: female deposits larvae on singing male crickets → larvae burrow, kill host.
  • Sensory specialization
    • Female auditory receptors tuned to cricket song frequency; male’s are not.
    • Auditory tuning curves demonstrate sex-specific sensitivity; example of neural filtering.

Synthesis: Genetics, Development & Neural Mechanisms (Exit Activity Cue)

  • Genetic architecture (e.g., supergenes) can hard-wire neural circuits or alter neurotransmitter expression → modifies behavioral phenotypes.
  • Developmental plasticity influences neural connectivity (e.g., predator-induced morphs may entail neuroendocrine changes influencing behavior).
  • Evolutionary perspective: natural & sexual selection shape both genes and stimulus-filtering networks – maintaining adaptive match to ecological challenges.

Key Terms & Concepts

  • Phenotypic plasticity, Polyphenism, Kairomone
  • Behavioral polymorphism, Supergene
  • Neuron structure: dendrite, axon, synapse, action potential
  • Innate behavior, Fixed Action Pattern, Releaser, Innate Releasing Mechanism
  • Stimulus filtering, Cortical magnification
  • Circadian clock, Sun compass, Polarized light, UV receptors
  • A1/A2 receptor cells, Sonar jamming

Numerical & Formula Highlights

  • Predator-induced morph frequencies: \frac{18}{59}, \frac{11}{43}, \frac{30}{100}
  • Monarch flight misalignment when clock shifted +6\,\text{h}
  • Star-nosed mole reaction time <0.4\,\text{s}
  • Sun position compensation requires continuous phase information: \text{Heading} = f(\text{Sun azimuth},\,\text{Circadian phase})

Practical & Ethical Implications

  • Understanding exploitation of instincts informs conservation (e.g., brood parasite management).
  • Biomimicry: Ormia-inspired directional microphones for hearing aids.
  • Light pollution could disrupt monarch navigation via altered polarization patterns.
  • Pesticides affecting noctuid moth hearing may cascade to bat–prey dynamics.

Suggested Study Strategies

  • Draw neural pathway diagrams for moth bat-avoidance & monarch navigation circuits.
  • Create flashcards for key definitions & researchers (Tinbergen, Lorenz, Catania).
  • Relate sensory modalities to ecological niches: Why acoustic in nocturnal aerial hunters, tactile in subterranean foragers?
  • Practice explaining how supergenes can convert plastic variation into fixed polymorphisms.