Topics 9-11

Genes, Environment, and Behavior

  • Behavior as a Phenotype: Behavior is considered a phenotype, much like physical morphology. It is influenced by genes and is subject to microevolutionary forces.

  • Genotype-Phenotype Relationships:     - Genotype (Alleles) leads to Morphology (e.g., camouflage coloration, eye structure, claws, scales).     - Genotype (Alleles) leads to Behavior (e.g., fight and flight behaviors, herding, courtship behavior, pack hunting).

  • Evolution Definition: Descent with modification, which is a change at the population level from one generation to the next.     - Traits that change must be variable and heritable.

  • Two Primary Categories of Behavior:     
    -Innate (Fixed): Genetically determined and developmentally fixed behaviors.     
    -Learned: Actions influenced by the environment and experience.     

  • These exist on a continuum scale of possible behaviors between genotype and environment.



Characteristics and Types of Learned Behaviors

  • General Characteristics:     - Genes produce the structures necessary for the potential to learn.     - Once learned, behavior may become fixed or plastic (changeable).     - May require prior experience with a stimulus.     - Behavior can vary with internal and external stimuli and across individuals.     - A stimulus initiates the learned behavior.     - Evolution of Learned Behavior: Genes for learning should be favored in unpredictable or changing environments where multiple factors determine optimal behavior.

  • Specific Types of Learned Behavior:     
    1. Habituation: The loss of responsiveness to unimportant stimuli that are not associated with a specific response.     
    2. Associative Learning: Learning to associate a stimulus with a response via two methods:         - Classical Conditioning: Associating a neutral signal given before a behavior (reflex) to            train the association of a cue with a positive or negative reward.         
            - Operant Conditioning: Trial and error learning where reinforcement or punishment            occurs after a behavior, brought about directly by the object of the behavior.     
    3. Observational Learning: Learning by watching others and copying their actions


Characteristics and Examples of Innate Behaviors

  • General Characteristics:     - Behavior is genetically determined and occurs without prior experience.     - Developmentally fixed and unchanging.     - Individuals exhibit similar behavior despite differences in internal or external stimuli.     - Stimulus initiates the behavior.     - Evolution of Innate Behavior: Genes for fixed behavior should be favored when the opportunity to learn is low and the costs of mistakes are high (dangerous or deadly).

  • Specific Types of Innate Behavior:     
    1. Fixed Action Pattern (FAP): A fixed sequence of behaviors that is performed the same way every time, continues to completion (must restart if interrupted), and is linked to a simple trigger.     
    2. Key Stimulus: The specific trigger that initiates a Fixed Action Pattern; often a subset of total environmental stimuli.


Behavioral Continuum and Influence

  • Integrated Behavior: Most behaviors contain a fixed (innate) and learned component.

  • Imprinting: A form of learning where the young of a species associate an aspect of a stimulus with their caregiver. Contains both fixed and learned components, irreversible learned information and requires a stimulus from the environment.


Animal Movement in the Environment

  • Kinesis: innate, non-directional movement in response to the intensity of a stimulus. The rate of movement or frequency of turning is altered.

  • Taxis: innate, directional movement relative to a stimulus gradient. Positive Taxis: Toward the stimulus. Negative Taxis: Away from the stimulus.

  • Orientation: innate and learned, ese of a compass direction to determine movement. May involve sun, star, or magnetic compasses.

  • Piloting: learned, movement relative to specific landmarks; requires prior experience.

  • Navigation: learned, movement involving both Orientation and Piloting.


Macroevolution and Species Concepts

  • Macroevolution: The origin of new species. Requires microevolution and a reproductive isolation mechanism.

  • Species Definition: Related organisms that maintain a distinct set of traits in nature. Effectively the largest gene pool possible under natural conditions.     
    - Subspecies: Populations with some different traits but not distinct enough for a new species rank.     
    - Ecotypes: Genetically distinct populations adapted to local environments.

  • Four Main Species Concepts:     
    1. Morphological Species Concept: Defines species based on unique physical characteristics. - Pros: Applies to asexual species and fossils.         - Cons: Difficulties with sexual dimorphism, cryptic species, and intra-species variation.     
    2. Ecological Species Concept: Defines species based on the ecological niche (habitat resources and environmental influence).         
    - Pros: Applies to asexual and extinct species.         - Cons: Variation within species and niches can be hard to define.     
    3. Phylogenetic (Molecular) Species Concept: Unique species based on a shared common ancestor, often using DNA sequence analysis.         
    - Pros: Uses objective molecular data.         - Cons: Can lead to oversplitting species based on minor genetic variations.     
    4. Biological Species Concept: Defines species based on the potential to interbreed and produce viable, fertile offspring.         
    - Pros: Focuses on reproductive isolation.         - Cons: Cannot be used for fossils or asexual organisms.


Requirements for Speciation

  • Speciation involves two main requirements:     1. Microevolution: Any form (Mutation, Selection, Non-random mating, Drift).     2. Reproductive Isolation: The existence of barriers that prevent two populations from producing viable, fertile offspring.



Reproductive Isolating Mechanisms (R.I.M.s)

  • Reproductive Isolating Mechanisms (R.I.M.s): Barriers preventing gene flow between diverging populations.

  • Prezygotic Barriers: Prevent zygote formation.     
    1. Habitat Isolation: Populations live in different habitats or are separated by geographic barriers.     
    2. Temporal Isolation: Populations reproduce at different times (times of day or seasons).     
    3. Behavioral Isolation: Differences in mate selection traits (songs, dances, pollinator preference).     
    4. Mechanical Isolation: Morphological features (genitalia or body size) prevent successful mating.     
    5. Gametic Isolation: Gametes fail to unite or fertilization is unsuccessful.

  • Postzygotic Barriers: Prevent development of fertile offspring after a zygote is formed.    
    6. Reduced Hybrid Viability: Impaired embryonic development or low survival.   
    7. Reduced Hybrid Fertility: Hybrids are viable but sterile.     
    8. Hybrid Breakdown: First-generation hybrids are fertile, but next generations have decreased fitness.



Modes of Speciation

  • Allopatric Speciation: "Other Country." Speciation while geographically isolated.     
    - Occurs due to environmental changes (canyon, mountains, rivers) or populations moving to new regions.     
    - Process: Initial R.I.M. is Habitat Isolation due to geographic barrier -> Divergence via microevolution -> Secondary contact outcomes:         
    - Reinforcement: Isolation is maintained; divergence continues due to new R.I.M.s (Behavioral, Temporal, etc.).         
    - Fusion: R.I.M.s are insufficient; populations merge into one.         
    - Stability: Occasional hybrids form, but two distinct species are preserved.

  • Sympatric Speciation: "Same Country." Speciation without geographic separation.     
    - Initial R.I.M. is not geographic habitat isolation.           
    - Mutation: Polyploidy (possessing more than 2 sets of chromosomes, e.g., in Angiosperms, Ferns, some frogs).         
    - Habitat Differentiation/Local Adaptation: Adaptation to local environments within the same area (e.g., Hawthorn vs. Apple maggots).         
    - Sexual Selection: Divergence in mate choice leads to Behavioral Isolation (e.g., Cichlid fish in different lighting).


Fundamentals of Phylogenetics

  • Phylogenetic Tree: A depiction of the branching pattern of evolution as populations diverge.

  • Key Components:     
    - Tips: Extant (living) or sometimes extinct organisms being compared (Taxa).     
    - Branches: Independently evolving lineages.     
    - Nodes: Branching points representing a population divergence (the common ancestor).     
    - Clade: Monophyletic group consisting of a node and all of its descendants.     
    - MRCA (Most Recent Common Ancestor): The nearest node joining a specific clade.     
    - Root: The MRCA for all organisms on the tree.

  • Reading Trees:     
    - Nodes can be rotated (flipped) without changing the clades or evolutionary relationships.      - Relatedness is determined by the most recent common ancestor; taxa sharing a more recent node are more closely related.      - Sister Taxa/Clades: Pairs of taxa or clades that share a common ancestor and are each other's closest relatives.


Patterns of Character Evolution: Homology vs. Homoplasy

  • Homology/ Vestigial Structure: Structures derived from the same feature in a common ancestor. Example: Tetrapod limbs in humans, whales, and bats.     - Vestigial Structure: An inherited structure that no longer serves a function (e.g., pelvic bones in whales).

  • Homoplasy/ Convergent Evolution: Similar structures in form and function that evolved independently due to similar selective pressures. Example: Wings in insects vs. birds; the camera eye in squids vs. vertebrates.

  • Distinguishing through Parsimony: If a trait is found in distant groups, scientists compare the number of "losses" required for homology versus the number of independent "gains" for homoplasy to find the most parsimonious explanation.

Classification, Taxonomy, and Divergence Time

  • Taxonomy: Classification based on rank similarity (Artificial groups).

  • Phylogeny: Reconstruction of evolutionary history (Natural clades).

  • Clade Status:     
    1. Monophyletic: Includes the common ancestor and ALL descendants.     
    2. Paraphyletic: Includes the common ancestor and SOME descendants.  
    3. Polyphyletic: Grouping that does not include the common ancestor.