Animal Behavior Module 3

Definition: Evolution

The change in the frequencies of different alleles in a population over generations.

Definition: Alleles

Alternate versions of a specific gene (e.g., T and t for height).

Definition: Population

A group of interbreeding organisms belonging to the exact same species.

What evolutionary event can occur when populations are separated and prevented from breeding with each other?

Speciation (the formation of a new species).

What type of breeding selection in domesticated animals did Charles Darwin use as a parallel to understand natural selection?

Artificial selection

Darwin’s Observation 1 (Phenotypic Variation)

Individuals within a given population will vary in their expressed phenotypes (such as appearance, strength, and behavior).

Darwin’s Observation 2 (Heritability)

Some varying phenotypic traits are inheritable, meaning they are genetically based and stem from genotypic differences.

Darwin’s Observation 3 (Differential Reproductive Success)

Inheritable traits that confer an advantage give individuals a reproductive edge or survival edge (e.g., avoiding predators, finding food), making them more likely to produce more offspring.

Darwin’s Modification Conclusion

Because offspring are more likely to inherit their parent’s beneficial traits, these traits will increase in frequency in a population over time, while traits from less reproductively successful individuals will decrease.

Definition: Adaptations

Genetically based traits that exist because they allow individuals to survive and outcompete other members of their population.

Definition: Adaptation (as a process)

The process of change over evolutionary time occurring specifically through Natural Selection.

Case Study: How do male elephant seals initially establish mating territories before females arrive?

They arrive at mating beaches a few weeks early and stake out portions of the seashore; more powerful males defend larger, preferable portions of the coastline.

Case Study: How do female elephant seals choose where to reside upon arriving at beaches?

They select the best, largest territories to reside in, because larger territories provide more physical room for females.

Case Study: Explain the two-tier progression of territorial defense fights between male elephant seals.

Threat displays: Rearing and roaring. If one male outclasses the other, the lesser male backs down.

2. Physical combat: If they are similar in size, they engage in brutal fights where raw strength, stamina, and larger size win.

Case Study: What three specific physical/behavioral traits have been naturally selected for over time in male elephant seals due to sexual competition?

Increased overall body size, physical strength, and a larger proboscis (which facilitates a deeper, more intimidating roar).

Definition: Fitness (Individual vs. Allelic perspective)

Individual: The reproductive success of an individual relative to other individuals within the same population.

Genetic: The reproductive success of an allele relative to other alleles within the population

Definition: Direct Fitness

The fitness gained by an individual through its own reproduction, measured directly by counting the number of offspring it produces.

Definition: Indirect Fitness

The fitness gained by an individual through helping its relatives raise more offspring than those relatives would have been capable of rearing alone.

Why can an individual benefit from Indirect Fitness from a genetic standpoint?

Because relatives share many of the same genes. By boosting a relative's direct fitness, the individual ensures many of its own genes survive and proliferate.

What dictates the degree of indirect fitness gained?

The closeness of the genetic relationship; a closer genetic relationship yields a higher degree of indirect fitness

Case Study: Provide an example of animal species practicing indirect fitness.

Year-old offspring of bird species (e.g., Scrub Jays, Sand Hill Cranes) staying behind to help their parents raise the next year's clutch of offspring.

Definition: Inclusive Fitness

The sum of both an individual's direct fitness and its indirect fitness.

True or False: Natural selection always favors traits that benefit the species as a whole.

False. Fitness strictly involves traits that increase the reproductive success of the individual, not necessarily the species.

What target does natural selection actually act upon: the genotype or the phenotype?

The phenotype. Selection works strictly on expressed traits, which cause the changes selected for or against

How is a deleterious recessive trait hidden from natural selection?

It is masked in the heterozygous condition and can only be expressed and selected against when it appears in the homozygous recessive state.

Does natural selection create genetic variability? Explain.

No. Natural selection only responds to existing variation. Genetic variability is generated primarily by mutation and genetic recombination.

Definition: Mutation

A permanent change in an organism's sequence of DNA.

What condition must a mutation meet to be evolutionarily significant? Give an example of an insignificant one.

It must be capable of being passed down to subsequent generations via gametes or gametogenic tissue. (Example of insignificant: A somatic cancer mutation) .

Large-scale Mutations

Loss, duplication, or inversion of entire genes, suites of genes, or chromosome portions. Highly likely to be deleterious.

Small-scale Mutations

Deletion or addition of a single nucleotide base pair (though these can still cause severe effects)

Definition: Genetic Recombination

A change in the combination of genes in an organism's offspring compared to its own parental genotype, occurring naturally via sexual reproduction and meiosis.

What two processes during meiosis cause genetic recombination?

1. Random segregation of diploid genes.

2. Crossing over during Meiosis I, where homologous genes physically exchange alleles.

What is the core evolutionary advantage of sexual reproduction?

It yields extensive genetic variation, providing a population with the genetic plasticity required to survive unexpected environmental changes.

Case Study: How does genetic variation in mouse nest-building behavior provide a selective advantage if the climate turns cold?

Mice with genes for building larger nests have a selective advantage because their larger nests better insulate both themselves and their vulnerable offspring.

What is the phenotypic distribution of a population under normal conditions, and who is best adapted?

A bell-shaped curve. Individuals at the center (the population average) are the most numerous and best adapted to current conditions.

Definition: Stabilizing Selection

A type of selection that occurs when environmental conditions remain stable, favoring the optimal phenotype at the center of the curve and preventing the curve from shifting.

Definition: Directional Selection

Selection that occurs when environmental conditions shift, favoring phenotypic traits away from the original center, causing the entire bell curve to move in that direction over time.

Give an example of a slow/minor directional selection shift vs. a dramatic/rapid shift.

Slow: Regional variation in the coat color of timber wolves accruing over long generational time.

Dramatic: Rapid shifts toward accelerated sexual development in smaller fish within a population due to heavy commercial overfishing.

Definition: Gene Flow

The physical movement of genes from one population to another via migrating, interbreeding individuals; it prevents genetic isolation and increases variation.

Case Study: Explain larval streamside salamander behavior in permanent pools

Fish predators are abundant. Larvae reduce feeding and remain immobile to escape detection.

Case Study: Explain larval streamside salamander behavior in ephemeral streams.

Fish predators are absent. Larvae feed heavily and move constantly to grow rapidly and metamorphose before the water dries up.

Case Study: How does the distance between pools affect predator avoidance in streamside salamanders?

Greater distance: Higher predation avoidance overall (less disruptive gene flow).

Lesser distance: Poorer predation avoidance overall because high gene flow from neighboring ephemeral stream populations constantly floods the pool with "high-activity" genes.

Definition: Genetic Drift

An evolutionary change in a population's allele frequencies resulting purely from random events. It has a significantly greater impact on small populations.

Definition: Adaptive Landscape

A graphical representation mapping gene frequencies against a population's resulting fitness levels.

Case Study: Explain the finch beak adaptive landscape (BB, Bb, bb) where only large and small seeds are available.

Big-beaked (BB) individuals have high fitness (can crack big seeds).

Small-beaked (bb) individuals do well manipulating small seeds.

Medium-beaked (Bb) individuals have the lowest fitness because they are poorly suited for both seed sizes, creating a valley in the adaptive landscape.

How can a neutral or negative trait persist via Correlated Traits?

If a neutral/negative trait is genetically tied to a highly beneficial trait being actively selected for, it will remain in the population as long as overall fitness is positive.

Definition: Pleiotropy

A genetic phenomenon where a single gene controls or affects multiple entirely different phenotypic traits (e.g., rare coat color and abnormal vision in Siamese cats)

Definition: Linkage (Genetic)

Genes located physically close to one another on a chromosome. Due to proximity, when one is exchanged during crossing over, its neighbor tag-alongs.

Case Study: Explain the correlated physical and behavioral traits in the Mosquitofish (Gambusia holbrooki).

Melanistic (dark-colored) male mosquitofish are significantly more aggressive, chasing more females and attempting more matings. This links a physical trait (melanin) with a behavioral trait (testosterone production)

Definition: Frequency-Dependent Selection

An evolutionary process where the fitness of a given phenotype is explicitly dependent on its commonality or rarity relative to other phenotypes in the population.

Definition: Negative Frequency-Dependent Selection

Selection that occurs when a trait is favored specifically because it is at a lower frequency, giving a distinct reproductive/survival edge to rare alleles

Case Study: Negative Frequency Dependence in Lake Tanganyika Cichlids

These scale-eating predatory fish attack prey from either the left or right side. If most predators attack from the right, prey adapt to defend their right side, which shifts the selective advantage to the rarer left-attacking fish.

Definition: Frequency-Dependent Predation (and what it drives)

Predators target prey that look/act most like their typical, common prey. Rare-looking individuals survive and reproduce, making this a major driver of polymorphism in prey species.

Definition: Frequency-Dependent Reproduction / "Rare Male Mating Effect"

Females select a male with a unique, rare phenotypic feature (e.g., rare color patterns in guppies). Over time, this rare pattern becomes common, shifting female preference back to the new rare form and maintaining variation.

Definition: Positive Frequency-Dependent Selection (and its effect on variation)

Selection that favors common alleles over rare ones (e.g., predators recognizing and avoiding a common warning coloration of a poisonous species while killing rare morphs). It decreases genetic variation.

Definition: Negative Assortment Mating

A mating strategy where individuals actively choose mates whose phenotypes differ fundamentally from their own (often serving to prevent harmful inbreeding).

Case Study: Negative Assortment Mating in White-Throated Sparrows (Zonotrichia albicolis)

They have two color forms: tan-striped and white-striped. Females of both morphs prefer tan-striped males, while males of both morphs prefer white-striped females, ensuring continuous interbreeding between types

Definition: Evolutionarily Stable Strategy (ESS)

A behavioral strategy that, once adopted by all or most members of a population, cannot be replaced or invaded by an alternate strategy because no other strategy confers higher reproductive success.

What branch of mathematics forms the modeling foundation for ESS?

Game Theory.

Pure ESS

Consists of a single, uniform strategy adopted by the entire population.

Mixed ESS

Consists of several distinct strategies existing simultaneously in a state of stable equilibrium.

Case Study (Pure ESS): The Handicap Principle

Proposed by Amotz Zahavi; animals evolve costly, survival-lowering behavioral displays to reliably signal high genetic quality. Example: A gazelle stotting (jumping high on all four legs) upon seeing a predator to signal superb condition so the predator abandons the chase.

What two ways can a Mixed ESS physically arise in nature?

1. Each individual varies or alternates its behavioral strategy over time depending on success.

2. Entirely different genotypes are fixed within the population, each responsible for a distinct strategy.

Case Study (Mixed ESS): Independent Strategies in the Ruff (Philomachus pugnax)

Establish and aggressively defend physical territories on leks to attract females.

Case Study (Mixed ESS): Satellite Strategies in the Ruff (Philomachus pugnax)

Forego territories; behave submissively to gain sneaky access to Independent territories.

Case Study: How do Satellite ruffs compensate for getting fewer lek copulations to maintain equal lifetime reproductive success?

The strategy is low-cost and low-benefit. Satellites may enjoy increased overall longevity/lifespan, and they successfully sneak copulations off the leks and during migration periods.

What is the fundamental, primary metric animal behaviorists look at to determine if a behavior has a true selective advantage?

Average offspring production (enhanced reproductive success) compared to individuals lacking the behavior.

Methodology: The Experimental Approach

Identifying alternate possible benefits of a behavior and testing them all in a rigorously controlled experiment to discover which benefit holds true.

Methodology: The Comparative Approach

Comparing a specific type of behavior among different closely related species to deduce the evolutionary origin or extent of that behavior.

Give an example of a behavior studied using the Comparative Approach.

Nuptial gift presentation by robber fly males to prospective females.

Methodology: Optimality Modeling

A mathematical model that evaluates the survival costs and reproductive benefits of alternate behavioral strategies to identify which strategy maximizes fitness.

Definition: The Optimal Strategy

The behavioral alternative that maximizes the difference between costs and benefits, thereby maximizing overall individual fitness