Bio 130 Unit Three

Evolution

Change in allele frequencies over time - individuals don’t evolve, populations do - driven by natural selection, mutation, gene flow, and genetic drift

Vestigial Organs

Biological structures that have lost most/all of its original functions but remains present in a species - developed for ancestral use but its lost its usefulness - ex. human appendix

Structural Homology

The similarity in the three-dimensional shape or architecture of biological macromolecules (typically proteins) that reflects a shared evolutionary origin

Sarawak Law

“Every species has come into existence coincident both in space and time with closely allied species" - new species evolve from pre-existing, related species instead of appearing independently

Population

A group of individuals of the same species that live in the same geographic region at the same time

Teleology

Explaining living things, organs, or behaviors by their function, goal, or end purpose

Fitness

An organism’s ability to survive, find a mate, reproduce, and pass its genetic material to the next generation - genotypes with higher fitness become more abundant through natural selection - depends on both genes and the environment

Fitness Tradeoff

When improving one trait, function, or adaptation means you decrease performance in another, because of a limited supply of energy, time, nutrients - caused by principle of allocation, antagonistic pleiotropy, functional conflicts, etc.

Genetic Constraint

A limitation or restriction on how an organism can evolve or adapt, caused by the structure of its genes, lack of genetic variation, or how genes interact with one another - ex. pleiotropy, genetic linkage and epistasis, etc.

Historical Constraint

An organism's evolutionary path is limited by the traits, body plans, and genetic architecture it inherited from its ancestors

Hardy-Weinberg Equilibrium Model

Predicts allele frequnecies under no evolutionary mechanisms -allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences - assumes large population size, random mating, and no mutation, migration, or natural selection - null hypothesis for evolution

Directional Selection

A mode of natural selection where a single extreme phenotype is favored over all other variations, causing the allele frequency and trait mean of a population to shift in one direction over time - changes the average value of a trait - caused by changes in the environment (like pollution, climate change, or disease) - ex. moths and pollution changing their tree color

Stabilizing Selection

A type of natural selection that favors average, middle-of-the-road phenotypes while selecting against extreme variations - reduces the amount of variation in a trait - ex. human birth weights

Disruptive/Diversifying Selection

A mode of natural selection where extreme trait values are favored over intermediate values within a population - increases the amount of variation in a trait

Sexual Selection

Mating preferences - differential reproductive success due to variation among individuals in success at getting mates - a mode of natural selection where members of one biological sex acquire mates either by competing with members of the same sex or by choosing attractive partners from the opposite sex

Bateman’s Principle

Females are more choosy because they make a big investment in their gametes, men mate lots and compete because their gametes are a small investment - reproductive and mating success vary much more widely in males than in females, because cheap sperm make males eager to mate while costly eggs make females a limiting resource

Quality → female

Quantity → male

Types of Intrasexual Competition

Members of the same sex are competing for access to mates or mating resources

• Combat

• Alternative Mating Strategies

• Infanticide

• Sperm Competition

Intersexual Competition

Members of one sex choose mates based on specific traits, colors, behaviors, or ornaments displayed in the opposite sex - typically female choice - choosy females get better genes for their offspring and/or direct benefits from males

Cooperative Interaction

An interaction where 2+ organisms work or act together to increase the fitness of the participants - can include mutualism or intraspecific competition

Selfish Interaction

A social behavior where the performer/organism benefits at a fitness cost to the recipient

Altruistic Interaction

A behavior where an individual acts in a way that decreases its own reproductive fitness while increasing the reproductive fitness of another individual - ex. animals helping their genetic relatives survive and make offspring even when this decreases their own chances (kin selection)

Spiteful Interaction

A social behavior where both the performer/organism and the recipient suffer a fitness loss

Kin Selection

A type of natural selection where an organism acts in a way that helps its genetic relatives, even if it lowers its own personal survival or reproduction - altruistic interaction

Indirect Fitness

The measure of an organism's genetic success based on the survival and reproduction of non-descendant relatives (siblings, cousins, nieces, nephews, etc.) who share a portion of the same genes

Coefficient of Relatedness (r)

The probability that two individuals share a specific gene (allele) inherited from a recent common ancestor - ranges from 0 (completely unrelated) to 1 (identical twins or clones) - for standard diploid species, r depends on the genetic distance between relatives

r = (1/2)ⁿ where n is the number of generational steps between the two individuals

Biological Species Concept

The idea that a species is a group of individual organisms that can naturally interbreed and produce fertile offspring - for non-breeding organisms (isolated populations, asexual species, hybrids, fossils), this concept can’t apply so scientists use shared physical traits (morphology), genetic sequences (DNA), or evolutionary history (phylogeny)

Evolutionary (Phylogenetic) Species Concept

Defines a species as the smallest group of organisms that share a common ancestor and can be distinguished from other such groups by unique inherited traits - smallest monophyletic group

Morphological Species Concept

Defines a species as a group of organisms that share distinct, observable physical characteristics (body shape, size, color, skeletal structure) making them look alike and different from other groups

Ecological Species Concept

Two taxa are defined as a species if they are “ecologically exchangeable” (same nice) - defines a species as a set of organisms adapted to a specific ecological niche (the unique role, diet, habitat, and resource set it uses in its environment)

Allopatric Speciation

The process by which new species form when a single population becomes divided by a geographic barrier (such as a mountain range, river, ocean, or canyon) that stops individuals from migrating and sharing genes - caused by vicariance and dispersal

Sympatric Speciation

An evolutionary process where a new species evolves from a single ancestral species while inhabiting the same geographic region, without any physical or spatial barriers separating them - can be caused by polyploidy (where certain individuals can’t breed with others), behavioral changes, specialization, etc.

Isolation by Vicariance

An evolutionary process where a continuous population is physically split into isolated subgroups by the appearance of a new geographic barrier - causes allopatric speciation

Isolation by Dispersal

A small subset of individuals actively or passively crosses a pre-existing geographic barrier (ocean, mountain range, river, etc.) to colonize a new, isolated area - causes allopatric speciation

Phylogenetics

The study of the evolutionary history and relationships among groups of organisms (such as species, populations, or genes)

Monophyletic Group

A collection of organisms that includes a single common ancestor and all of its descendants - aka a clade

Eidos

Plato thought there was a “fixed essence” - variations from this are accidental imperfections

Scalae Naturae

Aristotle made a "great chain of being” based on size and complexity that basically put humans above all other species

Lamarck

Species are not static, but change.- simple organisms originate at the base of the chain and move up the ladder over time - evolution is progressive, leading towards “better,” larger, more complex species - adaptation via inheritance of acquired traits (i.e. giraffes stretched their necks and passed this on)

1800s Biological Observations (gave evidence for evolution

1. Nested Hierarchical Structure of Life

2. Evidence for Extinction

3. Succession of Fossil Types

4. Geographical Relationships of Similar Species (Sarawak Law)

5. Shared Embryonic Features (developmental homology)

6. Common “Design Blueprints” for Structures with Different Functions (structural homology)

7. Vestigial Organs in Many Species

Nested Hierarchical Structure of Life

Linnaeus made a classification system based on shared similarities (with latin names) - proponent of “natural theology” in the 1800s (helps people to better understand God’s wisdom)

Succession of Fossil Types

Order in the fossil record worldwide (old fossils low → new fossils) - Lyell proposed “uniformitarianism” because of this

Uniformitarianism

Lyell proposed that the processes happening today are the same as what happened in the past (slow, gradual changes)

Atavism

The reappearance of a lost evolutionary or ancestral trait in an organism after skipping one or more generations

Analogous Traits

Traits shared from convergent evolution (no common descent so it’s not homology) - ex. tasmanian tigers and wolves

Genetic Homology

Similarity in the DNA nucleotide sequences, RNA nucleotide sequences, or amino acid sequences - another line of evidence today for evolution

Postulates of Natural Selection

1. Biotic Potential (the animal is reproducing as much as it can)

2. Limiting Factors (environment limits which/how many offspring can survive)

3. Mutations (variation in population)

4. Differential Fitness (some organisms are better at surviving/reproducing than others)

5. Heritability (your fitness advantage must be heritable/genetic)

6. Environmental Changes (environment changes over time so population and traits are always shifting)

If variation exists among individuals, that variation is heritable, and some variants survive and reproduce better than others, then natural selection will occur

Five Mechanisms of Evolution

1. Mutation

2. Migration

3. Genetic Drift

4. Non-Random Mating

5. Natural Selection

Population Genetics

Changes in relative abundance of traits in populations are tied to relative abundance of frequencies of alleles that underpin those traits

Mutation

Slow evolution by itself, useful in combination with natural selection - creates the building blocks for evolution but not super effective on its own

Migration

Movement of alleles between populations (joins new breeding populations) - dependent upon the number of migrants and the population size (can be a big deal but it depends) - gene flow homogenizes populations (makes them more similar)

Genetic Drift

A random change in allele frequencies due to chance - as population sizes increase, allele frequencies are closer and closer to the original - small populations have more pronounced evolution by drift - includes the founder effect where immigrants establish a new population with different allele frequencies - also includes bottleneck effect

Non-Random Mating

With extreme inbreeding, heterozygous decreases to almost nothing (inbreeding depression) - or, with extreme outbreeding (mating with opposite genotype), heterozygous increases - affects genotype frequencies, not allele frequencies (doesn’t change evolution by itself) - can include choosing mates with the same trait, choosing mates with the opposite trait, inbreeding with relatives, choosing mates based off specific traits (like bright feather colors), etc.

Natural Selection

Adaptive evolution - favors traits with higher fitness, leads to evolution - traits responsible for differential success will become more common over time (evolution)

Three Kinds of Evolution by Natural Selection

1. Directional Selection

2. Stabilizing Selection

3. Diversifying/Disruptive Selection

Misconceptions of Natural Selection

• Individuals don’t sacrifice themselves “for the good of the species”

• Not all traits are adaptive - some are neutral (ex. earlobe attachment)

• Not all traits are possible - there are constraints and tradeoffs (no perfect organisms)

  • Fitness tradeoff, genetic constraint, historical constraint

• Evolutionary change does not occur in individuals - it occurs in populations

• Adaptations don’t occur because organisms want or need them

Fitness and Mating

Individuals produced by self-fertilization or close relatives have low fitness - individuals produced by matings between unrelated parents have high fitness

Sexual vs. Asexual Reproduction

Sexual reproduction increases genetic variation, asexual reproduction accumulates mutations

Sexual Reproduction Pros

• Repair of damaged DNA

• Sibling competition reduced

• Eliminating “genetic load” (accumulated mutations)

• Avoiding synergistic epistasis among mutations

• Adaptation to fluctuating environments

• Enhanced adaptation under directional selection

Sexual Reproduction Cons

• Produces fewer offspring than asexual reproduction

• Costly

  • Takes time and energy

  • STDs, predation risk, resources, competition

Two Types of Sexual Selection

1. Intrasexual Selection - male-male competition

2. Intersexual Selection - female choice

Speciation

A splitting event that creates 2+ distinct species from a single ancestral group - results from genetic isolation or genetic divergence (allopatric or sympatric speciation)

Species Concepts

How do we define a species?

1. Biological

2. Phylogenetic

3. Morphological (Linnean)

4. Ecological

5. Evolutionary