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Lecture 1: Introduction to Evolution (08/29/2023)
● What type of adaptation would you expect to see in an organism living in an
environment with visual predators? What about in an environment with predators
which rely primarily on their sense of smell?
○ Adaptation in an environment with visual predators: In an environment with visual
predators, you would expect to see adaptations related to camouflage, warning coloration, or mimicry. Organisms might evolve to blend in with their surroundings, have colors or patterns that make them hard to spot, or mimic harmful or unpalatable species to avoid being eaten ○ In an environment with predators that rely primarily on their sense of smell, adaptations might involve chemical defenses, the release of strong odors to deter predators, or the evolution of strategies to mask or confuse their scent.
● Why would it be advantageous for an organism to resemble something else; i.e.
a caterpillar that looks like bird droppings or an orchid that smells like carrion?
Can you think of other kinds of advantages of resembling something else?
○ Resembling something else can provide several advantages. Mimicry, such as a
caterpillar looking like bird droppings or an orchid smelling like dead animals, can deter predators or attract pollinators. Other advantages include protection from predation, better access to resources, or increased reproductive success.
● In what ways have humans changed how selection acts on other organisms?
○ Humans have changed selection on other organisms through activities like
selective breeding of domesticated plants and animals, habitat destruction, pollution, and the introduction of invasive species. These actions can alter the selective pressures acting on populations, leading to changes in their traits and behaviors.
● What makes an invention an example of bio-inspired design? Can you come up
with examples other than the ones discussed in class?
○ Bio-inspired design involves drawing inspiration from biological systems to create innovative technologies or solutions. Examples include Velcro inspired by burdock burrs and the development of self-cleaning surfaces modeled after lotus leaves. ■ Wind turbines: Whales are highly efficient swimmers, and their streamlined shapes have evolved over millions of years to minimize drag as they move through water. Similarly, wind turbines are designed with aerodynamic principles to minimize resistance to the wind, ensuring efficient energy conversion. In this sense, wind turbine blade design can
be inspired by the streamlined bodies of whales to optimize their performance in the fluid medium of the atmosphere.
● *** How have humans used evolution as a tool? Provide an example and
ellaborate.
○ Humans have used evolution as a tool in various ways. One example is the
selective breeding of crops and livestock to improve yield, taste, or disease resistance. Through controlled breeding, humans accelerate the evolution of desired traits in these organisms, leading to more productive and resilient agricultural systems.
● What kind of experiment would allow you to determine whether the change in
cranial capacity of urban rodents was due to an evolutionary change or
plasticity? In addition to describing the experiment, explain what the predicted
result would be for each case (i.e., evolution and plasticity).
○ To determine whether the change in cranial capacity of urban rodents was due to
evolution or plasticity, you could conduct a reciprocal transplant experiment. In this experiment, you would exchange urban and rural rodents between their respective habitats and monitor their cranial capacity over several generations. ○ Predicted result for evolution: If the change is primarily due to evolution, you would expect that the cranial capacity of urban rodents transplanted to rural environments would gradually shift toward the rural phenotype, and vice versa. This shift should persist over multiple generations. ○ Predicted result for plasticity: If the change is primarily due to plasticity, you would expect that the cranial capacity of transplanted rodents would eventually revert to their original phenotype once they are exposed to the new environment. There would be no persistent change across generations.
Lecture 2: Natural Selection on Phenotypes in the Wild (08/31/2023)
● *** What’s the difference between evolutionary change and plasticity? What
factors are required for each to occur?
○ Difference between evolutionary change and plasticity: Evolutionary change
refers to genetic changes in a population over generations, driven by natural selection, mutation, and genetic drift. Plasticity refers to the ability of an organism to change its phenotype in response to environmental cues without genetic changes.
● In class, we talked about the work of Peter and Rosemary Grant on Galápagos
finches. Why were these finches a good system in which to study evolution? Give
three reasons.
● What is one way that the stickleback and finch examples are similar? What is
one way they are different?
○ Similarity: Both examples demonstrate how environmental pressures can drive
evolutionary changes in populations.
○ Difference : Stickleback research focuses on morphological traits, while the finch
research emphasizes beak size and its correlation with food sources. Additionally, stickleback studies involve controlled breeding experiments, while finch studies rely on field observations.
● Why is it incorrect to say that evolution is a completely random process?
○ Evolution not a completely random process: Evolution is not entirely random
because it operates on the basis of natural selection. While mutations introduce genetic variation randomly, the differential survival and reproduction of individuals with advantageous traits are not random. Natural selection results in the non-random accumulation of traits that enhance an organism's fitness in a specific environment, making evolution a directional process.
Lecture 4: (9/7/2023)
● A trait in certain individuals within a population increases their fitness by 3%, can this trait be considered an adaptation? What information do we need to know if this is an example of adaptation. ○ Fitness is a measure of an individual's ability to survive and reproduce in a given environment. It encompasses factors like survival rate, reproductive success, and the number of offspring produced. An adaptation is a trait that has evolved through natural selection and enhances an organism's fitness in its specific environment. ○ To determine if a 3% increase in fitness represents an adaptation, we need moreinformation: ■ a. Is the trait heritable? (Can it be passed on to offspring?) ■ b. Has it persisted over multiple generations? ■ c. Does it provide a consistent advantage in the population's natural environment? ■ d. Are there alternative explanations for the fitness increase (e.g., random chance, genetic drift)? ● Define fitness. What factors can influence the fitness of an individual? ○ Fitness is the ability of an organism to survive and reproduce, contributing its genes to the next generation. Factors influencing an individual's fitness include: ■ Survival and lifespan. ■ Reproductive success, including the number of offspring produced.
■ Ability to compete for resources. ■ Adaptations and traits that enhance survival and reproduction in a specific environment. ● What is anisogamy, how did it evolve and what sexual system did it likely arise from? ○ Anisogamy refers to the difference in size or morphology between male and female gametes (sperm and eggs). It likely evolved from isogamy, where gametes are similar in size and morphology. ■ Anisogamy likely evolved as a result of selective pressures favoring gametes with different roles: smaller, more mobile sperm for fertilization and larger, nutrient-rich eggs for supporting early development. ■ This transition likely occurred in species where the costs and benefits of gamete size differentiation were advantageous for reproduction. ● What is the difference between natural selection and evolutionary response? What conditions must be met for an adaptive trait to evolve? Under what conditions can natural selection act on a population without producing an evolutionary response? ○ Natural selection is the process where certain heritable traits become more or less common in a population due to their effects on an individual's fitness in a specific environment. ■ Natural selection can act on a population without producing an evolutionary response when there's no heritable variation for the trait in question or when the selective pressures are weak or fluctuating. ○ Evolutionary response refers to the observable changes in the genetic makeup of a population over generations as a result of natural selection. ■ Evolutionary response = natural selection + heritable traits ■ For an adaptive trait to evolve, it must be heritable, provide a fitness advantage, and be subject to variation within the population.
- Natural Selection: Natural selection is the process by which certain traits become more or less common in a population due to differential reproductive success. It is the mechanism that drives evolutionary change.
- Evolutionary Response: Evolutionary response refers to the actual change in the frequency of a trait within a population over generations as a result of natural selection. For an adaptive trait to evolve:
- There must be genetic variation in the trait within the population.
- The trait must be heritable, meaning it can be passed on to offspring.
- The trait must provide a fitness advantage in the given environment. Natural selection can act on a population without producing an evolutionary response if the trait in question lacks genetic variability or if the selective pressures are not strong enough to overcome other factors like genetic drift.
● Associated Assumptions/Conditions: Fitness is relative and depends on the specific environment and the competition within a population. Those individuals with higher fitness are more likely to leave offspring. ● Application: In a population of rabbits, a rabbit with strong legs that can escape predators and find food more efficiently has higher fitness. Natural Selection: ● Definition: Natural selection is a fundamental mechanism of evolution. It refers to the process by which traits that increase an organism's fitness become more common in a population over generations. ● Conditions for Evolution by Natural Selection: ● Variation in traits within a population. ● Heritability of traits, so they can be passed on to offspring. ● Differential reproductive success, where individuals with advantageous traits produce more offspring. ● Application: Peppered moths are a classic example. During the Industrial Revolution, darker moths had a survival advantage in polluted areas, leading to an increase in their frequency over time. Phenotypic Plasticity: ● Definition: Phenotypic plasticity is the ability of an organism to express different phenotypes (observable traits) in response to environmental factors. It allows individuals to adapt to changing conditions without genetic changes. ● Associated Assumptions/Conditions: Phenotypic plasticity relies on the existence of multiple phenotypic options within a single genotype, and it's often reversible. ● Application: Plants that can change their leaf shape or color in response to light conditions demonstrate phenotypic plasticity. Evolution: ● Definition: Evolution is the process by which populations of organisms change over time. It involves the accumulation of genetic changes (mutations) and the action of natural selection, genetic drift, and other mechanisms. ● Associated Assumptions/Conditions: Evolution requires genetic variation, heritability, and environmental pressures that select for certain traits. ● Application: The evolution of the human species from common ancestors with other primates is a well-documented example of long-term evolutionary change. Anisogamy: ● Definition: Anisogamy is a type of sexual reproduction where two different-sized gametes (reproductive cells) are involved, typically a small motile male gamete (sperm) and a larger non-motile female gamete (egg). ● Associated Assumptions/Conditions: Anisogamy is common in many species and is often associated with the specialization of roles between male and female gametes. ● Application: Humans exhibit anisogamy, with tiny, mobile sperm fertilizing larger, immobile eggs during reproduction. This type of gamete size difference is common in many animal species.
Let's address each of your questions:
- A trait in certain individuals within a population increases their fitness by 3%, can this trait be considered an adaptation? What information do we need to know if this is an example of adaptation? Whether a trait can be considered an adaptation depends on various factors. A 3% increase in fitness is a relatively small advantage, so it might not definitively indicate adaptation. To determine if it's an adaptation, you would need to consider:
- Heritability: Is the trait genetically inherited? If it's not heritable, it may not be an adaptation.
- Environmental Consistency: Does the trait confer an advantage consistently across different environments? An adaptation should be advantageous in a specific ecological context.
- Selection Pressure: Are there strong selective pressures in the population's environment favoring this trait?
- Time Scale: Adaptations typically evolve over many generations, so long-term data on the trait's persistence would be informative.
- Define fitness. What factors can influence the fitness of an individual?
- Fitness in biology refers to an organism's ability to survive and reproduce in its environment. Factors that influence an individual's fitness include:
- Survival rates: How likely an individual is to survive to reproductive age.
- Reproductive success: How many offspring an individual produces and how well those offspring survive.
- Competitive abilities: An individual's ability to obtain resources, mates, and avoid predation.
- Genetic factors: The individual's genetic makeup, including advantageous or disadvantageous traits.
- What is anisogamy, how did it evolve, and what sexual system did it likely arise from?
- Anisogamy is a type of sexual reproduction involving two different-sized gametes (sperm and egg). It likely evolved from isogamy, where gametes are of similar size. Anisogamy provides advantages in terms of specialization, allowing one gamete to be smaller, more mobile (sperm), and the other larger, more nutrient-rich (egg). This specialization likely increased reproductive efficiency.
- What is the difference between natural selection and evolutionary response? What conditions must be met for an adaptive trait to evolve? Under what conditions can natural selection act on a population without producing an evolutionary response?
Describe a complete, biologically plausible scenario in which the phenotypic difference described below is the result of evolution by natural selection. From your scenario, it should be clear how all the conditions for evolution by natural selection are met and why phenotypes differ in the two environments (note: this question does not ask for an experiment): Periwinkle snails living low in the intertidal zone have thicker shells than periwinkle snails that live higher in the intertidal zone Conditions: Variation: Within a population, there must be genetic variation. Individuals in a population must differ from one another in terms of traits that are heritable (traits that can be passed down from one generation to the next through genetic inheritance). Inheritance: The genetic variations that provide a selective advantage must be heritable. This means that the traits allowing individuals to survive and reproduce better must be passed on to their offspring. Differential Survival and Reproduction: Not all individuals in a population survive and reproduce at the same rate. Some individuals possess traits that make them better adapted to their environment, increasing their chances of survival and reproduction. These advantageous traits become more common in the population over time. Overproduction of Offspring: Populations tend to produce more offspring than can survive to maturity. This leads to competition for limited resources and increases the likelihood that only the fittest individuals with advantageous traits will survive and reproduce. Environmental Pressure: There must be some form of environmental pressure or selective force that favors certain traits over others. This pressure can be biotic (such as predation or competition) or abiotic (such as changes in climate or habitat). Time: Evolution by natural selection is a gradual process that occurs over many generations. Significant changes in a population's traits and characteristics take time to accumulate. Adaptation: Over time, the traits that confer a selective advantage become more prevalent in the population, leading to adaptation. Adaptation is the process by which a population becomes better suited to its environment.
