BIOL 2200 Lecture 3: Evidence for Evolution

Lecture Overview

• Title: BIOL 2200 Lecture 3: Evidence for evolution

• Reference: Darwin, 1845. Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy, R.N. 2d edition.

Learning Objectives

• Investigate how natural selection drives evolution in natural populations.

  • Natural selection drives evolution in natural populations through the differential survival among individuals, variation in heritable traits, and advantageous traits that likely to pass on and become more common in a population

• Review historical evidence for natural selection in humans.

  • Natural selection in humans comes in the form of lactase persistence and lactose intolerance

  • Due to the instance that mammals stop producing lactase the enzyme that breaks down lactose and dairy after weaning caused many populations develop lactose intolerance. The LCT mutation in areas of Western Europe and Northern Africa after cows were domesticated caused many to develop an inability to break down or consume lactose, due to some of the population not producing lactase and only 30% of humans producing lactase

  • This shows that natural selection favored those w/o the LCT mutations they were able to consume lactose and dairy products allowing them to have a higher fitness and hence produce more offspring, who can also digest lactose

• Consider how homologies and fossil evidence support descent with modification.

  • Homologies support that many species derive from a common ancestry as they may have similar features yet they may come in a different form and function completely different

    • Descent with modification supports that over generations species can adapt to their environments, by passing down traits that change throughout many generations

• Compare phenotypic plasticity to evolution.

  • Phenotypic Plasticity is the ability of a genotype to produce various phenotypes to adapt to an environmental change in one generation, this is not a heritable trait

  • Evolution is the ability for a species to evolve and pass down the most favorable traits to offspring across many generations resulting in change of variation and adaptability to its environment, this is heritable

Examples of Potential Evolution

• Bacteria and Antibiotics: A line of bacteria can become resistant to antibiotics in weeks.

• Chameleon Color Change: A chameleon changes color when moving between trees.

• Island Lizards: Lizards on islands have larger toepads that help them survive hurricanes.

• Genetic Disorders: Descendants of Dutch settlers in South Africa show a high rate of Huntington’s disease.

Evolution by Natural Selection

• Definition: Evolution is the change in heritable traits of a population over generations

• Natural Selection: The mechanism that drives evolution, characterized by:

  • Differential survival among individuals.

  • Variation in heritable traits.

  • Advantageous traits that increase fitness are more likely to be passed on and become more common.

Natural Selection Observed in Nature

• Examples:

  • Galapagos Finches: Notable for beak adaptation.

  • Peppered Moth: Color changes related to pollution.

  • Anolis Lizards: Adaptations in morphology (structure of body) observed in various environments.

Threespine Sticklebacks

• Characteristics: Small, drab fish in coastal waters or lakes in the Northern Hemisphere.

• Subject of Study: A model system for studying evolution due to morphological variation and environmental changes.

Variation in Sticklebacks

• Phenotypic Differences: Sticklebacks display different phenotypes in marine vs. freshwater environments.

  • Alizarin red is a stain that binds to calcium in preserved fish as seen in the marine stickleback

Variation in Lateral Plates

• Heritability of Traits: Lateral plates are a heritable trait controlled by the Eda gene.

• Adaptive Function: Spines and lateral plates offer protection against predators.

Environmental Influence on Plate Variation

• Historical Context: Marine sticklebacks colonized lakes during the last ice age, leading to different predator dynamics.

• Adaptive Cost: In freshwater, the production of lateral plates may contribute to growth and breeding opportunities.

  • This occurs due to the lateral plate in freshwater sticklebacks being less vast across the stickleback’s body leading it to survive longer and potentially breed more offspring. Predators have caused marine sticklebacks to produce a larger lateral plate to adapt against predation.

    • The difference is freshwater sticklebacks don’t have to worry about predation hence their small lateral plate and higher susceptibility to grow larger and breed more, but marine sticklebacks do, hence their larger lateral plate.

Evolution can be Rapid

• Example: Loberg Lake stickleback populations established from marine origins in 1982 show rapid evolutionary changes.

  • Lateral plate coverage increased after invasion to adapt to predation and in protecting itself seen in the graph

Exceptions to Rapid Evolution

• Stable Trout Populations: Trout in Lake Washington shows minimal genetic change, providing clues about genetics and adaptation.

  • In the two images we see how the more recent picture is bigger meaning less predation to worry about, but the older picture shows a smaller fish before adaptive changes

  • Lake cleanup, led to increased water clarity allowing for trouts to eat more sticklebacks. higher visibility= higher predation

Evolution of Resistance

• Examples of Resistance:

  • Antibiotic resistance in MRSA, TB, gonorrhea.

  • Pesticide and herbicide resistance.

Lactose Tolerance in Humans

• General Pattern: Mammals typically stop producing lactase around weaning; about 30% of humans persist in producing lactase.

• Cultural Implications: Rapid selection linked to cow domestication about 10,000 years ago, particularly in Europe and North Africa.

  • Due to the genetic variations in the LCT mutation the enzyme lactase and the fact that humans stop producing lactose at weaning some humans could breakdown lactose, but others could not break down lactose which led to lactose intolerance in the areas of Western Europe and North Africa where lactase persistence was fairly to moderately high when cows domesticated to these areas

Homology in Evolution

• Definition: Shared characteristics due to common ancestry, including anatomical and molecular homologies.

  • Form and function may be very different as seen in the image

Homology and the Fossil Record

• Fossils: Evidence from late Devonian fossils shows traits common between lobe-finned fish and early tetrapods.

  • This supports descent with modification and homology as species change over time passing down traits that change throughout the many generations but share common anatomical homology.

Homology vs. Convergence

• Differences: Homology arises from common ancestry, while convergent evolution leads to similarities due to environmental pressures.

Phenotypic Plasticity: Assessing Evolution

• Definition: Ability of a single genotype to produce different phenotypes based on environmental conditions.

  • Ex. predators present for marine sticklebacks and no predators for freshwater sticklebacks resulting in differently sized lateral plates

    • Note: Plasticity is not heritable, showing phenotypic changes occur in one generation.

Conclusion: Distinguishing Evolution from Adaptation

• Evolution versus phenotypic changes must be understood in the context of heritability and environmental influence.

Answer: D

Answer: C

Answer: A

Answer: D