Molecular Clock and Natural Selection

Molecular Clock

• A figurative clock used to measure evolutionary time
• Measures random neutral mutations in DNA at a constant, predictable rate
• Neutral mutations are not selected for or against in natural selection
• Organisms that diverged recently have fewer nucleotide differences
• Organisms that diverged long ago have many nucleotide differences

What is a Molecular Clock?

• A method to estimate when lineages diverged from a common ancestor
• Based on the assumption that mutations accumulate at a constant rate in DNA
• Used to date evolutionary events (e.g., the divergence of species)
• Can be used to measure evolutionary time

Natural Selection

• The process by which organisms better adapted to their environment are more likely to survive and reproduce, passing advantageous traits to future generations.
• Natural selection is not perfection, but rather favors traits that improve reproductive success
• Natural selection in nature involves competition for resources, and this can lead to conflict and cooperation, depending on ecological context. It does not create harmony or justify human actions.

Types of Natural Selection

• Stabilizing Selection: Favors average traits; individuals with average or moderate traits are more likely to survive and reproduce.
• Examples: Human babies of intermediate birth weight have higher survival rates compared to very small or very large babies; nesting birds.
• Diversifying Selection: Favors multiple extreme phenotypes and leads to increased genetic diversity in a population.
• Examples: Gray and Himalayan rabbits; color in peppered moths
• Directional Selection: Favors one extreme phenotype, causing the population to shift in that direction.
• Examples: Light-colored peppered moths are more common when the environment is pristine, but dark-colored peppered moths are better camouflaged against a sooty environment; Industrial melanism
• Kin Selection: A natural selection process that favors traits that help an organism's relatives reproduce, even if it means the organism sacrifices its own survival and reproduction.
• Traits include helping relatives, sharing food, and defending relatives.
• This can lead to altruism, in which individuals act in ways that benefit others at a cost to themselves to benefit relatives; social insects like ants, bees, wasps, and termites

Founder Effect

• A phenomenon that occurs when a small group of individuals from a larger population establishes a new population
• The new population's gene pool is a smaller and potentially different representation of the initial pool.
• This can lead to higher or lower concentrations of genetic mutations that cause otherwise rare diseases
• Examples: Eastern Pennsylvania Amish/ Old Order Amish; Sephardic Jews in Ecuador

Asexual vs. Sexual Reproduction

• Asexual reproduction is more advantageous in stable environments without competitors or predators.
• It allows for quick population growth without the need to find a mate and produces offspring with the same genetic makeup as the parent
• Reproduction is efficient in stable environments where finding mates is difficult.

Positive vs. Negative Assortative Mating

• Positive Assortative Mating: Individuals choose to mate with similar individuals based on physical characteristics or genotype. This can increase homozygosity.
• Negative (Disassortative) Assortative Mating: Individuals choose to mate with dissimilar individuals. This can increase heterozygosity.

Inbreeding

• Inbreeding occurs when two closely related individuals mate and have offspring.
• It significantly increases the likelihood of the offspring inheriting harmful recessive genes which are more common in a small population..
• Higher risks of genetic disorders, reduced fertility, and reduced genetic diversity.
• Inbreeding depression describes the overall reduced fitness in a population.

Spirochetes Bacteria

• Pathogenic species cause human diseases such as syphilis, Lyme disease, and periodontal disease.

Polyandry in the Spotted Sandpiper

• Sandpipers can be found in the Arctic and subarctic regions.
• The spotted sandpiper has invaded temperate climates, allowing for a longer breeding season; early breeding season.
• Females arrive at breeding grounds before males and compete for them.
• A female lays multiple clutches with different males, and each male incubates the eggs and care for the young.

The Red Queen Hypothesis

• Species are locked in a coevolutionary arms race.
• Adaptations in one species drive the evolution of counter-adaptations in another.
• Continuous cycle of adaptation to stay alive, keep up with competitors and predators.
• Sexual reproduction is advantageous—leads to greater genetic diversity that makes it harder for parasites or predators to adapt to a single host genotype

Who are the Fungi?

• A major branch of Eukarya;
• They have cell walls containing chitin.
• Heterotrophs- digest food extracellularly; absorb it
• Most are multicellular, but some have reverted to unicellular forms (yeasts)
• Many ecological associations, including decomposers, parasites, mutualists, and commensals.

Land Plants

• They use chlorophyll a and b
• These include Bryophytes (liverworts, mosses, hornworts), Seedless vascular plants (ferns, horsetails), Gymnosperms (conifers). Angiosperms (flowering plants)..
• They typically reproduce through spores or seeds, and have various adaptations for survival in different environments, including damp or arid environments.

Protostome vs. Deuterostome

• Protostomes: First opening is the mouth in embryo development
• Deuterostomes: First opening is the anus in embryo development; a later opening will lead to the formation of the mouth
• This is a crucial distinction in animal phylogeny

Higher Level Taxonomic Branches

• Higher level taxonomic diversity within species reflects an important concept
• Represents a loss of diversity among species within a larger group like an order, or class and this is important due to the loss of species in a genus, order, class and so on.
• For example, if the tuatara disappears, then a whole class of reptiles will disappear too; an entire branch on the tree of life will be lost.

What are the largest groups of animals on Earth?

• The Ecdysozoa are a remarkably large group among all animals.
• This group includes arthropods (insects, crustaceans, and spiders) and nematodes.
• It contains a large portion of all known species on Earth.

Whale Watching

• Whale watching generates significant revenue
• Whales act as ecosystem engineers, playing an important role in nutrient cycling and fertilizing the water.
• Tourism brings more revenue than whaling; which is environmentally detrimental.

Ecosystem Services

• Ecosystem services are the direct and indirect benefits humans receive from ecosystems. Supporting: Nutrient cycling (water and soil), photosynthesis. Provisioning: Food, fresh water, fiber, biomass fuel, and medicine. Regulating: Air quality, water runoff, , climate, natural hazards. Cultural: Existence, ethical and recreation values, ecotourism

Explore the concepts of molecular clocks and natural selection in this quiz. Understand how molecular clocks estimate evolutionary time and the role of natural selection in shaping species. Test your knowledge on mutations, lineage divergence, and the implications of evolutionary mechanisms.