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Critical Thinking Ch 7 - 10

Chapter 7 Learning Objectives

  • Focus on concepts of evolution and adaptation.

  • Understand the mechanisms through which evolution occurs.

  • Differentiate between microevolution and macroevolution.

Evolution and Adaptation

  • Process of Evolution: Depends on genetic variation. Can occur through random processes or selection.

    • Microevolution: Operates at the population level.

    • Macroevolution: Operates at the species level and higher taxonomic organization.

Definition of Evolution

  • Evolution: "Change in the genetic composition of a population over time."

    • More specifically, it refers to a change in the frequency of alleles in a population over time.

Mechanisms of Evolution

  • Evolution can occur through several mechanisms:

    • Natural Selection: Process by which traits that increase an organism's chances of surviving and reproducing become more common in successive generations.

    • Artificial Selection: Human-directed breeding of organisms to select for desirable traits.

    • Genetic Drift: Random chance events cause changes in allele frequencies in a population, more pronounced in small populations.

Genotype, Environment, and Phenotype

  • Genotype: Genetic makeup of an organism.

  • Phenotype: Outward expression of environmental effects on an organism’s genotype.

    • Includes all observable traits such as morphology, development, and behavior.

Natural Selection Explained

  • Natural Selection: "A change in the frequency of genes in a population through the differential survival and reproduction of individuals that possess certain phenotypes."

  • Genetic variation may be observed with genetically identical twins under different environmental conditions.

Sources of Genetic Variation within Species

  • Genetic variation can be characterized as:

    • Silent Variants: Changes that do not affect protein coding regions.

    • Deleterious/Fatal Variants: Harmful variations that could lead to loss of fitness.

    • Beneficial Variants: Traits that enhance survival or reproduction in a local environment (occurring at random, not by design).

  • Random Assortment: During meiosis, gametes are formed via shuffling and independent assortment of genes; the allele combinations in gametes vary.

  • Sexual Reproduction: Merges haploid gametes from two parents creating novel combinations of alleles.

  • Mutations: Permanent changes in DNA that can involve deletion, insertion, or substitution of nucleotides.

Evolution through Natural Selection

  • Benefits or harmful effects of an allele influence the likelihood of successful reproduction of individuals carrying those alleles; this leads to adaptations in future generations.

  • Evolution can also occur through random processes:

    • Genetic Drift: Changes in allele frequencies due to random events, particularly impactful in smaller populations.

Understanding Genetic Drift

  • Genetic Drift:

    • Loss of genetic variation due to random events in mating, mortality, and fecundity.

    • More pronounced in small populations as random events can significantly influence genetic variations.

    • Example: Eye pigmentation in cave fish populations shows variations due to genetic drift.

Effects of Genetic Drift

  • Bottleneck Effect: A sudden reduction in population size results in a loss of genetic diversity.

  • Founder Effect: A small group breaks away from a larger population, leading to reduced genetic diversity in the new group compared to the original population.

Ecological Theater, Evolutionary Script

  • Different types of selection impact trait evolution:

    • Stabilizing Selection: Favors average traits, eliminating extremes.

    • Directional Selection: Favors one extreme trait, causing a shift in the population’s trait distribution.

    • Disruptive Selection: Favors both extreme traits, potentially leading to speciation.

Artificial Selection

  • Artificial Selection: Human intervention in breeding with specific goals for traits.

    • Seen in livestock, domesticated animals, plants (e.g., maize from teosinte).

Speciation Types

  • Allopatric Speciation: Evolution of new species through geographical isolation, leading to divergence until interbreeding can no longer occur.

  • Sympatric Speciation: Evolution of new species within the same geographical area, facilitated by distinct habitats or niches available.

    • Example: Cichlid fish in Lake Tanganyika evolving into multiple species.

Chapter 8 Learning Objectives

  • Focus on life histories and the trade-offs organisms face in their lifecycles.

  • Life histories differ among species based on ecological and developmental factors.

Life History Traits

  • Life History: Represents the schedule of an organism's life, influenced by trade-offs.

  • Organisms differ in reproductive patterns and eventually reach senescence.

Trade-offs in Life History

  • Trade-off in Allocation: Investment in time and energy among growth, reproduction, and survival to maximize fitness.

    • Influenced by both extrinsic (ecological) and intrinsic (physiological, developmental) factors.

K vs. R Strategy

  • K Strategy: Characters of organisms that invest heavily in a few offspring with high parental care, long maturity time.

  • R Strategy: Characterizes species with high fecundity, low parental investment, and shorter life spans.

Intraspecific Variations

  • Intraspecific: Variations occurring within species can impact traits like offspring number versus seed size.

  • A trade-off example is shown in goldenrod plants where more seeds are associated with smaller seeds.

Growth Patterns

  • Distinction between Determinate Growth (no further growth after reproduction) and Indeterminate Growth (continues growing post-reproduction).

Resource Availability and Timing

  • Fluctuations in resources dictate the timing of life history events, impacting individual growth and fecundity based on resource levels (hence survival).

Phenological Responses to Climate Change

  • Meta-analysis by Parmesan (2007): Investigated impacts on 203 species in relation to climate changes, outlining shifts in breeding patterns.

Population Decline and Phenological Mismatches

  • Observed declines in bird populations related to food resource mismatches due to climate-induced timing changes.

Chapter 9 Learning Objectives

  • Understanding reproductive strategies, both sexual and asexual, and their evolutionary implications.

Asexual vs. Sexual Reproduction

  • Asexual Reproduction: Leads to genetically identical offspring through processes like budding and fragmentation.

  • Sexual Reproduction: Produces genetically diverse offspring through fertilization of gametes.

Costs and Benefits of Sexual Reproduction

  • Benefits: Genetic variation aids adaptation, reduces mutations, and benefits from biparental investment in offspring care.

  • Costs: Includes the energy cost of mating behaviors, risk of predation, and loss of genetic contributions due to meiosis.

Red Queen Hypothesis

  • Red Queen Hypothesis: Coevolutionary dynamics favor sexual reproduction due to interactions with parasites, promoting genetic variation in populations.

Self-Fertilization and Mixed Mating Systems

  • Self-fertilization: Common in hermaphrodites but carries the risk of inbreeding depression.

  • Mixed Mating: Incorporates both self-breeding and outcrossing, often responsive to mate availability.

Genetic and Environmental Sex Determination

  • Genetic Sex Determination: Typically involves chromosomal inheritance patterns (XX for females, XY for males in mammals).

  • Environmental Sex Determination: Phenotypic plasticity based on environmental factors, such as temperature affecting sex in some reptiles.

Mating Systems and Sexual Selection

  • Mating System: Defines mate number and the permanence of mating relationships.

  • Sexual Selection: Leads to traits facilitating reproduction, resulting in primary (fertilization-related) and secondary (body size, courtship) differences between sexes.

Runaway Sexual Selection and The Handicap Principle

  • Runaway Sexual Selection: A cycle where preference for a trait and the trait itself enhance each other until genetic variance is reduced.

  • Handicap Principle: An individual carrying a greater handicap (e.g., disease) must be able to offset it successfully-propagating desirable traits.

Chapter 10 Learning Objectives

  • Explore social behaviors and their implications in various species.

Benefits and Costs of Group Living

  • Benefits: Includes improved survival through defense mechanisms, resource gathering, and mating opportunities.

  • Costs: Increased risk of disease spread, competition for resources, or predation due to higher population density.

Optimal Group Size

  • Theoretical optimal group size results from balancing the benefits and costs of group living, considering genetic information.

Types of Social Interactions

  • Classification based on impact on donor and recipient:

    • Cooperation: Positive outcomes for both.

    • Selfishness: Benefit for donor but harm to recipient.

    • Altruism: Harm for donor but benefit for recipient.

    • Spitefulness: Negative impact on both parties.

Direct and Indirect Fitness

  • Direct Fitness: Success in passing down genes to offspring.

  • Indirect Fitness: Success through aiding relatives to pass down shared genes.

  • Inclusive Fitness: Combination of direct and indirect fitness contributing to evolutionary success.

Evolution of Altruism Equation

  • Altruism can be evolutionarily favored if the fitness benefit times the coefficient of relatedness exceeds the cost to the altruist (B × r > C).

Characteristics Defining Eusociality

  • Definition includes adults living in groups with generations overlapping, cooperative brood care, and reproductive dominance.

Haplodiploid System and Eusociality

  • In systems like hymenopteran, sisters have a higher relatedness coefficient fostering the evolution of eusocial behavior due to significant genetic overlap among workers.