Bioscience 2_Chapter 18_JKele

Chapter 18: Evolution and Origin of Species

• Course: BIOL 122: Bioscience II

• Instructor: Joseph Kele, Ed.Dc., M.S.

• Semester: Spring 2025

• Source: Information adapted from Openstax Biology 2e

Learning Outcomes (Section 18.1: Understanding Evolution)

• Describe how scientists developed the present-day theory of evolution

• Define adaptation

• Explain convergent and divergent evolution

• Describe homologous and vestigial structures

• Discuss misconceptions about the theory of evolution

Charles Darwin

• Found of natural selection

• Darwin’s postulates:

  • Most characteristics are heritable, passed from parent to offspring

  • More offspring are produced than can survive; there is competition for resources

  • Characteristics of offspring vary, and these variations are heritable

  • Adaptation

Charles Darwin’s Observations

• Observed variability in beak shape among finch species

• Here, beak adaptations allowed finches to access different food sources, showcasing natural selection in action

Natural Selection vs. Artificial Selection

• Focus on natural selection, where organisms better adapted to their environment tend to survive and reproduce

• Artificial selection is driven by humans, selecting for desired traits in crops and domesticated animals

  • Selective breeding leads to ideal hybrids and breeds

Homologous Structures

• Similar structures in different organisms indicate shared ancestry

• Examples include:

  • Human limbs

  • Dog legs

  • Bird wings

  • Whale flippers

Convergent vs. Divergent Evolution

• Convergent Evolution: Distinct species develop similar traits not due to common ancestry

  • Examples: Birds, butterflies, bats

• Divergent Evolution: Two or more species diverge from a common ancestor

  • Examples: Wolves and dogs

Gene Flow versus Genetic Drift

• Gene flow: Exchange of genes between populations through migration

• Genetic drift: Random events affecting allele frequencies, especially in small populations

  • Population size impact: Gene flow is more prominent in larger populations; genetic drift causes significant impact in smaller populations

Speciation

• Defined as the process where one species splits into two

  • Helps explain shared traits among organisms due to common ancestry

Microevolution & Macroevolution

• Microevolution: Changes in allele frequencies in a population over time

• Macroevolution: Broad patterns of evolution above the species level

  • Examples include new groups like mammals or flowering plants from series of speciation events

Learning Outcomes (Section 18.2: Understanding Evolution)

• Define species and how they are identified

• Describe genetic variables leading to speciation

• Identify prezygotic and postzygotic reproductive barriers

• Explain allopatric and sympatric speciation

• Describe adaptive radiation

Species

• A species is a group that interbreeds and produces viable, fertile offspring, separate from other groups

• Reproductive compatibility unites members of a biological species

  • Example: All humans are classified as Homo sapiens

The Biological Species Concept

• Focuses on potential to interbreed, not on physical appearance

  • Example: Eastern vs. western meadowlark, differing songs prevent interbreeding despite similar looks

  • Example: Despite diversity, all humans are a single species based on reproductive compatibility

Speciation Overview

• Allopatric Speciation: Splitting due to geographic isolation

  • Methods: Dispersal and vicariance

• Sympatric Speciation: Occurs in the same geographic area

  • Methods include chromosomal errors leading to polyploidy

  • Habitat differentiation and sexual selection play roles

Reproductive Isolation

• Crucial for new species formation

• Biological barriers preventing interbreeding:

  • Includes prezygotic (before fertilization) and postzygotic (after fertilization) barriers

  • Hybrids result from interspecific mating yet often do not produce viable offspring

Prezygotic Barriers

• Three categories:

  • Temporal isolation: Different breeding times

  • Habitat isolation: Different environments

  • Behavioral isolation: Difference in mating behaviors

Postzygotic Barriers

• Focus on barriers after fertilization:

  • Hybrid inviability: Offspring fail to survive

  • Hybrid sterility: Offspring fail to reproduce

Other Definitions of Species

• Morphological Species Concept: based on structural features

• Ecological Species Concept: defined by ecological niche and interactions

Allopatric Speciation

• Occurs when populations are geographically separated

  • Example: Water level drops creating smaller lakes

• Divergence of gene pools can lead to distinctive traits and speciation

Example of Allopatric Speciation

• Kaibab Squirrel: Located on the North Rim of the Grand Canyon; geographically isolated from Abert’s Squirrel, leading to distinct characteristics

• Potential for classification as a separate species in the future

Sympatric Speciation

• Occurs in the same geographical area through:

  • Polyploidy: Chromosomal errors during cell division

  • Habitat differentiation: Use of different resources

  • Sexual selection: Traits that impact mating success

Factors Influencing Sympatric Speciation

• Polyploidy: Extra chromosome sets resulting from errors in cell division

• Aneuploidy: Resulting from non-disjunction during meiosis, leading to imbalances in chromosome numbers

• Allopolyploidy: Cross-species mating resulting in viable, but sometimes sterile offspring

iClicker Questions

• Various scenarios to assess understanding of evolution, reproductive isolation, and speciation processes

Learning Outcomes (Section 18.3: Reconnection and Speciation Rates)

• Describe pathways of species evolution in hybrid zones

• Explain major theories on rates of speciation

Hybrid Zones

• Regions where different species meet, potentially producing hybrids

• Example: Fire-bellied toads living at different altitudes with a hybrid zone where they meet

Outcomes for Hybrids

• Reinforcement: Strengthening prezygotic barriers

• Fusion: Weakening barriers leading to merging species

• Stability: Hybrids surviving better in some environments than parent species

Rates of Speciation

• Two models:

  • Punctuated Model: Quick changes followed by stability

  • Gradual Model: Slow, steady changes over time

• Focus on how species diverge and adapt over time