BIOL 120 Chapter 24 Notes

BIOL 120: Chapter 24 Study Notes

Species Concepts
  • Definition of Species: There are several ways to define species, with the key concepts being:
    • Biological Species Concept
    • Definition: Defines species based on the potential to interbreed and produce viable, fertile offspring.
    • Reproductive Isolation: This involves prezygotic and postzygotic barriers preventing reproduction with individuals of other species.
    • Limitations: Not applicable to fossils (since mating information is unavailable) and does not account for species capable of hybridization.
    • Morphological Species Concept
    • Definition: Based on body shape and structural features used to identify species.
    • Functionality: Useful for classifying fossils and certain species that can hybridize (e.g., polar bears and grizzly bears).
    • Challenge: Determining which morphological features are critical for species classification.
    • Ecological Species Concept
    • Focus: Emphasizes the ecological niche occupied by a species.
    • Phylogenetic Species Concept
    • Focus: Uses genetic analysis to trace common ancestry and assess genetic distance between species.
    • Question Addressed: How distinct must DNA be for species to be classified separately?
Reproductive Barriers
  • Identification Table: Fill in types of reproductive barriers based on descriptions and examples
    • Reduced Hybrid Viability
    • Type: Postzygotic
    • Description: Species interbreed, but hybrids do not develop properly.
    • Example: Some hybrids of salamanders do not develop properly.
    • Reduced Hybrid Fertility
    • Type: Postzygotic
    • Description: Hybrids are vigorous but sterile due to genetic incompatibility.
    • Example: Mules (the hybrid of horses and donkeys) are sterile.
    • Mechanical Isolation
    • Type: Prezygotic
    • Description: Morphological differences prevent successful mating.
    • Example: Flowers pollinated by different pollinators; wrong pollinator leads to unsuccessful pollen transfer.
    • Behavioral Isolation
    • Type: Prezygotic
    • Description: Differences in courtship behaviors prevent species from recognizing each other as mates.
    • Example: Different mating songs of Eastern and Western Meadowlarks.
    • Habitat Isolation
    • Type: Prezygotic
    • Description: Species inhabit different environments, preventing mating opportunities.
    • Example: Polar bears and grizzly bears occupy different habitats during mating seasons.
    • Hybrid Breakdown
    • Type: Postzygotic
    • Description: Hybrid offspring are viable and fertile, but their own offspring cannot interbreed with parent species.
    • Example: Many crop species show this phenomenon.
    • Temporal Isolation
    • Type: Prezygotic
    • Description: Species may potentially hybridize but breed at different times.
    • Example: Spotted skunks mating in late summer versus striped skunks in late winter.
    • Gametic Isolation
    • Type: Prezygotic
    • Description: Even if mating occurs, gametes are incompatible.
    • Example: Marine species where sperm can only fertilize their own species' eggs.
Evolutionary Terms and Concepts
  • A. Allopolyploidy
    • Definition: A polyploid organism that contains the genomes of two or more different species.
  • B. Reproductive Isolation
    • Definition: The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring.
  • C. Microevolution
    • Definition: Change in allele frequencies of a population over many generations.
  • D. Macroevolution
    • Definition: Broad patterns of evolution above the population level yielding new species, families, orders, etc.
  • E. Speciation
    • Definition: The formation of new species based on various mechanisms.
  • F. Anagenesis
    • Definition: Accumulation of mutations over time leading to a new species undistinguished from its ancestor.
  • G. Cladogenesis
    • Definition: Branching evolution, where a new species arises from a parent species that continues to exist.
  • H. Allopatric Speciation
    • Definition: The formation of new species in populations that are geographically isolated from one another.
    • Example: Very similar species of snapping shrimp evolving due to geographic barriers such as the isthmus of Panama.
  • I. Sympatric Speciation
    • Definition: The formation of new species in populations that live in the same geographic area. This can occur through mechanisms such as polyploidy (especially in plants) or habitat differentiation.
  • J. Polyploidy
    • Definition: A chromosomal alteration in which the organism possesses more than two complete chromosome sets. Common in plants, leading to rapid speciation.
  • K. Autopolyploidy
    • Definition: A polyploid organism that contains multiple sets of chromosomes from a single species.
    • Example: New species of Tragopogon formed through hybridization and chromosomal doubling.
  • L. Heterochrony
    • Definition: An evolutionary change in the rate or timing of developmental events.
    • Example: Differing growth rates in anatomical features between species, such as humans and chimpanzees.
  • M. Paedomorphosis
    • Definition: The retention in an adult organism of juvenile features of its evolutionary ancestors.
    • Example: Axolotls retaining juvenile features into adulthood.
  • N. Homeotic Genes
    • Description: Class of genes specifying the positional development and organization of body parts.
    • Example: Hox genes determining limb formations in various species.
  • O. Hox Genes
    • Definition: A type of homeotic gene that plays a crucial role in specifying the anteroposterior axis and segment identity during embryonic development. These genes are shared across diverse animal phyla and determine the basic body plan.
  • P. Reinforcement
    • Definition: A process in which natural selection strengthens prezygotic barriers to reproduction, reducing the chances of hybrid formation.
  • Q. Fusion
    • Definition: The weakening of reproductive barriers between species, leading to increased hybridization and potentially the collapse of distinct species into one.
  • R. Stability
    • Definition: A phenomenon where hybrid zones are stable over time, with hybrids continuing to be produced.
Summary of Key Points
  • Species concepts provide different perspectives on defining and understanding species:
    1. Biological focuses on interbreeding potential.
    2. Morphological looks at physical characteristics.
    3. Ecological considers niche occupation.
    4. Phylogenetic analyzes genetic relationships.
  • Understanding reproductive barriers helps to clarify species interactions and the complexity of speciation.
  • Evolutionary processes include both gradual changes (microevolution) and large-scale changes (macroevolution) leading to new species either through anagenesis or cladogenesis.