Speciation and Species Concepts

  • Speciation

    • Introduction to Chapter 16:

    • No exact number of species; estimates vary.

    • Currently, 1.9 million officially described species.

    • Estimated total numbers vary between 9 million and 100 million.

    • Many undiscovered species likely exist in unexplored areas, particularly in oceans.

    • Example: Over 3,000 species of catfish identified.

  • Definition of Speciation

    • Speciation is the process of creating new species

    • Ongoing since the start of life, resulting in 9-100 million species today.

    • Evolutionary biologists aim to understand the forces driving speciation.

  • What is a Species?

    • Commonly defined as populations that can interbreed and evolve independently.

    • Isolation is key; no gene flow distinguishes different species.

    • Documentation of this concept varies depending on species type.

  • Naming a Species

    • Example: Monachus schauinslandi

    • Named after Hugo Schauinsland, who discovered a skull in 1899.

    • Common name: Hawaiian monk seal (NOAA).

  • Species Concepts

    • Different species concepts help define criteria for species recognition.

    • Each concept focuses on various aspects of biology and may suit specific species.

  • Morphospecies Concept

    • Uses phenotypic measurements to define species.

    • Benefits:

    • Applicable to both living and extinct specimens.

    • Also useful for asexual species.

    • Drawbacks:

    • Difficult to define thresholds; minor differences can alter species classification.

    • Fails to consider non-morphological variations among species.

  • Phylogenetic Species Concept

    • Defines species based on monophyletic lineages (ancestor + all descendants).

    • Benefits:

    • Works on fossils and asexual lineages.

    • Valid if a phylogenetic tree can be constructed.

    • Drawbacks:

    • Variability in tree construction can affect species boundaries.

    • Changes can lead to confusion when applied to previously defined groups.

  • Biological Species Concept (BSC)

    • Defines species as groups that are reproductively isolated.

    • Isolation can mean no mating or mating yielding no fertile offspring.

    • BSC, promoted by Ernst Mayr in 1942, is widely used.

    • Recognizes evolutionary independence via reproductive isolation.

  • BSC in Practice

    • Difficult to test due to spatial separation of populations.

    • Focuses on actual or potential interbreeding.

  • Challenges with BSC

    • Assessing extinct and asexual organisms is problematic.

    • Example: Bacteria and archaea reproduce asexually with limited gene exchange.

    • Hard to define microbial species using BSC criteria.

  • Bacteria and Archaea

    • Gene exchange in bacteria occurs in a one-way manner, defining species by gene sets.

  • Worksheet Activity

    • Form groups of ~4 students for discussion.

    • Complete a worksheet together.

    • Instructor will circulate and assist as needed.

  • Case Study: Marine Phytoplankton

    • Focus on the genus Pseudo-nitzschia, which can produce harmful algal blooms.

    • Utilized multiple species concepts to understand and define species.

  • Using Multiple Concepts

    • Morphological species concept used with different microscopy techniques.

    • Phylogenetic and biological species concepts corroborated; all indicated eight distinct species.

  • Significance of Species Identification

    • Important for practical reasons, such as identifying species for food sustainability (e.g., swordfish).

    • Example: Genetic barcoding to differentiate species in conservation genetics studies.