WEEK 3 MICROTAXONOMY

• "The theory and practice of delimiting organisms and classifying them"


  Simpson 1961
• kinds of organisms are recognized and delimited

  microtaxonomy
• kinds of organisms are classified

  macrotaxonomy
• alpha taxonomy - recognition and description of species and first classification
• beta-taxonomy - classification of species in an hierarchical system
• y-taxonomy -evolutionary factors
• A group of organisms that are very similar to each other and is capable of interbreeding is a species
• • species - any different kind of thing (Plato)
• Any unit possessing a common essence (Principle of logical division by Plato)
• True breeding; variations are by accident (John Ray)
• deviant forms were not deserving to the rank of species but rather of variety (Linnaeus)
• Specific form "conditioned by function" (Cuvier)
• Individuals closely resembling each other and does not much differ from the term variety (Ernst Mayr)
• Morphological Species Concept - members of a species are individuals that look similar to each other
• • MSC
  • Smallest groups that are consistently and persistently distinct and distinguishable by ordinary means (Cronquist)
• • MSC
  • Easily organized kinds of organisms based on simple gross observation (Shull)
• • MSC
  • Distinct morphological characters are enough to entitle it (Regan)
• • MSC Problems
  • Arbitrary - individuals of two populations were very hard to tell but would not mate with one another
• • MSC Problems
  • Mimicry - organisms of the same species can look similar to one another
• • MSC Problems: Mimicry
  • Batesian Mimicry - mimic resembles a model that is poisonous; usually based on appearance, calls, scents
• • MSC Problems: Mimicry
  • Mullerian mimicry- Two or more equally poisonous or distasteful species have a similar color pattern
• • MSC Problem
  • Sexual Dimorphism -systematic difference in form between iof different sex in the same organism
• • MSC Problems
  • Allometric Variation - different structural proportions in different life stages
• • MSC Problem
  • Metamorphosis
• • MSC Problems
  • Heteroblasty - plants has a rapid change in the ontogenetictraits
• Biological Species Concept (BSC) - a species is a group of actually or potentially interbreeding individuals who are reproductively isolated from other groups
• • BSC Problems
  • Testing for interbreeding under natural conditions:
  • There are asexually reproducing organisms
• • BSC Problems
  • Sympatric speciation- reproductively isolated organisms
  • Allopatric speciation - geographical isolation
• Horizontal gene transfer makes classification difficult
• • BSC Problems: Reproductive isolation
  • Hybridization is common
• Evolutionary Species Concept (ESC) - a lineage evolving separately from others with its own unitary evolutionary role and tendencies
• • ESC Advantage
  • Solves the problem of intermittent hybridization
• Phylogenetic Species Concept (PSC) - smallest recognizable monophyletic group; has share derived characters
• • PSC Problems
  • Distinguishing between gene trees and species trees
• What is the best way to define a species?

  • Pluralism is the key biological species concept
  • The BSC helps us ask for species are formed
• • CONCEPTS OF SPECIATION: Reproductive Isolating Mechanisms
  • Prezygotic Mechanisms

  Prevents mating from occuring
• • CONCEPTS OF SPECIATION: Reproductive Isolating Mechanisms
  • Prezygotic Mechanisms
  • Isolated by time


  Temporal Isolation
• • CONCEPTS OF SPECIATION: Reproductive Isolating Mechanisms
  • Prezygotic Mechanisms
  • Same geographic area but with different habitats


  Habitat Isolation
• • CONCEPTS OF SPECIATION: Reproductive Isolating Mechanisms
  • Prezygotic Mechanisms
  • Different courtship rituals; little or no sexual attraction

  Behavioral isolation
• • CONCEPTS OF SPECIATION: Reproductive Isolating Mechanisms
  • Prezygotic Mechanisms
  • Structural differences in genitalia or flowers


  Mechanical Isolation