3.4.5 Species and taxonomy

• Species- population of individuals which can breed to produce living, fertile offspring, which are able to breed and produce more offspring
• Problems with a simple species definition:

  • Organisms have evolved
  • Artificial selection (where something has intervened to produce a new species)
  • Some organisms can't produce offspring (hybrids)
• Courtship behaviours:

  • Behaviour of closely related species is more similar than those in a different species
  • The ability to display a behaviour is genetically determined
  • Courtship behaviours evolve and influence the species chance of survival
  • Survival of the species is more important than the survival of the individual
• Simple courtship behaviours:

  • Visual displays
  • Releasing a chemical/ hormone
  • Making different sounds
• Complex courtship behaviours:

  • Fighting in front of the female
  • Building a part of a habitat
  • Dancing
• Advantages of courtship behaviour:

  • Allows species to recognise other members of their own species
  • Helps to identify a mate that is capable of breeding/ sexually mature and therefore fertile
  • Forms a pair bond
  • Synchronises mating
  • Can trigger females to be in season and become able to breed
• Artificial classification- grouping organisms based on features which can be visibly seen, like analogous characteristics (same function, but come from a different evolutionary origin)
• Phylogenetic classification- based on evolutionary relationships between generations, classifies species into groups using shared features from their ancestors. Groups are arranged into a hierarchy with no overlapping groups
• Taxonomy- hierarchy of taxa (groups) and the relationships between them
• Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
• The three domains:

  • Bacteria- single celled prokaryote, single circular loop of DNA, no histone proteins. No membrane bound organelles, cell wall is made of murein.
  • Archea- similar to bacteria, but with some differences- have no murein and their genes and protein synthesis is similar to eukaryotes.
  • Eukarya- made of one or more eukaryotic cell, have membrane bound organelles, no murein in any cell walls they may have.
• Naming species- Binomial species

  • Written in italics/ underlined if hand written
  • First part is the genus name and starts with a capital letter
  • Second part is the species name and is all lower case
• What can be used to clarify evolutionary relationships?

  • Genome sequencing- of DNA base sequences
  • Comparing amino acid sequences- from polypeptides in a protein
  • Immunological comparisons- using antibodies
• Sequencing the genome- involves the DNA sequence of a gene:

  • Gene has to be found in the selected species.
  • Base sequences are compared between species to see differences in the base sequences.
  • The more differences between the base sequences, the less closely related the species are.
  • The less differences between the base sequences, the more closely related the species are.
• Difference in amino acid sequence or type- a short amino acid sequence is taken from similar or the same proteins:

  • The less differences between the amino acid sequences of a species, the more closely related the species are.
  • The more differences between the amino acid sequences of species, the less closely related the species are.
• Agglutination- clumping together of antibodies, formed by antigen-antibody complexes
• Immunological comparisons between species using an antibody and similar proteins- measuring degree of agglutination:

  • Using serums of the organisms (without cells or platelets).
  • Antibodies are generated against the species being tested against.
  • Percentage of agglutination is measured against the other species being tested.
  • The more agglutination to the test species, the more related the species.
  • The less agglutination to the test species, the less related the species.
• Due to conflicting evidence, a variety of evidence is used to draw valid conclusions of the relationships between different organisms.