Invertebrate Zoology

Lecture Notes - Classification

Notes:  This is an outline of my class notes - details and visuals will be given in class!

Read: Chapter 10 in Hickman, Roberts & Larson.

1. The Role of Linnaeus
   1. Serious attempts to classify organisms go back to Aristotle
   2. Even "primitive" groups often have names for each species that is important to them.
   3. Carolus Linnaeus
      1. Born Karle von Linne in 1707 in Sweden
      2. Botanist at University of Uppsala
      3. Developed binomial nomenclature
         1. uses two names, one for Genus and one for Species
         2. latinized form (Carolus Linnaeus is the Latin form of Karle Linne)
         3. generic name is a capitalized noun
         4. specific name (specific epithet) is not capitalized, usually an adjective
         5. binomial is italicized or underlined.
         6. binomial is often accompanied by the name of the scientist who named the species and the year
            1. if the year is in parentheses this indicates that the generic name has changed since the species was originally described.
            2. the accompanying name is called the authority
         7. Examples:
            • Clemmys guttata (Schneider, 1792)
            • Libellula cyanea Fabricius, 1775
      4. Linnaeus also introduced higher categories
         1. There are now 7 mandatory taxonomic ranks for animals
         2. there are over 30 taxonomic ranks in all
         3. the mandatory ranks are: Kingdom, Phylum, Class, Order, Family, Genus and Species
         4. other ranks include subkingdom, superclass, subfamily, infraclass, tribe, etc.
         5. higher ranks are more inclusive, lower ranks are more exclusive
         6. with animals, all family names end in -dae
         7. taxonomic rank refers to these levels; taxa (singular taxon) refers to a specific grouping:

         Taxon	Taxonomic rank
         Pentatomidae	family
         Scudderia	genus

      5. Other rules for names:
         1. Names must be published along with a species description.
         2. A type specimen (holotype) must be deposited in a museum
         3. Paratypes or syntypes may also be deposited as well to better express the range of variation in the species
         4. If the species is ever split, the species name stays with the organisms represented by the holotype
         5. Priority - the first name published is the valid one
         6. The International Commission on Zoological Nomenclature handles all disputes.

1. Taxonomic Characters and Phylogenetic Reconstruction
   1. Phylogeny refers to the map of the evolutionary relationships between living organisms.  It is usually presented in the form of a "tree" diagram, since new species arise from the splitting of old species just as twigs branch on a tree.
   2. Characters are those features of an organism (often including behavioral or DNA evidence) that are used to infer phylogeny.
   3. If characters shared by two groups of animals are similar as a result of common ancestry, the characters are homologous.
   4. The character state exhibited by the oldest common ancestor is termed ancestral.
   5. Any deviations from the ancestral form are called derived characters.
      1. it is assumed, then that derived characters formed later than ancestral ones.
   6. Polarity of a character is determined by its resemblance to either ancestral or derived characters.
   7. To determine polarity, an outgroup comparison must be done:
      1. another group which is related to the group being studied is examined
      2. if a character state is shared by both the outgroup and the group being studied, that character state is determined to be ancestral.

         for instance, bees and flies are related (but placed in different orders).  Most bees have wings (as do most flies), and, in fact, most other insect orders have wings.  If bees are used as the outgroup for flies, the presence of wings in both groups can be inferred as an ancestral state - that is, the insects that gave rise to both bees and flies had wings.  Now, if we look at flies that do not have wings, we can infer this to be a derived state.

          

   8. Shared derived characters are called synapomorphies (hair is a synapomorphy shared by all mammals)
   9. Organisms that share a synapomorphy are called a clade.
      1. some clades are then assigned as taxa - i.e. mammals
   10. Symplesiomorphies are shared ancestral characters, and are not useful for determining clades.
       1. All eukaryotes share mitochondria - this is a synapomorphy that holds together the eukaryotes, but a symplesiomorphy when it comes to grouping within the eukaryotes.
   11. Clades are nested and a diagram of this nesting is called a cladogram.  A cladogram differs from a phylogenetic tree in that a cladogram doesn't take account of the names of the ancestral groups, when they existed, and for how long - like a phylogenetic tree does.
   12. There are 3 main lines of evidence used to construct cladograms:
       1. morphology - using physical characteristics of the organisms
       2. biochemistry - using differences in chemicals (including DNA) and chemical pathways
       3. cytology - using differences in the chromosomes
       4. some would add a 4th line of evidence - behavior

        

2. Theories of Taxonomy
   1. There are 2 theories in use today for constructing phylogenies: 
      1. Evolutionary taxonomy
      2. Phylogenetic systematics or cladistics
   2. To understand the differences between the two, you need to understand monophyly, paraphyly and polyphyly:
      1. monophyly: monophyletic taxa include the most recent common ancestor of the group and all of that ancestors descendents.
      2. paraphyly: paraphyletic taxa include the most recent common ancestor of a group, but not all of its descendents.
      3. polyphyly: polyphyletic taxa do not include the most recent common ancestor of the group.
   3. Evolutionary taxonomy:
      1. in this scheme, all groups must share a common ancestor (i.e. show common descent) and show unique adaptive features.
      2. both monophyletic and paraphyletic taxa are allowed
      3. has been practiced for some time but is being replaced? by cladistics
   4. Cladistics:
      1. In this scheme, all groups must share not only the common ancestor, but also all of its descendents.
      2. only monophyletic taxa are thus allowed
   5. As cladistics replaces evolutionary taxonomy, many changes will occur:
      1. Linnaean taxonomic ranks will disappear
      2. convenient (but paraphyletic) groupings will disappear (i.e. reptiles)

       

3. The Species Concept(s)
   1. There are several modern concepts of species.  Most of them share:
      1. requirement of common descent
      2. requirement that the groupings be as small as possible
      3. requirement that there be some reproductive exchange between the (sexually reproducing) members of a species
   2. We will discuss 4 species concepts, one ancient and the other 4 modern:
      1. Morphological species concept:
         1. this ancient concept held that morphologically similar organisms could be grouped into species; that species did not change over time, and that an ideal specimen existed for that species.  This is the concept that was in force when Linnaeus created his system and persists today in the concept of the holotype.
      2. Biological species concept:
         1. "A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature."  This concept focuses on reproduction and ecological role.  Morphology often will be useful in identifying such species, but in the case of closely related sibling species, the morphology may be identical but the populations don't interbreed.
         2. Problems with the biological species concept:
            1. are organisms which do not reproduce with each other  because of vast distances in space different species?
            2. are organisms which do not reproduce with each other because they live at different times (in history) different species?
            3. are organisms which do not reproduce with each other because they do not reproduce sexually valid species at all?
      3. Evolutionary species concept:
         1. "a species is a single lineage of ancestor-descendent populations that maintains its identity from other such lineages and that has its own evolutionary tendencies and historical fate."
         2. This concept avoids some of the problems with the biological species concept.
      4. Phylogenetic species concept:
         1. "a species is an irreducible (basal) grouping of organisms diagnosably distinct from other such groupings and within which there is a parental pattern of ancestry and descent."
         2. this approach is slightly different from the evolutionary species concept in that geographically isolated populations would be treated as separate species by the phylogenetic concept and as a single species by the evolutionary species concept.

             

4. Major Divisions of Life
   1. Currently we use 5 Kingdoms:
      1. Monera - all prokaryotes
      2. Protista - unicellular organisms
      3. Fungi - unicellular or multicellular, non-photosynthetic, non-motile
      4. Plantae - multicellular, photosynthetic (ancestrally)
      5. Animalia - multicellular, non-photosynthetic
   2. These groups are not monophyletic and will have to be revised as cladistics are adopted.

    

5. The Animals
   1. Above the level of the phylum, there are several groupings of animals that can be made.  The status of these groupings is also in flux, and will likely be changed in the near future as additional data, particularly DNA data, accumulates.