October 24, 2012 class notes

Class notes 2012.10.24

Outline

1. Classification & taxonomy
2. Taxonomy today
3. Reminder
4. Activity!

1. Classification & taxonomy

What is classification?

Classification is the grouping of things according to characteristics

The science of classifying organisms is known as taxonomy

Early classification systems:

l   Aristotle grouped animals according to the way they moved

l   John Ray (1627-1705) was the first to define the term “species”

Binomial classification:

Started with Linneaus (1707-1778)

•       a two name system for writing scientific names.

•       The genus name is written first (always Capitalized).

•       The species name is written second (never capitalized).

•       Both words are italicized if typed or underlined if hand written.

Example:   Felis concolor or F. concolor

l   "Formal" scientific names should have a third part, the authority.
The authority is not italicized or underlined.

l   The authority is written as an abbreviation of the last name of the person responsible for naming the organism. Since Carolus Linnaeus was the first person to name many plants, the L. for Linnaeus is very common in plant scientific names.

Examples: Quercus alba L.

Abyssoanthus convalis Reimer & Sinniger, 2009

Hierarchical Classification

l   Based on species. Classification goes down, but the basis is “bottom up”.

7 hierarchies in system:

Kingdom                                very broad

Phylum (Division)

Class

Order

Family

Genus

Species                                   very specific

The International Code of Zoological Nomenclature (ICZN) specifically governs the family-genus-species level.

Points to remember:

l   We only know about a fraction of the organisms that exist or have existed on Earth.

l   Taxonomists give a unique scientific name to each species they know about whether it’s alive today or extinct.

l   The scientific name usually comes from one of two “dead”  languages – Latin or ancient Greek.

l   Scientific names are used to avoid problems with common names. Examples: American mountain lion, and “chinu/kurodai”.

2. Taxonomy today

Linnaeus vs. Today

l   Linnaeus grouped plants and animals based on reproductive characteristics

l   Now we group plants and animals based on phylogeny

l   Phylogeny=Evolutionary history, or how the plants and animals are related.

l   We use genetics to figure out how plants and animals are related.

l   In Linnaeus’s day, scientists did not know what evolution was or what DNA and genetics was.

Phylogeny, the evolutionary history of an organism, is the cornerstone of a branch of biology called systematic taxonomy.

Systematics, as systematic taxonomy is commonly called, is the study of the evolution of biological diversity.

•       A phylogenetic tree is a shows a hypothesis about the evolutionary relationships thought to exist among groups of organisms.

•       Trees may or may not show the actual evolutionary history of organisms.

Phylogenetic trees are usually based on a combination of these lines of evidence:

•       Fossil record

•       Morphology

•       Embryological patterns of development

•       Genetic information

Brief discussion on:

1.     Adaptive radiation – and modification of homologous structures.

2.     Convergent evolution – evolving similar adaptations as organisms inhabit similar niches or play similar ecological roles. Analogous structures – traits that morphologically and functionality even though they do not have a common ancestor (organism, or tissue, etc.).

3.     Homology, parallelism, convergence, analogy.

4.     A phylogenetic tree based on a cladistic analysis is called a cladogram.

5.     Dichotomous key: A key is a device for easily and quickly identifying:

a.     an unknown organism.

b.     The dichotomous key is the most widely used type in biological sciences.

c.      The user is presented with a sequence of  choices between two statements, couplets, based on characteristics of the organism. By always making the correct choice, the name of the organism will be revealed.

3. Reminder

In this class we will be discussing a small fraction of total diversity of life. Show a domain of life tree.

4. Activity:

Classification of organisms based on diagnostic characteristics, and group discussion to show how ICZN and decisions work in taxonomy. Discuss areas for mistakes and problems.