Classification

Old biology:

survey of life, emphasis on names, characteristics, etc

what is an echinoderm?

New biology:

evolutionary relationship and history

major events ( origin of sex, etc.)

how groups deal with special problems

why they are important to us (why should we care)

Taxonomy ; the science of naming things

Classification; The ‘grouping’ of things into categories.

Carl von Linne; 1707-1778,

Father of taxonomy and classification.

 Kingdom originally animal, plant and mineral Phylum     Class       Order         Family           Genus             Species

1. Hierarchy of categories

2. Binomial system of nomenclature

Genus             Species

1. Binomial system of nomenclature

•In Latin or Greek

•First name genus, and capitalized

•Second the species, not capitalized

•For Linneus and most today – based on morphology: if it looks different, it is different

Potential new way of doing things:

1 phyletic species = if it is a ‘separate lineage’ (not necessarily separate morphology

2 bar coding based on DNA

if DNA different, it is a different species

International Code of Botanical Nomenclature (Tokyo Code)

 

Adopted by the Fifteenth International Botanical Congress, Yokohama, August-September 1993

Prepared and edited byW. GREUTER, Chairman

F. R. BARRIE, H. M. BURDET, W. G. CHALONER,V. DEMOULIN, D. L. HAWKSWORTH, P. M. JØRGENSEN,

D. H. NICOLSON, P. C. SILVA, P. TREHANE, MembersJ. McNEILL, Secretary

of the Editorial Committee

1994Electronic version of the original English text. Contents.

Originally printed as:

International Code of Botanical Nomenclature (Tokyo Code). Regnum Vegetabile 131. Koeltz Scientific Books, Königstein. ISBN 3-87429-367-X or 1-878762-66-4 or 80-901699-1-0

© by International Association for Plant Taxonomy. This page last updated Sept. 4, 2001.

Rules for naming a species:

1. It is a valid species (distinguishable, separate, etc.)

2. Unique name

3. Earliest name used is the correct one.

4. Organism must be clearly described in the naming process.

5. Must be named in an available scientific journal.

An explanation for name changes.

1. find an older name with priority, or that a name was previously used.

2. Discover you are dealing with ‘sibling’ species.

3. Discover the species mates successfully with another.

Myrtle Warbler Audubon’s warbler

Townsend’s warbler Hermit warbler

Hybrid zone between two warbler ‘species’ open circles = hermit warbler, dark circles = townsends warbler.

Rassenkreis = ring species or superspecies

Continual variation around the poles; where they come together they behave as good species.

Rules for classifying a species into higher categories.

1. Grouped by similarity. – all members of a genus are similar, (today similar means closely related)

2. There is no “correct” system

3. There are, however, ‘favorite’ or “most accepted” systems.

4. Major issue – new content to a group can lead to a new name.

examples – Mammalia vs Eutheria, Metatheria, Monotremata

Mountain chickadee Great tit.

Once- all chickadees world wide = genus Parus. Now Parus is old world tits and Poecile is new world tits.

Is this ‘correct?’ - depends on whether it is adopted or not.

1. based on genetic differences, morphological differences, geography

2. major birding organizations – adopt it ; also recommend common names

3. American vs English groups, etc.

Major Systems of classification

• Phyletic

• Phenetic

• cladistic

– pattern based on relationship known from fossil record.

No special rules about classification

Types of Classification: Phylogenic

PheneticsPhenetics bases the classification of an organism entirely on measurable

similarities and differences; no assumptions of homology are made. Phenetics compares as many anatomical characteristics as possible to determine

relatedness. Skeptics of this approach claim that phenotypic similarity alone is not sufficient to judge phylogenetic relationships.

Result – a chart of “relationship” based on the concept that structural similarity = relationship

Problems; convergence, and which characters you pick.

Weighted characters.

Cladistics is the new ‘fad’ = favored system because it results in an

Unambiguous classification.(read less ambiguous)

Basic rule – all groups must be monophyletic (have a single common ancestor)

Apomorphy – a derived or shared character

Synaptomorphy – an apomorphy shared by two or more groups and their last common ancestor

Plesiomorphy – an ancestral or primitive character

So each new character = branch point. Each branch point = name change

• In order to add a time dimension to pattern

• Either fossil record (limited to certain groups)

• Or molecular clock.

Inferred pairwise nucleotide substitutions among 17 mammal species from seven gene products, as estimated from protein studies, plotted against date of divergence, as estimated from the fossil record. The line is drawn from the origin through the oldest point (marsupial / placental divergence at 125 MYBP). The strong linear relationship suggests that molecular differences between pairs of species are proportional to the time of their separation, rather than the degree of organismal difference.  Therefore, measures of genetic divergence can be used to date the time of divergence for species pairs for which no fossil data are available: genes function as Molecular Clocks.  (from A. C. Wilson 1976)

• Note – neutral mutations = could occur at constant rate

• Non-neutral mutations – could occur at a constant rate, but if selected for or against,

• Accumulate at a varying rate.

Why are whales no longer classified as fish? (as Linneus did)

• Why is it ok to eat beaver on Friday??

Problems with any classification.

1. Brushpile evolution – a lot of changes at beginning

2. People differ as to which characters are best to use

3. A structure may have arisen more than once

4. Evolution hasn’t always been linear!!!

5. There still is no “correct” system – just favorites by usage. Favorites can be; national, popular texts, ‘elegant’

Old “trees of life” = linear.

“Brushpile” or “broom” evolution; all major groups arise at about the same time.

Cause: major evolutionary advance, like becoming multicellular, or becoming bilateral (head and tail)

Luca = last universal common ancestor

Grey = evolutionary paths

Red = ‘vines’ or horizontal

gene transfer.almost all in bacteria.

Class Aves: birds, main character, feathers. Now Velociraptor among others = feathered dinosaurs. What to do?

Phylogenics – not much of a problem -

Phenetics – perhaps a problem

Cladistics – a big problem – need monophyly

Solutions:

1. Find a trait found only in birds, not in feathered dinosaurs.

2. Change the names, call birds dinosaurs – get back to a common ancestor = a cladistic solution

3. Call feathered dinosaurs birds – but feathers may have arisen more than once – pressure to control body temperature

4. The scientific solution vs the public acceptance solution. I know one when I see one!

‘mammalian; evolution, based on mol. Clock and fossil record

What is a mammal?

1. Has hair?? – then some “lizards” are mammals

2. Has one bone in lower jaw. Old definition, but not monophyletic

3. There are no mammals – only metatheria, eutheria and monotremata.

4. public opinion; are you happy being a eutherian vs being a mammal??

The point of classification

• Necessary in order to talk about things

• No complete agreement on a single system

• Names and systems can change

• The species is the only ‘real’ entity – all other categories are human constructs that attempt to show relationship as accurately as possible

Weird Aside: the order of organisms in field guides. Birds

Sequence could be: alphabetical

by color

by habitat (water birds, land birds)

by ‘ecology’ = carnivores, herbivores, insectivores

Sequence actually is by presumed evolution; most primitive to most advanced.

As such – sequence changes as we learn more.

Typical tree based on DNA work.

Distance from left to right indicates age of relationship.

Note that this is based on only a portion of the genetic information. Use different information, get different pattern?

This is probably more realistic.

It shows relationship of certain groups.

It also shows that many groups arose at about the same time – not sequentially.