Finding order in diversitySection 18.1

How are scientific names assigned? • Common names often vary between languages

or countries• Cougar, puma, panther and mountain lion• In UK a buzzard is a hawk, whereas here it is a

vulture

• In the 18th Century, European scientists recognized this confusion, and assigned Latin or Greek names to each species to help clear this up• Names were often very log due to the amount of

detail• Hard to standardize, as scientists focused on

different things

What is a Dichotomous key?

•A Dichotomous key is used to identify organisms through a series of paired statement or questions that describe alternative possible characteristics

Binomial Nomenclature

•With binomial nomenclature each species is assigned a two part scientific name• Always written in italics

•Polar Bear is Ursus maritimus • Ursus - genus organism belongs to (bear)• Maritimus – unique to each species

•Grizzly bear – Ursus arctos

• System created by Carolus Linnaeus in 1730s

Classifying species in larger groups

•Both living and fossil organisms are classified into larger groups• These groups must have biological significance• Organisms in one group are more similar to each other than to organisms in

other groups

•This science is called systematics • Goal – to organize living things into groups that have biological meaning• Groups are referred to as taxa

The Linnaean Classification system• Carolus Linnean also created a classification system that organized species

into taxa that formed a hierarchy

•Over time his hierarchy expanded to include seven hierarchical taxa • Kingdom – All multicellular animals are placed in the kingdom Animalia • Phylum – Shared body plan features • Class – Similar orders grouped into a class. Example - mammals• Order – Closely related families. Example - Camel, llama, deer and cattle – linkage

(hoofed animals, even number of toes)• Family – Several genera that share many similarities (camel, Llama)• Genus - Camels• Species – one hump vs two humps

• King Phillip Came Over For Good Soup!

Classification system

Problems with traditional classification

•Members of a species determine which organisms belong to a species through who they mate with and produce fertile offspring

•How is this different from how Linnaean assigned individuals to a species?

•What do we know that Linnaean did not?

• Linnaean had no idea about genetics and evolution, but was a hood scientists, and chose his characteristics carefully • Many of his groups are still valid under modern classification schemes

•Modern day systems assign species on the basis of how closlely related organisms are

Modern Evolutionary Classification

Section 18.2

The tree of life

•Darwin’s work lead to the idea that organisms can be classified on the basis of evolutionary relationships, not just on the basis of similarities and differences

•This lead to some Linnaean ranks to fall apart• Reptilia class isn’t valid unless birds

are reptiles. Dinosaurs also would fall into this class

Evolutionary classification

•Phylogeny – the evolutionary history of lineages• Phylogenetic systematics – group species into larger catergories that reflect

lines of evolutionary descent rather than simply similarities and differences

•Common ancestors - Organisms are placed into higher taxa when members are more closely related to one another then to members of any other group• The larger a taxon is, the farther back in time all of it’s members shared a

common ancestor

•Clades – a group of species that include a single common ancestor and all descendants of that ancestor (living and extinct)• Clades are monophyletic - a single common ancestor for all of its

descendants

What is a Cladogram?

•A cladogram links groups of organisms by showing how evolutionary lines or lineages branch off from common ancestors

•Each node represents the last point at which species in lineages abive the node shared a common ancestor

•Root of cladogram is common ancestor shared by all

Derived Characters

• A derived character is a trait that arose o the most recent common ancestor of a particular lineage and was passed along to its descendants

• Whether or not a characteristic is derived depends on the level at which you are grouping organisms• Four limbs is a derived character for then entire

clade tetrapoda • Hair is a derived character for the entire clade

Mammalia • But, for mammals, four limbs is not a derived

character, as other organisms besides mammals have this trait

• Although carnivores have four limbs and hair, neither are derived characters for this clade• Specialized shearing teeth are however a derived

character for this clade

Loosing traits• Snakes are reptiles, which form part of the clade tertapoda

• Why don’t snakes then have 4 legs?

•The ancestors of snakes must have had 4 limbs• Somewhere in the lineage the trait was lost

•Distantly related groups can sometimes lose the same character, absence of traits are not used in their analysis

How do you interpret a cladogram? • Lowest node represents last

common ancestor of all four limbed animals – the clade tetrapoda • Forks in the cladogram show the

various groups branched off from the tetropod lineage • In this example, specialized shearing

teeth evolved before retractable claws

• Each derived character along the main trunk, gives rise to the name of a clade

Linnaean classification and cladograms

• Some Linnaean classes do correspond well to clades• For example class Mammalia and clade Mammalia

• Presence of hair derived character

•Traditional groups do not always from clades • Reptiles and Birds share a common ancestor

• This was not recognized by Linnaeus, who put birds in heir own class

• Class Reptilia without birds is not a clade

• Birds form multiple clades• Aves, Dinosauria and Reptilia• An evolutionary biologist would call birds reptiles

DNA in classification

•Evolutionary biologists don’t just rely on physical characteristics

•Genes as derived characters • All organisms carry genetic information passed on from earlier generations • A wide range of organisms share a number of genes and show important

homologies that can be used to determine evolutionary relationships • Shared genes contain differences that can be treated as derived characters in

cladistic analysis • Similarities and differences in DNA can be used to develop hypotheses about

evolutionary relationships

•DNA has made evolutionary trees more accurate• Used to supplement data from anatomical analysis

Using DNA evidence• DNA evidence can be used when anatomical traits do not provide clear answers

• Example – giant and red pandas• Many anatomical similarities with bears and racoons

• DNA suggests that Giant pandas share a more recent common ancestor with bears than racoons

• DNA evidence also suggests that red pandas don’t form part of the bear clade

Building the tree of lifeSection 18.3

Naming organisms isn’t the biggest challenge..• It is one thing to name an organism,

but the real challenge is to group everything together in a way that reflects their evolutionary relationships

•These have produced a number of major changes from Linnaeus’s original scheme

Kingdoms of life through time

• Linnaeus divided the world into two kingdoms – Animalia and Plantae• This did not reflect the full diversity of life

•Classification systems have changed dramatically over the last few hundred years to reflect advances in understanding• Relationships among organisms are still changing today as new data is

gathered

Five kingdoms

• As biology developed, researchers realized that single celled organisms are significantly different from plants and animals

• Originally all micro-organisms were placed in their own kingdom – Protista

• Yeast, molds and mushrooms were placed in their own kingdom – fungi

• Prokaryotic bacteria placed in their own kingdom – Monera

• Single celled eukaryotic organisms placed in the kingdom Protista

Six kingdoms

•Monera was divided in to two distinct groups • Eubacteria and Archabacteria

•This division was on the basis of knowledge over the genetics and biochemistry of bacteria • Occurred in the 1990s

Three domains• Genomic analysis shows that the two main prokaryotic groups are even

more different from each other, and from eukaryotes than previously thought

• Domains are a new form of taxonomic category• Larger, more inclusive than a kingdom

• Three distinct kingdoms• Bacteria – corresponds to Eubacteria• Archea – archaebacteria• Euakarya – (Fungi, plantae, animalia and “protista”

• Protista not a true clade as no single common ancestor for all

What does the tree of life show?

•Currently the tree of life shows hypotheses regarding evolutionary relationships among the taxa within the three domains of life• But modern evolutionary

science is constantly evolving

• Cladograms are not hard facts, but instead are visual representations of hypotheses

Domain bacteria

•Unicellular and prokaryotic

•Cells have thick rigid walls that surround a cell membrane

•Cell wall contains peptidoglycan

•Ecologically diverse, ranging from free living soil organisms to deadly organisms • Some photosynthesize, others don’t• Some need oxygen, others don’t

•Corresponds to kingdom Eubacteria

Domain Archaea

•Unicellular and prokaryotic

• Live in extreme harsh environments • Volcanic hot springs• Brine pools• Black organic mud devoid of oxygen

•Many can only survive without oxygen

•Cell walls do not contain peptidoglycan

•Cell membranes contain lipids often not found in other organisms

•Corresponds to kingdom Archaebacteria

Domain Eukarya • All organisms that have a nucleus • Four remaining groups of the six kingdom system• Protista, fungi, plantae and animalia • ”Protista”

• Do not form a valid clade• Most are unicellular, with the exception of brown algae group• Some are photosynthetic, others are heterotrophic

• Fungi• Heterotrophs• Cell walls contain chitin• Feed on dead or decaying organic matter• Secrete digestive enzymes into their food source

• Fungi can then absorb small molecules

• Both single (yeast) and multi cellular (mushrooms)

Domain Eukarya cont…• Plantae -

• Autotrophs• Cell walls contain cellulose • Carry out photosynthesis using chlorophyll• Non-motile (cannot move from place to

place)• Includes green algae, mosses, ferns, cone

bearing plants and flowering plants

• Animalia • Multicellular and heterotrophic• No cell walls• Most can move about• A large amount of diversity