Classification Taxonomy –but why? · PDF fileBranch points = relative time of origin of...

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Classification Taxonomy – but

why?

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Biological Systematics

• Biological systematics =study of diversificationof life forms (past and present relationships of living things through time)

• Phylogeny = study of evolutionary history of organisms

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• Relationships are visualized as evolutionary trees

– Cladograms

– Phylogenetic trees

– Phylogenies

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Biological Systematics-Phylogenetic Tree

• Phylogenetic trees have two components:

– Branching order• Shows group

relationships

– Branch length• Shows relative

evolution

Branch points = relative time of origin of different groupsExample: Branch point for gorillas is lower than humans or chimps- this indicates egorillas originated earlier than humans and chimps

Branch points

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Biological Systematics – The Tree

• To interpret a tree, start at the bottom and work towards the top

• Every branch point represents the last time those groups shared a common ancestor

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Whats phylogeny?

• Phylogeny is the study of the evolutionary history of organisms.

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Relationships via diagram

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• Phylogenetic trees of species and higher taxa are used to study:

– Evolution of traits

– Anatomical or molecular characteristics

– Distribution of organisms

• Systematics, in other words, is used to understand the evolutionary history of life on Earth

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Systematic Biology vs. Taxonomy

• Two terms are often confused and used interchangeably

• Are defined in relationship to one another as follows:

• Systematic biology, or systematics, is the field that:

– Provides scientific names for organisms

– Describes them

– Preserves collections of them

– Provides classifications for the organisms, keys for their identification, and data on their distributions

– Investigates their evolutionary histories

– Considers their environmental adaptations

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• Taxonomy is the part of systematics that is concerned with:

— Providing scientific names for organisms

— Describing them

— Preserving collections of them

— Providing classifications for the organisms, keys for their identification, and data on their distributions

• Taxonomy is more specifically the identification, description, and naming of organisms

– =Nomenclature

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• Classification is focused on placing organisms within hierarchical groups that show their relationships to other organisms

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Systematics

• Systematics uses taxonomy as a primary tool in understanding organisms

– Nothing about an organism's relationships with other living things can be understood without it first being properly studied and described in sufficient detail to identify and classify it correctly

• Scientific classifications are aids in recording and reporting information to other scientists and to laymen

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Systematics

• Systematics is fundamental to biology because it is the foundation for all studies of organisms

• Shows how any organism relates to other living things

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Systematics

• of major importance in understanding conservation issues (it attempts to explain biodiversity)

• can be used in allocating limited means to preserve and protect endangered species (e.g. considering genetic diversity among various taxa and deciding effects/preservation…)

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Lumpers vs Splitters-Cladistics

• Cladistics groups species on the basis of their shared characters (Physical, Behavioral, Physiological, Molecular)

• Use Cladograms to show relationships (next slide)

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Cladogram

Each line represents a lineage that can branch into 2 lineages

A node = common ancestor of the two lineages

Lineage

Node

Node

LineageLineage

Clade x

A branch end = a clade (group that shares characteristics

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Cladistics

• Ideally, each clade is a monophyletic group

• A monophyletic group includes an ancestor and all its descendants

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Cladistics – not set in stone!

• Inherent challenge

• Because we don’t know all species and all characters, cladisticgroupings are hypotheses

• They will differ depending on which characters are used

• Clades change when new discoveries are made

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Cladistics

• Cladograms and other types of evolutionary trees summarize our best data supported hypotheses about how a group of species evolved

• Diagrams are used to visualize evolutionary trends and patterns

• Like any other hypothesis, evolutionary tree diagrams are constantly being revised

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Cladistics

• The diagrams are based on the solid premise that all species are interconnected by shared ancestry

• Every living thing is related if you just go back far enough in time

• Evolutionary biologist’s job is to figure out where the connections are

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Classification

• The action or process of categorizing something according to shared qualities or characteristics

• The arrangement of animals and plants into taxonomic groups according to their observed similarities

» Merriam-Webster Dictionary

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How Classification Works

• One and a half million species have been identified on the earth

• Estimate that there may be up to 80 million species on the earth altogether

• That's a lot of organisms to keep track of

• It’s natural for humans to organize large groups of things into smaller, similar groups

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• Grouping helps us to simplify

• It reduces large and complex systems into smaller, less complex systems

• The problem is that the categories we use are arbitrary and the boundaries we have stipulated between groups are artificial

• They are not part of the real world– They exist only in our minds

• So it's not surprising that the real world often doesn't fit neatly into our categories

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• But our systems of organization are useful anyway

• Without them we couldn't understand relationships between organisms

• Classification also allows us to make generalizations about the members of a group, applying knowledge gained from one member to all of the members

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• Classification works by looking for similarities between organisms and putting the most similar things together in the same group

• Over the last 250 years the specific structures we look at to find similarities has changed

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• At first it was large and mostly external features like flowers in plants, body plans in invertebrates or feathers in birds

• As technology got more sophisticated we moved on to comparisons of internal organs, embryos, behavior and chemical composition

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• Microscopes allowed us to use the structure of tissues and cells to look for similarity

• We have been able to look at the internal instructions, the DNA

• Compare it in different species to see how closely they are related and to hypothesize about who our common ancestors were

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• Multicellular organisms

– Us

– Worms

– Sponges

– Plants

– Mollusks

• are built of smaller things called organs

and tissues

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• Organs and tissues are built of smaller things called cells

• Cells are made of molecules

• Molecules are made of various chemical elements

• Knowing where the differences are in these things tells us how different species are related to each other

– For example, all living things are made of the same chemical elements (carbon, hydrogen, oxygen, nitrogen) and basic molecules (amino acids, sugars, fats and nucleic acids)

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• This discovery was one of the most important stepping stones in discovering how evolution works

• Such common structure could not have occurred in millions of different species by chance, so it was most likely due to descent from common ancestors who all started off with the same array of molecules making up their bodies

• The knowledge that we are all made of the same chemicals doesn’t allow us to form groups

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• When we look at larger things like cells and tissues, organs and body plans, differences are more obvious

• They allow us to sort living things into smaller and smaller groups

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• Invertebrates and vertebrates are both sets of animals that have the same chemicals and in some cases the same kinds of cells and tissues

• But we differ in body coverings, body plans and organs

• It makes sense from a scientific perspective to consider all organisms that have a specific kind of tissue as having descended from a common ancestor at some remote point in our evolutionary history

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• In the same way all kinds of similarities, from DNA to bones, from proteins to leaves, help us to classify organisms so that we can study them and their evolutionary history more easily

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Classification SystemsFive Kingdom System

• For many years, living organisms were divided into five kingdoms - still found in biology textbooks:

• Monera

• Plantae

• Protista

• Fungi

• Animalia

• based on molecular and cellular data, systems of classification that use 14 or more different kingdoms

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Three Domain System

• Carl Woese (University of Illinois) proposed a classification scheme based on molecular evidence

– Ribosomal RNA

• Organisms are divided into three Domains (a level of classification above kingdom)

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Three Domain System

Note that Domain Archaea and Domain Eukarya are more closely related to each other than to Domain Bacteria

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Three Domain SystemDomain Bacteria

• Domain Bacteria (eubacteria or "true bacteria") contains the simple prokaryotic life forms described above in Kingdom Monera

• These are unicellular organisms that usually lack a nucleus

• This includes bacteria and cyanobacteria

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Three Domain SystemDomain Archaea

• Domain Archaea contains the simple life forms called archaeans, formerly part of Kingdom Monera

• This prokaryotic group includes:

– Thermoacidophiles that live in very hot acidic environments,

– Methanogens that produce methane gas

– Halophiles that live in very salty environments

• Recent analysis of the 1,738 genes of a species of this group showed that about half of its genes were totally unique

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Three Domain SystemDomain Eukarya

• Domain Eukarya contains complex organisms (the eukaryotes) that have cells with nuclei

• These organisms include:

– Protists

– Plants

– Animals

– Fungi

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Five Kingdoms in theThree Domain System

Bacteria Archaea Eukarya

Monera Monera Protista

Bacteria Thermoacidophiles Plantae

Cyanobacteria Methanogens Animalia

Halophiles Fungi

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The Nature of NamingScientific Nomenclature

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What’s in a Name? - Common

• "A rose is a rose," it has been said

• And most of us know a rose when we see one

• As we know the African marigolds

• Maples, elms, cedars, and pines that shade our backyards and line our streets

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Which Cedar? What’s in a Name?

• Usually use their common names

• However- "cedar" can refer to many different trees!:

Eastern red cedar, Incense, Western Red, Atlantic White, Spanish, etc!

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Why is Common Name a Problem?

Really confusing if trying to accurately identify an organism; for example “cedars” are found in three separate, different plant families!(Having a specific name for each is useful….)

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Binomial System of Classification• = 2 name (Carolus Linneaus, 18th century

Swedish botanist)

• Format = Genus species

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Binomial System for Plants

• botanical name often followed by letter or letters (stand for botanist that named plant)

• For example: The coffee plant botanical name is Coffea arabica L. (with “L” for Linneaus)

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Binomial System Naming

• Other often used abbreviations are Sarg. for Charles Sprague Sargent, founder of Harvard University's Arnold Arboretum

• Lam. for Jean Baptiste Lamarck, French evolutionist and botanist

• Audub. for John James Audubon, ornithologist, naturalist, and painter

• Hmmmm - this convention (naming the discoverer) is not found in naming animals

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Binomial System of Classification

• Linneaus's book Species Plantarum (The Species of Plants), published in 1753, continues to influence the naming of plants today

• It is the starting point for checking whether a name has been used previously to insure that each plant is given a unique name

• The earliest name for a plant is usually the official name should a dispute arise

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List the levels of taxonomic classification, from largest to smallest

Domain Eukarya

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Rodentia

Family Sciuridae

Genus Sciurus

Species Sciurus niger

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