Systematics and PhylogeneticsCh. 23.1, 23.2, 23.4, 23.5, and 23.7

Diversity Matters• Not all species, even closely

related ones, interact with their environments the same way

• Mosquitos and Plasmodia– Plasmodia causes malaria– Only 3:6 mosquito species can

carry the disease and spread it• Understanding and

categorizing species is important in all areas of biology

• Systematics study of life’s diversity and all evolutionary relationships

Linnaeus System• Binominal nomenclature (two

name system); uses genus and specific epithet (species name) to categorize similar species

• Taxonomy groups species through different taxa (levels of similarity)– Domain most general;

Bacteria, Archaea, Eukarya– Species most specific; Homo

sapien• Names come from location of

habitat, physical trait, scientist who discovered it, etc…

Taxonomic Hierarchy• Classification

limited to more inclusive groups (taxa) as you specify the organism– Domain– Kingdom– Phylum– Class– Order– Family– Genus– Species– Subspecies

Phylogenetics• Just categorization is no

longer important; now we are looking for the evolutionary connection between organisms

• Phylogeny evolutionary history of a species

• Phylogenetic tree visual representation of their phylogeny– Species at the base are

common ancestors– Species in the branches are

close variants

Anagenesis• Trees can be large; cover

all known organisms• Trees can be small; cover

only a specific genus• Trees can show specific

changes through format– Straight lines show

anagensis; gradual changes as a new species changes from the original population; no increase in biodiversity

Cladogenesis• Branching points depict two

species diverging from a common ancestor; increase in biodiversity – Branches meet at their common

ancestor– Branches can split again into

“branchlets” which can form “twigs”• Every node (branching point) is the

“root” for the generations that spring from it (clade)– Aves clade for birds– Birds of Prey nested clade inside

Aves• Sister clads clades that share

same node• Sister spices species that share

the same node

Types of Phylogenetic Trees1) Monophyletic– All species connected to one

ancestral clade– Felidea clade all species of

cat (tigers, house cat, lion, etc…) lead back to

– Animalia clade all animals lead back too

2) Polyphyletic– Organisms of different clades

but not their common ancestor

– Vertebrates capable of flight (Birds and Bats); common ancestor (extremely ancient) not included

Types of Phylogenetic Trees3) Paraphyletic – Clade of an ancestor but

not all its descendants– Clade of birds and

terrestrial dinosaurs; linkage to birds shown but not all descendants made by terrestrial dinosaurs

• Depending on what information needs to be explained, this different types are necessary

Cladistics• Traditional systematics

organizing trees based on morphology and evolutionary relationship– Popular up till the 1960s

• Cladistics phylogenetic trees should reflect just evolution patterns of physical traits (characters; character states)

• Ancestral character states original traits of the common ancestors

• Derived character states new traits branching from the ancestral ones

Making a Cladogram• Cladistic method groups

species into clade by shared derived characteristics; generate a cladogram– Hypothesized evolutionary

connection– Node common ancestor– Branch monophyletic group;

sometimes contain specific synapomorphies in clade

• Molecular sequencing (protein, DNA, RNA) also used with synapomorphies comparisons– Help deal with convergent

evolution, which presents false synapomorphies

Comparing Character States• Character states can be

compared to each other in any number of ways– Often compared with other

species that don't possess the character

• Apomorphy derived character

• Synapomorphy derived character found in multiple species– Shared characteristics shows

species are part of the same clade

– Markers for monophyletic lineages; adaptive radiation after major adaptation

Principle of Parsimony• Large cladograms, with 100s of

species, have too many factors for humans to consider

• Computer programs must be used to find the “best” cladogram– Principle of Parsimony simplest

evolutionary history is the most likely; rare for many complex evolution events to have occurred

• Molecular statistics have a major effect– Non-coding DNA, degenerate DNA

codons, substitution rates of nucleotides all influence the statistical amount of mutation a population can experience

Statistics is the Key• Taking both fossil and

evolutionary statistical data, two methods can be used to find the best cladogram

1) Maximum Likelihood Method– Data compared with other

established cladograms to find the “most likely” clade

2) Bayesian Method– Compares the distribution of

character traits to the evolutionary model that would be needed for them to occur

Using Synapomorphies• Comparison of the

species that do and do not have an apomorphy can organize the clade

• Vertebral column in animals:– Most species of animals

are invertebrates (no backbone)

– Vertebrates (fish, mammals, birds, etc…) do have a backbone

– Comparing the synapomorphies:• No backbone Ancestral• Backbone Derived

Using Synapomorphies to Support Data• If there is not enough data

from fossils, apomorphies can still be compared with outgroup comparisons– Ingroup species in question

with derived trait– Outgroup closely related

species (not in clade) with ancestral trait

• Butterfly legs groups of 6 and 4– Outgroup comparisons show

most insects have 6 legs– 6 legs ancestral – 4 legs derived

Using Molecular Data• Clades can have conflicting

models that both have large support

• Molecular comparing is sometimes the only method of categorizing group properly

• Domains: Archaea, Bacteria, and Eukarya– All similar to each other in various

ways– Evolution places Eukarya

branching from Bacteria and Archaea branching from Eukarya

– However, after their branching point, the transfer of some genetic material may have occurred (Horizontal gene transfer) through transformation, transduction, and even viral infections

Homework• Suggested Homework:– Test Your Knowledge

• Actual Homework:– Discuss the Concepts #3– Design the Experiment– Interpret the Data

• Test Next Wednesday on Ch. 22, 23, and 24!

• Final covers All chapters since mid-term (not 18 and 19)