Chapter 26: Phylogeny and the Tree of Life

BIOL 1030

Biodiversity

the variety of life on Earth

Taxonomy

the naming and grouping of organisms

Systematics

the science of figuring out relationships between organisms

• form biogenetic trees

Phylogeny

the evolutionary history itself

Taxon

The named group at ANY level

• Ex: Mammalia at taxon level or Panthera at genus level

Clade

A special group

• Ancestors plus all its descendants

Binomial Nomenclature

Two part naming system

• Genus (always capitalized)

• species epithet (always lowercase)

• if typed, italicize

• if written, underline

Carl Linnaeus

Father of modern taxonomy

Linnaean Classification (Hierarchy)

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Spain

Domain

Most inclusive group of hierarchy

Species

Most exclusive group in hierarchy

Nested hierarchy

Lower, simpler levels are contained within higher, more complex levels

• “Russian Doll” formation

• Ex: Species are more nested than Order

Broader traits

More inclusive

Narrower traits

less inclusive

Bacteria

Prokaryotes, diverse

Archaea

Prokaryotes, extremophiles, closer to Eukarya

Eukarya

Nucleus; protists, fungi, plants, animals

All life comes from a

Single common ancestor

Linnaean System

• based on physical characteristics only

• does not always reflect evolutionary relationships

• Groups become static (don’t account for change over time)

• resulted in misclassification

Static

Groups are not accounted for changes over time

Modern taxonomy is based on…

Phylogeny (evolutionary relationships) rather than just physical similarities

Phylogenetic Trees

Shows a branching pattern that matches how systematists classify groups or organisms nested within more inclusive groups

Systematics go hand in hand with ___

Phylogeny

Root of a Phylogenetic Tree

“origin”

• ancestral population from which all the other species originate

Node of Phylogenetic Tree

Common ancestor

• a branching point form the ancestral population

Branch of Phylogenetic Tree

Lineage

Clade of Phylogenetic Tree

A piece of phylogeny that includes an ancestral lineage and ALL the decendants of that ancestor

Sister Taxa

Groups of organisms that share a common ancestor that is not share by any other group

• members of a sister group are each other’s closest relatives

Trees show__

Relationships, NOT progress

• they serve as testable scientific hypotheses

• Can make predictions that are close to the facts

Morphology

The study of the form and structures of plants and animals

• fossils, anatomy

Homologies

Phenotypic and genetic similarities due to shared ancestry

Similar morphologies____

Doesn’t always mean organisms will look similar

Analogies

Similarities between organisms that are due to convergent evolution

• Ex: bats, birds, and butterflies all have wings BUT have different reasons for developing them

Convergent Evolution

Occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different lineages

• No common ancestor

Morphology alone is____

misleading

Cladistics

Method of classification based on ancestry

• Biologists attempt to place species into groups called clades

• Clades are nested within larger clades

• Systematics relies on cladistics

Monophyletic

True clade

• Ancestor + ALL descendants

Polyphyletic

groups of organisms form MULTIPLE ancestors

• Do not share a common ancestor

• Not a clade

Paraphyletic

Includes an ancestor but NOT ALL its descendants

• Not a clade

Ancestral Characters

A character that originated in an ancestor of the taxon

Derived Characters

New traits that are unique to a clade

• most useful in building trees

Outgroup

Lineage that diverged earlier

• a species or group of species that is closely related to but not part of the group of species of interest (ingroup)

Longer branches mean___

A species has evolved more rapidly

Maximumm Parsimony

Seeks to investigate the simplest explanation that is consistent with the facts

Apomorphy

new (derived) trait that evolved in a group, different from the ancestral condition

Plesiomorphy

old (ancestral trait) found in earlier ancestors

Synapomorphy

Share new (derived) trait that two or more groups have

Autapomorphy

unique (derived) trait found in one lineage, not shared

Homoplasy

“false similarity” (similar trait not due to share ancestry)