Lecture 4: Phylogeny and Primates

What are the goals of Phylogenetic Analysis?

1. taxonomy - to describe evolutionary relationships and name taxa

2. Reconstruction - infer ancestral traits of organisms

3. Comparative Analysis - to test casual associations between traits

How to reconstruct phylogenies

1. Select a group of species (A,B,C) and measure a trait (e.g. amino acid

sequences).

2. Measure differences between all pairs of them species.

3. Apply the assumption that species that are more similar are more closely related.

4. Draw a phylogenetic tree that represents the structure of differences.

The molecular clock

• mutation add up at a constant rate unrelated species

• more time passes ore mutations (differences)

• can’t use coding DNA because of selection

• 3 mutations per cell division

• look at non-coding regions of DNA

Nuclear DNA

• good for distantly related species

• slow rate of mutation accumulation

Mitochondrial DNA

• fast rate of mutation accumulation

• good for migration studies or very recent evolutionary splits

Derived Traits

traits that evolved more recently in a particular lineage

• unique to a specific group or clade

• apomorphines

• ex: hair in mammals → derived trait of mammals

Maximum Parsimony

is a method for constricting phylogenetic trees by choosing the tree that requires the fewest evolutionary changes

***the simplest explanation, the tree with minimal step is preferred***

Ancestral traits

traits inherited from a distant ancestor

• present in both the group being studied and its earlier relatives

• also called plesiomorphies

• ex: mammals having vertebrae → inherited from early vertebrate ancestors

Why do derived and ancestral traits matter?

• derived traits scientists identify evolutionary relationships

• ancestral traits are les informative for distinguishing closely related groups

• Key concept: for phylogenies and cladistics

Ancestral traits are inherited from distant ancestors and shared broadly, while derived traits are newly evolved features unique to a particular lineage

Why is it sometimes difficult to distinguish between ancestral and derived traits in nature?

because traits can be similar across species due to shared ancestry or convergent evolution, making it hard to tell if a trait is inherited from a common ancestor (ancestral) or evolved more recently in a specific lineage (derived)

Why do we study primates?

• reasoning by homology

  • we share inherited similarities in anatomy and behavior

• Reasoning by analogy

  • how does evolution shape bodies and behaviors

• Interpret human fossils

  • adaptions in environments occupied by our ancestors

What is a Primate?

What are some physical features of a Primate?

• grasping hands and feet

• nails instead of claws

• enhanced vision reduced olfaction

• forward-facing eyes encased in bone

• all primates have the same kind of teeth

What are some movements associated with Primates?

• Hind-limb driven locomotion

Life History of Primates?

• increased dependent on learning and behavioral flexibility

• larger brain (relative to body)

• long gestation

• small litters (one or two)

• long juvenile period

• long life spans

Where are Primates usually located?

primate biogeography - tropical animals, mostly forest-dwelling, arboreal animals

modern range - Central and South America, Africa, Asia

fossil range - included North America, Europe

What are some features of Strepsirrhines - Lemurs and Lorises

Features:

• mostly nocturnal

• mostly solitary

• tooth comb

• claws instead if nails

• acute sense smell

• wet nose

• scent glands

Strepsirrhines Morphology

• dental comb

• slightly smaller brain

• tapetum (reflective layer in back of eye