IB 360 E1- Wk3 Evolutionary Hypothesis & Wk4 Phylogenies and Shared History

What are the 3 major approaches to testing evolutionary hypotheses? 

1) Experimental

2) Intraspecific (within-species) comparisons of adaptation

3) Phylogenetic comparative methods 

How is the Experimental Approach Set Up?

• manipulate independent variables to measure the dependent variable 

• keep all other variables the same 

What is the goal of experimental approaches? 

• establish proximate causal links 

What are the strengths of the experimental approach? 

• simple 

• establish clear causal links 

What are weaknesses of the experimental approach?

• typically not ethical to study in humans 

• limited in scopes

Intraspecific Comparisons of Data, Methods

• correlates trait variation within a species with differences in environments and cultures to infer selection

Intraspecific Comparisons of Data, Goal

• Identify conditions that may explain trait variation

• can be used to inform future studies using experimental approach

Intraspecific Comparisons of Data, Strengths

• uses existing natural experiments, more ethical

• can test several covariates 

Intraspecific Comparisons of Data, Weaknesses

• correlation isn’t causation 

• confounding variables 

Phylogenetic Comparative Methods

-uses information on the historical relationships of species (phylogenies) to tests evolutionary hypotheses

Phylogenetic Comparative, Goals

• infer evolutionary history of some character across species

Phylogenetic Comparative, Strengths

• allows us to account for shared evolutionary history (enhances accuracy)

• can be applied to living and extinct organisms 

Phylogenetic Comparative, Weaknesses

• often assumes specific model of trait evolution

• depends on quality and completeness of the phylogeny tree and data (could lead to biased results)

Tinbergen’s 4 Types of Biological Explanations 

1) Development, Historical Sequence and Proximate Explanations (Ontogeny) 

2) Evolutionary History, Historical Sequence and Ultimate Explanations (Evolution) 

3) Mechanism, Slice in Time and Proximate Explanations (Causation) 

4) Function, Slice in Time and Ultimate Explanations (Survival  Value) 

Benefits of Tinbergen’s Framework

• helps identify hypotheses that are complementary

• makes larger questions more tractable

Issues of Tinbergen’s Framework 

• modern techniques and understanding have blurred the boundaries of the categories 

Draw Bergman and Beehner’s Recast of Tinbergen’s Framework

Contingency in Phylogeny

-existence of something depends on the existence of something else

Non-Independence in Phylogeny

-organisms share history, similarities between them can be due to shared ancestors who possessed those traits

Convergent Evolution in Phylogeny

-describes similarities that aren’t due to shared evolutionary history

Outgroups In Phylogeny

-allow the tree to be rooted

Nodes in Phylogeny

-represents a common ancestor

Branches in Phylogeny

-evolutionary connections between organisms

Terminal taxa in Phylogeny

-end points on phylogeny tree that represent the species being studied

What are phylogenies based on?

-built on shared traits (homologies) not homoplasy

-parsimony

What are 4 types of data used to construct phylogeny? 

1) morphological 

2) fossils 

3) behavior 

4) molecular

What region of DNA has the highest rates of nucleotide substitution?

-in regions that have the least effect on protein function noncoding

What are challenges in building phylogenies?

-homoplasy (convergent evolution)

-complex traits 

-number of included taxa