Evolution Chapter 10 - Life-History Evolution

What are Life-History Traits?

A Trait Directly Associated With Reproduction and Survival

What are Some Examples of Life-History Traits?

Size at Birth, Growth Rate, Age and Size at Maturity, Number of Offspring

In the Absence of Trade-Offs…

We Would Expect to Get a “Darwinian Demon”

What is a Darwinian Demon?

An Individual That Matures at Birth, Gives Birth to Infinite Number of Offspring With the Same Traits, Lives Forever, and Outcompetes All Competitors

Why Don’t Darwinian Demons Exist?

Because Trade-Offs Constrain Evolution

Trade-Offs Influence Selection on:

• Age and Size at Which Individuals Start to Reproduce

• How Resources are Divided Among Offspring

• How Resources are Divided Among Reproduction, Growth, and Maintenance

What is Evolutionary Optimization?

When Organisms Evolve Traits to the Point Where the Net Benefit is the Greatest

To Understand Evolution of Life-History Traits, We Need to Consider:

1. Age- and Size-Specific Fecundity and Survival in the Population

2. Risk of Reproductive Failure

3. Heritability and Plasticity of Traits

4. Trade-Offs Among Traits

5. Phylogenetic Context of the Species

Age- and Size-Specific Fecundity and Survival in the Population:

The Probability of Giving Birth and Dying Vary With Age and Size, and as a Result, the Strength on Selection on Traits Varies With Age and Size

Risk of Reproductive Failure:

Outcome of Natural Selection is Shaped by Risks

What is Bet-Hedging?

Selection Often Favors Spreading of Risk

Heritability and Plasticity of Life-History Traits:

Many Genes Influence Life-History Traits, so Most Life-History Traits Can Respond to Selection

Trade-Offs Among Traits:

Life-History Traits are Connected by Trade-Offs and the Response of Life-History Traits to Selection Depends on the Strength of the Trade-Off Present

Phylogenetic Context of the Species:

Comparative Method Can be Used to Estimate How Much of a Pattern in Life-History Traits is Due to History vs. Recent Microevolution

Early Maturation Costs and Benefits:

Costs:

• Yields Fewer Offspring

• Offspring Have Higher Mortality

Benefits:

• Reduces Juvenile Mortality

• Reduces Generation Time