Evol Bio LT 4 - Fitness

How do Organisms vary in lifespan and reproductive capacity 

1. Some reproduce once then die

2. Some reproduce repeatedly like humans

3. Some mature in 10 days, others over a decade (humans)

What is Life History

1. Factors that affect an organism’s survival and reproduction at each stage of life as well as the niches they occupy comprise their life history 

What is Reproductive effort and what constitutes a portion of this?

1. The fraction of resources spent on reproduction (think about humans) 

   1. Making gametes 

   2. Physiological changes (like puberty) 

   3. Maintenance of sex organs 

   4. Nourishment of the young 

   5. Defense of the young 

2. Reproductive cost is the trade off between reproduction and all other functions

What is the Cost of Reproduction

Lifetime Reproduction Success

What is Semelparous

reproduce once and die 

What is Iteroparous

1. Reproduce multiple times 

   1. Multiply fecundity and survival throughout the life cycle

What is Senescence 

1. Old age accompanied by physical and functional loss

2. Evolution of long life beyond reproductive age rarely occurs

3. Change of fitness per life stage: advantages of increasing fecundity early on

What is the “Grandmother Hypothesis”

1. Senescent, post-fecund individuals provide other roles that enhance group survival 

What is mutation accumulation

1. Proposed by Peter Medewar 

2. mutation accumulation: mutations that compromise biological functions reduce fitness less, the later in life they exert these effects. That is, selection against these mutations is weaker, and so they persist at higher frequencies in the population than if they affected younger individuals 

What is a selection shadow

1. Selection shadow- bad genes and features occurring late in life escape the chopping block of evolution. —> the progressive weakening of natural selection's power as an organism ages past its reproductive years

2. Example

   1. Huntington’s disease 

   2. Alzheimer’s disease

What is Antagonistic Pleiotropy

1. a single gene controls multiple traits, but the traits have opposing effects on an organism's survival or reproductive success

2. a great many genes are likely to affect allocation to reproduction versus self-maintenance—that is, they incur a cost of reproduction. Alleles that increase allocation to reproduction (reproductive effort) early in life will thus reduce function later in life. 

2 types of density dependent growth

1. K selected- suited for denser populations 

2. R-selected- rapid growth, unsuited for dense populations

What are the characteristics of K selected organisms

1. Slow rate of increase; BUT

2. Less mortality at higher densities 

3. Better for stable environments (build well for a stronger foundation) 

   1. Late sexual maturity and delayed fecundity

   2. High parental care

What are the characteristics of R selected organisms

1. Fast rate of increase; BUT

2. Higher mortality at high densities

3. Better for unstable and changing environments (grow, reproduce and “bahala na”) 

   1. Early sexual maturity 

   2. Little parental care 

Why do some organisms have early maturation, rapid reproduction and short life

1. Many organisms are susceptible to predation and injury while young 

Why do some organisms delay reproduction at a later time:

1. Focus first on growth and defense, which allow them to resist challenges 

2. Delayed fecundity will lead to greater fitness 

What is the ideal number of offspring

1. The ideal number of offspring depends on a balance between the ability of parents to help survival in offspring and produce more children in the future 

Why is there a risk of having too few children?

1. risk that none survive  

Why is there a risk of having too many children?

1. Too many- all cannot be cared for adequately 

2. Too many- reduced brood from parents in future reproductive efforts 

Why would an organism be Specialized

1. efficient in the utilization of resources 

Why would an organism be Generalized

1. can survive more diverse conditions 

Can specialization occur even without trade-offs

Yes