From Biol301

Contents 1 Life History Trait study 2 Lifespan: the last life history trait 2.1 Why do organims have varying lifespans? 2.2 Why do organims have limited lifespans at all? 2.2.1 Mutation Accumulation 2.2.2 Antagonistic Pleiotrophy

Life History Trait study

• Guppies upstream have predation only until they are fully grown.
  • They should spend energy growing; when grown they should put lots of energy into few, large offspring.
• Guppies downstream have continual predation.
  • Should put much energy into reaching sexual maturity as quickly as possible; should attempt to make many, small offspring as they may die the next day anyway.
• Lab experiments have shown there is a legitamate genetic difference that leads to the life history trait (lht) differences between up and downstream guppies.
• The same sort of arrangement of lht is seen in other streams.
• Is this lht difference due to differences of adult:child mortality rates in upstream areas and downstream areas?
  • Method: transplant downstream guppies into upstream population; measure phenotypic changes
  • Results:
    • Found that fish in the upstream transplanted population matured later, had a bigger body size, etc.
    • Copied experiment in a second location and found that at 4 years only the males were showing changes. Could be due to male-male competition. At 7 years the famales were beginning to show phenotypic changes.
• Keep in mind, too, that differences in environment and microclimates can be blamed here too.

Lifespan: the last life history trait

• Closely related species can have very different lifespans
• Even within a species there can be a wide range of lifespans

Why do organims have varying lifespans?

Why do organims have limited lifespans at all?

• Most organisms do not die of old age.
• Selection is greatest on those genes for survival at young age.
• Any mutation with a later age onset won't be removed by selection.
• Natural selection is more effective at early age.
• Mutations that affect fitness only in later age accumulate in population.
• Two theories of why this is:

Mutation Accumulation

• Aging results from the accumulation of mutations in a population that have deleterious effects only after the age at onset of reproduction.
• Will vary with life history and age-specific risk of mortality

Antagonistic Pleiotrophy

• Aging results from mutations that have positive effects in the young but harmful effects in the old
• As stated by Leips: Aging results from mutations that have positive effects on traits that improve fitness of young individuals but deleterious effects late in age
• Depends on age-specific risk of mortality.
  • Pleiotropy: one gene affecting more than one trait.