Lecture 22: Adaptation part 2: Lifespan Flashcards
Darwinian demon (3)
A hypothetical organism that can maximize all elements of reproductive fitness at once:
-Reproduce at birth, infinite lifespan, infinite reproductive episodes, large numbers of viable offspring
-Why dont we see this? Because of finite time and resources cause trade-offs ie you cant do everything at once
Principle of Allocation
Resources available are finite and you only have so much time to gather them before you develop! Orgs must “choose” how much of their resources they want to allocate to maintenance, survival, growth, and reproduction
Evolution of lifespan (2)
-Aging organisms all experience Senescence = deterioration in fitness, both reproductive and survival with age
-If aging reduces fitness, why does it happen? shouldn’t natural selection just drive evolution towards longer and longer lifespans?
Evolution of lifespan two theories (2)
-Rate-of-living theory
-“evolutionary” theories
Rate of living theory (4)
-there is a physiological limit to cell and tissue repair
-Short life, high metabolic rate and cell division rate vs long life, low metabolic rate and cell division rate
-Selection SHOULD place populations at their physiological limit BUT in fruit fly studies, lifespan was increased without significant changes in metabolic rate
-more research required
“evolutionary” hypothesis for aging (3)
1). mutation accumulation
2). trade-offs between reproduction and repair
Not mutually exclusive
Mutation accumulation (3)
-Late-acting deleterious mutations accumulate because selection becomes weaker with age. ex genes causing cancer or Alzheimer’s
-Because these death causing mutations only occur late in life, they don’t have strong selection acting against them as the species has already likely reproduced
-If true, inbreeding depression should increase with age
Trade-offs between reproduction and repair (2)
-There is strong evidence that reproducing earlier is advantageous, even when it is at the expense of lifespan = Mutations for early breeding can have negative effects late in life but still be advantageous
-This is because increasing reproductive ability reduces growth and survival in many animals and plants as they are devoting less resources to it
Contributions to mortality (2)
-Intrinsic factors : Accumulation of late acting deleterious mutations and trade-offs between reproduction and repair
-Extrinsic factors: Predation, disease, resource depletion
Menopause (3)
-Most women have stopped ovulating by age 55 even though they live way longer
-Non-adaptive hypothesis: Increased longevity with modern healthcare / social supports
-Adaptive hypotheses : allows them to care for children until they reach maturity and/or allows for time and energy to care for grandchildren
Menopause in Orcas (3)
-Orcas also undergo menopause, and show similar behavior where post-reproductive females help their offspring survive
-Middle-aged orca mothers approaching menopause suffer high reproductive costs when competing to reproduce = offspring more likely to die
-Older females go through menopause because they often loose mates to their own daughters, so genes may be better represented in later generations if they invest in their adult children and grandchildren
