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            Life history characters, ch 12



  Finite amount of energy and time inevitably leads to trade-offs.
                   Heritability of various traits
Life-history traits show slightly less
      heritability than behavioral,
      physiological or morphological
      traits.
Why?
They are more inclusive of fitness
     therefore less variable and less
     heritable. That is, more of the
     additive genetic variation is       cumulative
     exhausted b/c it affects fitness     frequency
     and is selected at the expense
     of alternative alleles.



                                                      h2
  Trade-off in energy allocation and time to reproduction



female sand crickets – two morphs
1) well developed: wings, flight muscles, triglycerides stores
- all useful in dispersal




2) well developed: ovaries, phospholipid deposition into eggs
- useful in shortening time to reproduction
      Trade-off between size and number of F1

body-size adjusted investment in egg number and size.



                   fruit flies                          fish
                     Trade-off’s are innumerable




                    time to maturity    size at maturity
                    size of offspring   number of offspring
tolerance to environmental variation    ability to exploit a specific parameter
                                    Senescence
The inevitable deterioration accompanying aging
Why is it inevitable?



1.   Rate of living
2.   Deleterious mutations
                                                  evolutionary theories of aging
3.   Negative pleiotropy (trade-offs)
                                       Senescence

1.    Rate of living - metabolism generates damage that
      NS can’t stop
      Predictions:


      1) rate of aging should be proportional to
      metabolic rate
      2) there is no genetic variation for longer life span



     By selecting embryos from older flies, delayed
          senescence was selected.

     Conclusion: Senescence is under control of natural
          selection in some way.
                         Evolutionary theory of aging

     Why doesn’t NS favor longer life spans?

1.      Rate of living
2.      Deleterious mutations    Deleterious mutations that are expressed later are more likely to accumulate
3.      Negative pleiotropy
                        Evolutionary theory of aging

Why doesn’t NS favor longer life spans?

 1.    Rate of living
 2.    Deleterious mutations
 3.    Negative pleiotropy


 After reproduction commences
        residual reproductive
        value diminishes.
 From a gene’s perspective its
      organisms value as a
      survival machine =
      probability of survival x
      RS
 Extrinsic causes of mortality
       will always cause a
       decrease in residual
       reproductive value with
       age.
                        Evolutionary theory of aging

Why doesn’t NS favor longer life spans?

 1.    Rate of living
 2.    Deleterious mutations                      No mutation
 3.    Negative pleiotropy                Deleterious mutation


 Therefore, the later-acting a
      deleterious mutation is
      the less likely/quickly NS
      will remove it – natural
      selection is relaxed as
      residual reproductive
      value of organism
      declines.
                        Evolutionary theory of aging

Why doesn’t NS favor longer life spans?

 1.    Rate of living
                                                        pop 1           pop 2
 2.    Deleterious mutations
 3.    Negative pleiotropy                                              xx
                                                          xx            xx
 Hughes, et al., ’02 made 10 inbred lines and crossed
     in a factorial design.
                                                          xx
 The selfed lines were highly inbred.
 The others were now heterozygous/outbred.                          x
                                                                x   x
                                                                x
                        Evolutionary theory of aging

Why doesn’t NS favor longer life spans?

 1.    Rate of living
                                             *
 2.    Deleterious mutations
 3.    Negative pleiotropy


 Hughes, et al., ’02 made 10 inbred lines
     and crossed in a factorial design.
 The selfed lines were highly inbred.
 The others were now
      heterozygous/outbred.

Inbreeding depression increased
     with age. Indicating that
     deleterious mutations
     expressed late in life were
     more numerous than early-              * (Woutbred – Winbred) / Woutbred
     acting mutations. Predicted
     by deleterious mutation theory
     of aging.
                           Evolutionary theory of aging
    1.    Rate of living
    2.    Deleterious mutations
    3.    Negative pleiotropy – trade-offs


Because of the high survival
     probability at age 2,
     there is a huge benefit
     to earlier reproduction.
In other words: b/c of the
      decline in residual
      reproductive value, a
      slight change in onset
      of reproduction can
      outweigh the loss of
      several years of
      survival when old.
Some genes may trade-off
    early and late-life
    success.
                         Evolutionary theory of aging
                                        age-1: intracellular signaling during development
1.   Rate of living
                                        1) hx546 allele increases longevity 80% with no apparent cost (a).
2.   Deleterious mutations
                                        2) Under nutritive stress hx546 is strongly selected against (b).
3.   Negative pleiotropy – trade-offs
                                        Wild-type young adults were able to reproduce sooner than the
                                              hx546 young adults.
                                        Implication: under stress, WT allele allows younger reproduction,
                                              but at a cost to later survival.
                      no food stress
                                                                              caloric restriction
                        Evolutionary theory of aging

Fitness will always decline over life because of extrinsic mortality (disease, predation, fighting,
      meterorites, falling trees…)
Therefore, natural selection favors a finite life:
1) mutation-selection balance favors an increase in deleterious mutations expressed after the onset
     of reproductive age (deleterious mutation theory of aging).


2) trade-off’s between reproduction and maintenance will favor traits that facilitate RS at a younger
      age at an expense to RS or survival at an older age (negative pleiotropy theory of aging).
             Conflicts between life history stages

Between mates: each sex should encourage investment in their offspring by their mate.


genomic imprinting = turning off a gene through DNA hyper-methylation in the early development;
    thereby affecting F1 gene expression.
   Conflict-based imprinting hypothesis
                                       (Haig, 1993)
                     Developing
                      embryo
                                       Egg
         Sperm




Male’s imprint the                Female imprint the
sperm’s genome to                 egg’s genome to
increases female                  equalizes female
investment in his                 investment among
offspring                         her offspring
                   Conflicts between life history stages

   Between mates: each sex should encourage investment in their offspring by their mate.


   genomic imprinting = turning off a gene through methylation in the gametes; thereby affecting F1 gene
       expression.
                                                                            paternal copy maternal copy
Mice

IGF-II (insulin like growth factor) – stimulates cell division and growth          on        off


MPR (mannose-6-phosphate receptor) – sink for IGF-II                               off       on

Support: MPR doesn’t bind IGF-II in chickens and frogs (where no imprinting of it occurs)
              Conflicts between life history stages
Sexually antagonistic coevolution: how important is it? Rice (’96) made haplotypes male-limited
                       Experimental                                    Control

Generation        male           female (naive population)      male             female
      1                      x                                             x


      2                      x                     discarded               x


      3
                                                   discarded
      .
      .
      .
                  autosomal genes average 100% of                 autosomal genes average 50% of
     30                     their time in males                          their time in each sex
              Conflicts between life history stages

Sexually antagonistic coevolution: how important is it? Rice (’96) made haplotypes male-limited

				
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posted:4/18/2013
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