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									Quantitative Genetics in Red Squirrels:
       mechanisms of adaptation

          • Basics
          • Red squirrel examples
              – Parturition date
              – Growth rate
          • Genomics and the future


                  Andrew McAdam
         University of California, Santa Cruz
            mcadam@biology.ucsc.edu
             Quantitative Genetics
     Examines the genetics of
       continuously varying
        (quantitative) traits


 Traditional Quantitative Genetics                                750
                                                                  700
                                                                  650

 estimates sources of trait variation by                          600
                                                                  550
                                                                  500

 examining the phenotypic resemblance




                                                 # observations
                                                                  450
                                                                  400
                                                                  350


 among known relatives.                                           300
                                                                  250
                                                                  200
                                                                  150
                                                                  100
                                                                   50
                                                                    0
                                                                        <= 0   (0,.5]   (.5,1]   (1,1.5]      (1.5,2]    (2,2.5]   (2.5,3]   (3,3.5]   (3.5,4]   >4
                                                                                                           Growth rate (g/day)




Understanding the genetic basis to quantitative traits allows us to predict
future evolutionary responses to selection
                R=   h 2   S
R. Rothman




    J. Merilä              Schroeder
Quantitative Genetics
  in Red Squirrels

  1. Sources of variation
     • Heritability
     • Maternal effects                    350


                                           300

  2. Selection

                            Spruce Cones
                                           250



  3. Response to                           200



     selection                             150


                                           100


                                           50


                                            0
                                                 1988 1990 1992 1994 1996 1998 2000
                                    Parturition Date

                                   12
                                                                                                                             180




                                                                                  Mean number of spruce cones available
                                                                                   during a female's reproductive lifetime
                                   10                                                                                        160
Average spring temperature ( oC)




                                                                                                                             140

                                   8
                                                                                                                             120

                                                                                                                             100
                                   6
                                                                                                                             80

                                   4                                                                                         60

                                                                                                                             40
                                   2
                                                                                                                             20

                                   0                                                                                               89   90   91   92    93     94      95   96   97   98
                                        1975   1980   1985   1990   1995   2000
                                                                                                                                                       Year of birth


                                   Increase in Temperature                               Increase in Food Abundance
  Parturition Date - Heritability


                   Matrilineal Pedigree (1989-2001)
                              1059 breeding events
                                        568 females
                                      5 generations


                   Paternity and Maternal Effects??



h2 = 0.16 ± 0.03
                                    - Réale et al., 2003, Evolution
       Parturition Date - Selection

Fitness: total number of




                           Lifetime fitness residuals
offspring produced in




                                                   4
lifetime.




                                                   2
Considered females dead


                                                   0
prior to 2000 (n=303)
                                                   -2
    S = - 8.96 ± 2.56                                   -2     -1    0       1       2
                                                             Parturition Date (s.d. units)
                                                                                            3




                                                                         - Réale et al., 2003, Evolution
                                 Response to Selection (R)
                                                                            Predicted R = - 1.4 days/gen.
                                             R=     h2    S                 Observed R = - 6.0 days/gen.

                                 160                                                                                        0.5
                                                                                                                                   133   98          105      38

                                 150                                (1991-2001)                                             0.0
Age Corrected Parturition Date




                                                                     n = 11 years




                                                                                          Estimated breeding value (days)
                                                                                                                            -0.5
                                 140
                                                                                                                            -1.0

                                 130
                                                                                                                            -1.5

                                 120
                                                                                                                            -2.0


                                 110                                                                                        -2.5


                                                                                                                            -3.0
                                 100

                                                                                                                            -3.5
                                 90
                                                                                                                                   1     2                3   4
                                       0.0    0.5   1.0     1.5      2.0    2.5     3.0
                                                                                                                                             Generation
                                                          log LYC



Plasticity = - 23.1 days/cone index
                                                                                                        - Réale et al., 2003, Proc. Roy. Soc. L., B
     Parturition Date Questions
1.   Does food supplementation result in the plastic
     advancement in breeding?
2.   Are there differences in the heritability of
     parturition date between the experimental and
     control populations?
3.   Does selection on parturition date differ between
     experimental and control populations?
4.   Do these differences in selection result in
     experimental evolution of earlier breeding?
         Maternal Effects
Occur when the phenotype of a mother causes
     phenotypic effects in her offspring

            www.sbgmath.com


                              •   Widespread
                              •   Strong in mammals
                              •   Predicted to have
                                  important effects on
                                  evolutionary dynamics…if
                                  heritable
                 Nestling
               Growth Rate
                  (g/day)

Cross-Foster



                  ~25 Days
Percentage of variation in
  growth in body mass
              10%         Genetic
                  9%      Maternal
                          GxE
                          Error
            81%


     h2   = 0.09 ± 0.04
                        Maternal Growth Rate




Maternal                           h2 = 0.09
Effects
     Litter Size
     Parturition Date   Offspring Growth Rate
                   Maternal Growth Rate




Maternal                         h2 = 0.09
Effects
               +
                   Offspring Growth Rate
  h2t = 0.31
                          - McAdam et al., 2002, Evolution
                                      Food Effects on Growth

                                                                                                           2.1




                                                                                     Growth rate (g/day)
                              2.2
                                                                                                           2.0
                                    1989 - 2001
                              2.0
                                                                                                           1.9
Average Growth Rate (g/day)




                                                                                                           1.8




                                                                                                                  n = 176




                                                                                                                                     n = 32
                              1.8




                              1.6
                                                                                                           1.7




                                                                                                                            n = 72
                                                                                                           1.6
                              1.4

                                                                                                           1.5
                              1.2
                                                                  n = 13 years                                   1999 2000 Food
                                      0.0   0.5        1.0        1.5    2.0   2.5

                                            log Cones in Previous Year
                                                                                                                 Cross-fostered
                                    Slope = 0.23 g/day/log conest-1
                           0.25
                                  1999
                                         cov(dir,mat)
                                              0.043
                                                                            h2t = 0.52*
                                  2000        0.079                              (h2 = 0.10)*
Coefficient of Variation




                                  Food      - 0.005
                           0.20



                           0.15                                              h2t = 0.70
                                                                                 (h2 = 0.12)
                           0.10



                           0.05
                                                                              h2t = 0.57
                           0.00                                                   (h2 = 0.57)
                                      Direct                 Maternal
                                     Genetic

                                     1999             2000          Food
                                                                           - McAdam & Boutin, 2003, J. Evol. Biol.
                                   Viability Selection on Growth
                                          Fitness: survival to potential breeding age

                                          Other variables in model: Litter size, parturition date, sex, year
                                   1.6

                                                        *                              *
Linear selection gradients (β')




                                   1.2



                                   0.8
                                                                                                              No spatial variation in selection

                                                   *                                                 *
                                   0.4



                                   0.0



                                  - 0.4                              *
                                            1990       1992   1994       1996   1998       2000   All years
                                                                                                              - McAdam & Boutin 2003, Evolution
Components of Selection
   Birth
                    Spring
                 temperature (-)
   Emergence



   Recruitment

                 Previous year’s
   Breeding         cones (+)
                         Maternal Effects
  Selection                   h2




Corrected                   Corrected
Growth (t)                  Growth (t+1)
              Response
                                 Maternal Effects and the
                                  Response to Selection

                   0.5

                   0.4
                                        *
                                                                            1. Observed response greater
Response (g/day)




                   0.3
                                                                               than predicted by h 2
                   0.2

                   0.1
                                                                            2. Response not independent of
                   0.0
                                                                               selection in the previous
                   -0.1                                                        generation
                   -0.2
                                                           *     *
                   -0.3
                          1989   1991       1993   1995   1997       1999

                                            Year



                                                                              - McAdam & Boutin 2003, Proc. Roy. Soc. L., B
     Growth Rate Questions
1.   Does food supplementation increase nestling
     growth rates?
2.   Does food supplementation eliminate maternal
     effects?
3.   Does selection on growth rates differ between
     experimental and control populations?
4.   Do these differences in selection result in
     experimental evolution of earlier breeding?
5.   Do maternal effects contribute to evolution in the
     control population but not the food supplemented
     one?
        Genetic Mechanisms of
             Adaptation

Quantitative Trait Loci (QTL’s)
It has recently become possible
to use genetic markers to
determine regions of the
genome (loci?) that contribute
to quantitative variation.

QTL’s can be mapped for natural populations with extensive pedigrees
and many molecular markers
Genetics of Speciation in Sticklebacks




                            - Peichel et al., 2001, Nature
   Ecological and Evolutionary
  Functional Genomics (EEFG)



Genes   Genotype        Phenotype   Phenotype’




                   Evolution
Genes   Genotype        Phenotype   Phenotype’




                   Evolution

								
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