Download 2016 Week 2 - Lec 2 - Introduction to trait genetics and

WFSC 448, Fish Ecophysiology
Introduction to Evolutionary Adaptation
(9 Sep 2016)
Biological Diversity:
From where comes the diversity of nature?
Everywhere you look in nature you see a complex array of life, each form more
intricate and fascinating than the next, all woven into a tapestry that is at once
fierce, unforgiving and cold, and yet economical, complimentary, and nurturing.
You can see it even in a jar of pond water. From where does it come?
Ecology, science of: study of the distribution and abundance of organisms
(Adrewartha & Birch)
Evolution, science of: study of the distribution and abundance of organismal form
(DeWitt & Langerhans)
Physiology, science of: study of a group of internal traits of organisms, largely
encompassed by organ system functions and their interactions with each other,
and their response to the external environment (DeWitt, just now)
Evolution—distr. & abundance of organismal form
Evolution by natural selection can be axiomatized into three
necessary and sufficient steps:
1) organisms exhibit variations
variation
2) variations are heritable
heredity
3) variations perform differently
fitness
Evolution by nat. selxn. creates adaptation…
harmony from tragedy
Charles E. Darwin
The tragedy is that beings less suited to the conditions of life
perish, or fail to reproduce. What arises however are
subsequent generations of better fit organisms that can live in relative harmony with
their environment. 
Premises 1&2—Phenotypic variation and heredity
Components of phenotypic variation, including heredity…
recall from intro bio or genetics, VP = VG + VE
 VG is genetic influence on phenotypic variation
 VE is environmental influence on phenotypic variation
(Note, for the genetically erudite that VP actually =
VG + VE + VG×E + 2 COVG,E + ε, and VG = VA + VI + VD + VM )
What we get then, from the confluence of all genetic and environmental effects
is a distribution of phenotypes, z, for a given population:
Frequency(z)
z
Evolution is driven by genetically based fitness differences:
Δz = h2 s
Δz – change in population mean of a trait
h2 – degree of trait similarity among relatives
s – trait difference between reproducers and population at large
Consider a population (pop “A”) with a distribution of trait values…
The blue distribution
is before selection;
the red distributiion
Frequency is
Fitness
the population
after (i.e. resulting
from) selection
trait value (z)

Now
“B”)…
consider a second population (pop
The cyan distribution
is before selection;
green is after (due
to) selection
Frequency Fitness
trait value (z)
And the outcome…
Pop B
Pop A
Divergence is reinforced by
selection against hybrids.
This favors the evolution of
mate choice not to
Frequency
hybridize. This process,
termed reinforcement,
further seals the process of
divergence
speciation!
traitinto
value
(z)
As Darwin said, “…[T]here is grandeur in this view of life!”
Summary of info/expectations from Dr. DeWitt’s material (not in book)…
1. Heritability is the magnitude of resemblance between relatives
2. Be able to draw a trait distribution for a population
3. Circle a tail and imagine only those breed
4.Draw the shifted trait distribution for this pop in the next generation
5.Understand the degree of shift, dz, is determined by the product of selection and
heritability: Δz = h² s
6. Divergent natural selection drives population differentiation
7. Reinforcement (evolution of reproductive isolation stemming from DNS) creates speciation
8. Ecology and evolutionary biology are intimately entwined. Understanding one requires
understanding the other.
9. Biological diversity deserves protection for aesthetic and utilitarian reasons. Protection
requires understanding natural systems.