Transcript Natural selection II

The components of fitness
Zygotes
Compatibility
selection
Survival (viability
selection)
Adults
Females Males
Gametes
Sexual selection
(mating success)
Gametic selection
Fecundity selection
Parents
from Futuyma, p. 369
When the components of
fitness are in conflict...
• sexual selection: female
túngara frogs prefer male calls
with more “chucks”
• natural selection: bats locate
chucking males better than
non-chucking males
• sexual selection is stronger—
most males chuck
from D.J. Futuyma, Evolutionary Biology, p. 346
The Nature of Natural
Selection
natural selection “acts” on
individuals, but its consequences
are felt in populations
None of the finches were altered by the drought, they
simply survived it or not, based on beak depth
The Nature of Natural
Selection
natural selection “acts” on
phenotypes, but evolution requires
these phenotypes to be
genetically determined
Selection:
yes.
Evolution:
no.
The Nature of Natural
Selection
natural selection is not “forward
looking”
Natural selection does not
“act” for the good of the
species
valid cases of true altruism are not
known to exist
Belding’s ground squirrels make “alarm calls” to warn of attack
by weasels,badgers, coyotes, hawks.
This behavior puts the caller at risk, and may benefit unrelated
individuals.
Is it altruistic?
from Sherman (1977)
If this were a true “altruistic” act, all individuals should
call equally.
But instead, females call most often.
from Sherman (1977)
Why? Kin selection.
Since females remain close to the natal burrow, females are
surrounded by sisters: they call to benefit close relatives.
Males disperse more and call infrequently, because they are
unlikely to be genetically related to others nearby.
Not so good for the species...
Natural selection “acts” on
existing variation—how can it
create new traits?
• Mutation provides a constant source
of variation for selection to act on
• Selection on “preadaptations” can
produce novel traits
Figure 3.18. Artificial selection on corn kernel oil content
(from Moose et al. 2004). Continuous selection yielded a range
of variation not present in the original plants.
Mutation and recombination supply new variation for selection
to act upon, continuously.
Selection produces new traits
by modifying existing traits
The Panda’s
“thumb”: a
modified wrist
bone
(sesamoid) that
varies in the
bear family
from Futuyma (2005)
Preadaptations (or exaptations)
Wings in common murre
(Uria aalge) are
exaptations for diving
Wings are preadaptations
in penguins—modified for
swimming. So much that
they no longer allow flight!
from Futuyma (2005)
Selection cannot (usually)
replace traits, once lost
History constrains natural
selection
Cretaceous Hesperornis,
a marine bird with teeth
to grip fish
Modern birds have lost
teeth—this fish-eating
anhinga makes do
without them
from Futuyma (2005)
from Futuyma (2005)
Bill serrations serve the
same function in the fisheating merganser duck
Problems with the Theory of
Evolution by Natural Selection
The Argument from Design
Irreducible complexity
Graded
complexity of
multicellular eyes
• (a) pigment spot or (b)
pigment cup
– flatworms,
polychaetes, crabs
and shrimp, "lower"
vertebrates
– detecting light for
orientation and
monitoring day length
Optic cup
• narrow aperture (like a
“pinhole camera”)
probably creates
poorly-developed
images
• nemerteans, annelids,
copepods,
archaeogastropods
(abalone) and
nautiloids (Nautilus)
Lensed eyes
• form complex images
• graded complexity in molluscs:
immovable lens in some
gastropods
the eye of the
pulmonate land
snail Helix
• through "cameralike" lens in
octopus, squids
and cuttlefish
Through the lensed eye
of "higher" vertebrates.
These form the most
complex, high resolution
images, in part because
the lens can rapidly
change shape — it is
compressible and served
by a fine musculature
The Argument from Design
Irreducible complexity in
biochemical systems
An argument for intelligent
design
• Michael Behe, author of
Darwin’s Black Box (1996):
the cilium is a “molecular
machine” (1998)
– without all its tiny intricate
parts, would not function
• “irreducibly complex”
• evolution of this structure by
natural selection, bit by bit, is
impossible
Typical cilia and flagella
outer and inner dynein arms bridging
peripheral microtubule pairs, a central pair of
microtubules, spokes joining central to
peripheral pairs
Chlamydomonas flagellum
(© 1998 Gwen Childs,
Univ. TX)
Human respiratory tract cilia
(© Visuals Unlimited)
Yet, outer dynein arms, spokes, and
central microtubules are missing in the eel
sperm flagellum (arrow marks one of the
missing dynein arms), still the structure is
fully functional. From: Woolley (1997).
– Many other exceptions exist (Miller 1997)
– pf14 mutants of Chlamydomonas lack
flagella spokes, but can swim