Transcript Adaptive evolution

Happy Birthday Darwin!
Sexual Selection
Some examples
http://www.youtube.com/watch?v=eI_quJRR
Gxk
http://www.youtube.com/watch?v=AZszAaJy
VTc
http://www.youtube.com/watch?v=DU4xW79
ASsg
http://www.youtube.com/watch?v=L54bxmZy
Sexual Selection
The component of natural selection that is
associated with success in mating
Primary sexual character: geneticallydetermined sex characteristics associated
with reproduction (i.e., genitals)
Secondary sexual character: features that
distinguish the sexes but are not directly part
of reproduction
Anisogamy
Female limitation: Number of eggs produced
Male limitation: Number of eggs they can fertilize
A single egg of this
splendid fairy-wren may
weigh 15-20% of her
entire mass
This male splendid fairy wren may
have 8 billion sperm in his testes
at any given moment
The two processes
• Male-male competition
• Female mate choice
*switch those around in sex-role reversed
species
Extreme sexual size dimorphism in elephant seals
Antlers in bighorn sheep are employed directly
in contest competition for access to mates
Male dung beetles fight for mates and long
horns are advantageous, but come with a cost –
tissues that go into horn construction are no
longer available for building eyes
Extremely high variance in male reproductive success (one of the three key
ingredients to evolutionary change) can lead to exaggerated male traits and
displays
Size dimorphism in pinnipeds
Video
Female mate choice: Why be
choosy?
1) Direct benefits
- Offspring provisioning (or mate provisioning)
- Territory quality/access to resources
- Protection/safety
2) Indirect benefits
- Good genes
- Sexy sons
- Sensory bias
Number of eyespots predicts
survival of offspring
Number of eyespots is
also negatively
correlated with white
blood cell count (an
indicator of fighting
infection)
How do ecological factors
influence the evolution of
ornamental traits?
The streak-backed oriole is
sedentary and
monocrhomatic
The migratory Bullock’s orioles
are sexually dichromatic
Generally speaking, it pays to be the
biggest, most dominant, or most attractive
male. What happens if you’re not?
Other alternative tactics
While dominant gray seal males fight over access to
females that are hauled out on beaches with their
pups, sub-dominant males look for and find mates
swimming out in the water near the colony
It takes 3 minutes for a male marine
iguana to ejaculate and small males
are forcibly removed from females.
To cope, small males ejaculate prior
to mating and store their sperm in
their bodies, then evert their penis
when mating with their partner.
Distinct mating tactics
Orange – dominant, polygynous
Blue – monogamous, mate guarding
Yellow – sneakers
Sperm Competition
Competition among males to fertilize
females doesn’t stop at ejaculation
1st male advantage – often seen in external fertilizing
species, as well as species with sperm storage
capabilities
Last male advantage – Common in species that can
remove competing sperm
Sperm competition
Selection can act on sperm morphology,
sperm number, as well as females’ ability to
control fertilization success
Drosophila bifurca have 58mm long sperm!
Wood mice sperm have an apical hook
used to attach to other sperm and create
mobile trains, which have higher
fertilization success than individual
sperm
A splendid fairy wren
male may have 8 billion
sperm at any given time
In birds, there is a direct relationship
between levels of extra-pair
paternity and testis mass
Removing competing sperm
Male black-winged damselflies use a spiky, modified penis to scrub out and
remove gametes from the female’s sperm storage organ before transferring their
own sperm.
Male dunnocks peck at the
cloaca of their partners if they
find another male near her.
This behaviour results in her
ejecting a droplet of ejaculate
from the other male.
Copulatory plugs
Observed in mammals, spiders, reptiles, and
insects, copulatory plugs are inserted just
after copulation in order to limit subsequent
copulations by another male.
The golden orb spider, Nephila fenestra males take this
to a whole new level
Copulation attempts drop quickly after the
first egg is laid
Frequent copulations decrease the risk of
cuckoldry in presence of sperm competition