Evolution Exam 3 Review – Comprehensive Study Guide & Revision Notes
Sexual Dimorphism - correct answer ✔✔Traits that differ between males and females of a
species.
-Peacock Example:
-Selection is operating differently on males and females.
-Plumage is brighter in males. Size is often larger.
-Includes a great variety of organisms.
-Often comes with a "cost".
Examples of sexual dimorphism - correct answer ✔✔-Irish Elk = re-grow large antlers every year
(costly).
-tungara frog = behavior makes males susceptible to predators.
-Bower birds = males create an ornate spot out of grass, and line the 'stage' with shells.
-Widow-birds = males have extremely long tail plumage.
-Collared lizards = males have bright colors, while females blend into surrounding habitat. Males
show higher signs of attempted predation.
Problem with Sexual Dimorphism - correct answer ✔✔Seems to violate evolutionary theory,
because it is a 'waste' of time and energy and reduces survival.
Solution:
The currency of selection is not really survival, but successful reproduction!!
Darwin (Ch. 4) coined the term "sexual selection". "Sexual Selection...depends, not on a struggle
for existence, but on a struggle between the males for possession of the females; the result is
not death to the unsuccessful competitor, but few or no offspring."
Types of Sexual Selection: Direct - correct answer ✔✔Direct Competition between males for
access to females.
,-Often violent engagements between males (elephant seals, Elk, Beetles, etc.)
-This type of selection usually produces armaments within the males - to aid in physical
contests.
Types of Sexual Selection: Ladies Choice - correct answer ✔✔Female choosiness among
possible mates, and usually selecting the 'showiest' or the one with the best looking traits.
-This type of selection is generally more "of a peaceful character" (Darwin).
-Indirect competition between the males, winner is decided by the females.
Mate Choice: Males Attracting Females - correct answer ✔✔Experiment suggested by Wallace.
Pick a bird, modify the male's ornaments, and see if it affected female choice.
-enlarge tails/shorten tails
-watch to see if it increases/decreases survivor-ship and mating success.
-In Grackles, it seems that the males have NOT evolved a longer tail, because its likely that long
tails will reduce longevity more that it would increase reproductive success.
Males Compete for Females, Why? - correct answer ✔✔1) Size of the Sex Cells = Sperm and
Egg.
-Sperm is very easy "cheap" to produce, while eggs are very difficult "costly" to produce.
2) Parental Investment and care.
-Females in many species (mammals, birds, insects, spiders etc.) generally have the largest
investment, and provide the largest amount of parental care.
Variation of Mating Success - correct answer ✔✔FEMALES: will always have high mating success
= little variance.
MALES: usually must compete to mate with a female. There is HIGH variation in mating success
in males.
-One male might mate a lot (alpha male, wins contests, best traits etc.), while MOST males will
not mate at all.
, Why Sex? Why not all just reproduce asexually? - correct answer ✔✔Any individual who
reproduces sexually sacrifices 50% of its genetic contribution to the next generation compared
to an individual who reproduces asexually.
-Twice as many genes are put into the next generation during asexual reproduction (re-product
a copy of the organism).
Advantage:
-Random shuffling of genes (genetic recombination)
-Faster evolution to deal with changing environment
Does Mating Success Increase Fitness? - correct answer ✔✔FEMALES: Doesn't increase,
because the female mating success rate is already high (when comparing, the slope is close to
zero).
MALES: Yes! The more mates the male has = the more offspring he sires.
Examples of Sexual Dimorphism: Elephant Seals - correct answer ✔✔-Males are much larger
than females, largest males are often the most successful in mating with a harem of females.
-Smaller males don't mate, direct competition keeps other males away from the females.
Examples of Sexual Dimorphism: Red-winged Blackbird - correct answer ✔✔-Do male
ornaments increase fitness and ward off other males?
-During experiments, when scientists painted the birds black, males lost 70% of their territories
(compared to control group) :(
-Muted males also lost their territory.
Post-Mating Competition - correct answer ✔✔1) Guard females after mating.
-To reduce the chance that another male will fertilize the female.
2) "Penis scoops".
-In dragonflies, holds onto female after mating, so that she physically can't mate again.
Sexual Dimorphism - correct answer ✔✔Traits that differ between males and females of a
species.
-Peacock Example:
-Selection is operating differently on males and females.
-Plumage is brighter in males. Size is often larger.
-Includes a great variety of organisms.
-Often comes with a "cost".
Examples of sexual dimorphism - correct answer ✔✔-Irish Elk = re-grow large antlers every year
(costly).
-tungara frog = behavior makes males susceptible to predators.
-Bower birds = males create an ornate spot out of grass, and line the 'stage' with shells.
-Widow-birds = males have extremely long tail plumage.
-Collared lizards = males have bright colors, while females blend into surrounding habitat. Males
show higher signs of attempted predation.
Problem with Sexual Dimorphism - correct answer ✔✔Seems to violate evolutionary theory,
because it is a 'waste' of time and energy and reduces survival.
Solution:
The currency of selection is not really survival, but successful reproduction!!
Darwin (Ch. 4) coined the term "sexual selection". "Sexual Selection...depends, not on a struggle
for existence, but on a struggle between the males for possession of the females; the result is
not death to the unsuccessful competitor, but few or no offspring."
Types of Sexual Selection: Direct - correct answer ✔✔Direct Competition between males for
access to females.
,-Often violent engagements between males (elephant seals, Elk, Beetles, etc.)
-This type of selection usually produces armaments within the males - to aid in physical
contests.
Types of Sexual Selection: Ladies Choice - correct answer ✔✔Female choosiness among
possible mates, and usually selecting the 'showiest' or the one with the best looking traits.
-This type of selection is generally more "of a peaceful character" (Darwin).
-Indirect competition between the males, winner is decided by the females.
Mate Choice: Males Attracting Females - correct answer ✔✔Experiment suggested by Wallace.
Pick a bird, modify the male's ornaments, and see if it affected female choice.
-enlarge tails/shorten tails
-watch to see if it increases/decreases survivor-ship and mating success.
-In Grackles, it seems that the males have NOT evolved a longer tail, because its likely that long
tails will reduce longevity more that it would increase reproductive success.
Males Compete for Females, Why? - correct answer ✔✔1) Size of the Sex Cells = Sperm and
Egg.
-Sperm is very easy "cheap" to produce, while eggs are very difficult "costly" to produce.
2) Parental Investment and care.
-Females in many species (mammals, birds, insects, spiders etc.) generally have the largest
investment, and provide the largest amount of parental care.
Variation of Mating Success - correct answer ✔✔FEMALES: will always have high mating success
= little variance.
MALES: usually must compete to mate with a female. There is HIGH variation in mating success
in males.
-One male might mate a lot (alpha male, wins contests, best traits etc.), while MOST males will
not mate at all.
, Why Sex? Why not all just reproduce asexually? - correct answer ✔✔Any individual who
reproduces sexually sacrifices 50% of its genetic contribution to the next generation compared
to an individual who reproduces asexually.
-Twice as many genes are put into the next generation during asexual reproduction (re-product
a copy of the organism).
Advantage:
-Random shuffling of genes (genetic recombination)
-Faster evolution to deal with changing environment
Does Mating Success Increase Fitness? - correct answer ✔✔FEMALES: Doesn't increase,
because the female mating success rate is already high (when comparing, the slope is close to
zero).
MALES: Yes! The more mates the male has = the more offspring he sires.
Examples of Sexual Dimorphism: Elephant Seals - correct answer ✔✔-Males are much larger
than females, largest males are often the most successful in mating with a harem of females.
-Smaller males don't mate, direct competition keeps other males away from the females.
Examples of Sexual Dimorphism: Red-winged Blackbird - correct answer ✔✔-Do male
ornaments increase fitness and ward off other males?
-During experiments, when scientists painted the birds black, males lost 70% of their territories
(compared to control group) :(
-Muted males also lost their territory.
Post-Mating Competition - correct answer ✔✔1) Guard females after mating.
-To reduce the chance that another male will fertilize the female.
2) "Penis scoops".
-In dragonflies, holds onto female after mating, so that she physically can't mate again.
