Lecture 5

Question 1

What is sexual dimorphism?

Answer 1

• males and females have different PRIMARY sexual characteristics

ex. different sex organs and glands

• in sexual dimorphism, males and females also have different SECONDARY sexual characteristics, characteristics not directly needed for fertilization

ex. feathers, antlers, colours, size, beards in men, lion manes, etc.

Question 2

What is the origin of secondary dimorphisms?

Answer 2

• sexual selection!

Question 3

How is natural selection different from sexual selection?

Answer 3

• sexual selection is differences in sex
• darwin was bothered by the origin of male traits that were costly to maintain, and without obvious survival value
• like what is the adaptive benefit of bright colours in male birds
• dull colours in females made natural selection sense for protective camouflage on nest and with young

Question 4

what are the 2 required things for sexual selection?

Answer 4

If for one sex (binary gender) within a species:

1. there is heritable variation for a sexual trait
2. the variation in a trait results in differential reproductive success (number of mates and number of fertile offspring)
   ex. has a fitness benefit

then that trait will evolve by sexual selection

• in other words: some males have more mates and more offspring than others. characteristics that help a male attract mates can evolve by sexual selection, even though such traits may actually reduce long-term survival!

Question 5

explain sexual selection using the example with peacocks

Answer 5

considering the eyespots on the tail feathers in male peacocks:

1. there is heritable variation in the total number of eyespots a male possesses
2. females prefer males with more eyespots; males with more eyespots tend to have more mates and more offspring

the number of eyespots on tail feathers of male peacocks is therefore subject to evolutionary change by sexual selection, and may lead to “runaway sexual selection”: extreme traits

Question 6

What are the two forms of sexual selection?

Answer 6

1. female choice
2. male-male competition

Question 7

explain sexual selection: female choice

Answer 7

• ex. mate choice is made by females!
• (also called intersexual selection); between sexes
• male ornaments (colours, behaviours) that females like increase probability of mating

Question 8

explain sexual selection: male-male competition

Answer 8

• sometimes bloody
• ex. direct competition for mates by males
• (also called intrasexual selection) within one sex
• development most extreme in polygamous species (one male mates with many females)
• male armaments rather than ornaments

Question 9

What is intersexual selection?

Answer 9

• female choice theory (females select healthy males with “good genes”)
• type of sexual selection where members of one sex choose members of the opposite sex based on certain desirable traits

Question 10

who invests more energy in mating?

Answer 10

• females have a higher energy “investment” in their eggs and offspring than males: so females should be choosy in selecting mates (sperm from males are abundant and low energy compared to eggs, and later parental care)

Question 11

explain red and yellow and bright colours in animals

Answer 11

• red and yellow plant carotenoid pigments are a dietary component that birds cannot synthesize. Bright red, yellow, and orange feathers and beaks reflect food gathering success
• experiments with Australian zebra finches test whether female finches prefer to mate with males that have strong carotenoid colours in their beaks and cheeks
• males that have had a good feeding success in growing up are healthier and more likely to have stronger carotenoid colours that others: colour brightness may indicate “good genes”

Question 12

Female Zebra finches prefer what on males?

Answer 12

• colourful beaks
• other birds could have feather colour and display, lizards have a dewlap (skin) colour, frogs and toads calls and sings (large size correlates with lower frequency croaks)
• they’re not always colourful but still distinctive and eye-catching

ex. African Nightjars have wing banner feathers to be more noticeable

Question 13

What triggers sexual behaviours for breeding seasons in animals?

Answer 13

• sexual behaviours for most animals are cued by environmental factors (seasonal climate) combined with social factors

Question 14

explain the sexual behavior of lizards, specifically Anolis lizards

Answer 14

• frequency of dewlap extensions and push-ups by males increases significantly depending on social factors, like the presence of a female
• this is intersexual selection (supports female choice in mate selection)

Question 15

what kind of competition for mates are for males?
explain what it is.
What are some common characteristics of male-male competition?

Answer 15

• intrasexual competition
• males compete with each other for access to resources
  ex. male elephant seals compete for territory on the beach and access to females (polygamous species)
• common characteristics: size, strength, armaments (ex. antlers, teeth, tusks, etc)

Question 16

what could increase predation risk, reducing survival

Answer 16

• conspicuous or cumbersome ornaments and behaviours
• being colourful makes you more noticeable to prey, frogs are more detectable during their calls, peacocks are very noticeable, etc.
• Darwin worried about the costs of these traits that are not favoured by natural selection

Question 17

What are the direct and indirect benefits of intersexual selection (female choice)

Answer 17

• Direct benefits: may benefit the female directly
  ex. best food access, best nest sites, protection of a strong mate
• indirect benefits: benefits that affect the genetic quality of the female’s offspring

Question 18

What is the “sexy son” hypothesis

Answer 18

• females may select males with attractive characteristics with the expectation (not consciously) that the “quality” genes will be conferred on their sons, who will likely have more breeding success than their competitors.
• how do you know they have good genes?
• Warning: extension of animal observations to more socially complex humans may prove erroneous!
  ex. human sexual motives often not obviously reproductive

Question 19

explain altruism

Answer 19

• behaviors that are self-sacrificing, for the benefit of someone else

Question 20

What are the 3 conditions for Hamilton’s Rule about altruistic behavior?

Answer 20

1. Fitness benefits are high for the recipient
2. the fitness cost to the altruist is low
3. the altruists and the recipient(s) are close relatives!

Question 21

How does Hamilton’s findings give rise to the concept of inclusive fitness?

Answer 21

• bc it shows that individuals can pass on their alleles to the next generation without reproducing themselves (but helping close genetic relatives reproduce)

Question 22

What is the math to Hamilton’s Rule?

Answer 22

• If Benefit (B) times relatedness of the recipient (r) is greater than the cost (C), alleles for the altruist behavior will be favored by natural selection!

Br>C

• Coefficient of relatedness (r) is the measure = fraction of genes shared
• range: 0.0 (no relation) to 1.0 (identical twins)

ex. parent and child, or, brothers and sisters, r=0.5
grandparents and grandchildren, or half siblings, nephews and nieces, r=0.25
great grandparents and great-grandchildren, or cousins, r=0.125

Question 23

give an example of when altruism is favoured using wild turkeys

Answer 23

• two displaying brothers of wild turkeys can attract more females than a single male
• even if only 1 brother (r=0.5) mates, the non-mating male still gets a genetic fitness benefit in the next population from genes he shares with the brother’s offspring (nephews and nieces: r=0.25)

Question 24

What is inclusive fitness? Who defined it?

Answer 24

inclusive fitness = direct fitness + indirect fitness

• defined by William Hamilton

Question 25

What is the concept of “kin selection”?

Answer 25

natural selection in favor of behavior by individuals that may decrease their chance of survival but increases that of their kin (who share a proportion of their genes).