CH. 6 (Why Sex?)

Question 1

Sexual dimorphisms

Answer 1

traits that differ between males and females of a species (often sexually dimorphic traits in males violate evolutionary theory as they can waste time, energy and reduce survival)

Question 2

What is the currency of evolution?

Answer 2

Successful reproduction (not survival)

Question 3

Sexual Selection

Answer 3

selection that increases an individual’s chance of getting a mate (it’s a subset of natural selection that produces “nonadaptive” adaptations).

Question 4

Types of Sexual Selection

Answer 4

Direct competition between males and female choosiness

• direct competition produces armour, strong bodies, sharp spikes, larger body size etc (to help in a fight)
• female choosiness produces bright colours, ornaments, mating dances, etc

Question 5

Polygynous

Answer 5

Male that mates with many females during one breeding season
- elephant seal males fight each other to mate w females. Alpha mates with up to 100 females which encourages evolution of fiercer males

Question 6

Floaters

Answer 6

unmated males who try to invade established territories to sneak copulations with females
- red wing blackbirds flash red epaulets on their shoulders to ward off floaters

Question 7

Post-mating Competition

Answer 7

After a male inseminates a female he must prevent other males from fertilizing her again and stealing paternity
- can involve physically guarding her, chemically blocking up reproductive tract, injecting with an anti aphrodisiac.

Question 8

Marion Petrie and Tim Halliday

Answer 8

experimented on sexual advantage of peacock tail feathers in males by cutting off and gluing on spots.

Question 9

Disadvantages of sex (6)

Answer 9

• individual loses 50% of its genetic contribution to the next generation (eggs and sperm only contain half of its genes)
• requires time and energy to find a mate
• increased energetic costs
• risk of predation and infection
• cost of producing males
• break up of adaptive gene combos

Question 10

What is meant by the two-fold cost of sex?

Answer 10

asexually reproducing females can produce double the number of child bearing (female) offspring compared to sexual females.

Question 11

Parthenogenetically

Answer 11

Producing eggs that develop without fertilization (seen in aphids, lizards, and fish)

Question 12

Benefits of Sex

Answer 12

• random shuffling of genes produces new combos that can be really good or bad (bad are selected against purging them, good selected for (either way the gene pool is changing)).
• promotes faster evolution to deal with aspects of environment that are constantly changing (genetic lottery good in temporally/spatially heterogenous environments)

Question 13

Differential Investment

Answer 13

Discrepancy in investment of time/resources/energy by the male and female. Investment in expensive eggs vs. cheap sperm. Also, in many species the females raise the young

Question 14

Offspring Potential

Answer 14

Potential to have offspring, females have limited, males have essentially unlimited because they produce lots of sperm.

Question 15

Why are females picky?

Answer 15

They invest much more time in offspring. In 90% of mammals, a male’s only investment in offspring is his sperm.

Question 16

Socially Monogamous Species

Answer 16

Species where male and females pair up and rear young together HOWEVER adulteration is super common! The male display sexually dimorphic traits because 3/4 of the species mate w individuals other than their social partner. 90% of bird species.

Question 17

Why would a male and female of the same species look similar?

Answer 17

Potentially because extreme dimorphism in size, colour, and behaviour are found in species where the males compete to mate with females (and only a few males get most of the mating). When males and females look alike the species tends to be truly monogamous.
- parrots, geese, penguins, pigeons

Question 18

Polyandrous

Answer 18

one female mates with many males (seahorses, pipe fish)

- usually in these scenarios the differential investment is flipped.

Question 19

What three types of genes will increase in frequency together?

Answer 19

• genes for male indicator trait reflecting that he has good genes
• genes that make a female prefer that indicator trait
• the “good” genes whose presence is reflected by the indicator

Question 20

Females choose mates and can benefit…

Answer 20

Directly - a male that will help her produce more/healthier youth during ACT of CHILDCARE

Indirectly - a male that has better genes than other males (will give offspring a leg up)

Question 21

How are female preferences and extravagant male traits related?

Answer 21

They co-evolve (gene frequencies increase together). The co-evolution of female preferences and ridiculous male traits only stops when the trait becomes so exaggerated that any further increase would reduce his survival more than it would increase his likelihood of getting a mate.

Question 22

Sensory Bias Model

Answer 22

model that claims that evolution of sexual dimorphism is driven simply by pre-existing biases in a female’s nervous system. Females do not get direct or indirect benefits.