Chapter 12

Question 1

Primary Sexual Charateristics

Answer 1

The genital and organs of reproduction

Question 2

Secondary sexual characteristics

Answer 2

morphological differences in the sexes that are not directly involved in reproduction

Question 3

Isogamy vs. anisogamy

Answer 3

Isogamy is when the gametes are the same size

Anisogamy is when the gametes are different sizes

Isogamy is ancestral, how did anisogamy evolve?

Question 4

Bateman’s hypothesis

Answer 4

the hypothesis that female reproductive success is most strongly limited by the number and success of the eggs she can produce, while male reproductive success is limited by the number of mates he has.

Question 5

Parental investment theory

Answer 5

the hypothesis that the sex that pays the higher cost of parental investment should be choosier when it comes to mates

Parental investments increase the survival of the offspring at the cost of the parent

The other sex, the one that is not being choosy will thus experience more intense sexual selection

Females have to put more energy into making the eggs, have to carry the burden of the pregnancy
Intense sexual selection means females are making the choice and the males have to compete

Question 6

Operational sex ratio

Answer 6

the ratio of the number of sexually receptive males to sexually receptive females
The parent that is investing in the child will not be available for mating

Question 7

Bateman’s hypothesis and parental investment flies

Answer 7

Virgin males and females were placed in milk bottles and allowed to mate
Each adult was heterozygous for a different dominant mutation so the parents of ¾ of the offspring could be determined by the phenotype
Females produced offspring in 96% of trials whereas the males only produce offspring in 79% of the trials
Bateman then concluded that males have higher variation in reproductive success
Bateman inferred that the intensity of sexual selection was in general higher on males and that this increased intensity of sexual selection was due to male-male competition
The results from his experiments also show that the males reproductive success increased more with the number of mates obtained than does female reproductive success

He concluded that female reproductive success is primarily limited by egg production and that male reproductive success was limited by the number of mates obtained
Because females produce less gametes than males, there will be intense competition among males for fertilization of female gametes

Question 8

Who should be choosier?

Answer 8

Females are often the more invested sex, therefore they will be choosier. This means that the males will often exhibit exaggerated morphological traits used in competition for females
Weapons are used for male to male competition
Ornaments are used for male to female attraction

Question 9

Sexual Selection

Answer 9

A form of natural selection that acts on heritable traits (genetic characteristics) that affect reproduction via mate competition (intra-) and mate choice (inter-)

Question 10

Mate competition

Answer 10

Selection in which one sex competes with other members of the same sex for access to the other sex for reproduction

Question 11

Mate choice

Answer 11

Selection by one sex for members of the other sex for reproduction

Question 12

Difference between gametes

Answer 12

• difference in the number of gametes
• size of gametes between males and females,
• females gametes house much more nutrients than sperm

Question 13

Model for Anisogamy Assumptions

Answer 13

1. In the ancestral marine environment, individuals in a population produce different-sized gametes
2. Each parent has a fixed amount of energy to allocate to gamete production, resulting in a size-number trade-off : as the number of gametes produced increases, their size will decrease

-There is a fixed amount of energy to the production of energy
-The amount of resources that goes into producing an egg is much more relative to the production of sperm
The eggs are more nutrient dense
-There is a trade off, if you are producing high quality eggs, there is going to be a trade off somewhere else, energy will not be used as much

3. Zygote viability is related to its size. Larger zygotes have higher viability because they contain more resources for survival

Smaller gametes have a numerical advantage, they will produce the most zygotes but larger gametes produce, but larger gametes have the highest zygote survival. Intermediate have the lowest fitness because they do not have either advantage

There is thus disruptive selection against intermediate sized gametes

Highest fitness by either the proto males (many gametes) or proto females (large gametes)

Question 14

Bateman’s Fly experiment

Answer 14

• Used the mutant (red) fly
• Mutant flies have different eyes and wingspan than the WT
• He used the mutant so that he could track the offspring easily by looking at phenotypic traits
• He collected data on males and females and compared the number of mates to the mean number of offspring produced

Results:
For the males, there is a linear relationship between the number of mates and the number of offspring
For females, there is not this linear relationship

When we think about reproductive success (number of offspring), in the case of males it is limited by the number of mates, but in the case of females it is not limited by the number of mates, but actually limited by the number of eggs produced

Question 15

Antlers as Weapon in Red Deer

RQ, M, R

Answer 15

Research question: Are antlers weapons used in mate competition? (Kruuk et al. 2002)

Methods:

• Red deer (Cervus elephas)
• Collect and weigh antlers shed
• Use blood samples to determine reproductive success (paternity)
• The antlers are naturally shed during the winter, they were collected and weighed by the researchers
• Blood samples used to determine reproductive success

Lifetime breeding success and antler size.

(a) Red deer males possess large antlers lacking in females.
(b) The average antler mass over an individual’s lifetime was positively correlated with his total lifetime breeding success. Each dot represents one male (Source: Kruuk et al. 2002).

The breeding success correlated with the size of the antlers (ornaments)
Antlers are ornaments because they are attractive to the female and competition with other males

Graph: Antler mass (xaxis) and lifetime breeding success (yaxis)

Question 16

Weapon size and fighting success in dung beetles

RQ, H, P, M, R

Answer 16

Male beetles have different types of ornaments (horn like projection)

Research question: What is the role of male’s horn-like projection? (Pomfret & Knell 2006)

Hypothesis: Large horns provide an advantage in mate competition
Male male aggressive encounters

Prediction: Males with the larger horn will win most fights

Methods:

• Dung beetles (Euoniticellus intermedius)
• Staged fights between males matched for body size but not horn length
• Recorded outcome of interactions and mating success

Results

• Males with horns smaller than their opponents where more likely to lose to those with horns that are larger in size
• The males with the larger horns are more competitive with other males and are chosen more by females

Winner was able to enter the nest of the female and stayed for more than 24 hrs while the loser was not allowed to enter the burrow

Graph
X axis difference in horn length
Y axis fight outcome

Question 17

Ornaments and Mate Choice in Peafowl

RQ, M, R

Answer 17

Peacock males gather on a lek which is an area that lack resources where males aggregate and display to females. Males must compete to establish and defend the display site. Males fight for status and prefered position on the lek.

Research question: Are peacock tails an ornament used in mate choice? (Loyau, et al. 2005)

Methods:
Peacocks (Pavo cristatus)

Measured:
Tail length and male body size
Number and duration of tail displays
Number of vocalizations and copulations

Results:
Y axis: Likelihood to acquire a display site
X axis: Tarsus length and in graph 2 train length

• taurus bone is an indirect measure of body size
• individuals with larger body size are more likely to get the display site
• males with larger train length are more likely to acquire a display site

note that it is not cause and effect, there are some larger males that do not get access to the site

There was a positive correlation between the likelihood of defending the territory and both body size and tail length; larger males, larger tails had more chance to acquire the display site

Additionally, the number of eyespots in the train increases and so does the number of copulations

OVERALL CONCLUSION
The researchers concluded that the evolution of the tail was related to both mate competition and mate choice
-Male often use their tails for aggressive displays
-Females prefer tails with more ocelli and higher display rates

Question 18

Sensory bias hypothesis

Answer 18

the hypothesis that female mating preferences is a byproduct of pre-existing biases in a female’s sensory system
Biases are presumed to have evolved in a non mating context

Sensory refers to our senses (hearing, touch, smell etc)
Bias means favouring one thing over another

Question 19

The Origin of Sexually Selected Traits: The Sensory Bias Hypothesis in Guppies

RQ, H, P, M, R

Answer 19

Research question: How does a male trait become selected in female mate preference? (Rodd et al. 2002)

Hypothesis: Sensory bias hypothesis – female mating preferences are a byproduct of preexisting biases in a female’s sensory system
We need to study both males and females in a population and we need to get an understanding of what their sensory biases are

Prediction: Males and females should be attracted to orange-coloured objects because orange is associated with carotenoids

-Orange should be favoured by both males and females in the population if it was originally not a sexually derived preference
-Carotenoids have antioxidants valuable for the immune system
-Animal take a preference that exists in a non mating context and apply it to sexual
Some males have more orange in them than others

Methods:

Guppies (Poecilia reticulata)
Several populations
Placed small colour discs on leaf in water
Different coloured disc
Recorded all approaches and pecks