Sexual Selection

Question 1

Sexual Selection

Answer 1

Form of non-random mating which occurs when individuals within a population differ in their ability to attract
Determines who reproduces

Question 2

Intersexual Selection

Answer 2

Mating success determined by between-sex interactions
Looks at mate choice (choice exerted by members of the opposite sex)
Female choice of males (males must show themselves to be genetically attractive to females)

Question 3

Intrasexual Selection

Answer 3

Mating success determined by within-sex interactions
Looks at individuals competing to obtain mates (competition between members of the same sex)

Question 4

Fundamental Asymmetry of Sex

Answer 4

Results from the fact that in most species females invest more in their offspring than males

Question 5

Male-Male competition

Answer 5

The ability to win fights and produce offspring is determined by body size, then alleles for a large body size have a fitness advantage
Males that win battles monopolize mating with females in their territory
Dramatic head butting
Tusks on male elephants and walruses
Horns in male sheep and beetles
Enlarged claws of male fiddler crab

Question 6

Sexual Dimorphism

Answer 6

Any trait that differs between males and females of the same species
Weaponry
Ornamentation and behavior in courtship
Body size

Question 7

Biological Fitness

Answer 7

Reproductive success and reflects how well an organism is adapted to its environment
Greater fitness means the organism leaves more viable/living offspring

Question 8

Explain the relationship between Natural Selection and Sexual Selection

Answer 8

Natural selection determines who survives while Sexual selection determines who reproduces

Question 9

Differentiate between intersexual selection and intrasexual selection

Answer 9

Intersexual - looks at mate choice (choice exerted by opposite sex)
Intrasexual - looks at individuals competing to obtain mates (competition between members of the same sex)

Question 10

Examples of intersexual selection

Answer 10

ex. Male satin bowerbird decorates its nest with blue materials to attract females
Females red-collared widowbirds prefer mating with males with longer tails
Female hanging fly will not mate with male unless he brings her a large offering of food

Question 11

Examples of intrasexual selection

Answer 11

Male-Male combat over females or resources vital to mates
Tusks on male elephants and walruses
Horns in male sheep and beetles
Antlers on male moose
Female spotted hyenas are larger and more muscular than males, compete to be the alpha

Question 12

2 important consequences of the fundamental asymmetry of sex

Answer 12

Female fitness is limited by the ability to gain resources needed to produce more eggs and healthier offspring, so females produce few offspring during lifetime
Male fitness is limited by the number of females he can mate with, he can mate frequently because sperm are so energetically inexpensive

Question 13

Predictions associated with the Bateman-Trivers hypothesis

Answer 13

Females, not males, should be choosy about mates since they invest a lot in each egg (opposite should be true for males)
Males will compete with each other for mates
Alleles that increase a male’s attractiveness or success in male-male competition should increase in population (sexual selection should act more strongly on males than females)

Question 14

Ideas on why females tend to be choosy when searching for a mate

Answer 14

Gives rise to “good genes” hypothesis which states that the traits females choose when selecting a mate are indicators of the males ability to pass on genes that will increase the survival of reproductive success of her offspring
Physical characteristics that signal male genetic quality
Behavioral characteristics of the male that indicate their ability to provide parental care

Question 15

Sexual Dimorphism
examples?

Answer 15

Mandarin ducks - males have a bright red beak and colorful plumage, female’s colors are more muted
Male elephant seals have large proboscises that resemble elephants trunk, females don’t
Size of canines in baboons are more than twice as large as that of female canines
Males lions are larger than female and have an elaborate mane

Question 16

Monogamy
example?

Answer 16

Pattern of having one mate at a time (one male and female have an exclusive mating relationship)
Parental care involves both parents
ex. bald eagle (only form new bond if partner dies, male barn owls (provide dead mice and screech while interested females respond by croaking)

Question 17

Polygamy
3 different types?

Answer 17

Pattern of having more than one mate at a time - one or more males are bonded socially with one or more females
Polygyny, Polyandry, Polygynandry

Question 18

Polygyny
examples?

Answer 18

One male mates with two or more females, most common polygamous mating system, female usually provides most parental care
ex. male walrus grab female attention with loud vocalizations, elephant seals, common pheasants, gorillas, spotted hyenas

Question 19

Polyandry
examples?

Answer 19

One female mates with two or more males, males usually provide most parental care
ex. spotted sandpiper (females compete for territories in order to attract males), pipefishes (relative of seahorses)

Question 20

Polygynandry
examples?

Answer 20

2 or more males mate with 2 or more females, advantageous from females perspective allows her to have multiple males care for her blood
ex. red foxes, European badgers, sea spiders, ground squirrels

Question 21

Promiscuity
examples?

Answer 21

Mating system where there is no pair bonding, females mate with multiple males and males mate with multiple females
Female raises the young alone
ex. bonobos, dolphins, hummingbirds

Question 22

Pair Bonding

Answer 22

Also known as monogamy
One male and female have an exclusive mating relationship

Question 23

Differentiate between “good genes” hypothesis “sexy sons” hypothesis

Answer 23

The explain the evolution of female preferences in species where females do not receive direct benefits from mating
“Good Genes” hypothesis - the traits females choose when selecting a mate are indicators of the males ability to pass on genes that will increase the survival or reproductive success of her offspring
“Sexy Sons” hypothesis - a females ideal mate choice among potential mates is one whose genes will produce males with the beat chance of reproductive success, other benefits the father can offer the mother are not important (parental caregiver and resource access)

Question 24

Differentiate between Polygynandry and Promiscuity

Answer 24

Polygynandry - two or more males mate with two or more females are bonded socially
Promiscuity - any male can mate with any female and vice versa without social ties

Question 25

Examples of animals that use specified mating systems

Answer 25

Monogamy - bald eagle, barn owls, hammerhead sharks
Polygyny - walruses, elephant seals, gorillas
Polyandry - spotted sandpiper, pipefishes
Polygynandry - red foxes, European badgers, sea spiders
Promiscuity - dolphins, bonobos, hummingbirds

Question 26

Bateman-Trivers Hypothesis

Answer 26

Pattern - traits that attract members of the opposite sex are more elaborate in males
Process - eggs are more energetically costly to create than sperm

Question 27

2 crucial variables in a mating system

Answer 27

Male and female dispersion (space between)
Desertion by either sex (giving up parental care)