Sex and Sexual Selection

Question 1

Apomixis

Answer 1

Asexual Reproduction
Egg develops into embryo without being fertilized (parthanogenesis)

Question 2

Automixis

Answer 2

Asexual Reproduction
Production of haploid gametes via Meiosis, but diploidy is usually restored by the fusion of haploid nuclei from the same Meiosis

Question 3

Amphimixis

Answer 3

Sexual Reproduction
1. Recombination
2. Gamete Production
3. Gamete Fusion

Question 4

Muller’s Rachet

Answer 4

Deleterious alleles (BAD genes) accumulate in asexual populations
-Sex can reduce deleterious alleles

Question 5

Red Queen Hypothesis

Answer 5

Organisms are forever evolving to counteract the defenses of their enemies

Question 6

Anisogamy

Answer 6

Different sized gametes (trade-ff between gamete size and number of gametes)
-Females are limiting factor because limit on amount of eggs

Question 7

Sexual Selection

Answer 7

Preference by one sex for certain characters in individuals of the other sex
-Usually females are choosy with finding a mate

Question 8

Intrasexual Selection

Answer 8

Competition between members of the same sex (usually males) for access to mates

Question 9

Intersexual Selection

Answer 9

Where members of one sex (usually females) choose members of the opposite sex

Question 10

Female Sensory Bias

Answer 10

Females prefer traits that are not an indicator of male quality

Question 11

Monogamy

Answer 11

1 male and 1 female

Question 12

Polygyny

Answer 12

1 male and 2 females

Question 13

Polyandry

Answer 13

2 males and 1 female

Question 14

Polygynandry

Answer 14

Multiple males and multiple females

Question 15

Costs and Benefits of Sexual Selection

Answer 15

Cost
-50% of DNA being passed on
-Female 50% related to offspring
-Number of individuals you can produce over time is limited
-Two Fold Cost (population growth is slower)
-Predation when trying to mate (energy cost)
-Searching and courting takes time and energy
-Increased risk of disease (STDs)
Benefits
-Reduction in deleterious mutations (Muller’s Ratchet)
-Beneficial alleles accumulate faster (Fisher-Muller Hypothesis)
-Sex provides hosts with a way around parasites/local pathogens/diseases (Red Queen Hypothesis; sexual reproducing species will outcompete asexual species because advantageous mutations will increase in the reproductive species quicker)
-Lower infection rates
-Variation
-Quicker adaptations to the unexpected

Question 16

Explain Key Steps that lead to Genetic Variation in Sexual Reproduction

Answer 16

1. Recombination: the crossover between homologous chromosomes, which produces new chromosomal variants.
2. Gamete production: the production of haploid gametes by diploid individuals via reductive meiotic division.
3. Gamete fusion: gametic exchange between individuals, in which haploid gametes fuse to produce a diploid offspring.

Question 17

Explain the evolution of anisogamy

Answer 17

Imagine a population of individuals in which a wide range of gamete sizes are produced, and suppose that;
(1) there is a trade-off between the size of gametes and the number of gametes, so that the larger the gamete, the smaller the number of gametes an individual can produce
(2) the larger the size of a gamete, the less mobile it is
(3) the probability that a zygote survives increases with its size, where the size of the zygote is a function of the sizes of the fusing gametes
-Selection may favor proto-eggs that differentially fuse with proto-sperm, producing disruptive selection for proto-eggs and proto-sperm
Proto-Sperm: tiny tiny sperm
Proto-Egg: large egg

Question 18

Describe the effects of sexual selection on males versus females (sexual dimorphism, sexual conflict, etc.)

Answer 18

1. Sexual Dimorphism: Sexes of the same species exhibit different characteristics, particularly characteristics not directly involved in reproduction
2. Sexual Conflict: Traits evolved in one sex may be detrimental to other sex
3. Females are limited by the amount of eggs produced
4. Conflicts of interest may also arise when a trait, expressed in only one sex, has positive effects on individuals of that sex but negative effects on members of the opposite sex
5. Competition over which mating system should be in place is not the only way that conflicts of interest can manifest themselves in sexual selection

Question 19

Describe different forms of intrasexual selection

Answer 19

-Male-to-Male competition by cuckoldry or sperm competition
-Traits that evolve in one sex may be detrimental to individuals of the other sex (Sexual conflict)

Question 20

Describe forms of intersexual selection

Answer 20

-Selection will favor females who choose mates that possess “good genes”; that is, genes that code for some suite of favorable traits
-Benefits may include nuptial gifts or protection from predators
-Costly signaling
-Female nervous systems respond to an uncommon trait that does not indicate male quality either because it is associated with some benefit outside of mate choice or simply as an artifact of how the stimulus excites their nervous systems (Sensory Bias Hypothesis)