Chapter 11 | Sexual Selection

Hermaphrodites

One organisms has both male and female genitalia

Asexual reproduction

Produces genetically identical offspring through mitosis, best for stable environments

Muller’s rachet

Genomes of an asexual population accumulate irreversible deleterious mutations because there is no recombination

Genetic load

Burden of accumulated mutations increase over time

Sexual reproduction

Produces genetically diverse offspring through meiosis; best for variable environments

Twofold cost of sex

Finding a mate takes time, energy, effort, and risk of predation

Reduced relatedness

Offspring produced through sexual reproduction only contain ½ of the parents’ genetic material

Red Queen effect

Populations constantly innovate and generate new mutations to increase fitness, allowing for coevolution

Sexual seelction

Individuals with certain inherited characteristics are more likely to acquire mates than those without them

Sexual dimorphism

Sexes have different appearances

Males

The sex with the smaller gamete; can maximize reproductive success by maximizing matings

Anisogamy

Sexes have different sized gametes

Females

The sex with the larger gamete; maximize reproductive success by choosing quality mates and investing in offspring

Variation in reproductive success

A key factor in predicting which sex experiences more sexual selection

Intrasexual selection

Competition within sexes

Intersexual selection

Competition between males and females

Ornaments

Attractive traits that increase mating success

Armaments

Weaponry used to outcompete other individuals

Make choice

Choosy sex selects mate (usually the female)

Female choice

1. Direct

2. Good genes

3. Sexy offspring

4. Sensory bias

Nupital gifts

Tasty food from spermatophores allows female to produce more and larger eggs

Cannibalism

Females cannibalize after mating, or males voluntarily sacrifice themselves

Good genes

Individuals with trait have better fitness — “honest signal” of good genes

Arbitrary choice / sensory bias

Individual is more attractive

Fisherian run-away

Preferences are inherited and choice perpetuates future generations

Sexy sons hypothesis

Sons inherit attractive trait, daughters attracted to that trait; increase in trait until it is opposed by natural selection

Handicap principle

Trait that is preferred may eventually interfere with survival

Monogamy

A pair containing a female and male

Polygyny

A male with multiple female mates

Polyandry

A female with multiple male mates

Promiscuity

Everyone x everyone

Social or serial monogamy

A relationship pattern of having a series of exclusive, consecutive partnerships, where one ends before the next begins, often without significant breaks — allows parental care from both parents; mate guarding may occur