Sexual Selection

What is sexual selection?

Acts upon an organisms ability to obtain or successfully copulate with a mate

Monogamy

One partner for life

Low competition

Low sexual dimorphism

Equal parental care

Polygyny

One male, several females

High competition between males

High sexual dimorphism

females care for young

Polyandry

One female lots of males

High female competition

Low sexual dimorphism

Both sexes or only males care for young

Intrasexual selection

Male-male selection for mates e.g. secondary sexual characteristics

Intersexual Selection

mate choice e.g. ornaments and colouration

Indicator traits

traits that signify overall good health and well-being of an organism, increasing its attractiveness to mates

Sensory Bias

development of a trait to match a preexisting preference that exists in the population

Runaway selection (Fisher, 1958)

Assumes genes for male traits and female choice are linked e.g. if a female prefers males with a certain trait her sons are likely to have that trait.

Genetic compatibility

The creation of mate pairs that, when combined, have complementary genetics e.g. Major Histocompatibility Complex (MHC)

Sperm competition

Sexual selection favours greater sperm production

Sex ratios

Equal males and females within a population - there is an equal chance of inheriting the male or female genes