Sexual Selection

Phenotypic gambit

Ignore genetics and focus on the fitness of phenotypes

Useful way to test evolutionary hypotheses

Focus on reproductive success

Behavioural ecology

The study of natural selection as applied to behaviour

Estrus

The period around ovulation where the female is able to conceive

Concealed ovulation

Hiding that they are in ovulation

Ex. Humans

Use other cues like scent and proceptive behaviour

Reproductive success

An individual’s genetic contribution to future generation

Currency used to measure success

The number of offspring an individual produces

Sexual selection

Selection in relation to sex to natural selection

Intrasexual selection

Competition for mates

Intrasexual selection and precopulatory

Monopolize a single female

Intrasexual selection and postcopulatory

Multiple female matings

Intersexual selection

Choice of mates

Intersexual selection and precopulatory

Males displaying

Intersexual selection and postcopulatory

Female prevents sperm from contacting eggs directly

Sexual conflict and precopulatory

Intimidation and harassment

Sexual conflict and postcopulatory

Traumatic insemination

Mate guarding

The guarding a females that the male wants to mate with

Bateman Principle

Males benefit more by mating with multiple females while females only need one mating partner

Females produce a few highly nutritious gametes while pales produce a lot of smaller ones

Darwinian Sexual Selection

Females as the ecological sex and males as the mate getting sex

Ecological sex

Concern they have the resources that the fetus survives

Mate getting sex

Getting more mating opportunities

Sexual selection theory

Male primates are usually bigger than females

Better at fighting, more favoured, monopolize better, have more offsping

Polygynous

Many females per male

Males are usually bigger (more competitive)

Ex. geladas

Monogamous

One female per male

Body size dimorphism

Male body mass/female body mass

Canine size dimorphism

Male canine height/female canine height

Operational sex ratio

OSR

Number of sexually active males/Number of sexually receptive females

Polygynous breeding system (male traits)

Bigger than females

Bigger canines

Impressive looks

Aggression

Hormones

LRS

Lifetime reproductive success

Scramble competition

Conceptive efficiency

Faster sperm, plugs, etc.

4 step mammalian socioecological model

1. Predation + competition for food = FF relationships
2. Competition for mates = MM relationships
3. Infanticide, herding, harassment = Male coercive strategies
4. Female choice, alliance, pair bonding = Female counter strategies

Langurs

Colobine monkeys from Asia

Eat leaves, one male multiple females, natal females in the same group, society is calm until new male takes over

Infanticide

Killing of infants

Results in rapid inter birth interval (IBI)

Was assumed to be pathlogical


1. Case of selfish behaviour by natural selection
2. widespread in animals
3. Prevasive force affecting social behaviour/promoting groups

IBI

Inter birth interval

Pathology

Mental abnormality

Infanticide tendency

Is only seen with definite non offspring

Bruce effect in Wilde geladas

Females will unconsciously terminate their pregnancy when their is a case of infanticide due to hormonal cascade