L6 Mate Choice

Overview

Learned about the difference of investment size between sexes and the impact of this.

How conflicts between sexes occur.

Different mating systems and the benefits of them for each sex.

Key Concepts and Theories

Effects of Environment on Mating

Definition/Explanation

Species experiencing high predation will be dimmer/more camouflaged in colour to protect themselves, however in species where females choose to mate with bright males this means males from high predation areas are less likely to be mated with.

Example

Guppies (do everything above).

Conflict Between Sexes

Definition/Explanation

Due to anisogamy, how many partner to have, and why animals bother choosing.

Example

Anisogamy

Definition/Explanation

Refers to the disparity between number of sex cells in each gender, males have massive volumes of sperm which are produced constantly whereas females have few eggs produced every few days, therefore female sex cells are more rare and valuable.

Females also have a larger investment than males after fertilisation as males recover quickly and can reproduce multiple times a day, whereas females have a slow recovery included gestation and lactation.

Example

Male pigs produce 20-60 billion sperm while females produce <20 eggs every 18-24 days.

Female elephants have 660 days of gestation and lactate for 2-3 years.

Sexual Conflict

Definition/Explanation

Males want to maximise their own reproductive success (mating with as many females as possible) and minimise the success of other males whereas females want to maximise their success by mating with high quality males.

Example

Seed beetles take part in traumatic mating with the male genitalia being damaging to the female reproductive tract so females can’t reproduce well with other males, the females then have adaptations to limit damage.

Limitations on Mating

Definition/Explanation

Females are limited by access to resources like food, whereas males are limited by their access to females.

Example

Monogamy

Definition/Explanation

Each sex has one partner.

It’s favoured when input from both parents is needed to raise the offspring, male has to guard his mate to ensure he fathers the offspring, and their are low chances of meeting many females.

Example

A study in house sparrows showed that decreased time mate guarding led to more chicks produced by other males.

Difficulty in Finding Females

Definition/Explanation

There are few females to mate with in some species so they have strange adaptations.

Example

Male angler fish fuse to females to allow the male gametes to be inside her as it’s so rare to find a female the male will likely never find another.

Intersexual Selection

Definition/Explanation

One biological sex choose mates of the other sex to mate with.

Often females choosing the most optimal male, based on elaborate behaviour and or morphology.

Example

Female guppies mating with the most colourful males.

Female bower birds mating with the males who have the best and most intricate nests (bowers).

Intrasexual Selection

Definition/Explanation

Competition between members of the same sex for access to members of the opposite sex.

Often between males, they fight to establish dominance to either directly access females or to access resources which females want.

Example

Rutting in stags is physical competition for the right to mate with females.

Polygyny

Definition/Explanation

Males having >1 partner while females have 1 partner.

Favoured when one sex is operationally rare, males can control resources or females, and females can exert free choice.

Example

Stags/deer, also some killer whales found to sire disproportionate numbers of calves, especially once old.

Polyandry

Definition/Explanation

Females having >1 partner and males having 1 partner.

Very rare.

Example

Spotted sandpipers migrate to breeding grounds early and eat a lot before males arrive so they’re larger and females fight and defend territory like males which allows them to attract multiple males and skews reproductive success of certain females.

The eggs of the sandpipers can only be in groups of 4 per male nest and the chicks are precocial so they require little parental care, allowing females to mate with multiple males as they don’t have parental duties.

Polygyandry

Definition/Explanation

Males and females have >1 partner.

Male gains several females.

Males unable to defend female exclusively.

Females gain access to wide range of resources.

Females confuse males over paternity = increased paternal care, decreased infanticide.

Females gain access to many males and genetic benefits.

Favoured when males can’t monopolise females and females gain from multiple matings.

Example

Barbary macaque.

Female Decisions

Definition/Explanation

Females decide which mating systems to join based on the quality of the territory its based in as higher quality means higher reproductive success.

Joining a monogamous territory is often better than polygynous, so if a female joins a monogamous male then reproductive success is high, then if a second female wants to join success is lowered, however if the second female finds a male with higher quality territory with a female there already success will still be high enough.

Example

Pied flycatchers.

Why Females Choose

Definition/Explanation

There are energy and predation costs for females when looking for the best males.

Lek (areas of ground divided into defended territories for mating during breeding season) mating systems allow females to assess multiple males at the same time.

The benefits of choosing are that the female gains benefit and lives longer to produce more offspring, benefits include: territory, nuptial food, paternal care, reduced harassment.

Females determine benefits based on males signalling.

Example

Sage grouse hens are preyed on by eagles when moving between leks. (Gibson & Bachman 1992)

Sadge warbler’s make loud calls which show there is little predation in their area so it’s safe for females? (Buchanan & Catchpole, 2000)

The area of male peacock’s eyespots relate to chick survival. (Petrie , 1994)

Attractive fathers produce attractive sons so the offspring will successfully reproduce.

Runaway Selection

Definition/Explanation

Female trait choice is established and male traits become more exaggerated, daughters of successful pairings will choose a mate using the same preferences as their mother.

Sons of successful mating will possess same features as father.

Trait becomes fixed in population when all females choose it and all males carry it.

Example

Notes

Connections & Integration

Summary & Takeaways

Know causes and consequences of sexual conflicts.

Remember structure and drivers of mating systems in animal societies.

Consider the consequences of sexual conflict within sexes.