Social and Mating Systems

What is polygamy?

Mating with multiple partners

• Polygyny, polyandry, promiscuity

What does reproductive skew do?

Selection pressure for traits

What factors shape mating systems?

1. Differential investment between sexes

2. Ecological factors

3. Paternity certainty

4. Dependence of young and impact of care

How does differential investment between sexes shape mating systems? What mating system does this favour?

Sex investing more parental care is limiting resource-

• Males limited by matings they can obtain, females limited by eggs they can produce

• Polygyny (>1F + 1M) tends to be favoured

What kind of environment might see polyandry or monogamy?

Poor environment quality - need multiple helpers.

What do clumped resources or high predation risk create potential for and why?

High polygamy potential

• Females come together, males compete for access

How does certainty paternity influence mating systems?

More paternity certainty - more investment in parental care

Why would males guard mates? What may this lead to?

Increase paternity certainty, lead to monogamy

What are the consequences of mating systems?

• Secondary sexual characteristics

• Intra and inter sexual competition

What are explanations/types of polygyny?

• Female defence polygyny

• Resource defence polygyny

• Scramble competition polygyny

• Lek polygyny

What is resource defence polygyny, how is this different to female defence? Use examples

Grevy’s zebra - males defend areas where females congregate (near water)

Plains zebra - defend harems of females from rival males. Females congregate as anti-predaotor strategy

why would closely related species use different strategies for defence in polygyny?

If ecological conditions vary

What is scramble competition polygyny?

Females and resources not always defendable - when dispersed. Males scramble to find as many mates as possible

What is lek polygyny?

Hammerhead bat - massive cavern in head. Males congregate around big trees and make booming sounds to attract females

• Lekking - aggregating of males to display to females

• no resources from males - they are for mating.

Why is it weird to form leks?

Non-copulating male gets no benefits despite males working together

What about leks is good for females?

• Picls of males, can easily compare them and secure ‘good genes’

What type of polygyny causes a massive reproductive skew?

lek polygyny - 438 copulations in one season, 320 by a single male.

What are the hypothesis for males to form leks when many are gaining no copulations?

• Hotspot hypothesis: males cluster around routes of places frequented by females

• Hotshot hypothesis: subordinate males gather around attractive dominant males

• Female preference hypothesis: males cluster because females prefer sites with larger groups of males

What is the evidence for the hotspot hypothesis?

Four species of birds in Costa Rica used the same location to lek - topology determines where females go

What is the evidence for the hotshot hypothesis?

in the european sandpiper, removing the dominant male from the lek causes subordinates to disperse. Removing a subordinate did nothing

• Subordinate males cluster around sexy males

Which taxa has highest levels of monogamy?

Birds - 90%

How many mammals have monogomy?

3% of mammals, but 30% of primates. ??

What are the 3 hypothesis for monogamy?

i. Mate-guarding hypothesis:

ii. Mate-assistance hypothesis:

iii. Female-enforced monogamy hypothesis

What is the mate guarding hypothesis?

• Monogamy is adaptive when female left by one male readily mates with another male.

  • Mate guarding especially when female remain receptive after mating and difficult to locateW

What is an examples of a species that does mate guarding

Monogamous clown shrimp

What is the male assistance hypothesis? Give example of species

Monogamy is adaptive when parental care can greatly increase offspring survival - often in altricial species

• Pays for male to stay

• Californian mouse

What is the female enforced monogamy hypothesis? Give example

Males are not monogamous because it is in their best interest, but because females impose this

• Burying Beetles - Males try to attract a second female to the carcass using pheromones. Females detect pheromones and attack males - he stops releasing them.

When is monogamy not ‘monogamous’ ?

Many species of birds - males and females are socially monogomous but genetically promiscuous

What do females who are socially monogamous and genetically promiscuous engage in?

Extra pair Copulations (EPCs)

Why does this social monogamy occur?

• Mate guarding

• Rearing altricial offspring

• Eggs mean both parents can provide care