Mating Systems

Question 1

Review of parent-offspring conflict

Answer 1

• Trivers posited that conflict was both sibling-sibling and parent-offspring
• But parent-offspring conflict has proven challenging to demonstrate experimentally
• Places it can be studied: birds and clutches, + pregnancy
• Sometimes, birds lay synchronous broods (developmentally synchronized, hatch at the same time)
• Sometimes, they lay asynchronous broods (hatch in a sequence)
• David Lack hypothesized that:
• Asynchronicity produces a clear brood hierarchy - simple to reduce the brood if food is scarce and focus on just a few healthy survivors
• Synchronicity produces no clear hierarchy - parents might waste resources on producing many, but poor quality offspring

Question 2

What did David Lack hypothesize about asynchronous and synchronous broods?

Answer 2

• Asynchronicity produces a clear brood hierarchy - simple to reduce the brood if food is scarce and focus on just a few healthy survivors
• Synchronicity produces no clear hierarchy - parents might waste resources on producing many, but poor quality offspring

Question 3

Rob Magrath’s Blackbird Experiments (synchronous/asynchronous broods)

Answer 3

• Blackbirds feed their chicks worms, which are scarce when it’s dry
• Magrath experimentally made broods of four chicks:
• Synchonous (all at the same time)
• Asynchronous (clear size hierarchy)
• Results upheld Lack’s predictions: under poor conditions, asynchronous broods better, but under good conditions, synchronous broods produced more chicks

Question 4

Conflict during pregnancy

Answer 4

• In humans, during placental development, embryonic cells invade the arteries of the mother that supply the embryo with nutrition
• These cells break down arterial smooth muscle and nerves
• This prevents the mother from constricting the arteries and so increases the supply of nutrients to the embryo
• In short, the embryo has evolved to extract more resources from its mother than the mother is favored to give