Dioecy Flashcards

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1
Q

Define dioecy:

A

Having male and female sex organs on separate plants

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2
Q

How common is dioecy?

A

4% of angiosperms, 10-20% of trees and shrubs, 1-5% of herbs. Often associated with wind pollination

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3
Q

What is the origin of dioecy?

A
Multiple origins
Enforces outcrossing 
Recessive X carries male sterility, dominant Y = female sterility 
- only requires 2 mutations
Would still expect 50:50 sex ratio.
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4
Q

How is dioecy distribution geographically?

A

Higher frequency in tropical floras and oceanic islands.

- In tropical forests chances of inbreeding are high due to low species density –> inbreeding depression.

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5
Q

What are the benefits of dioecy?

A

Enforces outcrossing - prevents inbreeding depression
Prevents pollen clogging which can be an issue with self-incompatibility
Better resource allocation

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6
Q

Why are dioecy and resource allocation linked?

A

In tropics females produce large seeds (fleshy) due to large amounts of competition. Therefore requires lots of resources / input.

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7
Q

When is self-compatibility an advantage?

A

Colonising species use self-compatibility
Allows establishment after long distance dispersal
- Remote islands tend to be small and lack pollinators

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8
Q

How comes dioecy is common on oceanic islands?

A

Adaptation to enforce outbreeding following colonisation and establishment as self compatible.

  • More prevalent in endemic species
  • Frequency higher in older islands
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9
Q

Why is dioecy adaptively significant?

A

Many vacant niches exist - opportunity for speciation and diversification.
- This requires high genetic variability which is not going to happen with inbreeding
- Outcrossing mutations favoured - gyanceous (male sterile)
- Female sterility arises later
It is a lot easier than becoming self-incompatible.

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10
Q

How are dioecous species spread?

A

Fleshy seeds can be eaten by birds - contains male and female seeds.
- If self incompatible then fecundity is low due to being siblings (chances of successful offspring is decreased).

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11
Q

When is dioecy adaptive?

A

When founding populations are small and contain closely related individuals.

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