Plant reproductive strategies

Question 1

Types of plant mating system

Answer 1

1. Outbreeding

• Selected for by inbreeding depression

2. Inbreeding / selfish systems
   - Selected for by reproductive assurance
3. Asexual / apomixis

• Selected for by reproductive assurance

Question 1

Factors infliencing mating system evolution

Answer 1

a) Immobility
- Plants are imobile so most are hermaphrodites as cannot move to find mates.

b) Inbreeding depression
- maintains outcorssing
- most angiosperms outcross to some extent

c) Reproductive assurance
- Plants want to ensure they offspring if pollinators / mates scarce
- Leads to Inbreeding/ asexual reproduction

d) Optimal allocation of male + female reproductive effort

Question 2

Mating characteristics promoting outcrossing / avoiding self-fertilisation:

Answer 2

 Dichogamy – separates sexual organs in time

 Herkogamy – separates sex organs in space eg. distyly

 Dicliny – sexual polymorphisms (female plants and male plants)

 Self-incompatibility – recognise + reject own pollen

Question 3

Mating systems correlate with life history strategies

Answer 3

More woody perennials -> obligate outcross as can wait to reproduce as live a long time

Annuals -> self-compatible + selfers as must reproduce before they die

Question 4

Mating system correlates with ecology

Answer 4

Pollinator rich region: outcrossing and flower
morphology specialisation

Pollinator poor region: selfing / apomixism and generalisation

Question 5

Self incompatibility systems

Answer 5

SI is controlled by the S locus: Locus is 2+ tightly linked genes for pollen specificity and Pistel specificity

If S alleles are the same: incompatible

If S alleles are different: compatible

Number of S alleles in the population remains large due to frequency dependent selection

Question 6

Types of SI systems

Answer 6

Gametophytic GSI (Rosaceae, poppies)
o Incompatibility phenotype determined by pollen’s haploid genome
o S alleles / haplotypes = co-dominant in pistil
o Pollen germinates, grows style, then rejected

Sporophytic SSI (Asteraceae)
o Incompatibility phenotype determined by diploid genome of parental plant (Pollen behaves as diploid due to diploid tapetum around pollen)
o S alleles / haplotypes can show dominance in pistil / pollen
o Stops pollen germination v early
o More dominance leads to more compatibility

Question 7

Molecular mechanisms for SI

Answer 7

Diverse proteins controlling cell recognition

Self-recognition
- Products of genes at different haploid loci from the same S allele recognise each other
- Example: Brassicaceae-> Female S allele encodes a receptor kinase and male S allele encodes a protein ligand which inhibits pollen growth when bind.

Non-self recognition (in algae, fungi, MHC of vertebrates)
- Products of genes at different haploid loci from different S alleles recognise each other
- Example: RNAs systems -> Female S allele encodes an RNAse and Male S allele ecodes protein which recognises non-self RNAses. If there is selfing, the RNAs is not bound to a protein and is able to destroy RNA and inhibit pollen growth