lecture 16 Flashcards
What about sexual selection in plants?
- Similar patterns as seen in animals
- Pollen male gametes many small
- Ovules female gametes few larger
- example: Mercurialis annua (mercury), a common wind- pollinated southern European annual herb
Case study: Rapid evolution of pollen and pistil traits as a response to sexual selection
in the post-pollination phase of mating
- Increased sexual selection
- Evolution of pollen and pistil traits in response to sexual selection post-pollination
- Uses concept and framework of experimental evolution to test hypotheses
Case study: Rapid evolution of pollen and pistil traits as a response to sexual selection
in the post-pollination phase of mating
What was studied?
- Mercurialis annua, common wind-pollinated annual herb
- Lots of diversity
- Throughout Europe
Case study: Rapid evolution of pollen and pistil traits as a response to sexual selection
in the post-pollination phase of mating
What did they do?
- experimentally evolved mercury plants for 3 generations, under conditions of high or low density
- High density conditions = expecting stronger sexual selection (more competition) among pollen donors
- Lower density conditions = less sexual selection
- after 3 generations, they grew plants in a common garden and compared reproductive traits
- Remove for any differences due to the parents and all raised after evolution in the same condition
- The only difference now is the evolution which occurred separately in the two treatment groups
- expected high density treatment to result in stronger competition among pollen donors for fertilizing ovules
Case study: Rapid evolution of pollen and pistil traits as a response to sexual selection
in the post-pollination phase of mating
Results?
- High density plants evolve faster-growing pollen tubes
- Measured pollen tube length - relates to faster fertilization of ovule - Proteomic (i.e. genetic!) differences between high and low density plants
- mass spectrometry of pollen coat extracts - isolate proteins (not easy, not a model organism, and the tissues are difficult to extract proteins from)
- out of 144 proteins identified, 10 were much more highly expressed in high density treatments
- Found: 10 of 144 identified proteins were more expressed in the high density treatment
- Compare the amount of peptide produced when you control for everything else between the two treatments - so whatever is controlling the expression of these genes is responding to the conditions - Protein g13338
- related to Arabidopsis thaliana quartet protein 2 (QRT2), a polygalacturonase involved in breakdown of the cell wall surrounding the pollen mother cell (& necessary for separation of the 4 haploid gamete products)
A) wildtype Arabidopsis
B) quartet mutants - don’t break apart
properly
C) fused pollen grains
within a quartet tetrad
So how would you perform an experimental evolution to remove or reduce sexual selection?
Mosquito case study
Case study: Male competition and the evolution of mating and life-history traits in experimental populations of Aedes aegypti
- studied Aedes aegypti
- Reducing sexual selection
- Manipulating the opportunity for sexual selection
Case study: Male competition and the evolution of mating and life-history traits in experimental populations of Aedes aegypti
What did they do?
- Performed experimental evolution by manipulating the opportunity for sexual selection:
- lines with high male competition vs lines with no male competition (a single male & a single female)
- After a few generations, they bring the lines together to remove the effects from the parents or other conditions to compare the genetic variation
- Measuring mating success when they’re in competition - not with each other, but with a standard unselected group of males that were the source of the original experiment (control - raised in regular setting)
What did they know about mosquito mating:
- Males gather and attract females
- Males and females make sounds of different frequencies - harmonic convergence - they will both change their frequencies to match each other before mating
Case study: Male competition and the evolution of mating and life-history traits in experimental populations of Aedes aegypti
Results?
- Competition-selected males have higher mating success in competition
- Competition-selected males have lower harmonic convergence & mating success in single pairings
- proportion of convergence in an individual pair: did they reach the same singing frequency
- Proportion of successful attempts
- No competition males often had higher rate of reaching convergence
- It’s complicated to show the complexity of interactions between the individuals to produce the phenotypes and variances
Follow-up study: Release from sexual selection leads to rapid genome-wide evolution in Aedes aegypti
- sequenced the genomes of the selected lines
- documented many genetic changes (like the pollen sexual selection study)
Conflict and coevolution between the sexes
What is coevolution?
reciprocal evolutionary change between interacting lineages
Conflict and coevolution between the sexes
What is the conflict?
there can be conflict between the evolutionary interests of the two sexes (selection in one sex to maximize matings)
Conflict and coevolution between the sexes
Prediction?
conflict should be greater when there is multiple mating (polygamy»_space;» monogamy)
Case study: Correlated evolution of male and female morphologies in water striders
- in species where males have exaggerated grasping morphology, females have evolved counter-adaptations against grasp (e.g. G. incognitus)
- Morphological variation following a correlated pattern in males and females
- Males and females matched morphologically
- Gerrus thoracious - not much dimorphism
- Gerrus incognitus - males have differently shaped abdomens for grasping and females have evolved counter adaptations agaisnt grasp
