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
Examples of traits involved in sexual reproduction often evolve rapidly
- Ex. Speciation in seedeaters
- traits associated with male sexual selection evolved faster
- Females of different species indistinguishable
- Male plumage and songs very different - Ex. ground beetles
- Male reproductive organs evolving - Ex. antagonistic water strider evolution
if KA«_space;KS
purifying selection
- we know non-synonymous mutations are more common, but if we aren’t seeing that many, natural selection must be acting strongly to remove these
if KA≈ KS
your gene is evolving close to neutrally
if KA»_space; KS
positive selection
- coevolution or conflict
- ex. pathogen-host interactions (ex. mud snails)
- Genes involved in reproduction - the most rapidly evolving
Genes involved in reproduction are the most rapidly evolving (KA»_space; KS)
(KA»_space; KS)
- Amino acids evolving most rapidly so they look the most different
- Proteins in immune response but also reproduction
Reproductive proteins are among the fastest- evolving in mammals
- Divergence (%) at the Amino acid level
- Almost all data close to left - 948 have almost no divergence (under purifying selection) (ex. ubiquitin)
- Tail to the right:
- Proteins that are evolving rapidly
- Ex. Transition protein 2 - 68% divergence in humans to mice
- Immune response gene may be essential and still look different in order to avoid pathogens
Human fertilization protein zonadhesin evolves very rapidly
do introns or exons evolve faster
exons evolve faster than introns!
Human fertilization protein zonadhesin evolves very rapidly
- On egg surface
- Mediates fertilization
- Exon = protein coding with AA
- Intron = the control
Exon and intron branch lengths
Exon branches way longer - branch length = more change has occurred (not more time, it’s the same gene)
What was unusual about the introns and exons
- Usually see less exon evolution (more conserved) but not here
- More intron evolution –> below the line
- More exon evolution (unusual pattern) = above the line = more evolution of exons
Case study: Rate of molecular evolution of the seminal protein gene
SEMG2 correlates with degree of polygamy
- Evolves more rapidly in species where there is more sexual reproduction
- More mating-> increased testis size
- Species with more sexual selection, their gene has more evolution at amino acid sites
What is so special about Pkd2
One of the fastest evolving genes in Drosophila flies
* Calcium-activated ion channel that activates sperm
* Pkd2 mutants are sterile (If you break the gene completely they are sterile): they produce and transfer sperm, but it does not successfully swim
The diagram of Pkd2
- very high number of nonsynonymous mutations in Pkd2 (shown in yellow)
- so Pkd2 is essential, yet evolves rapidly
Yellow is the number and nonsynonymous mutation
If genes are essential there is no change but not for sure?
Why is Pkd2 evolving under positive selection?
- Two closely related flies can have two very different looking Pkd2 genes
2 hypothesises
1. Sperm competition hypothesis
2. Coevolution with females hypothesis
Sperm competition hypothesis
Different males, competition for access to fertilization, could have variation in ways to avoid interaction from competing male sperm could be driving selection on Pkd2
Coevolution with females hypothesis
If females are producing different products or compounds to interfere with or modulate male sperm could be driving selection on Pkd2
