HW from today’s class due Wed Feb 12 at beginning of classPlant Evolution- Origin of land plants 475 mya- Origin of vascular plants 425 mya- Origin of extant seed plants: 305 myaFocusing on vasculature todayEvolution: change in the allele frequency of a population between generationsList evolutionary mechanisms:- Natural selection- Mutation- Genetic drif- Gene flow (migration)Land plants: closely related, grouped together- Differences: vascular tissue (transport water quickly)o TracheidsThick, strong walls  grow taller to get closer to sunlight (competition)- Nonvascular: relies on osmosis and capillary action (cohesion and adhesion)o Like paper towel slowly taking up water“Clicker”: Which mechanism consistenly leads to adaptive evolution? A genetic drifB natural selectionC MigrationD mutationHow did vascular plants evolve from non-vascular plants?Plants colonized land 475 mya (no vascular tissues evolved yet)50 million years later (425 mya): few inidivduals have produced cells that look like primitive tracheids“Clicker”: How did tracheid-like cells arise in a population of plants that originally did not possess them?A Plants needed tracheid-like cells to better adapt to dry landB random genetic mutation caused the formation of tracheid-like cells in some individualsC plants that transport more water eventually develop tracheid like cells to assist themD Both A and BMutations are actually random and not because it was needed; also rareAll else being equal plants with tracheid-like cells would be better able to transport water In comparison to the original population, would you expect the next generation to have:A a greater proportion of individuals producing tracheid like cellsB a smaller proportion of individuals producing tracheid like cellsC an equal proportion of individuals producing tracheid like cellsHow did vascular plants evolve from non-vascular plants?- There was a mutation in some individuals which led to genetic variation- Phenotypic variation- Interaction of phenotypes with environment- Some phenotypes more likely to leave offspring than others- More alleles passed to next generation- change of allele frequency of next generation (EVOLUTION)Why “tracheid-like” cells?- Some characteristics in common but not exactly the same- They have continued to evolve to this day- Very simple  now they are very complexAn organism has greater fitness than another if:A it is stronger, and therefore has greater chance of surviving to maturityB It can acquire more essential resourcesC It leaves more fertile offspringD It is better able to avoid predationFitness: End result of survival and reproduction- Survival is important to reach reproductive age but producing offpsirng is very importantNatural selection shows environment-dependence- Selects which has the better fitness- Adaptations are ofen trade-offs- Ex: Skunk cabbage: releases lots of energy as heat (50° more than surroundings) but not as muchATP; germinates early and melts through snow- One that releases lots of heat: good for cold environments- One that release less heat but more ATP: good for warm environmentsTesting natural selection in diff environemtnsLets suppose we collected a few hundered individualsTransplant half to dry and half to moistMoist habitat Dry habitatGeneration 1 Generation 2 Generation 1 Gen 2% of pop that doesn’t orduce tracheid like cells95% 91%  74% 95%% of pop that do produce tracheid-like cells5% 9 %  26% 95%Dry habitat: “Clicker”: Would you expect % of population that do produce tracheid-like cells to: A increaseB decreaseC stay the same- Organism with them would better transport water which is perfect for dry environmentsMoist habitat: “Clicker”: Would you expect % of population that do produce tracheid-like cells to:A increaseB decreaseC stay the same- Same reason for last question- Could be detrimental by taking in too much water- No benefit to having tracheids, then they wouldn’t have advantage but ones without it would be fine too so it could stay the same as well- As long as you can provide evidence, you can have a good answerDuring the evolution of vascular plants:A each offspring had a lot more vasculature than its parentsB each offspring had a little bit more vasculature than its parentsC each offspring had roughly the same amount of vasculature as its parents- Changes in populations (frequency not offspring vs parentsExample- Tall x Tall: mostly tall plants- Short x short: mostly short plants- Tall x short: lots of variation- All tall plants are chopped off- Short plants randomly mate: mostly short with some variation- Massive evolutionary change in just 2 generations (huge evolutionary shif)Key to evolution by natural selection- Variation in heritable traits- Successful individuals live to reproduce- Less successful individuals have lower fitnessHow did present-day vascular plants evolve from non-vascular plants?- More cycling of bottom half of evolution flow chart- Last step back to interaction of phenotypes with environment- Cycled through whole flow chart, back to interaction of phenotypes but for more xylem, needs to be another mutation and cycle through evolution chart Why natural selection can’t lead to “perfect” organism- Adaptation are ofen trade-offs o depends on environmento physical limitations based on adaptations (taller plants become weaker)- Environments (selective pressures) changeo Could be very close to being “perfectly” adapted but then the environment changeso Ex: whole world covered in glaciers only 10,000 years ago- Random chance also plays a part (too many coincidences not likely)HWGoal: to demonstrate understaning of evolution by natural selection thru your ability to apply concept to a novel scenarioTask: describe how present day flowering plants produce complex flowers may have evolved through process