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Transcript
Pieris Project Using evolution and genetics to understand nature Lesson 1 Evolution: Understanding the processes that drive species diversity Photo: University of Southampton/PA Wire What is evolution? Descent with modification from a common ancestor It’s simply the change in allele frequency of a population through time - Each color is a different “allele” for a gene 4 3 6 Reproduce (produce offspring) 2 Amoeba population at generation 2 Amoeba population at generation 1 Time What causes evolution? Natural Selection 3 conditions are required Variation in trait (phenotype) Differential fitness Inheritence of trait Bird photo credit: Dûrzan cîrano Butterfly photo credit: Andy Emcee How can a trait not be inherited (“heritable”)? Phenotypic plasticity - variation in a trait due to the environment Some variation in the traits of a species are not due to genetic differences, but differ because the environment they inhabit is different Photo credit: Scott Wylie Evolution without natural selection? Mutation Migration Genetic Drift Mutations: create genetic and sometimes phenotypic diversity (it also provides the raw material for natural selection to act upon) C A G T Replicating strands Mutation (supposed to be ) Migration / Gene flow Population 1 Population 2 Photo credit: Evan Twomey Genetic Drift Change in the genetic composition of a population that is due to random chance. Fitness differences have nothing to do with phenotypes (traits). The difference between the “winners and losers” is just due to chance. Remember Evolution is simply a change in the genetic composition of a population over time Evolution can be Adaptive – result from natural selection where different traits lead to differences in fitness AND Non-adaptive - have nothing to do with fitness (mutation, migration/gene flow, and genetic drift) Lesson 1 Activity: Small Group Discussion on Misconceptions of Evolution Lesson 2 Phylogenetics A tool for estimating the evolutionary relationship among species Phylogentics: understanding the evolutionary relationship between different species Illustration credit: James McInerney Which animals are most closely related? Which animals are most closely related? OK, that was easy, how about these? So how do we go about determining the evolutionary relationship between species? Evolutionary Tree - Phylogeny Similar to a family tree, scientists use evolutionary trees, or phylogenies, to show the evolutionary relationship among species clade More recent Common ancestor Past Building a phylogeny To build a phylogeny, biologists must identify a set of characters and then conmpare these characters among the different species Requirements of characters: - Present in some, but not all species - Have a shared ancestry (“homologous” characters) These can be phenotypic characters or genetic characters What might be a shared character for this phylogeny? What might be a shared character for this phylogeny? evolution of limbs evolution of lungs Which two species are most closely related? Photo by: Oliver Bain Photo by: Oryan Espanto Photo by: Angell Williams Which two species are most closely related? Photo by: Oliver Bain Photo by: Oryan Espanto Photo by: Angell Williams There’s a problem…. Convergent evolution – traits can look similar between species (especially if they are used for similar functions, such as flying), but have evolved independently (that is, they do not share a common ancestor); they are not homologous, they are analogous. Let’s build a phylogeny Character Taxa Activity: Construct a phylogeny Character Taxa Eyes Vertebrae Four limbs Hair Virus Insect Fish Lizard Wolf 0 1 1 1 1 0 0 1 1 1 0 0 0 1 1 0 0 0 0 1 Does our phylogeny match the fossil record? Lesson 3 Pieris Project (Part 1) Using genetic information and citizen science to track the spread of a butterfly across the globe Let’s use our understanding of phylogenetics to do some “forensics” Have you seen me? 150 yrs ago 2,000 yrs ago 100 yrs ago Photo credit: NASA Why were these butterflies so successful in spreading across the world? • What they eat is what we eat ☺ • They eat plants in the Brassicaceae (mustard) family Photo credit: Alan Buckingham Photo credit: Chrissine Rios Photo credit: Linda How can we use genetics to “reconstruct” the invasion of this butterfly? Not only can traits (phenotypes) be used as characters to construct a phylogeny, but DNA contains characters too Native population 1 Native population 2 Non-native (introduced) population SNP: Single Nucleotide Polymorphism So far we have been focusing on “deep” divergence between species But we can also look at the very “tips” of the tree France Your City (USA) Spain Germany Finland Turkey China Russia Mitochondrial DNA • Why is this type of DNA useful to looking at an organism’s lineage? Maternally inherited No recombination (haploid) Participate in the Pieris Project as a citizen scientist We sequence a portion of a mitochondrial gene from each of the butterflies sent in from citizen scientists – people just like you – from around the world. We can then use that genetic data to infer where the butterflies invaded from. Individually and/or as a class, collect a few cabbage white butterflies from around your neighborhood. Visit the Pieris Project website for a break down on the proper protocol for this study Send in your butterflies and we’ll put your samples on our map and send you back the genetic data so we can identify the country from which the butterflies you collected originated. A walk through of the Pieris Project Photo by: Woodleywonderworks Photo by: John Taylor Step 1. Find a cabbage white butterfly. They’re pretty much everywhere, but most common in urban environments (e.g., side of the road, near farms, in gardens, and meadows) Male Female Mike, Nick and Dasco Photos by Dennis Walker Step 2. Catch a cabbage white butterfly. It will help to have a net. It’s also easiest if you wait until they land, but they are one of the easier butterflies to catch – they are not too fast. Check out our video on how to properly swing a butterfly; yes, there is a technique =) Step 3. Place each butterfly in their own individual envelope. You can make these envelopes very easily. Check out our video on how to make an envelope. Record the date (month/day/year) and the location – watch a video on how to use your iPhone to get GPS coordinates. Step 4. Place the butterflies in the freezer overnight. This is a humane way to euthanize the butterflies, which is something we have to do in order to collect DNA from them. AVOID FREEZE-THAW CYCLES (ONLY PUT SPECIMENS IN THE FREEZER ONCE). IF YOU ARE NOT READY TO SEND THEM YOU CAN LEAVE THEM IN THE FREEZER UNTIL YOU ARE READY TO SHIP. GOING FROM FROZEN TO THAWED MULTIPLE TIMES WILL SHEAR THE DNA INTO VERY SMALL FRAGMENTS, WHICH IS VERY BAD. Step 5. After taking them out of the freezer, let them dry in their envelopes somewhere where they won't be in direct sunlight or near moisture. The key is to let them dry quickly, so mold doesn't grow on them while they dry out. If left in their envelopes and placed on some paper towels for 3-4 days at room temperature (~20°C or 70°F) should be good enough to dry them out. (No need to heat them, this is bad for DNA as well.) Mail to: Pieris Project (attn: Sean Ryan) USDA-ARS 1600/1700 SW 23rd Dr Gainesville FL, 32608 Step 6. Send in your butterflies. Be sure to use a crush-proof container (e.g., old Altoids or CD case, Tupperware, candy box, … feel free to be creative) – for shipping the butterflies without them getting squished What will we do with the butterflies you send in? First, Dr. Ryan will extract the DNA from some of your butterflies and sequence a mitochondrial gene that can you will be able to use to construct a phylogenetic tree and determine where in Eurasia the butterfly you collected originated. Which of these butterflies is most closely related to yours? Next, we can also use the DNA inside the butterfly to look for the presence of other organisms. Yes, seriously! There is a bacteria called Wolbachia that infects many different species of insects. What is really interesting is that the infection of this bacteria can actually prevent some insects from carrying diseases (like malaria), turn males into females, and even prevent infected individuals from producing offspring with uninfected individuals. Wolbachia Surprisingly, no one knows whether this bacteria infects cabbage white butterflies in the USA or whether some regions of the USA have different “species” of this bacteria living inside these butterflies. Help us find out! Next, Anne Espeset will photograph your butterflies so that we (and you!) can measure their phenotypic variation – their size and shape. Many butterflies are known to change in size and color throughout the summer and with these photographs we can measure we these changes. Last, we will look at how the diet of these butterflies affects their color. Researchers have shown that cabbage white butterflies that eat a lot of nitrogen as caterpillars, tend to have more white pigment in their wings. Agricultural fields usually have lots of extra nitrogen that has been added by famers to help their crops grow. Given that cabbage white butterflies like to eat many agricultural plants (cabbage, broccoli, kale, etc.), what would be expect? photo: Dennis Walker photo: Richard Hurd To determine this, Anne will measure a pigment on the wings called pterin, which gives the wings its white color. Using a machine called a wand spectrophotometer she will measure how much light the wings reflect (the more they reflect, the more pterin present).