Chapter 17: Coevolution and MutualismObjectivesPairwise interspecific interactionsFluidity of interspecific relationships:Symbiosis:***Define ‘coevolution’:Slide 7Batesian mimicry: “a sheep in wolf’s clothing” shows 1/2 of coevolution equation; selection by predator on preyBatesian mimicry: palatable species mimic unpalatable models.Mullerian mimicry cross-mimicry benefits both speciesMullerian mimicry: unpalatable species resemble each other. Each species is both model and mimic. Get benefit of warning from two species.Slide 12Gene - for - gene concept: ‘evolutionary arms race’Slide 14Slide 15Slide 16Coevolution between chemical defenses of plants and their herbivores; uses phylogenetic relationships to build an inferential argument.Experimental Evidence: Question: Do ants and treehoppers have a mutualistic relationship?***Develop an “if…then…that addresses this question.Slide 20Slide 21Mutualism: two species specialized to perform a complementary (positive) function for each other.Legumes and N-fixing RhizobiumEndomycorrhizae in root cells of orchidSlide 252) Mutualism: defensive Species receive food or shelter in return for defending against natural enemies.Ant-plant defense mutualism: Acacia and Pseudomyrmex antsSlide 28***Predict a possible evolutionary response when a plant, but not the ant, invades an island. On the mainland they are mutualists. What is the assumption?3) Mutualism: dispersive Animal vectors move plant pollen and seeds (gene flow) in return for food rewards.Pollination syndromes provide circumstantial evidence of at least diffuse coevolution.Some plant-pollinator interactions are highly specific (obligate mutualism).Seed dispersal (no or diffuse mutualism)Plant-seed disperser mutualismAnt-plant mutualism: elaisomesConstraints on evolution of strict mutualismsAnother obligate strict mutualism of a plant-pollinator/seed predator.Some adaptations were present before the establishment of the mutualism (preadaptations) and occur in close relatives that are not mutualists.Exam question: Acacia trees have a mutualistic relationship with ants. 1. Develop an “if…then…” relating to the benefit of the mutualism to the plant. 2. Does the existence of the mutually beneficial traits in this mutualism confirm this relationship as an example of coevolution? Explain, including what is the best evidence of coevolution. 3. Not all species of acacia form a mutualism with ants. In a setting where herbivore pressure is low, why might the mutualism not have arisen? 4. In some areas where herbivore pressure is high, the mutualism with ants has not arisen. Predict two alternative anti-herbivore defenses these acacias may be using.Chapter 17:Coevolution and MutualismYucca and yucca mothObjectives•Types of pairwise interactions•Coevolution• Strict (one-on-one) vs. diffuse• Gene-for-gene concept• Evidence for•Mutualism• Types• Specificity• Constraints against strictPairwise interspecific interactions***Which is: +/-, +/0, +/+, -/-, -/0 ? •Mutualism •Facilitation (Commensalism) +/0•Amensalism -/0 •Herbivory•Predation • Parasitism• Disease•CompetitionFluidity of interspecific relationships:• Can evolve from one type to another.• Switch + and - signs of interaction, e.g. +/+ to +/-.Symbiosis:•an intimate and often obligatory association of two species, usually involving coevolution. May be parasitic or mutualistic.Lichen = algae + fungus***Define ‘coevolution’:•Interacting species evolve in response to each other (how many species?)•Traits of each species affect fitness of individuals of other species.•Traits have variation and a genetic basis.•May be mutualistic or antagonistic relationship.•Strict coevolution:•One species stimulates evolution in one other species and vice versa.•Limited to a pair of species•May be rare and limited to very strong interactions•Diffuse coevolution:•Species simultaneously respond to an array of complex interactions with many other species.Batesian mimicry: “a sheep in wolf’s clothing”shows 1/2 of coevolution equation; selection by predator on preywasp-unpalatable(model)Mantid + mothpalatable(mimic)Batesian mimicry: palatable species mimic unpalatable models. ***Which is more common: model or mimic? What must predator do to make system work?Figure 4Mullerian mimicrycross-mimicry benefits both speciesBoth have stingers that release toxins.Figure 5Mullerian mimicry: unpalatable species resemble each other. Each species is both model and mimic.Get benefit of warning from two species.Mullerian mimics: unpalatable organismsshare pattern of warning coloration.Gene - for - gene concept: ‘evolutionary arms race’• E.g. plant - pathogen interaction• Based on: single gene conferring resistance • vs. single gene for virulence• Back and forth:• change in gene, then selection: favor plant, then pathogen, then plant, then pathogen… • Race escalates with addition of each new trait.Describe the coevolutionary ‘arms race’ between rabbits and myxoma virus. Includethese concepts:Genes for resistanceGenes for virulencePre-adaptationTimeIntroduce virusCoevolutionExplain the patternin terms of:changes infrequency of virulence andresistance genesClosely relatedgroups of herbivoresfeed on closelyrelated host plants.Suggests a longevolutionary historyof interaction.What evidence isused to infercoevolutionaryrelationships?Coevolution between chemical defenses of plants and their herbivores; uses phylogenetic relationships to build an inferential argument.Insects most specializedExperimentalEvidence:Question: Do ants and treehoppers have a mutualistic relationship?QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.Treehoppers - herbivoresSpiders - predators of ‘hoppers***Develop an “if…then…that addressesthis question.Hypothesis: Prediction: Experimental Design?? What is independent? dependent variable?QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.What is major conclusion?? Mutualism or not?Figure 1Mutualism: two species specialized to perform a complementary (positive) function for each other.•1) Mutualism: trophic•Partners