Chapter 15 - Mutualism PDF

Chapter 15 Mutualism © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. ...

Chapter 15 Mutualism © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Outline Concept 15.1 Plants benefit from mutualistic partnerships with a wide variety of bacteria, fungi, and animals. Concept 15.2 Reef-building corals depend upon mutualistic relationships with algae and animals, with an exchange of benefits paralleling those between terrestrial mutualists. Concept 15.3 Theory predicts that mutualism will evolve where the benefits of mutualism exceed the costs. © 2019 McGraw-Hill Education.  Introduction Mutualism – interactions between individuals of different species that benefit both partners. Facultative mutualism occurs when a species can live without its mutualistic partner. Obligate mutualism occurs when a species is dependent on a mutualistic relationship. Margulis and Fester amassed evidence eukaryotes originated as mutualistic associations. © 2019 McGraw-Hill Education.  15.1 Plant Mutualisms Plants benefit from mutualistic partnerships with a wide variety of bacteria, fungi, and animals. Plants are the center of mutualistic relationships that affect structure and processes of terrestrial ecosystems. Nitrogen fixation. Nutrient absorption. Pollination. Seed dispersal. © 2019 McGraw-Hill Education.  Plant Performance and Mycorrhizal Fungi Mycorrhizal fungi provide plants with greater access to inorganic nutrients (K, Cu, Zn, N). Two most common types of mycorrhizae: Arbuscular mycorrhizal fungi. Fungus produces arbuscules (exchange sites), hyphae (fungal filaments), and vesicles (energy storage organs). Ectomycorrhizae. Fungus forms mantle around roots and netlike structure around root cells. © 2019 McGraw-Hill Education.  Arbuscular Mycorrhizae and Ectomycorrhizae Copyright © McGraw-Hill Education. Permission required for reproduction or display. © 2019 McGraw-Hill Education. a: © Dr. Nancy Collions Johnson; b: © Dr. Jeremy Burgess/Science Source  Mycorrhizae and the Water Balance of Plants Allen and Allen studied impact of mycorrhizae on water relations of grass Agropyron smithii. Plants with mycorrhizae maintained higher leaf water potentials. May be indirect effect – fungus may provide greater access to phosphorus, leading to greater root growth and more efficient extraction and conduction of water. © 2019 McGraw-Hill Education.  Plant Water Balance in Clover Hardie suggested mycorrhizal fungi provide more extensive contact with moisture in rooting zone. Provide extra area for water absorption. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Nutrient Availability and Mutualistic Balance Sheet Johnson investigated whether fertilization can select for less mutualistic mycorrhizal fungi. Fungal partner receives an equal or greater quantity of photosynthetic product in trade for lower quantity of nutrients. Plants release more carbohydrates in root exudates in nutrient-poor soils, less in richer soils. Mycorrhizae in rich soils should be more aggressive in carbohydrate acquisition. © 2019 McGraw-Hill Education.  Nutrient Availability Found that mycorrhizae differed between fertilized and unfertilized soils. Greenhouse experiments with Andropogon, mycorrhizae from fertilized and unfertilized soils, and varying nutrients. Higher shoot mass with mycorrhizae and nutrient supplements. Higher root: shoot ratios in low-nitrogen conditions. Inflorescences only with added nitrogen. © 2019 McGraw-Hill Education.  Effect of Nutrient Additions and Mycorrhizae Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Fig. 15.8 © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Ants and Swollen Thorn Acacias Ants (Pseudomyrmex) are mutualistic with swollen thorn acacia. Herbivores attempting to forage on acacia encounter many fast, agile, highly-aggressive defenders. Thorns provide living space to ants. Foliar nectaries provide sugar for ants. Beltian bodies provide oils and protein. Ants protect acacia from herbivores and competition from other plants. © 2019 McGraw-Hill Education.  Experimental Evidence For Mutualism Janzen demonstrated ants significantly improve acacia performance. Acacias without ants had more herbivorous insects. Suckers growing from acacia stumps occupied by ants lengthened at seven times rate of suckers without ants. Suckers with ants survived at twice the rate of suckers without ants. © 2019 McGraw-Hill Education.  Growth by Bullhorn Acacia Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Potential Conflict Between Mutualists Acacia depend on other mutualisms as well. Nitrogen-fixing bacteria, mycorrhizae, pollinators. Potential for conflict between mutualists. Ants and pollinators rarely overlap spatially. Inflorescences also produce ant repellent. A. hindsii inflorescences do not produce nectar. © 2019 McGraw-Hill Education.  A Temperate Plant Protection Mutualism Ants are attracted to aspen sunflowers because they produce nectar at extrafloral nectaries. Rich in sucrose and amino acids. Inouye and Taylor observed 5 ant species collecting nectar from extrafloral nectaries, but never from blossoms nor tending aphids on plant. Extrafloral nectaries sufficient attractant. © 2019 McGraw-Hill Education.  Benefit to Aspen Sunflower Proposed ants may protect sunflower’s developing seeds from seed predators. Predators damaged over 90% of seeds produced by some flowers. Found flowers without ants suffered 2 to 4 times more seed predation. Excluding ants caused more seed predation. Ant-sunflower relationship is facultative. Flowers are susceptible to frost; therefore not a reliable nectar source for ants. © 2019 McGraw-Hill Education.  Seed Predation and Ants Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  15.2 Coral Mutualisms Reef-building corals depend on mutualistic relationship with algae and animals. Ecological integrity of coral reefs depends on mutualism. Coral reefs have exceptional productivity and diversity. Approximately 0.5 million species. Yet reefs are surrounded by nutrient-poor oceans. Explained by mutualism with zooxanthellae. © 2019 McGraw-Hill Education.  Zooxanthallae and Corals Zooxanthallae live within coral tissues. Receive nutrients from coral. In return, coral receives organic compounds synthesized by zooxanthallae during photosynthesis. Corals induce release of organic compounds with “signal compounds” that alter permeability of zooxanthallae cell membrane. © 2019 McGraw-Hill Education.  Coral Influence on Zooxanthellae Corals also control rate of zooxanthallae population growth and density by influencing organic matter secretion. Cause zooxanthellae to secrete 90 to 99% of their fixed carbon for coral to use. Main zooxanthallae benefit appears to be access to higher nutrient levels, especially N and P. Also uptake ammonium excreted by coral. © 2019 McGraw-Hill Education.  A Coral Protection Mutualism Glynn found 13 coral species protected by crustacean mutualists. Crustacean mutualists substantially improved chances coral will avoid attack by sea stars. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Other Benefits of Crustaceans Also found crab activity promotes coral health and integrity. Without crabs, corals showed tissue death. Pocillopora coral increases production of fat bodies in the presence of crabs. Digestive tract of crabs inhabiting corals contained large quantities of lipids. © 2019 McGraw-Hill Education.  15.3 Evolution of Mutualism Theory predicts mutualism will evolve where the benefits of mutualism exceed the costs. Keeler developed models representing relative costs and benefits of several types of mutualistic interactions. Successful mutualists. Give and receive benefits. Unsuccessful mutualists. Give, but do not receive benefit. Nonmutualists. Neither give nor receive benefit. © 2019 McGraw-Hill Education.  Fig. 15.21 © 2019 McGraw-Hill Education.  When Does Mutualism Occur? For a population to be mutualistic, fitness of successful mutualists must be greater than unsuccessful or nonmutualists. Combined fitness of successful and unsuccessful mutualists must exceed that of nonmutualists. If not, natural selection will eventually eliminate the interaction. © 2019 McGraw-Hill Education.  Facultative Ant-Plant Mutualisms Keeler proposed for a facultative ant-plant mutualism to evolve and persist: Proportion of plant’s energy budget that ants save from destruction by herbivores must exceed proportion of the plant’s energy budget invested in extrafloral nectaries and nectar. Plants surviving on tight energy budget unlikely to invest in attracting ants. © 2019 McGraw-Hill Education.  Conditions Producing Benefits Conditions that may produce higher benefits than costs: High probability of attracting ants. High potential for herbivory. Low effectiveness of alternative defenses. Highly effective ant defense. © 2019 McGraw-Hill Education.  Review Introduction. Plant Mutualisms. Coral Mutualisms. Evolution of Mutualisms. © 2019 McGraw-Hill Education.