01%20Plants%2009[1]

01%20Plants%2009[1] - I Parasitic Plants (No Chapter) 2009...

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69 I Parasitic Plants (No Chapter) 2009 [Guest lecture by Dr. Brian Axsmith] A. Introduction 1. The parasitic life-style has evolved less frequently among plants than animals a. Only 1 species of parasitic gymnosperm b. Less than 2% of the described species of dicotyledons are parasitic 2. Implications of autotrophy (plants) vs. heterotrophy (animals) a. Selective advantages from acquiring energy-containing compounds from another organism may not outweigh costs of circumventing host defenses for organisms that undergo photosynthesis b. Situations where parasitism could provide a selective advantage to an autotroph (1) Acquisition of inorganic nutrients from hosts (2) Shaded environments where competition for light is intense 3. Divergent evolution: Most parasitic plants [=PPs] are on outside of hosts rather than inside as is the situation with animal parasites 4. Convergent evolution: PP and animals show many similar traits a. PPs have lost structures found in taxonomic relatives: Indian pipes have no chlorophyll Picture Slide: Indian Pipes Lack Chlorophyll; Raven et al, 1986, Biology of Plants 4th ed. Fig. 18-40b b. High rates of reproduction: PPs such as witchweed produce smaller but orders of magnitude more seeds than their host plants Picture Slide: Relative Seed Size of Hosts and Parasite; Witchweed seeds (center) compared with corn (left) and sorghum (right); Parker & Riches, 1993,
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01%20Plants%2009[1] - I Parasitic Plants (No Chapter) 2009...

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