Bio153_lecture9_Pollination_sv-1 - Introduction COEVOLUTION...

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COEVOLUTION: PLANTS AND POLLINATORS Introduction • > 90% of existing plant species are flowering plants • co-evolution between pollinators and early angiosperms Why so successful? – mutation – natural selection 130mya 142mya Fossilized flowers Cross Pollination Pollination – pollen transfer Bisexual flowers – contain both pollen-producing stamens and ovule-containing carpels Some plants can self-pollinate Question: Why do so many plants cross-pollinate? Cross Pollination Outbreeding – fertilization of egg and sperm from genetically different organisms of the same species Advantages: recessive genes genetic diversity evolutionary flexibility Reducing inbreeding: -in some angiosperms, genes expressed in the cells at the stigma surface only allow genetically distinct pollen of the same species to germinate - enzymes inhibit the growth of pollen tube - anthers mature before carpels Anemophily • Wind pollination – gymnosperms – approx 10% of angiosperms NA hickory tree Maple keys Advantages Works well in: - open areas - low diversity stands - monocultures - areas of low-moderate rainfall Mountain cedar
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Disadvantages - requires windy conditions - requires open spaces - distances are a factor - dry environments better than wet environments - energy costs to producing pollen Alnus viridus ragweed Aquatic Plants - approx 30 genera use water to transfer pollen - flowers float at the water’s surface where pollen transfer occurs e.g., Vallisneria -A few species are pollinated under water e.g., Ceratophyllum –stamens float to surface where pollen is released - pollen sinks and contacts stigma - many aquatic plants produce flowers above the water - may be wind pollinated or animal pollinated Animal Pollination Zoophily - most flowering plants pollinated by animals - mutualism - adaptive radiation of angiosperms - likely evolved from wind pollination and - from exploitative animal-plant interactions
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Bio153_lecture9_Pollination_sv-1 - Introduction COEVOLUTION...

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