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Flower: a Specialized Shoot with 4 Whorls of Modified Leaves Sepals

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Flower: a Specialized Shoot with 4 Whorls of Modified Leaves Sepals Flower: a specialized shoot with 4 whorls of modified leaves sepals (calyx) sterile petals (corolla) stamen (filament + anther) pistil (stigma + style + ovary) F H Dimorphic gender expression M the presence of two sexual mating types in populations M ca. 10% of all angiosperm species H M H F Cosexual gender expression H F combine both gender functions within individuals Monomorphic the presence of a single sexual F mating type in a population M H H F F Male-sterility mutation F Female-sterility mutation M M Challenges & complications… Finding potential mates •! Lack sophisticated sensory abilities, behaviors Abiotic pollination •! Rooted to the ground •! Use wind/water to move pollen •! Dependent on vectors for pollen dispersal •! Not very efficient •! Modular construction & the “packaging” of gender •! Floral specialization •! Cosexual gender expression & the potential for self-fertilization Finding potential mates Biotic pollination •! Exploit sensory systems of animals Visual cues (color, nectar guides) Morphology (symmetry, tubes) Olfactory Mimicry (sexual, resource) Rewards (pollen, nectar) •! Floral specialization •! Pollination “syndromes” Arum volatiles Arum volatiles Identified active odor compounds Same active odor compounds in in Arum inflorescences… carrion volatiles Arum inflorescences and carrion Characterized the response of flies to odor of Arum flowers… Stensmyr et al. Nature (2002) Stensmyr et al. Nature (2002) Arum volatiles Finding potential mates Pollination syndromes Same active odor compounds in •! Facilitate finding mates” carrion volatiles Arum inflorescences and carrion OR Blowfly antennae responded identically to sulphide odors from Self pollination/fertilization carrion and Arum world famous selfer, Arabidopsis thaliana The evolution of selfing is perhaps the most common transition in angiosperm evolution Stensmyr et al. Nature (2002) Self-fertilization Self-fertilization seems like a good idea among flowers on the same plant reasonable under some circumstances •! Isolated individuals •! Plants at the edge of a species range •! In years with poor pollinator service •! Locally adapted populations Anthoxanthum odoratum (Poaceae) within a flower Ability to self-fertilize Self-fertilization seems like a good idea , but… Some groups tolerate self-fertilization… inbreeding depression often a problem and seemingly have adaptations to promote it! reasonable under some circumstances or evolved as a consequence of it (selfing) •! Isolated individuals •! Plants at the edge of a species range Outcrossed plants Selfed plants •! In years with poor pollinator service •! Locally adapted populations Flowers do not open; obligate selfers (e.g., violets) IBD in white clover (Trifolium repens) Eichhornia crassipes Some lineages of plants (Pontederiaceae) Some lineages of plants tolerate self-fertilization tolerate self-fertilization outcrossing selfing (A) Brazil - outbreeding population Amsinckia spp. (Boraginaceae) 5 generations of self-fertilization Significant IBD Flowers from selfing populations are smaller than those in outcrossing pop’lns (B) Jamaica - selfing (inbred) population) Plants from selfing populations make fewer 5 generations of flowers than those in outcrossing pop’lns self-fertilization No Outcross >200 vs. Selfed <100 significant IBD outcrosser selfer Prediction for inbreeding depression? .
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