Plant Reproduction Plant Ecology What is reproduction? • reproduction : the formation of new individuals • In plants not always clear • sexual reproduction new genets • asexual reproduction new ramets • sometimes considered reproduction • sometimes considered growth Vegetative reproduction • vegetative reproduction : formation of new ramets by vegetative growth • occurs in most herbaceous perennials, many shrubs, a few trees Stolons • stolons : branches at or just above the surface of the soil; generate ramets at nodes touching the ground Rhizomes • rhizome : underground horizontal stems growing near the soil surface • examples: • ginger (ขิง) • turmeric (ขมิ ้ น) • galangal (ข่า) • fingerroot (กระชาย) Bulbs • bulb : an underground rosette stem that stores nutrients • can divide to create daughter bulbs • examples • onions • garlic • lilies • tulips
Transcript
Plant ReproductionPlant Ecology
What is reproduction?
• reproduction: the formation of new individuals
• In plants not always clear
• sexual reproduction new genets
• asexual reproduction new ramets• sometimes considered reproduction• sometimes considered growth
Vegetative reproduction
• vegetative reproduction: formation of new rametsby vegetative growth
• occurs in most herbaceous perennials, many shrubs, a few trees
Stolons
• stolons: branches at or just above the surface of the soil; generate ramets at nodes touching the ground
Rhizomes
• rhizome: underground horizontal stems growing near the soil surface
• examples:
• ginger (ขงิ)
• turmeric (ขมิน้)
• galangal (ขา่)
• fingerroot (กระชาย)
Bulbs
• bulb: an underground rosette stem that stores nutrients
• can divide to create daughter bulbs
• examples• onions• garlic• lilies• tulips
Suckers
• sucker: a basal shoot that grows from the base of a plant
• may arise from the roots of trees that have been cut down
Agamospermy
• agamospermy – production of embryos without fertilization
Reproduction in Seed Plants
• gymnosperms• wind-pollinated• produce large numbers of pollen grains
• angiosperms• animal-pollinated (ancestral)• some are wind-pollinated (derived)
• hydrophily• Aquatic plants• Flowers at or under water surface• https://www.youtube.com/watch?v=7-7QqpmaOSY
Animal pollination
• advantages: much more directed and precise• produce fewer pollen grains• more efficient, less waste of pollen
• disadvantages: requires pollinators; low or no reproduction when pollinators are scarce or absent
Attracting animal visitors• attractant
• attract animal via vision, odor, etc• bright perianth (corolla and/or calyx)• volatile compounds emitted by flowers
• reward• nectar (rich in sugars)• pollen (rich in protein)• waxes, resins, chemical compounds, location for eggs
• plants can also exclude unwanted visitors• long corolla tubes or nectar spurs• timing of flowering (diurnal or nocturnal)• color (ex: red flowers deter bee visits)
• some animals take nectar or pollen without pollinating the flower
• “nectar robbers”
Pollination syndromes
• pollination syndrome: a suite of floral traits associated with the attraction of a specific group of pollinators
Insect pollination
• entomophily• extremely common
Bee pollination
• melittophily or hymenopterophily• flowers are showy, colorful, fragrant• nectar guides (attract & orient insects)• landing platforms
Butterfly pollination
• psychophily• showy, colorful, fragrant flowers• no nectar guides• long, nectar-filled tubes or spurs
spur
Moth pollination
• phalaenophily• large, white, fragrant flowers• no nectar guides• long, nectar-filled tubes or spurs
Fly pollination
• sapromyiophily• maroon or brown in color• unpleasant smell (e.g., rotting material)
Beetle pollination
• cantharophily• uncommon• open flowers• fruity or foul odor
Bat pollination
• chiropterophily• nocturnal anthesis (open at night)• large, white or colorful• abundant nectar and/or pollen
Bird pollination
• ornithophily• red or other bright colors• relatively large• flowers often tubular• abundant nectar
Breeding Systems
• outbreeding (outcrossing, allogamy, xenogamy): transfer of pollen between genetically different individuals
• advantage: increases genotypic and phenotypic variation within a population• Can adapt to changes in environment
• disadvantage: risk of reproductive failure• If plants are far apart, or pollinators are rare
Mechanisms that promote outcrossing
• dioecious: male (staminate) and female (pistillate) flowers occur on separate plants
Other terms to know:
monoecious: male and female flowers occur on the same plant
hermaphroditic: flowers are perfect (have both male and female organs)
Mechanisms that promote outcrossing
• dichogamy: temporal separation of male and female floral organs
• protandry: male component matures before the female component• pollen is released before gynoecium is receptive
• protogyny: female component matures before the male component• gynoecium is receptive before pollen is released
Mechanisms that promote outcrossing
• protandry: male component matures before the female component• pollen is released before gynoecium is receptive
Mechanisms that promote outcrossing
• protogyny: female component matures before the male component• gynoecium is
receptive before pollen is released
Mechanisms that promote outcrossing
• herkogamy: spatial separation of male and female floral organs
• distyly: two floral morphs• pin flowers – long style,
short stamens• thrum flowers – short
style, long stamens
Mechanisms that promote outcrossing
• herkogamy
• tristyly: three floral morphs
Mechanisms that promote outcrossing
• herkogamy
• enantiostyly: style curves to left or right
Mechanisms that promote outcrossing
• herkogamy
• movement herkogamy: floral parts move
• Ex: stigmas close after being touched• https://www.youtube.com/watch?v=o1PaPppjHAQ
• Ex: a pollinator triggers the sudden movement of stamens• https://www.youtube.com/watch?v=pg1k_mXes_E
Mechanisms that promote outcrossing
• self-incompatibility: inability for fertilization to occur between gametes of the same genotype• prevents fertilization within a flower • prevents fertilization between flowers of the same plant
Breeding Systems
• inbreeding (selfing): self-fertilization; union of gametes from same individual
• advantage: ensures reproduction when other plant individuals or pollinators are absent
• disadvantage: limits genetic variation
• disadvantage: can lead to inbreeding depression(accumulation of deleterious alleles)
Types of inbreeding
1. autogamy: inbreeding within a single flower2. geitonogamy: inbreeding between flowers on the
same individual
12
Inbreeding depression
• inbreeding depression: when inbreeding (mating among close relatives) decreases fitness
Dominant allele Recessive deleterious allele
Inbreeding Outbreeding
• outbreeding depression: when outbreeding (mating among distant relatives) decreases fitness
Outbreeding depressionBalancing inbreeding and outbreeding depression
inbreeding depression
outbreeding depression
genetic distance between parents
fitn
ess
of
off
spri
ng
Assortative mating
• assortative mating: when plants with similar phenotypes are more likely to mate (more likely than chance alone)• a pollinator prefers a specific flower color• early-blooming plants mate, late-blooming plants mate
• disassortative mating: when plants with different phenotypes are more likely to mate (more likely than compared to chance)• self-incompatibility• heterostyly
Seed Dispersal
• seed dispersal: movement of fruits/seeds away from the parent plant
• typically a mutualistic interaction• animal disperses seeds for plant• plant provides reward (fruit pulp) for animal
• fruit: a mature ovary
• frugivore: an animal that eats fruit (pulp)
Patterns of animal dispersed seeds & frugivores• positive correlation between diversity and
abundance of frugivores with diversity and abundance of fleshy fruits
• tropics: high abundance and diversity of animal-dispersed fruits and frugivores, where fruits can grow year-round
• temperate: fruits absent for much of the year, so fruit specialists are unusual and typically nomadic
Importance of seed dispersal
• seed dispersal is important because most plants are immobile
• seed dispersal leads to:• succession• forest regeneration• increased plant community diversity• increased gene flow and genetic diversity
• in the tropics, 50-90% of vascular plants have animal-dispersed seeds (depends on habitat)• some canopy species are wind-dispersed, most species below
the canopy are animal-dispersed
Benefits of seed dispersal
• may increase offspring survival• reduces competition with
parent plant• reduces competition with
siblings• escape from seed/seedling
predators or pathogens
Benefits of seed dispersal
• allows a plant species to colonize favorable or new areas
• lights gaps in a forest
• different sites
Benefits of seed dispersal, specific to animal-dispersed seeds• directed dispersal to favorable habitats
• Ex: rodents bury seeds at depth of 5-25 mm • survival is 5 times higher
than seeds on forest floor
• Ex: ant-dispersed seeds often have greater germination on ant mounds than off the mounds
Leal et al. 2007, Ann. Bot.
Benefits of seed dispersal, specific to animal-dispersal
• some seeds germinate better after passing through an animal gut• increased permeability• increased germination
rates
Traveset et al. 2008Ecology, 89(1)
Non-animal dispersal
• wind dispersal = anemochory
• seeds flutter to the ground
• seeds float on the breeze
Dipterocarpus alatusDipterocarpaceaeMalvales
Taraxacum sp.AsteraceaeAsterales
Non-animal dispersal
• water dispersal = hydrochory
Non-animal dispersal
• some conifer species are serotinous (require fire to melt the resin on cones, and release seeds)
Non-animal dispersal
• ballistic seed dispersal:
• https://www.youtube.com/watch?v=8iyKAq_s7-M
Animal dispersal
• animal dispersal = zoochory• ectozoochory – propagules are carried on the outside of
an animal• endozoochory – seeds are eaten but passed through the
gut unharmed
• granivores (animals that eat seeds or grains) are sometimes important dispersers• accidentally drop seeds• bury seeds but fail to return
Ectozoochory
• relatively uncommon means of dispersal• can disperse seeds long distances
• very common form of dispersal, particularly in tropical habitats
• generally a mutualistic relationship• plants reward animals with fruit (surrounding or
attached to the seed)• animals disperse seeds for plants
• birds and mammals are the most common dispersers• turtles, fish, etc. can also transport seeds
Adaptations to attract dispersers
• bright colors• attractive smells• tasty fruit pulp, elaiosome, etc.
Adaptations to delay frugivory
• plants benefit when frugivory occurs after seeds are mature
• cryptic coloration (green fruits blend in with leaves)
• unpalatable textures (thick skins)
• resins and saps
• hard outer coats, spines, thorns
• secondary metabolites
Seed shadows
• often leptokurtic
• bat and bird dispersed seeds often have a longer tail than gravity or wind dispersed seeds
Rey & Alcantara 2014Perspectives in Plant Ecology, Evolution and Systematics
Seed dispersal by birds
• common dispersal method
• birds are limited by aerodynamic constraints• consume small fruits• eat the pulp and drop the seeds• quick passage through the gut• regurgitate seeds
• many species are opportunistic dispersers• fruits are low in protein• consume other resources like insects
Seed dispersal by non-flying mammals
• primates, elephants, ungulates, etc.
• can eat larger fruits
• ingested fruits can remain in gut for hours, days, or weeks
• seeds often deposited in large masses (clumped dispersal)
Seed dispersal by bats
• bats typically carry fruit from the parent plant to a “feeding roost”• avoid predators• can carry larger fruits than birds (30% of body mass)
• large seeds: pulp is chewed off, seed is dropped
• small seeds: seeds are swallowed and defecated
Large seed dispersers• hornbills, chimpanzees, tapirs, etc.
• able to disperse large seeds
• but poaching and habitat loss has led to population declines
• negative impact on seed dispersal
Seed dispersal by ants
• myrmecochory
• seeds have an elaiosome• “food body”• rich in lipids, amino acids
• ants carry seeds to colony, feed elaisome to larvae, discard seeds in underground chamber• favorable conditions• protection from seed predators
Seed dispersal by ants
• has evolved independently at least 100 times• occurs in > 3,000 plant species• most common in dry habitats• dispersal up to 180 m, but typically 0.5-1.5 m
Seed dispersal by “seed predators”
• seed predator: an animal that eats seeds (killing the embryo)
• but some species hoard seeds • if they don’t come back to eat the seeds, the seeds can
germinate
An example of seed dispersal in Thailand
• Khao Phra Bang Khram Wildlife Sanctuary, Krabi
• Established as a wildlife sanctuary in 1987• 19 rubber & oil palm plantations were
cleared patches of grassland
An example of seed dispersal in Thailand
• Chiang Mai University (Forest Restoration Unit) planted ~1,000 trees (2006-2008)
• >80% of the seedlings died during long drought
• natural seed dispersal by bats and birds?
• What are your hypotheses?
Dispersal by bats vs. birds
1 m
1 m
Results: seed rain in microhabitats Results: seed dispersers
