Mating Systems in Higher Plants

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Mating Systems in Higher Plants
Gender/Mating systems
Yampolsky and Yampolsky 1922 survey of 121,492
species
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Monoecy
Gender/Mating systems

• Separate male and female flowers on the same
  plant
• Repro effort is partitioned in time and space,
  selected for maximum efficiency (e.g. seed
  production, seed dispersal, pollen donation)
• Examples alder, pine, cucumber

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Monoecy
Gender/Mating systems

• Arisaema triphyllum plants are sex changers
  male when small or after fruit formation, female
  when large

Bierzychudek 1984. Oecologia 6514-18
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Dioecy
Gender/Mating systems

• Separate male and female plants
• Prevents selfing often see spatial segregation
  due to differential mortality and nutrient
  requirements (selection for separation of sexes?)
• Examples indian plum, coconut, holly

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Dioecy
Gender/Mating systems

• Large females (dotted) die more often than males
  (dashed) juveniles (solid) also have high
  mortality in Chamaelirium luteum

Mortality
Leaf number
Meagher and Antonovics 1982. Ecology 631690-1700
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Dioecy
Gender/Mating systems

• Sex determination may be genetic (Silene
  latifolia has a sex chromosome) or environmental
  (some orchids if in sun, female)

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Semelparity vs. Iteroparity
Timing of reproduction

• Semelparity monocarpy reproduce once and die
  (big bang reproduction)
• Iteroparity polycarpy reproduce repeatedly
  prior to death

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Semelparity vs. Iteroparity
Timing of reproduction

• Life history determined by fecundity and residual
  reproductive value
• Fecundity how does offspring production respond
  to resource allocation?
• Residual reproductive value how much resource
  is left over to allow survival and another chance
  of reproduction?

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Semelparity
Timing of reproduction
Two optima all or none
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Iteroparity
Timing of reproduction
Intermediate optimum
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Semelparity vs. Iteroparity
Timing of reproduction

• What determines fecundity curve?
• Cost of reproduction (seeds, supporting
  structures for inflorescence, etc.) may lead to
  concave curve (semel)
• Density dependent factors among offspring may
  lead to convex curve (itero)

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Semelparity vs. Iteroparity
Timing of reproduction

• What determines RRV curve?
• May differ among habitats, e.g. steeper decline
  in marginal habitat (semel)

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Dispersal
Seed Dispersal

• Seed size/number trade-offs
• Why disperse?
• Escape hypothesis
• Colonization hypothesis

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Seed size/number trade-off
Seed Dispersal

• A general rule seed size and number trade off,
  as resource pool is always finite
• Predicted optimum for investment and offspring
  fitness

Constant returns
Offspring success
Investment per offspring
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Seed size/number trade-off
Seed Dispersal

• Seed size can affect survival, probability of
  germination, early growth

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Why disperse? Escape hypothesis
Seed Dispersal

• Mortality of seedlings highest near parent seed
  predators, disease, sibling competition

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Why disperse? Escape hypothesis
Seed Dispersal

• Datura seeds dispersed short distances (cm to m)
  by ants
• Seed predation by rodents on Datura greater under
  parent plant than 1-3 meters away on ant middens,
  or under different plant species

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Why disperse? Escape hypothesis
Seed Dispersal

• In contrast, one way to make sure your offspring
  escape is to swamp out seed predators

Plant fecundity
Fruit remaining
Weevil attack
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Why disperse? Escape hypothesis
Seed Dispersal

• Masting a special case

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Escape hypothesis
Seed Dispersal

• Masting a special case
• Panel a ponderosa pine and chalcid wasps
• Panel b ponderosa pine and abert squirrels

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Why disperse? Colonization hypothesis
Seed Dispersal

• Particular habitats are required for
  establishment
• Applies especially to disturbed habitats,
  unpredictable in time or space

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Why disperse? Colonization hypothesis
Seed Dispersal

• Dispersal among islets near Bamfield Cody and
  Overton 1996. J. Ecol. 8453-61
• Lactuca muralis (wall lettuce) weedy, wind
  dispersed (pappus and achene)

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Dispersal and morphology in Lactuca
Seed Dispersal

• Drop time longer when pappus volume/achene volume
  ( wing loading) was high (interpret?)

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Problem 7

• Describe the general changes over time to Lactuca
  propagules when plants colonize islets, as
  compared to propagules of mainland plants.
• What do you hypothesize was the selection
  pressure for rapid evolution of propagule
  morphology in island populations?

Population size
Achene volume
Pappus volume
Wing loading
Age after colonization of island
Mld mainland
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Dispersal syndromes
Seed Dispersal

• Self gravity or explosive
• Abiotic wind, water
• In both cases, seeds are nondescript (brown or
  green) wind dispersal selects for various
  modifications

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Dispersal syndromes
Seed Dispersal

• Insects
• Ant dispersed seeds have elaiosomes, oil-rich,
  fleshy appendages

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Dispersal syndromes
Seed Dispersal

• Vertebrate
• Nuts etc., buried and (sometimes) forgotten
• Attached, have hooks or spines

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Dispersal syndromes
Seed Dispersal

• Vertebratemost common ingested
• Brightly colored, fleshy fruits
• Content of fruit often varies over season
  species that produce fruits during peak bird
  migration have higher lipid content
• Advertisement may also vary over season

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Dispersal syndromes
Seed Dispersal

• Fruit color may vary seasonally within communities

Burns Dalen. Oikos 96 463-469
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Vertebrate dispersal
Seed Dispersal

• Why does salmonberry have two fruit colors?
• Birds prefer red morph in choice tests (Gervais
  et al. Oikos 8477-86)
• But

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Invertebrate dispersal
Seed Dispersal

• Banana slugs suppress germination of red morph
  (Gervais et al. Am Mid Nat 140103-110)

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Summary Life history

• Pollination, dispersal, timing and amount of
  repro all depend on interactions between biotic
  and abiotic factors
• We can predict life history adaptations by
  analyzing selection pressures