Download Pollination biology

Pollination
Angiosperms – Flowering plants
Flowering plants (250k sp) comprise the dominant plant life form
on earth
Evolved ~ 130 – 140 mya a modest beginning but…
20 – 30 million years later increased in diversity
Insects Become Modern – the Cretaceous and Tertiary
times
The Cretaceous (145 – 65 MYA) is one of the most significant
geological periods for insect evolution
1. Devonian – Hexapods
2. Carboniferous – Winged insects
3. Permian to Triassic – earliest members of most modern orders
4. Cretaceous – Nascent modern biota (amidst unprecedented geological
and evolutionarily change)
Insects Become Modern – the Cretaceous
During Cretaceous period many modern families 1st appeared (some as
early as Jurassic or Triassic), others like schizophoran flies & ditrysian
leps evolved in the Tertiary – 65 million to 1.8 mya
Estimated that perhaps half or more of recent families appeared in
Cretaceous
Appears to be related (both cause and effect) to the radiation of the
angiosperms
The Cretaceous
Earth was geologically more active than at most times
Dramatic climate change and
Tectonic activity which resulted in widespread volcanism, splitting and
drifting of the continents
Fragmentation of Gondwana into the present southern continents is
often invoked for contemporary distributions of various plant and
animals
The Cretaceous
Appear to be little affected by KT boundary events (at gross scale)
Geologic record from this time forward better preserved than earlier
periods
Evolved from Pollinivory in early seed plants
• 250 + MYA
(late Paleozoic, Mesozoic)
• e.g. Cycadales, seed ferns
• Probably Beetles
•
Pollination perhaps inadvertent initially,
but floral traits that increased chances of
pollination and encouraged visits by most
efficient pollinators were favored by selection
•Beetles also can destroy ovules-this may
have promoted carpel closure and
possibly evolution of inferior ovary
Basal Angiosperms – e.g. Apetalous magnolias insect pollinated,
probably Diptera, Coleoptera (early Cretaceous ~ 150 MYA)
(Anemophily – wind pollination – derived later)
Taxonomic Distribution
2/3 + of Angiosperms are animal pollinated + a small
proportion of Gymnosperms (e.g. Ephedra, cycads)
Pollinators include:
•Flies (Diptera), Ants, bees, and wasps
(Hymenoptera), Beetles (Coleoptera), Butterflies and
moths (Lepidoptera)
•Hummingbirds, sunbirds, honey eaters
•Bats, rodents, small marsupials
• Oddities: Frogs, slugs, earthworms
Insect Pollination
Entomophily
Cantharophily
Myophily
Sphecophily
Myrmecophily
Melitophily
Phalaenophily
Psycophily
Traditional Pollinator “syndromes”
suggest some degree of coevolution
Faegri and van der Pijl (1979)
Alison Brody: effects of pollinators, herbivores, and seed predators
on flowering phenology.
Competition for pollinator
services has often been
suggested as the primary
selective force molding
flowering schedules.
Flowering and reproductive characters
are likely to reflect an evolutionary
compromise of responses to various
selective forces.
Apparent competition or associational
resistance may be important to the
composition and flowering patterns of
plant communities.
Two Big Ideas
- Evolution has tended towards specialization
of pollinator–plant interactions, which has led
to “tight” coevolution (not just diffuse) between
these groups
and..
- Coevolutionary interactions between insect
pollinators and angiosperms are responsible
(at least in part) for the incredible
diversification of these two groups
Early Angiosperms
Generalized flowers
Many pollinators
Open
Sturdy (beetles)
Recent Angiosperms
Specialized flowers
Rosidae
few pollinators
Zygomorphic-complex
Nectaries
Bees (50 MYA)
Should specialized plant-pollinator associations evolve?
Benefits
Costs
Plant
-Avoid pollen loading
-Minimize pollen & nectar
theft
-Efficient movement of
gametes
-Rewards large?
-Risk of pollinator
extinction & Dependence
on pollinator populations
Animal
-Neurological efficiency?
-Shorter “Handling time”
-Rewards large?
-Reduced Competition
-Reduced foraging
efficiency
-Longer travel times
-Phenological dependence
-Dependence on plant
populations
Are plant-pollinator associations tightly
co-evolved?
Are plant-pollinator associations largely
specialized?
Some are:
Expect specialized plants if long-lived,
many reproductive episodes
(continuous), pollinators whose
populations fluctuate slightly
Fig wasps
Figs
Tegeticula yuccasella
•Local host Specificity
•Oviposition into flower
•Limited seed destruction
•Pollination causing
behavior
40 MYA!
But many apparently coevolved pollinator mutualisms
are asymmetric - antagonistic exploitation
E.g. the Orchidaceae
At least 8-10,000 species offer
no reward, only deception and
fraud
- capture pollinators
- intoxicate them
- Prostitution
- mimicry (rivals, enemies,
prey)
Basically parasitism of insect by
plants
Robbers
Thieves
Unfaithful Cheaters
Most plants are visited by a variety of potential
pollinators
Robertson 1928 - Illinois
Clements & Long 1923 – Pikes Peak, CO
Pollinating animals tend to visit many plant
species
Clements & Long 1923 – Pikes Peak CO
Ranunculaceae
Even “advanced,”
presumably
Orchidaceae
specialized, plant
families tend to be
moderate generalists
Polemonianceae
Bees, most of which
rely obligately and
solely on floral
resources, also tend
to be moderate
generalists
Andrenidae
Halictidae
Apidae
Geographic ranges of plants and pollinators rarely
correspond closely
Plants often successful in new geographic areas,
despite leaving their mutualists behind
- Hawaiian ieie (Freycinetia arborea) formerly
pollinated by extinct honeycreepers
- In New Zealand Freycinetia baueriana lost
bat pollinator
Why are pollination syndromes so weak?
or
What prevents coevolution?
Thompson 1999: Geographic mosaic theory of coevolution –
dynamics of coevolution occur at a geographic scale above the
level of local populations and below the level of the fixed traits
of interacting species.
Did insect pollination cause increased seedplant diversity?
Root Gorelick, Biological Journal of the Linnean Society (2001) 74:407-427.
• Poaceae (grasses) diverse
(10,000 sp.), almost all wind
pollinated
• Ants diverse, generally not
pollinators
• Cycads, Gnetales other groups of
insect pollinated plants were either
never diverse, or diversified and
became extinct
• Insect “diversity” decreased when
angiosperms originated
However, these are rather poor arguments
- Orchidaceae -25,000 species, almost exclusively
insect pollinated, many specialized (Fabaceae,
Asteraceae,Rubiaceae, Euphorbiaceae)
- Bees: 20,000 species, few of which could exist
without angiosperm flowers.
- Rhopalocera = butterflies + skippers, almost all
visit flowers: 20,000 species
- Large families of Diptera (e.g. Syrphidae,
Bombyliidae) rely heavily on floral resources
Most of the species
diversity of angiosperms
originated < 50 MYA
e.g.
• major eudicot families
• Orchidaceae
…and insect groups did diversify coincident
with the angiosperms in the cenozoic
Families…
Angiosperms – Flowering plants
Insects were original partners of angiosperms as pollinators and
herbivores
Undoubtedly pollinating insects facilitate and can control gene flow
in most angiosperms and must effect speciation
Questions ?