Lecture 17: Field Observations & Complex Pollination Strategies

Field Trip Prelude (Lake Travers, Eastern Algonquin – Dawn Excursion)

  • Departure: pre-daybreak, 2.5-hour drive, air temp -4 Celcius, ice skim on ponds

  • Conditions: mirror-calm water at launch, clouds later, generally calm all day

  • Waterfowl observations

    • Loons: two 1st-year birds (scalloped back, winter plumage)

    • Common mergansers: returning northern males (black & white, greenish head); females remain in summer to rear young

    • Hooded mergansers: late-staying females/juveniles

  • Beaver activity

    • New lodge + “iceberg” food pile (branches/alders stacked; bulk submerged)

    • Extensive fresh mud on active lodges (winter insulation sign)

    • Unusual duplex lodge built atop a beaver dam

    • Submerged-bank lodge inferred where only food pile visible; tunnel access suspected

  • Mammals & Sign

    • Close wolf pack howl; attempted howling response—no success

    • Fresh black bear scat (hair + plant matter); absent on outbound drive; ground too hard for tracks

  • Other fauna/flora highlights

    • Barred-owl call playback attracted male Black-backed Woodpecker (yellow fore-crown)

    • Berries: Winterberry heavily laden (“drupe” with single stone); expect cedar waxwing feeding in winter

    • Lichens: pixie-cup, reindeer lichen photographed for later ID; aesthetic reflections of sedges & cattails

Fundamental Pollination Framework

  • Plants enlist animals as “sex couriers” to transfer pollen → genetic exchange

  • Two main food bribes

    • Pollen (protein-rich) – relatively few consumers (e.g., bees)

    • Nectar (energy-rich sugar water) – ubiquitous lure

Food Bribe ① – Pollen

  • Some specialized flowers produce only pollen reward (e.g., One-flowered Wintergreen)

    • Anther/stamen tubes with apical poricidal pores

    • bees perform buzz pollination to shake out pollen

  • Electrical dimension

    • Pollen grains carry negative charge; insect bodies achieve positive charge via flight

    • Electrostatic attraction enhances adherence

Food Bribe ② – Nectar & Nectaries

  • Nectar (sugar water) composition varies (sugar types & concentration) → species-specific flavor profile

  • Nectar is stored in discrete nectaries – spatial diversity critical

    1. Buttercup – sleeve at petal base

    2. Columbine – petal long spurs; nectar at distal tip

    3. Dutchman’s Breeches – paired long spurs, long tongue; accessed by long-tongued bees & bee-flies

    4. Cardinal Flower – long red spurs; primarily hummingbird-pollinated (bees red-blind)

    5. Milkweed – shallow cup nectaries → accessible to diverse mouthparts (flies, skippers, ants, sphinx moths, hummingbirds)

Long-Tongue / Long-Bill Guild

  • Bumblebees (long-tongued group): extensive glossa reaches spur ends

  • Bee-flies: rigid proboscis nearly body-length

  • Hummingbirds: long bill + extendable bifurcated tongue

Electro-Pollination Insights (Emerging Field)

  • Flowers emit negative field; visitation lowers potential

  • Pollinators detect electrical field differential via specialized mechanosensory hairs → choose fresher, more charged blooms (higher reward probability)

  • Rapidly developing research area; search keywords “floral electric field” in journals

Advertising & Attraction – Long-Range Visual Signals

  • Each species fixed color + form signature

  • stands out because insects perceive leaf-green as grey

  • Different combinations of colour and form attract different pollinators

  • Shape and colour are long range visual advertisements (attractants)

  • Insect color perception quirks

    • Bees favor blues

    • flies often favor yellows

    • Many insects red-blind; “insect red” = red-edge of yellow spectrum

      • approx 610-630 nm

    • Cardinal Flower’s true red targets hummingbirds, not bees

  • Spectral wavelengths diagram helps map human vs insect perception

Close-Range Cues – Scent & Nectar Guides

  • Scents (non-pheromonal)

    • scents are close range attractants

    • Pleasant: Trailing Arbutus, Twinflower (only detectable at close range)

    • Nocturnal release: Evening Primrose opens at dusk; fragrance attracts Primrose Moth (adults hide in pink-aging petals by day)

    • Fetid: Red Trillium (aka “Stinking Benjamin”) emits carrion odor → brood-site deception for carrion flies

  • Brood-Site Deception: Flower mimics egg-laying substrate; insect gains no reward (e.g., red trillium)

  • Wild Ginger update: eastern populations self-pollinating;

    • old fungus-gnat deception hypothesis now questionable

Visual Nectar Guides Aids

  • Nectar Guides: visual close range guide to show where the pollinator needs to go

  • Converging lines, bull’s-eyes, color patches guide pollinator to sexual organs & reward

    • Examples: Pipsissewa (yellow spots), Grass-of-Parnassus (ornate petal windows), Wood Sorrel (purple lines), Painted Trillium (central blaze), Bindweed (maroon stripes), Butter-and-Eggs (landing patch), Wild Iris (signal patch), Pickerelweed (yellow eye-spot manipulates head position)

  • Ultraviolet (UV) patterns – invisible to humans

    • Pigment combo: UV-absorbing + UV-reflecting → bicolor bull’s-eye (e.g., Black-Eyed Susan, Marsh Marigold)

    • Documented via black-and-white UV photography (special Kodak filter anecdote)

Why Avoid Self-Pollination? Evolutionary Rationale

  • Cross-pollination ↑ genetic diversity → long-term adaptability & fitness

  • Self-sterility / self-incompatibility: chemical & possibly electrical recognition prevents self-pollen tube growth

Mechanisms Preventing Self-Pollination

Spatial Separation (Monoecious vs Dioecious)

  • Conifer example (monoecious)

    • Male cones lower; female cones upper → wind carries pollen upwards to other trees

  • Dioecious herbs (e.g., White Campion): entire plants are male OR female

Within-Flower Morphology

  • Bottle/Closed Gentian

    • Bumblebee forces entry; pathway requires descent over stigma (pollen offload) & ascent past anthers (pollen pickup) → self-pollen bypassed

Temporal Separation – Dichogamy (sex change over time)

  • Jewelweed: Day 1 male (pollen on anther cap); after pollen removed, anther cap falls → female phase exposed

  • White Water-Lily

    • Day 1: Female; stigmatic fluid draws flies/beetles

    • Night closure → Day 2: Male; stamens release pollen; no fluid

  • Lady’s-Tresses Orchids (spiral raceme)

    • Flowers open bottom-up; newly opened are male, older become female

    • Enhanced scent guides pollinators to older (female) blooms first → upward pollen flow avoids selfing

    • When first open = male

    • older flowers become female = dichogamy

    • female flowers offers stronger attractions

    • pollinators start at lower flowers and work up the spiral

      • Go from female to male

    • Direction of pollen flow prevents self-pollination

Heterostyly (Style-Length Polymorphism)

  • Principle: Pollen effective only when stamen & style lengths match

  • Purple Loosestrife (tristyly)

    • Three floral morphs: short-style, mid-style, long-style; each with two stamen tiers

    • Cross-compatibility matrix ensures inter-morph pollen flow; Darwin classic study

  • Pickerelweed: native tristyly analogue

  • Primula (e.g., Bird’s-Eye Primrose): distyly (pin vs thrum forms)

Advanced Deceit & Mechanical Traps

  • Pink Lady’s-Slipper (Cypripedium acaule)

    • has 3 forms of flowers

      • each form is on a separate plant: this is in relation of how long the style is in relation to the 2 sets of stamens

      • Short style form

      • Medium style form

      • Long style form

    • employ’s a placement strategy and also use deceit and a trap

    • Inflated pouch with narrow entrance;

      • insect enters → exit paths only via two backlit windows flanking central staminode

      • both are partially blocked by the staminode and the sticky pollen masses

    • Escape route forces back under sticky stigmatic surface (pollen offload) then past adhesive pollinia (pollen pickup)

  • Rose Pogonia (bog orchid)

    • Lip sports pseudopollen tufts; attracts bees/flies expecting pollen reward; sexual parts above lip effect pollination

  • Grass-of-Parnassus

    • Pseudonectaries (glistening stamen appendages) mimic nectar droplets; deceive flies

Key Vocabulary & Definitions

  • Nectary – discrete nectar container (sleeve, cup, spur)

  • Poricidal anther & Buzz pollination – pollen shaken out by wing vibration

  • Brood-site deception – flower simulates oviposition site

  • Self-incompatibility / self-sterility – genetic barrier to self pollen

  • Monoecious – male & female flowers on same plant; Dioecious – sexes on separate plants

  • Dichogamy – temporal sex change (protandry vs protogyny)

  • Heterostyly – differing style lengths within species (distyly, tristyly)

  • Staminode – sterile stamen, often modified (e.g., lady’s-slipper trap roof)

Connections & Implications

  • Pollination studies intersect physics (electrostatics), chemistry (floral volatiles), ecology (mutualisms/deception), and evolution (sexual selection parallels)

  • Ethical note: Many “weeds” (e.g., jewelweed, pickerelweed) are native keystone species supporting pollinator networks

  • Practical: Understanding heterostyly & self-incompatibility guides crop breeding; electric-field research could inform robotic pollinator design

  • Conservation: Mislabeling “purple loosestrife apocalypse” shows need for balanced, data-driven invasive-species management

Numerical & Statistical References

  • Temperature during outing: -4 Celcius

  • Drive duration: 2.5 h

  • Tri-style = 3 floral morphs

  • Di-style = 2 floral morphs

  • UV wavelength range referenced approx 300-400 nm

  • human visible yellow approx 560-590 nm

  • insect “red edge” approx 610-630 nmapprox 610–630\,\text{nm}$$

Study Tips & Suggested Activities

  • Field practice: examine buttercup nectary with hand lens; test jewelry-weed sex phases across days; locate heterostylous pickerelweed forms in wetland

  • Night observation: bring chair & flashlight to witness Evening Primrose bloom + scent release; search for Primrose Moth

  • Photography experiment: replicate UV bull’s-eye imagery using converted camera or UV filter + B&W sensor/film