Pollination Biology – pop up text

A Brief History of Selected RMBL Ipomopsis Research and Researchers

Waser 1976

<a href=”http://rmbl.info/rockymountainbiolab/Waser76Condor.pdf”>

While working as a field assistant with a scientist studying hummingbird nesting, Nick set up small study plots and characterized the timing of bloom (phenology) of several species of wildflower that the birds rely on for nectar. Take-home points: Hummingbirds start nesting when the first profitable flower, Delphinium nelsonii

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del.jpg” width=”125″ height=”150″>

comes into bloom, and they shift to other species (such as Ipomopsis aggregata)

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

as these start to flower. Nesting success depends on a reliable succession of profitable flowers during the summer.

Contributions to later research:

a) The fact that D. nelsonii

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del.jpg” width=”125″ height=”150″>

and I. aggregata

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

share pollinators and flower sequentially led Nick to ask whether these plants compete for  hummingbird pollination during the time of flowering overlap.

b) Realizing that the seasonal timing of flowering is critical for pollination and pollinators has kept phenology on the minds of RMBL researchers.

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Waser 1978


During his doctoral work, Nick studied competition between <a href=”#” class=”popup”><i>D. nelsonii

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del.jpg” width=”125″ height=”150″>

and <a href=”#” class=”popup”>

I. aggregata

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>for pollination by their shared hummingbird pollinators, using both experimental and observational methods.

Take-home points: Flowering overlap between these two species varies from year to year. During natural or experimentally-induced flowering overlap, flowers of both species produce fewer seeds. Several mechanisms contribute to reduced seed production. Both species are pollinated by multiple types of pollinator.

Contributions to later research:

a) Nick perfected a number of techniques that proved useful in later studies, including use of potted-plant arrays, simulating hummingbird pollination, measuring the nectar content of flowers and how much pollen they have received.

b) This study stimulated thinking on the precise mechanisms of competition for pollination services

c) The chance observation that most Delphinium

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del.jpg” width=”125″ height=”150″></span>

flowers are deep blue, but occasional plants make white flowers, led Nick and Mary to ask why the albinos

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del_albino.jpg” width=”125″ height=”150″>

are rare.

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Sharaf and Price 2004

<a href=”http://rmbl.info/rockymountainbiolab/Sharaf%26Price04.pdf”>

Kate Sharaf was another undergraduate intern.

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″></span></a>

Ipomopsis workers had been annoyed to find that the flowering stalks of their experimental plants tended to disappear into the mouths of deer. By this time they knew a lot about the life history of Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″></span></a>

(the description of how individuals grow, eventually flower only a single time, and then die) and they concluded naturally enough that herbivory by deer would reduce Darwinian fitness. For her senior  thesis, Kate asked whether the detrimental effects of browsing occurred because browsed plants flower later in the summer than undamaged plants and thereby miss the seasonal peak in activity of hummingbird pollinators.

Take home points: Although experimentally clipped plants did flower later than control plants in two years, between-year variation in the timing of hummingbird migration caused damaged plants to match the hummingbirds in one year, but to miss them in the other.

Despite this variation in match, clipping lowered seed production equally in both years. The conclusion is that resources, not pollinators, limit the ability of clipped plants to compensate for damage.

Contributions to later research:

This result suggested an obvious follow-up study to test the conclusion, ask whether adding nutrients and water allows clipped plants to compensate better for clipping.

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Mayfield et al 2001

<a href=”http://rmbl.info/rockymountainbiolab/MayfieldEtAl2001AnnBot.pdf”>

This paper again involves an undergraduate intern. Margie Mayfield did a straightforward (this does not mean easy!) field experiment comparing the seed set of virgin Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

flowers after visits by different pollinators, harking back to the initial list from Waser, 1978.

Take home points: Hummingbirds, the most frequent visitors to Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″></span>

flowers, are not the most effective pollinators on a per-visit basis, bumble bees deposit 3 times more pollen per visit than do hummingbirds, and as a consequence flowers produce 4 times more seeds after a bumblebee visit. This result is surprising, because many traits of Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

flowers (red color, tubular shape) are interpreted as adaptations for pollination by hummingbirds.

Contributions to later research:

a) The surprising result of this study stimulated thinking on the nature of floral adaptation to different types of pollinators.

b) This study stimulated further work on color vision of bees, which often are described as being red-blind.

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Irwin and Brody 1999

<a href=”http://rmbl.info/rockymountainbiolab/Irwin%26Brody99.pdf”>

In the 1980s, Alison Brody began PhD work (partly under Nick’s guidance) on insects that attack Ipomopsis flowers.

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

She argued that such enemies must be included in attempts to understand ecology and evolution of flowering. Rebecca Irwin worked with Alison first as an undergraduate intern and then as a PhD student, and the resulting paper is part of Becky’s dissertation work.

Take-home points:

a) Nectar robbers reduce the amount of pollen flowers export to other flowers, as well as the receipt of pollen and number of seeds produced.

b) This detrimental effect occurs because legitimate pollinators avoid nectar-robbed flowers.

Contributions to later research:

a) This paper pioneered experimental approaches for studying nectar-robbing.

b) The focus on plant enemies enriched our understanding of ecological interactions between plants and flower visiting animals and set the stage for further work on the variable effects of flower visitors on plant fitness.

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Campbell et al. 1991

<a href=”http://rmbl.info/rockymountainbiolab/DRCetal91Evol.pdf”>

During the 1980s, while this Delphinium

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del.jpg” width=”125″ height=”150″>

work and work on Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

was going forward, Dr. Diane Campbell began to work at RMBL, initially as Nick’s postdoctoral associate. With a solid background in mathematical genetics, she undertook a series of studies of natural selection on traits of Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

flowers that vary among plants within populations. <

Take-home points:

This 1991 paper used field and flight-cage experiments to understand why Ipomopsis

<img src =”http://rmbl.info/rockymountainbiolab/ipo/ipo.jpg” width=”125″ height=”150″>

plants that have wide flowers are more successful in exporting pollen to other plants than are plants with narrow flowers. The primary conclusion is that wide flowers are better males because they produce more nectar and receive more hummingbird visits than narrow flowers, and because they export more pollen during each hummingbird visit.

Contributions to later research:

a) Results of this study stimulated follow-up research to understand why wide flowers export more pollen per visit.

b) The study pioneered methods for studying pollen export and deposition by hummingbirds in a flight cage.

c) The mix of evolutionary/genetical perspectives and ecological perspectives led to novel insights into mechanisms of natural selection on flower traits.

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Waser and Price 1985

<a href=”http://rmbl.info/rockymountainbiolab/W%26P85OecNectarGuides.pdf”>

To understand why white-flowered Delphinium

<img src =”http://rmbl.info/rockymountainbiolab/ipo/del_albino.jpg” width=”125″ height=”150″>

plants are rare in natural populations, Nick and Mary conducted a series of observational and experimental studies to show how natural selection weeds out white-flowered mutants from natural populations.

Take-home points: Both bumblebees and hummingbirds visited white-flowered plants 20% less frequently than blue-flowered plants. This undervisitation caused less pollen to be deposited on white flowers, which in turn resulted in lower seed production. The pollinators avoided white flowers because these flowers lack a contrasting color target (a nectar guide) that saves precious time. Both bumblebees and hummingbirds took longer to extract the same amount of nectar from white than blue flowers.

Contributions to later research:

a) This study pioneered methods for observing pollinator behavior under controlled conditions in a flight cage, and manipulating flowers in simple ways (e.g., changing their color pattern with artist paints).

b) It was one of the first studies and an important element of many subsequent pollination studies.

c) By showing that handling time is important to flower choices of pollinators, it suggested how the color, size, and shape of flowers might affect the suite of animals that can visit them profitably.

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