Four major themes emerge from the 7 papers they chose:

1. Results from one study can suggest new questions and lines of research.
2. Techniques invented while pursuing one study enable future studies.
3. Chance observations made during one study suggest new questions.
4. When multiple scientists work on single systems, their diverse perspectives and training stimulates new avenues for research.

A Brief History of Selected RMBL Ipomopsis Research

Waser, N.M. 1976 Food Supply and Nest Timing of Broad-Tailed Hummingbirds in the Rocky Mountains. The Condor 78:133-135  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, comes into bloom, and they shift to other species (such as Ipomopsis aggregata) as these start to flower. Nesting success depends on a reliable succession of profitable flowers during the summer.

Contributions to later research:

1. The fact that D. nelsonii and I. aggregata share pollinators and flower sequentially led Nick to ask whether these plants compete for  hummingbird pollination during the time of flowering overlap.
2. Realizing that the seasonal timing of flowering is critical for pollination and pollinators has kept phenology on the minds of RMBL researchers.

Waser, N.M. 1978 Interspecific Pollen Transfer and Competition between Co-Occurring Plant Species. Oecologia 36:223-236 pdf

During his doctoral work, Nick studied competition between D. nelsonii and I. aggregata 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:

1. 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.
2. This study stimulated thinking on the precise mechanisms of competition for pollination services
3. The chance observation that most Delphinium flowers are deep blue, but occasional plants make white flowers, led Nick and Mary to ask why the albinos are rare.

Sharaf, K.E., Price, M.V. 2004 Does pollination limit tolerance to browsing in Ipomopsis aggregata? Oecologia 138:396-404 pdf

Kate Sharaf was an undergraduate intern. 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 (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.

Mayfield, M.M., Waser, N.M., Price, M.V. 2001 Exploring the “Most effective pollinator principal” with complex flowers: Bumblebees and Ipomopsis aggregata. Annals of Botany 88:591-596 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 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 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 flowers (red color, tubular shape) are interpreted as adaptations for pollination by hummingbirds.

Contributions to later research:

1. The surprising result of this study stimulated thinking on the nature of floral adaptation to different types of pollinators.
2. This study stimulated further work on color vision of bees, which often are described as being red-blind.

Irwin, R.E., Brody, A.K. 1999 Nectar-robbing bumble bees reduce the fitness of Ipomopsis aggregata (Polemoniaceae). Ecology 80:1703-1712 pdf

In the 1980s, Alison Brody began PhD work (partly under Nick’s guidance) on insects that attack Ipomopsis flowers. 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: Nectar robbers reduce the amount of pollen flowers export to other flowers, as well as the receipt of pollen and number of seeds produced. This detrimental effect occurs because legitimate pollinators avoid nectar-robbed flowers.

Contributions to later research:

1. This paper pioneered experimental approaches for studying nectar-robbing.
2. 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.

Campbell et al. 1991 Components of Phenotypic Selection: pollen export and flower corolla width in Ipomopsis aggregata. Evolution 45:1458-1467 pdf

During the 1980s, while this Delphinium work and work on Ipomopsis 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 flowers that vary among plants within populations.

Take-home points: This 1991 paper used field and flight-cage experiments to understand why Ipomopsis 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:

1. Results of this study stimulated follow-up research to understand why wide flowers export more pollen per visit.
2. The study pioneered methods for studying pollen export and deposition by hummingbirds in a flight cage.
3. The mix of evolutionary/genetical perspectives and ecological perspectives led to novel insights into mechanisms of natural selection on flower traits.

 

Waser N.M., Price M.V. 1985. The effect of nectar guides on pollinator preference: experimental studies with a montane herb. Oecologia 67:121-126  pdf

To understand why white-flowered Delphinium 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 under visitation 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:

1. 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).
2. It was one of the first studies and an important element of many subsequent pollination studies.
3. 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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