Diversity and Evolution of Pollination and Mating Systems of Tropical Plants

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Diversity and Evolution of Pollination and Mating Systems of Tropical Plants
Organized by:

  • W. John Kress, Department of Botany, Smithsonian Institution

  • Qing-Jun Li, Xishuangbanna Tropical Botanical, Chinese Academy of Sciences

The diversification of many groups of flowering plants has been attributed to adaptive radiation of pollination modes and mating patterns. Many unique and intricate pathways of floral evolution are evident within particular tropical families ands in recent years, many novel pollination mechanisms have been discovered in tropical ecosystems, providing the potential for comparative and phylogenetic studies of the evolution of reproductive traits. The main goal of this symposium is to describe and compare the evolution and ecology of pollination and mating systems of tropical plants, especially with regards to adaptive radiations, generalized vs. specialized systems, and evidence for coevolution in mutualistic relationships. Examples from Asian, African and American tropical habitats will be presented.

Pollinator generalization and specialization across a geographic mosaic: hummingbirds and heliconias of the eastern Caribbean
Ethan Temeles1, and John Kress2

1Dept. Biology, Amherst College

2Dept. Botany, Smithsonian Institution

Email: ejtemeles@amherst.edu
Thompsons (2005) Geographic Mosaic Theory of Coevolution predicts that the degree of specialization and interdependence between mutualistic species will vary in space and time. Here we use a geographic approach to examine how a hummingbird Heliconia relationship changes across islands in the eastern Caribbean and discuss the associated changes in floral and pollinator traits. On the island of Dominica, flowers of H. bihai are pollinated exclusively by female purple-throated caribs (Eulampis jugularis), and have long curved flowers matching the females long, curved bills. On Grenada, Trinidad, and Tobago, flowers of H. bihai are 30% shorter, yet are pollinated by as many as five different hummingbird species with bills ranging from 18 to 40 mm in length. Feeding experiments with natural and artificial flowers demonstrate that the long, curved flowers of H. bihai on Dominica are inaccessible to short-billed hummingbirds, whereas the short, curved flowers of H. bihai on Grenada, Trinidad and Tobago are easily accessed by short- and long-billed hummingbirds, as well as by hummingbirds with highly curved bills. We suggest that the extreme pollinator specialization on Dominica is a consequence of depauperate island flora and faunas resulting from increased geographic distance from mainland source pools, which facilitates both plant and pollinator character displacement.
Keywords: Pollination; Coevolution, Heliconias, Hummingbirds, Specialization

Maintenance of flexistyly in Alpinia spp. (Zingiberaceae): the role of morphology, ecology and genetics
Qing-Jun Li and Min Liu

Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences

Email: qjli@xtbg.ac.cn
Flexistyly is a novel sexual dimorphism by reciprocal style movements and pollen dehiscence, which found in genera Alpinia and Amomum of ginger family. Populations of flexistylous species comprise two floral morphs that differ in the direction of movement that styles undergo and time of pollen sheds during flowering, one releases its pollen in the morning, and holds its stigma out of the way of pollinators; the other morph holds back its pollen, but its stigma is downward-curved and receptive to pollen-laden insect. Around midday, these two floral morphs swap sexual roles through reciprocal style movement. Here, we propose that the maintenance of flexistyly in the population may depend on the genetic control, and the exact timing of stigma and anther maturity, and the pollination environments. We tested these hypotheses by hand pollinating between and within morphs, morph ratio survey of natural populations, style movement behavior related to the ecological environment, and mating system detections of four species. Our results show that one Mendelian locus with two alleles control the movement of the style and the time of pollen sheds, cataflexistylous morph is recessive homozygote (ss), anaflexistylous morph are dominant heterozygote (Ss). In the natural population, no chance to form homozygote anaflexistylous individuals, in this case, the morph ratio of 1:1 could be maintained. The study of four species’ mating systems indicate that flexistyly plays an important role to encourage outcrossing, but at the same time, interference between sexual functions also be prevented.
Key words: Alpinia; flexistyly, experimental pollination, heterodichogamy, mating system, Mendelian inheritance, morph ratio, sexual dimorphism, Zingiberaceae

Adaptive trade-off in corolla shape mediates specialization for flowers pollinated by bats and hummingbirds
Nathan Muchhala

University of Miami

Email: n_muchhala@yahoo.com
Evolution towards increased specificity in pollination systems is thought to have played a central role in the diversification of angiosperms. Theory predicts that the presence of trade-offs in adapting to different pollinator types will favor specialization, yet few studies have attempted to characterize such interactions in nature. I conducted flight cage experiments with bats, hummingbirds, and artificial flowers to examine effects of corolla width on pollination. I videotaped visits to analyze pollinator behavior, and counted pollen grains transferred to stigmas. Results demonstrate that flower-pollinator fit is critical to effective pollination; wide corollas guided bat snouts better and narrow corollas guided hummingbird bills better. Poor fit resulted in variable entry angles and decreased pollen transfer. A model using these results predicts that wide corollas will be selected for when bats make more than 44% of visits and narrow corollas when they make less. Intermediate corollas are never favored (i.e. generalization is always suboptimal). This is the first study to clearly document a pollinator-mediated fitness trade-off in floral morphology.
Keywords: Burmeistera, disruptive selection, fitness trade-off, flower-pollinator fit

Island invaders: the role of introduced mutualists in pollination in Mauritius
Christopher N. Kaiser1, Jane Memmott2 and Christine B. Muller3

1Ecosystem Management, ETH Zurich, Switzerland

2School of Biological Sciences, University of Bristol, UK

3Institute of Environmental Sciences, University of Zurich, Switzerland

Email: ch.kaiser@env.ethz.ch
Little is known about the effects of introduced species, or the removal of invasive plant species for habitat restoration, on native mutualistic plan-pollinator interactions. We used fully quantified flower visitation webs to investigate plant-pollinator communities of a restored and an unrestored site in Mauritius. Interactions between all flowering plant species and their pollinator species were recorded for both sites for an eight month period. The restored site showed higher plant and pollinator species richness and abundance than the unrestored site. Plant species in the restored site produced larger and heavier fruits, which contained more seeds per fruit than those in the unrestored site. Visitation webs in both sites were dominated by a few super-abundant, disproportionately well-connected plant and pollinator species, and many rare and specialised species. Most key animal species were introduced to Mauritius. Introduced plant species produced a high fruit set, despite being visited by relatively few pollinators. Our findings indicate that the effect of introduced species on plant-pollinator interactions may differ according to whether they are plants or pollinators. The low visitation rate to introduced plant species suggested a low level of indirect competition for pollinators with native plant species. However, the infiltration of the local pollinator community by introduced flower visitors suggested strong competition between native and introduced pollinators for floral resources, which may have resulted in the displacement of native pollinators and consequently the disruption of co-evolved plant-pollinator interactions.
Keywords: pollination, mutualistic networks, Indian Ocean, habitat restoration

Potential ecological and evolutionary responses of a plant-pollinator system due to human induced climate change
Luciano E. Lopes1 and Silvana Buzato2

1Programa de pos-graduaCao em Ecologia, Departamento de Ecologia, I.B., Universidade de Sao Paulo

2Departamento de Ecologia, I.B., Universidade de Sao Paulo

Email: llopes_br_2000@yahoo.com.br
Fossil records are the ancient proofs of how climate changes affect the species distribution as well as plant-animal interactions. Since the industrial revolution, global temperatures and atmospheric carbon dioxide have been rising steadily. Here, we examined the potential effects of human induced climate change on plant-pollinator interaction of Abutilon rufinerve (Malvaceae), a Brazilian montane forest species. Abutilon rufinerve is a self-incompatible species in which flowers opened at dawn and last 2 days (71% of the flowers), producing nectar by day and night at a rate equivalent to 21.9 Joules per hour. Flowers were visited by hummingbirds (0.98 visits.flower-1.hour-1) and bats (0.42 visits.flower-1.hour-1). Selective floral visitor exclusion

experiments resulted in similar fruit-set for nocturnal and diurnal pollinators. Bats, however, were more effective pollinators, accounting for ca. 70% of the seed-set, because fruits originated from bat pollination had more seeds. Bats leaving from shelter were correlated with air temperature, with almost no activity at nights with temperatures lower than 8o C at 6 pm, and frequency of visits are lower during colder nights. Nectar was found in open flowers in the end of night, but not at the end of the day, indicating that hummingbirds may be benefitted by lower activity of bats during colder nights. Considering Abutilon rufinerve interplant variation in floral color and size and differential response of nocturnal and diurnal pollinators to temperature variation, there is potential to increase differential selective pressure made by bats and hummingbirds with the recent climatic changes. We considered several alternative outcomes relating effects of climatic changes on nectar production and distribution of plants, bats and hummingbirds to the ecological and evolutionary fate for this plant-pollinator system. FAPESP03/07088-9.

Keywords: bats, global warming, hummingbirds, plant fitness, pollination

Between a rock and a hard place: figs, pollinators, and parasites in the Sonoran Desert
John Nason1, Kevin Day 1, Dan Gates1 and John Stireman2

1Iowa State University

2Wright State University

Email: jnason@iastate.edu
In recent years, study of mutualism has provided great insight into the processes of coevolution and the dynamics of species interactions. Increasingly recognized is that geographic variation in both the biotic and abiotic environment external to a mutualism must be considered to fully understand the fitness costs and benefits of mutualisms, how and why these benefits vary in space, and how mutualisms are stabilized over ecological and evolutionary time. Our research focuses on a fig-fig wasp system composed of the Sonoran Desert Rock Fig, Ficus petiolaris, its obligate pollinating wasp, and associated non-pollinating wasp parasites. This system represents the environmental limits of fig-fig wasp mutualisms in North America. In a stressful desert setting, F. petiolaris populations are often small, spatially isolated, and consequently at high risk of local pollinator extinction and mutualism breakdown. Mutualism in these populations may be stabilized by reproductive adjustments in the fig (intra- crown asynchrony, extended duration of receptivity to pollinators). These adjustments by the plant, however, may also prove beneficial to non-pollinating parasites, which can impact fig reproduction and pollinator persistence. Our work investigates the effects of geographic variation in population size on the stability of the fig-fig wasp mutualism, examining to what extent figs adjust their reproductive schedules to mitigate risk of pollinator loss, and assessing the effects of parasites on the maintenance of demographically stable pollinator populations. Our findings provide novel insights into how biotic and abiotic factors can modulate interactions among mutualists, influence local mutualism stability, and determine species geographic and environmental ranges.
Keywords: Mutualism, fig, pollinator, parasite

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