Susan Whitehead

Susan Whitehead
Virginia Polytechnic Institute and State University | VT · Department of Biological Sciences

PhD

About

43
Publications
15,378
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1,767
Citations

Publications

Publications (43)
Article
Full-text available
Interactions between plants and leaf herbivores have long been implicated as the major driver of plant secondary metabolite diversity. However, other plant-animal interactions, such as those between fruits and frugivores, may also be involved in phytochemical diversification. Using 12 species of Piper, we conducted untargeted metabolomics and molec...
Chapter
Apple trees host diverse communities of bacteria, fungi, viruses, and other microbes that occupy all plant surfaces and internal tissues. In the past two decades, our understanding of these communities has burgeoned due to new technologies that allow culture-independent characterisation of microbial communities. In this chapter, we provide a compre...
Article
Full-text available
The production of complex mixtures of secondary metabolites is a ubiquitous feature of plants. Several evolutionary hypotheses seek to explain how phytochemical diversity is maintained, including the synergy hypothesis, the interaction diversity hypothesis, and the screening hypothesis. We experimentally tested a set of predictions derived from the...
Chapter
Accumulating evidence indicates that the composition of the microbiota inhabiting an organism (both endo- and epiphytically) can have a profound effect on host physiology and defense responses. The role of the microbiota in plant health and physiology, however, is poorly understood, and few studies have focused on temperate fruit trees. A global ef...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
Full-text available
There is growing recognition of the role that the microbiome plays in the health and physiology of many plant species. However, considerably less research has been conducted on the postharvest microbiome of produce and the impact that postharvest processing may have on its composition. Here, amplicon sequencing was used to study the effect of washi...
Article
Full-text available
Carrot (Daucus carota L.) is an important root vegetable crop with high nutritional value, characteristic flavor, and benefits to human health. D. carota tissues produce an essential oil that is rich in volatile terpenes and plays a major role in carrot aroma and flavor. Although terpene composition represents a critical quality attribute of carrot...
Article
Full-text available
Abstract Morphological and chemical attributes of diaspores in myrmecochorous plants have been shown to affect seed dispersal by ants, but the relative importance of these attributes in determining seed attractiveness and dispersal success is poorly understood. We explored whether differences in diaspore morphology, elaiosome fatty acids, or elaios...
Article
This study investigated ant seed removal of Piper sancti‐felicis, an early successional Neotropical shrub. Neotropical Piper are a classic example of bat‐dispersed plants, but we suggest that ants are underappreciated dispersal agents. We identified eleven ant species from the genera Aphaenogaster, Ectatomma, Paratrechina, Pheidole, Trachymyrmex, a...
Article
Full-text available
Seed dispersal is a critical ecological process that determines plant population ecology and distribution. In the tropics, frugivorous bats play an important role in primary seed dispersal and forest regeneration. Secondary seed dispersal may be performed by an array of animals, including snakes that prey on frugivorous and granivorous animals.
Article
The paradoxical presence of toxic chemical compounds in ripe fruits represents a balance between plant enemies and allies: chemical traits can defend seeds against antagonistic herbivores, seed predators or fungal pathogens, but also can impose costs by repelling mutualistic seed dispersers, although the costs are often difficult to quantify. Seeds...
Article
Background and aims: Most crops have been dramatically altered from their wild ancestors with the primary goal of increasing harvestable yield. A long-held hypothesis is that increased allocation to yield has reduced plant investment in defence and resulted in crops that are highly susceptible to pests. However, clear demonstrations of these trade...
Article
Full-text available
Plant responses induced by herbivore damage can provide fitness benefits, but can also have important costs due to altered interactions with mutualist pollinators. We examined the effects of plant responses to herbivory in a hummingbird-pollinated distylous shrub, Palicourea angustifolia. Through a series of field experiments we investigated whethe...
Data
Differences in flower morphology and nectar production between thrum (T) and pin (P) flowers in Palicourea angustifolia. (DOCX)
Data
Volatile compounds in Palicourea angustifolia with differences in concentration in flowers and leaves. (DOCX)
Data
Summary of pollinator visitation to inflorescences on different branch treatments. Number of replicate plant pairs (of N = 26 total) in which a visitor was observed on any of the treatments. Statistical analyses were conducted only for taxa that were observed in five or more replicates. (DOCX)
Article
Full-text available
Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about mi...
Article
Full-text available
Agriculture is a dominant evolutionary force that drives the evolution of both domesticated and wild species. However, the various mechanisms of agricul- ture-induced evolution and their socio-ecological consequences are not often synthetically discussed. Here, we explore how agricultural practices and evol- utionary changes in domesticated species...
Article
Full-text available
For millennia, humans have imposed strong selection on domesticated crops, resulting in drastically altered crop phenotypes compared with wild ancestors. Crop yields have increased, but a long-held hypothesis is that domestication has also unintentionally decreased plant defences against herbivores. To test this hypothesis, we conducted a phylogene...
Article
Full-text available
For millennia, humans have imposed strong selection on domesticated crops, resulting in drastically altered crop phenotypes compared with wild ancestors. Crop yields have increased, but a long-held hypothesis is that domestication has also unintentionally decreased plant defences against herbivores. To test this hypothesis, we conducted a phylogene...
Article
Full-text available
Non-native plants introduced to new habitats can have significant ecological impact. In many cases, even though they interact with the same community of potential herbivores as their new native competitors, they regularly receive less damage. Plants produce secondary metabolites in their leaves that serve a range of defensive functions, including r...
Article
Full-text available
Aims: Ripe, fleshy fruits generally function as rewards to attract mutual-istic seed dispersers, but many fruits also contain high concentrations of toxic secondary metabolites. These compounds may serve a variety of adaptive roles in seed dispersal or as a defense against non-dispersing seed predators or pathogens. We tested the effects of iridoid...
Article
Full-text available
Although fleshy fruits function primarily to attract seed dispersers, many animal-dispersed fruits contain potentially toxic secondary metabolites. These metabolites can provide defense against seed predators and pathogens, but their effects on dispersers are still poorly understood. In some cases plants may experience a tradeoff, where the metabol...
Conference Paper
Plant defense theory suggests that plants in natural systems must allocate limited resources among different physiological processes, including growth, reproduction, and the production of chemical or physical defenses. However, it is unclear whether these same constraints apply in agricultural systems, which are generally characterized by high reso...
Article
Full-text available
Plants often recruit frugivorous animals to transport their seeds; however, gut passage can have varying effects on plant fitness depending on the physical and chemical treatment of the seed, the distance seeds are transported, and the specific site of deposition. One way in which plants can mediate the effects of gut passage on fitness is by produ...
Article
Full-text available
Many plants and ants engage in mutualisms where plants provide food and shelter to the ants in exchange for protection against herbivores and competitors. Although several species of herbivores thwart ant defenses and extract resources from the plants, the mechanisms that allow these herbivores to avoid attack are poorly understood. The specialist...
Article
Full-text available
Although ripe, fleshy fruits function primarily to attract seed dispersers, they must also be defended against diverse communities of seed predators and pathogens. For some plants, the concentration and diversity of secondary metabolites in fruits can exceed that of leaves and other plant parts, but little is known about the functional significance...
Article
Full-text available
Little is known about the evolution, diversity, and functional significance of secondary metabolites in reproductive plant parts, particularly fruits and seeds of plants in natural ecosystems. We compared the concentration and diversity of amides among six tissue types of Piper reticulatum: leaves, roots, flowers, unripe fruit pulp, ripe fruit pulp...
Article
Full-text available
Abstract Although the primary function of fleshy fruits is to attract seed dispersers, many ripe fruits contain toxic secondary compounds. A number of hypotheses have been proposed to explain this evolutionary paradox, most of which describe the potential adaptive role that secondary compounds may play in seed dispersal. However, some authors have...
Article
Full-text available
Interspecific hybridization among non-native plant species can generate genotypes that are more reproductively successful in the introduced habitat than either parent. One important mechanism that may serve as a stimulus for the evolution of invasiveness in hybrids is increased variation in secondary metabolite chemistry, but still very little is k...
Conference Paper
Background/Question/Methods The genus Lonicera (Caprifoliaceae) includes approximately 200 species worldwide, with 18 native and 16 introduced species in North America. Several Asiatic Lonicera species have become some of most problematic woody plant invasives in the United States (e.g., L. maackii, L. tatarica, and L. japonica), while native Lon...
Conference Paper
Background/Question/Methods Fleshy fruits attract animal seed dispersers by providing nutritional rewards; however, these rewards can also attract fruit pests such as insect seed predators and fungal pathogens. Thus, fruits must be both attractive to mutualists and defended against antagonists at the same time. Fruit secondary chemistry is likely...
Conference Paper
Background/Question/Methods One of the principal predictions of climate change models is an increase in extreme weather events, including heavy precipitation and exacerbated drought severity. Because these events could lead to dramatic changes in snowpack and soil moisture in alpine, Arctic, and Antarctic ecosystems, it is crucial to understand h...
Conference Paper
Background/Question/Methods Optimal defense theory predicts that plant parts that have the highest fitness value, such as flowers and fruits, should be protected with high levels of chemical defense, but that, in animal-dispersed fruits, these defenses should diminish upon ripening. Changes in fruit chemistry with ripening that match these predic...
Article
Full-text available
1. Herbivore attack can induce dramatic changes in plant chemical defences. These responses protect plants against future herbivory, but can also have important physiological and ecological costs. Ecological costs of defence have received recent theoretical attention; however, many proposed costs have not yet been demonstrated empirically. In parti...
Conference Paper
Background/Question/Methods Low temperatures, limited precipitation, and high salinity in the McMurdo Dry Valleys (MCM) of Antarctica constrain life to simple communities that are more easily interpreted in ecological studies. For these reasons, the MCM Long Term Ecological Research (LTER) site provides an ideal opportunity to address complex eco...
Conference Paper
Full-text available
Background/Question/Methods Mechanisms of recognition and discrimination are essential in determining the outcome of multi-species interactions. In the classic example of mutualism between ants and Acacia trees, ant colonies fiercely defend Acacia trees in exchange for resources provided by the trees. However, specialist herbivores can gain access...

Projects

Projects (3)
Project
Assessing the imprint of plant-frugivore interactions on evolutionary and organismal patterns of phytochemistry in the genus Piper. To what extent can selection imposed by separate sets of ecological interactions act independently on the secondary metabolome of vegetative and reproductive organs? Which sets of interactions are driving phytochemical evolution at the whole-plant level?
Project
The goal of this project is to determine whether seed dispersal metrics, such as dispersal rate and dispersal distance, differ between co-occurring rare and common Trillium congeners in the field. To complement the field experiment, it is the goal of a laboratory "cafeteria" experiment to determine whether ant dispersers prefer the seeds of rare or common Trillium congeners under controlled conditions.