Amanda Decker Benoit
evolutionary ecologist
Research
Indirect species interaction – when one species affects another through an intermediary species – are ubiquitous in nature, yet the eco-evolutionary dynamics of these indirect interactions and their effect on adaptive evolution and are poorly understood. Plant-pollinator interactions form a keystone mutualism that drives diversification and adaptive evolution. However, many predators prey upon pollinators altering their abundance and behavior. I explore the myriad ways that pollinator predators indirectly affect plants by altering pollinator abundance and behavior. Specifically, I am investigating the impact of crab spiders on interactions between a long-lived perennial wildflower Calochortus luteus [Liliaceae] and its pollinator community to determine how crab spiders: 1) affect the frequency and duration of pollinator visits and the taxonomic identity of floral visitors ; 2) alter phenotypic selection on floral traits; and 3) affect plant mating system, fitness and inbreeding depression within plant populations.
Review of pollinator predator effects on plants
Benoit, A. D. and S. Kalisz. 2020. Predator effects on plant-pollinator interactions, plant reproduction, and floral evolution. Annual Review of Ecology, Evolution, and Systematics. https://doi.org/10.1146/annurev-ecolsys-012120-094926
How crab spiders affect floral visitation and pollination
By manipulating crab spider presence and observing pollinator visitation, I determined that crab spiders decrease the frequency and duration of pollinator visits to C. luteus by ~60% each. Yet, surprisingly C. luteus plants with crab spiders present produced significantly more seeds than plants without crab spiders. I also have data (analysis in progress) which will allow me to determine whether different pollinator taxa have different responses to crab spider presence, and to determine which taxa are the most effective pollinators. I predict that smaller bodied pollinator will be more sensitive to the presence of predators because they are more susceptible if attacked. I confirmed through pollination experiments that C. luteus is self compatible. Therefore, I hypothesize that crab spiders can affect the proportion of seeds which are self-pollinated rather than outcross-pollinated by decreasing the amount of outcross pollen delivered to flowers. I have data (analysis in progress) of the seed set of emasculated plants versus intact plants to estimate the importance of self-pollination for seed set in this population. By affecting pollinator reliability, and the prevalence of self-pollination, predators such as crab spiders may drive the maintenance of mixed mating systems preventing the fixation of outing and selfing mating systems as theory predicts. This could help explain the discrepancy between theoretical predictions of fixation and empirical findings that mix mating systems are common.
How pollinator predators affect natural selection on floral traits
For my master’s thesis I developed a field experiment to investigate the effects of two pollinator predators with contrasting hunting modes on the strength and direction of pollinator-mediated selection on floral traits of the native wildflower Lobelia siphilitica. I found that dragonflies with an active pursuit hunting mode did not decrease the strength of plant-pollinator interactions and did not alter pollinator-mediated selection. However, ambush bugs (Phymata spp.) with a sit-and-wait hunting mode hunted from plants with larger daily display sizes and consequentially reversed the direction of pollinator-mediated selection on daily display size (Benoit and Caruso, in review, Ecology). I hypothesize that sit-and-wait pollinator predators are not randomly distributed across plant phenotypes, but rather hunt from plants with higher prey availability, and thus are associated with plant traits that attract prey. By hunting from plants with specific traits (e.g. large display size) and deterring pollinator visitation, sit-and-wait predators can alter the strength and even direction of phenotypic selection on those traits. Â
During my PhD, I examined interactions among crab spiders, pollinators and the long-lived perennial lily Calochortus luteus. I found that crab spiders hunted from C. luteus plants with larger flower diameters and significantly altered the strength of selection of flower diameter in both 2017 and 2018 (Benoit and Kalisz, manuscript in prep).
Predators and population genetics: Can predators facilitate self-pollination and increase the magnitude of inbreeding depression in plant populations?
My results that plants with crab spiders produce more seeds despite lower pollinator visitation, along with observing crab spiders coated in pollen while hunting within flowers, led me to hypothesize that crab spider can facilitate self-pollination by transferring pollen from anther to stigma within a flower. A common consequence of self-pollination is reduced offspring fitness due to increased homozygosity of deleterious recessive alleles. I designed a large multi-year greenhouse experiment to measure fitness metrics of C. luteus plants from four treatments: offspring of fully self-pollinated maternal plants, offspring of fully outcross-pollinated maternal plants, offspring of open-pollinated plants with crab spiders present, and offspring of open-pollinated plants without crab spiders. In addition to comparing fitness metrics over three seasons of growth, I will also compare rates of homozygosity between offspring of plants with crab spiders present and absent by sequence their genomes using a genotype by sequencing (GBS) method. Preliminary results follow the predicted pattern supporting my hypothesis.
Biography
Originally hailing from upstate New York, Amanda has lived and worked around the globe including Canada, Mexico, Costa Rica, and South Korea. She has a keen interest in education which began with a summer job as an Environmental Educator. After completing an honors BA, Amanda taught English in public elementary and middle schools in South Korea for two years. She began her PhD here at UT in 2016 and has been an active member of the EEB community serving on numerous committees, as the president of the graduate student organization GREBE, and as an organizer and mentor for the EEB Mentoring Program to connect undergraduate students with grad student mentors. In addition to serving as a teaching assistant, Amanda has been instructor of record for Field Botany and the Evolution Discussion seminar.
Amanda's hobbies include horseback riding, gardening, and hiking.
Contact Me
Dept. of Ecology and Evolutionary Biology
University of Tennessee, Knoxville
1416 Dabney Hall, Circle Drive
Knoxville, TN 37996
