Featured research: Results from our work on elaiosome phytochemistry and ant seed disperser preference in an eastern North American Trillium system (upcoming manuscript - Fall 2019).

Five species of Trillium were ranked from most preferred (1 - T. catesbaei) to least preferred (5 - T. decumbens) based on probability of seed removal in 1 hour from natural seed depots at sites in the southern Appalachian region. Phytochemical profiles of elaiosomes of each species were investigated using liquid-chromatography mass spectrometry; 122 known compounds and > 7,400 unknown constituents were identified. We performed a random forest regression analysis, followed by Boruta variable selection, to identify the most important known compounds differentiating profiles across species. Of those compounds, we found that pyroglutamic acid, ornithine, salicylate, arginine, citrulline, glucosamine, homocysteic acid, and sedoheptulose 1,7 - biphosphate were significantly, negatively correlated with preference (using Kendall's Tau rank correlation tests). Guanine and 3, 4 - dihydroxyphenylacetate were significantly positively correlated with preference. The figure below illustrates the correlations between compounds and ranked preference of the five species.    

See my poster at the upcoming Ecological Society of America conference in Louisville, KY for more details on this project!
Poster: #77902
"Composition of elaiosome phytochemical profiles and fatty acid concentrations drive seed disperser preference in myrmecochorous species of Trillium."
PS 12: Plant-Insect Interactions 
Date: Monday, August 12, 2019 
Session Time: 4:30 PM - 6:30 PM

Why endemic species?

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Endemic species are key components of global biodiversity and have been shown to contribute disproportionately to the functional stage of species assemblages, and thus the maintenance of ecosystems. Therefore, understanding the underlying processes affecting endemism and rarity is a critical aspect of ecosystem conservation. Endemic species play starring roles in conservation planning and are often of particular interest to the public. In addition, endemism is of great interest in the field of rare species biology. Discovering why some species are rare while others are common is central to our understanding of the dynamics of species and communities, and is a fundamental question in ecology.  

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(Trillium decumbens Harb. 2017.)

Comparisons of seed dispersal effectiveness for sympatric endemic and widespread Trillium ​congeners

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In flowering plants, aspects of rarity and commonness may be associated with dispersal syndromes. To test this hypothesis, I compare seed dispersal effectiveness (SDE) for co-occurring endemic and common congeners of Trillium, perennial understory herbs found throughout deciduous forests of the southeastern US. Trilliums are myrmecochores (their seeds are dispersed by leaf litter ants), so I quantify metrics of ant-mediated seed dispersal observed in the field and measured in the laboratory to determine if aspects of SDE differ for endemic-common Trillium ​species pairs.  


                                                                                                                      (Ants dispersing seeds of Trillium catesbaei Elliot. 2016.)

Seed chemistry and disperser preference

In ants, preference for food items can be detected through "cafeteria" experiments where two items are offered simultaneously. In myrmecochorous ants (those that disperse seeds), preference is likely shaped by physical and/or chemical attributes of seeds, including weight, length, width, or the ratio of elaiosome (a seed-coat derived appendage) to seed. Chemical cues, particularly oleyl-containing compounds, stimulate ants to carry food items to nests and have been shown to explain ant preference for myrmecochore seeds of low nutritional value. However, nutritional quality likely also impacts ant preference. To test whether ants display a preference for endemic or widespread Trillium congeners, I perform cafeteria experiments using captive ant colonies. To parse out the underlying mechanisms driving preferences, I use gas- and liquid-chromatography mass spectrometry to characterize seed chemical profiles. 


(Top - Simultaneous cafeteria experiments with captive colonies of Aphaenogaster rudis.)
(Bottom left - A colony replicate showing artificial nest environment and seed depot.)
(Bottom right - A worker disperses a seed from the depot. 2016.)

Trillium ​species distributions

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In addition to parsing out fine-scale ecological differences between endemic and widespread Trillium species, I test questions about landscape-level processes that impact geographic range sizes using Maxent environmental niche modeling. 



                                                                                  (Preliminary thresholded Maxent output for Trillium decumbens. 2018.)