This dissertation comprises two papers that shed light on how digital platforms are shaping consumer preferences and behavior.

Chapter 1 investigates a large card spending panel to understand how ChatGPT adopter changed their spending on other digital services. We employ Coarsened Exact Matching to balance early ChatGPT subscribers—those who began their subscriptions in distinct monthly cohorts from February to June—with those of later ChatGPT subscribers who joined between September and December. Then we use a triple-difference identification strategy to predict counterfactual digital service payments. We find an increase in consumers' spending on other AI products following the adoption of ChatGPT across five monthly adopter cohorts. The estimates rule out market share changes of 2\% for the majority of brands, with a few exceptions.

Chapter 2 examines online tipping in the gig economy, focusing on how digital platforms can boost tipping. We analyze 4.1 million transactions and find that a buyer's nationality and satisfaction levels are key tipping factors. We also run two field experiments to test if psychologically-based messages about norms and reciprocity could lead to more frequent tipping. The results show that informing buyers about social norms effectively increases tipping. Additionally, in a MTurk survey, we test various normative messages and find that descriptive norms, like highlighting high user tipping rates, effectively raise tipping intentions. This paper highlights the importance of understanding and shaping online tipping practices, not just for helping consumers navigate tipping decisions but also for improving gig workers’ financial stability.

The goal of this work is to develop an approach to the design of natural and immersive interaction methods for three-dimensional virtual environments. My thesis is that habitation and presence in any environment are based on a continuous process of perception and action between a person and his/her surroundings. The current practice of virtual environments, however, disconnects this intrinsic loop, separating perception and action into two different `worlds'--a physical one (for perception) and a virtual one (for action). This research is aimed at bridging the gap between those two worlds.

Being drawn from perceptual philosophy and psychology, the theoretical study in this dissertation identifies three embodiments of natural perception-action loop: direct perceptual acts, proprioceptive locomotion, and motor intentionality. These concepts form the basis for the interaction methods proposed in this work, and I demonstrate these methods by implementing pertinent prototype systems. First, I suggest a view-dependent, non-planar display space that supports natural perceptual actions, thereby enhancing our field of view as well as depth perception. Second, I propose Interactive Chair, which provides an intuitive locomotion control based on our sense of self-body movements. Third, I argue that pointing-based interaction techniques inhibit our motor-intentional behaviors, therefore demonstrate a line-of-sight, direct object manipulation method. I finally conduct a series of user tests to evaluate the proposed methods and systems, and confirm the contribution of suggested interaction design approaches to the natural experience of virtual environments.

The Sonchinae is the most widely distributed subtribe in the tribe Cichorieae, with a discontinuous, almost cosmopolitan, and very peculiar phytogeographic distribution. In particular, genus Sonchus subgenus Sonchus, appears to be responsible for the origin of several island endemics both in the Pacific Ocean (Dendroseris, Thamnoseris, Actites, Kirkianella and Embergeria ) and the Atlantic Ocean (woody Sonchus alliance in the Macaronesian Islands). So polyploidy Sonchus and their relative Pacific polyploidy endemics are an ideal system to study the polyplodization for the island plants. Several hypotheses have been proposed based on the morphology and karyology. We use the cloning technique to retrieve the different ITS repeat types in order to test the origin of several polyploidy Sonchus as well as polyploidy in the related Pacific islands. The Pacific endemics (Dendroseris, Embergeria, Kirkianella, and Actites) are all formed the monophyletic clade with all the their repeat types which support the single origin of these endemics. S. arvensis has been identified as a potential allopolyploid. The Stebbins hypothesis of allpolyploid origin for S. oleraceus is partially supported with confirmation of S. asper as one donor. The data also indicate a hybrid origin for S. hydrophilus which might have subsequently homogenized with ITS copies from the hybrid ancestor via concerned evolution.

The woody Sonchus alliance is one of the largest Macaronesia diverse endemic groups with 6 genera and approximately 31 species. Determining accurate phylogenetic relationships among the members of the woody Sonchus alliance presents challenges because of insufficient level of molecular variation and the convergent evolution of similar morphological traits in island settings. All taxa of woody Sonchus alliance were sampled to investigate the phylogenetic relationships as well as to test the potential role of hybridization and introgression using three independent low-copy nuclear genes: glyceraldehyde 3-phosphate dehydrogenase (G3pdh) , B12 and calmodulin (Cam) . B12 and CAM phylogeny is not well resolved due to the limited informative sites. The G3PDH data set was not significantly different from that of B12 and CAM,and subsequent combined analysis provided a better resolved and supported phylogeny within the alliance. In the MP combined tree, the basal lineages of monotypic genera were not identified. The all Taeckholmia species except T. arborea formed a well-support clade. It partly supports Boulos' classification to treat Taeckholmia as a genus. But the Dendrosonchus is highly polyphyletic which does not support either Boulos' or Aldridge's classification of tree Dendrosonchus. Assessment of the role of hybridization and introgression was limited due to low sequence variability of B12 and CAM genes, however, potential hybridization has been recognized comparing independent gene regions.

The members of woody Sonchus alliance display extensive morphological, ecological, and anatomical diversity, but all taxa have a uniform chromosome number. Furthermore, all the members have no crossing barriers, there are extensive opportunities for hybridization between these species. We include two independent low-copy nuclear genes: glyceraldehyde 3-phosphate dehydrogenase (G3PDH) and Calmodulin (CAM) with the cloning with several key species to test the possible homoploid hybrid speciation. There is no evidence in our data to support a hybrid origin for the monotypic species (Babcockia platylepis, Sventenia bupleuroides and Lactucosonchus webbii). The hybridization between Dendrosonchus and Taeckholmia is not supported in our data. S. tuberifer might have hybrid origin between herbaceous and small woody species.

Salvia subgenus Calosphace (Lamiaceae), the largest of 5 subgenera with some 500 species and strongly supported as monophyletic, has received no comprehensive systematic research since the initial establishment of 91 taxonomic sections. Representative taxa of 73 sections of Calosphace were sampled to investigate the phylogenetic relationships and identify major lineages using chloroplast (intergenic spacer, psbA-trnH) and nuclear DNA (ribosomal spacer region, ITS). Phylogenetic analysis of the combined data set established the monophyly of nine sections (Blakea, Corrugatae, Dusenostachys, Erythrostachys, Hastatae, Incarnatae, Microsphace, Nobiles, and Sigmoideae) and four major lineages (S. axillaris, “Hastatae clade”, “Uliginosae clade”, and “Core Calosphace”) corresponding with the four major stamen types identified within the subgenus. Disjunct sections spanning two or more centers of diversity are not supported by the results; no more than seven dispersal events to South America are required to account for the current disjunct distributions. One member of the subgenus, Salvia divinorum is hallucinogenic and used in traditional healing ceremonies by the Mazatec of Mexico. It was classified within section Dusenostachys and hypothesized to be an interspecific hybrid. Multiple DNA regions (ITS, trnL-trnF, and psbA-trnH) of 52 species representing the major lineages of subgenus Calosphace and six accessions of S. divinorum were sequenced to test its phylogenetic position and putative hybridity. Salvia divinorum should not be classified within Dusenostachys nor is it a hybrid according to the results; its closest relative is S. venulosa, a Colombian endemic. In addition to S. divinorum, there are many other Calosphace species that are used medicinally in North and South America. Ethnobotanical data was gathered for 150 species; those sharing the common names, medicinal uses, appearances, and similar compounds associated into medicinal plant complexes. Five new, previously undocumented complexes were identified: Mirto (5 spp. used extensively in the treatment of susto and other illnesses in Mexico), Ñucchu (7 spp. used as a symbolic element in religious prossessions and in the treatment of respiratory ailments in Peru), Lí'l++ (3 spp. used for food and medicine by the Chianantec), Cantueso (2 spp. used for respiratory ailments in Mexico), and Manga-paqui (3 spp. used for kidney and liver problems in Ecuador).

Background

Methods

Results

Conclusions