Over billions of years of earth history, organisms evolved amazing diversity of strategies, including life history, morphology and behavior, to cope with environment changes. The overarching question that I am interested in is: what is the genetic basis of adaptation and speciation? Flowering plants have a bewildering diversity of shapes and sizes. Regarded as “an abominable mystery” by Darwin himself, this diversity is likely generated through an explosive burst of diversification about 100 millions ago. Evidence suggests that pollinator interaction is one of the key to understanding this rapid diversification of flowering plants. There are two important questions to ask about this process: a, the material – what genetic changes modify the design of plant to cope with selection pressure? b, the force – what kind of selection pressure does pollinator poses to plant?
a. Advised by Dr. Toby Bradshaw, I am using a common wildflower Mimulus (monkeyflower) as a model system to understand the genetic basis for pollinator-driven adaptation. By using both forward genetics (QTL mapping, mutagenesis screen) and reverse genetics approach(comparative genomics, candidate gene method and stable transformation for functional verification), I am trying to map the genetic variations responsible for the floral difference (e.g. color and scent) between a group of closely related Mimulus species (shown below).
The phylogeny of Erythranthe section in Mimulus, adapted from Beardsley et al., 2003
(Mimulus lewisii flower has two anthocyanin patterns: pink region on the petal lobes and small red dots on the nectar guide. We found that the plant also has two sets of transcription factor genes to control the two patterns respectively. Mutagenesis and transgenesis can cleanly diminish or enhance one color patten, while not influencing the other pattern. Upper left: pelan, has dimished pink region; Upper right: negan, has diminished red dots; Lower left, roi, has enhanced pink region; Lower right, red tongue, has enhanced red dots)
b, Advised by Dr. Tom Daniel, I employ a novel combination of 3D-printing, electronic sensing, and computer vision to quantify the fitness effects of flower morphology variations. I measure the fitness parameter for equation-generated artificial flowers under the visit of real pollinators (hawkmoth and hummingbird). The goal is to construct a fitness landscape over flower morphological space to understand 1, how the flower morphology influence plant’s and pollinator’s fitness, respectively and 2, how different groups of pollinators drive flower morphology divergence.
(This is the top view and side view of some 3D printed artificial flowers, only varying corolla curvature.)
(This video illustrates the experiment setup in x-ray mode. Only the center flower (big black circles) is instrumented and supplied with nectar. The flowers on the two sides are used to distract the moth from the center flower. The moth is marked with a white dot. Once it enters the 12.5cm proximity of center flower, the circle will become black. The information on the top of the video shows some experiment information. Please notice the change of nectar information on the upper left corner. The nectar container is automatically replenished 2 secs every time after the moth left the center flower through a customized micorinjector)
(A 3D-printed flower with gradually changing corolla curvature visited by a hawkmoth. The video was taken with a high speed video camera and played 2.5 times slower than real time. The right side panel shows the nectar level and the accelerometer signal (the small part on top of the flower, which functions as a proxy of real flowers’ reproductive parts). Please note that while the moth can quickly locate the nectary, it barely touches the reproductive parts of the flower, which suggest less pollen transfer, thus lower plant fitness)
(This video is similar with the previous one. The only difference is that this flower has an abruptly changing curvature (more difficult for the moth to locate nectar). Please note that the moth hits the reproductive parts of the flower much more strongly than in the previous video, but has more failed attempt to locate the nectary)