I am interested in the genetics underlying the ecology and evolution of adaptive traits by investigating both patterns of gene expression and allelic variation. My particular interests lie in the field of plant speciation, plant-herbivore interactions and chemical ecology. The tools I use include qPCR, microarrays, molecular markers and genetic engineering. I think that non-domesticated species are particularly suited to address ecological and evolutionary questions and have studied a North American desert tobacco ( Nicotiana attenuata
), North American alpine columbines (mostly Aquilegia formosa
and A. pubescens
) and now work on New Zealand alpine cress (mostly Pachycladon enysii
, P. fastigiata
and P. novae-zealandiae
Pachycladon Projects (AWCMEE)
The genetic basis of diversification
I am taking a microarray approach towards understanding morphological and ecological differences across evolutionary young species of Pachycladon
, an alpine cress, endemic to New Zealand and Tasmania.
I will focus on:
- comparisons of species representing two clades suggested to have diverged by specializing on different geological substrates - P. fastigiata and P. novae-zealandiae - as well as
- comparisons of species within a clade which differ in morphology (e.g. trichomes) and habitat parameters other than substrate (e.g. altitude preferences) - P. fastigiata & P. enysii.
Ideally, in each comparison, I would like to separate within species - from between species-variation to find fixed expression differences between species. Such differences are ultimately due to differences in cis or trans regulation and thus help to discover genetic differences between species. These genetic polymorphisms may then be searched for signatures of selection and further investigated regarding their role in adaptation and reproductive isolation. Microarray studies across species are therefore a first but very informative step in explaining the adaptive genetic changes that drive diversification. Moreover, gene expression differences can be correlated with phenotypic differences observed downstream of gene expression, e.g. differences in proteomes, metabolomes, morphology, behavior, physiology and ecology.
All microarray experiments will be conducted in close collaboration with Peter Heenan (Landcare Research, Lincoln) and Bart Jansen (HortResearch, Auckland), respectively.
Aquilegia Projects (UCSB)
The evolution of flower color in North American columbines
The repeated loss of floral anthocyanins during the evolution of the North American Aquilegia
clade, which is partly associated with shifts to hawkmoth pollination, represents an interesting case of parallel evolution. We are investigating if this convergence in phenotype is mediated by convergence on the molecular level, in particular, if the phenotypic changes are brought about by similar regulatory or structural mutations.
Ultimately, we are interested in answering the following questions:
- How strongly is the evolution of a trait constrained by pleiotropic effects? Is phenotypic evolution mostly due to regulatory mutations?
- How much adaptive genetic variation is maintained in a species and likely to be exchanged between species through hybridization?
- Do the genes apparently mediating an adaptive trait show signatures of selection?
- Can we show that a trait is adaptive by studying the fitness consequences of natural or artificial (bred or genetically engineered) polymorphisms of a candidate gene?
Anthocyanins are phenotypically and molecularly tractable, exhibit great variation across Aquilegia
species and fulfill important ecological functions all of which predestines them for evolutionary studies.
Steps we take towards answering the above questions:
- Study the expression patterns of the six main structural genes underlying anthocyanin production across the North American columbine phylogeny (Whittall et al.)
- Clone the regulators of the anthocyanin biosynthetic pathway (ABP) and study their variation in expression and sequence across species
- Identify the molecular mechanism underlying the loss of floral anthocyanin in A. pubescens: Do any of the ABP loci map to a QTL for spur color?
- Establish causal links between genotype and phenotype by exchanging alleles via genetic engineering (transient transformation of Aquilegia by virus-induced gene silencing developed by Elena Kramer’s group)
The uniqueness of floral organs
Flowers ensure a plant’s reproduction by producing male and female gametes (in stamens and carpels, respectively) and by structures that promote the fusions of these gametes (conspicuous petals and sepals, nectary glands). Genes that determine which floral organ a floral meristem develops into have been extensively characterized in Arabidopsis thaliana
as well as other eu-dicot plants and are widely known as ABC genes. By taking a microarray approach and studying gene expression patterns in the five floral whorls of Aquilegia formosa
we are addressing several questions:
- How conserved is the ABC model at the base of the eu-dicots?
- What is the role of staminodia, a floral whorl inserted between stamens and carpels and that is specific to Aquilegia?
- Can petal-specific gene expression tell us something about the genes involved in the formation of the spur, a key innovation, believed to have accelerated speciation in the genus Aquilegia?
The arrays are designed based on an extensive EST collection (TIGR AQGI) in a concerted effort by Justin Borevitz (University of Chicago), Willem Rensik (The Institute of Genomic Research) and NimbleGen Systems, Inc.. They are customized high-density oligonucleotide arrays carrying about 17,800 genes with an average of 20 probes per unigene (a total of 356,000 spots).
- Whittall JB(1), Voelckel C(1), Kliebenstein DJ, Hodges SA (2006) Convergence, constraint and the role of gene expression in adaptive radiation: Floral anthocyanins in Aquilegia. Molecular Ecology 15: 4645-4657 (1) Equal contributors
- Schmidt DD(1), Voelckel C(1), Schmidt S, Hartl M, Baldwin IT (2005) Attack from the same Lepidopteran herbivore results in species-specific transcriptional responses in two solanaceous species. Plant Physiology 138: 1763-1773 (1) Equal contributors
- Voelckel C, Baldwin IT (2004) Herbivore-induced plant vaccination: II. Array-studies reveal the transience of herbivore-specific transcriptional imprints and a distinct imprint from stress combinations. The Plant Journal 38: 650-663
- Voelckel C, Weisser WW, Baldwin IT (2004) An analysis of plant-aphid interactions by different microarray hybridization strategies. Molecular Ecology 13: 3187-3195
- Voelckel C, Baldwin IT (2004) Generalist and specialist lepidopteran larvae elicit different transcriptional responses in Nicotiana attenuata, which correlate with larval FAC profiles. Ecology Letters 7: 770-775
- Voelckel C, Baldwin IT (2003) Detecting herbivore-specific transcriptional responses in plants with multiple DDRT-PCR and subtractive library procedures. Physiologia Plantarum 118: 240-252
- Voelckel C, Krügel T, Gase K, Heidrich N, van Dam NM, Winz R, Baldwin IT (2001) Anti-sense expression of putrescine N-methyltransferase confirms defensive role of nicotine in Nicotiana sylvestris against Manduca sexta. Chemoecology 11: 121-126
- Voelckel C, Schittko U, Baldwin IT (2001) Herbivore-induced ethylene burst reduces fitness costs of jasmonate- and oral secretion-induced defenses in Nicotiana attenuata. Oecologia 127: 274-280
- Kay KM, Voelckel C, Yang JY, Hufford KM, Kaska DD, Hodges SA (2007) Floral characters and species diversification. In: Harder LD, Barrett SCH, eds The ecology and evolution of flowers. Oxford University Press: in press
- Voelckel C, Baldwin IT (2004) Herbivore-specific transcriptional responses and their research potential for ecosystem studies. In: Weisser WW, Siemann E, eds Insects and Ecosystem function. Springer Berlin Heidelberg, Ecological Studies 173: 357-379