The research of my group is primarily concerned with the evolutionary response of plants to metal-contaminated soils, both natural (e.g. serpentine) or man-made (e.g. mines). We are also interested in using modern molecular techniques to study plant population and ecological genetics, particularly with respect to the interaction between plants and their pollinators. Much of my work has used Mimulus guttatus as a model system.
The soils overlying serpentine (ultramaphic) rocks contain high levels of heavy metals, particularly nickel, cobalt and chromium, and in many areas the flora colonising these soils is characterised by a number of species that are endemic to this substrate. It is not clear exactly what adaptations, if any, these species show, nor what processes drive the evolution of species in this context. We are investigating the morphological and physiological differences between serpentine endemics and excluded species in the Mimulus guttatus complex, and using modern molecular techniques (RAPDs) to construct a genomic map which we can use to quantify the number of genes determining the differences between the species.
Personnel:
Collaborator:Prof. Konrad Bachmann, IPG Gartersleben
Using primarily Mimulus guttatus, we have been investigating the genetics of copper tolerance. We have shown that there is one major gene for this character, with additional minor genes that amplify it. We looked at the costs of this adaptation: what prevents these plants growing in normal soil? Essentially we disproved the two current hypotheses, namely that tolerant plants grow slower and have a higher copper requirement than normal plants, but were unable to find any alternative explanation. We are also looking at whether the tolerance to different metals is independent of each other: many of the postulated mechanisms should result in, say, copper tolerance also giving, say, cadmium tolerance. So far we have not found any such co-tolerances.
Personnel:
Collaborators: Dr Fran Harper, Ms Sue Smith, Dr G. H. Tilstone
Most metal-tolerant plants restrict the metals to their roots, and translocate very little to their aerial parts. However, some plants endemic to metal contaminated sites do translocate substantial quantities, and these hyperaccumulators are of profound interest both scientifically and because of their economic potential. Scientifically, it is important to understand how plants can translocate and withstand such enormous amounts of metals, while economically these plants could be used to decontaminate metal-contaminated soils in situ. We looked at some rare copper hyperaccumulators from Zaire, and found that while they are very copper tolerant, they do not show any exceptional ability to translocate copper. We are currently working on a zinc hyperaccumulator Arabidopsis halleri (=Cardaminopsis halleri), which is closely related to Arabidopsis thaliana, to understand the genetics and molecular biology of the phenomenon. We are also looking at the evolution of this character, testing the hypothesis that the metal accumulation has evolved as an anti-feedant, and the phylogeneticdistribution of the character in the genus Thlaspi. But if using these plants to bioremediate soils were an option, it might have ecological consequences because of the inputs of metals into the food chain. We have been looking at the flow of arsenic from hyperaccumulators of this metal on arsenic mines in Devon and Cornwall through the food chain from small mammals to raptors.
Personnel:
Technician: Quinton Cumbes.
Collaborators: Dr B.V.Erry, Dr Andy Meharg (Aberdeen) and Dr Richard Shore, ITE, Monks Wood (on the arsenic food chain project). Dr P. Saumitou-Laprade, Dr V. Bert.
PhD students: Jane Kyriacou, Simone Huitson, Stacy Taylor
Variation in plant morphology and rewards will influence the behaviour of pollinators, which in turn will affect the patterns of pollen transport and deposition. We have shown that when plants offer rewards, pollinators show a preference for common flower colours, which should result in selection against floral diversity. However, when plants deceive pollinators, and offer no rewards, the pollinators over-sample rare colour morphs, which should promote diversity in colour, and produce differences in the genetic structure of populations. We have shown that there is negative frequency dependent selection in such plants for rare colour morphs, both in laboratory and field experiments.
Personnel:
Collaborator: Dr Ann Smithson.
PDRA: Dr Luc Gigord
In the Mimulus guttatus complex, a number of species have evolved autogamy associated with the evolution of a narrower ecological range than their outbreeding progenitor, M. guttatus. This is a common pattern in flowering plants, and selfing is often believed to have arisen as a means of protecting co-adapted gene complexes. But how effective is selfing at preventing gene flow? Selfing species which co-exist with an outbreeding species will tend to receive pollen from the outbreeder, and thus gene flow will be one-way from progenitor to derivative. We are testing the effectiveness of selfing as a barrier to gene flow. Another common feature associated with the evolution of selfing is a reduction in pollen size. We have found that pollen size is variable within M. guttatus, and theory suggests the variation in pollen size should be associated with ecological factors, particularly pollinator visitation rates. We are testing the heritability of this character, and the pleiotropic consequences of this variation in pollen size.
Personnel:
Collaborators: Dr J.E.Cresswell, Dr A. Smithson
PhD students: Ellen Lamborn, Jo Onparn
Prof Mark R. Macnair,
Email: M.R.Macnair@exeter.ac.uk
Last updated 17/01/01