Monthly Archives: August 2010

Pollen viability in Mediterranean orchids

Pollen viability in Mediterranean orchids
Pollen viability in Mediterranean orchids

Evaluation of pollen viability has generally been confined to a relatively low number of species. Bellusci et al. study five related Mediterranean orchid genera (Anacamptis, Orchis, Dactylorhiza, Ophrys and Serapias) that are characterized by different types of deceptive pollination and find that pollen viabilities of species groups with different deception types have significant differences, with sexually and shelter-deceptive species exhibiting a shorter life span than food-deceptive species. They propose that this relationship can be attributed to the different types of reproductive barriers, pre- or post-zygotic, that characterise Ophrys and Serapias and the food-deceptive species, respectively.

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Genetic relationships between sympatric and allopatric Casearia

Genetic relationships between sympatric and allopatric <i>Casearia</i>
Genetic relationships between sympatric and allopatric Casearia

Casearia sylvestris var. sylvestris inhabits humid, dense forests, while var. lingua is restricted to xeric habitats, yet despite differences in morphology and habitat preference, intermediate forms exist in transitional environments, complicating the delimitation of the taxa. Cavallari et al. examine nine microsatellite markers and conclude that the two C. sylvestris varieties are relatively independent biological units, rather than representing the genetic continuum of a single species. Evidence for the existence of putative hybrid zones between these two varieties is also considered.

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The Genetics Behind Evolution

Highlight Annals of Botany cover

Highlight Annals of Botany cover

Over the years, hundreds of papers have been published describing the genetic changes that occur during evolution of plants, and the differences evident between individual species. An equally high number of papers has been published about the definition of species, their separation and naming. Many have joined discussions of where and why new species form – by reproductive barriers or island colonization for example. But only now are we realizing that there is a strong genetic component to these events: speciation does not ‘just happen’.

We plan most highlight issues of Annals of Botany a year of more in advance. But the seven papers for the September Highlight issue, “Genes in evolution”, was just because these papers were all submitted around the same time. This shows that the control of diversity and speciation is a really hot-topic, where advances unforseen a year ago are now taking place – and the implications are widespread from the consequences of changing climate on natural ecosystems, to the breeding and selection approaches for new and improved crops.

The review by Rieseberg and Blackman (2010) identifies no less than 41 genes that can lead to reproductive isolation of populations. Interestingly, the genes are very diverse, and include those which have prezygotic and postzygotic effects. Simple geographical isolation is not seen as the only widespread cause of speciation and the cessation of gene flow between populations; nevertheless, both larger and smaller features of geography lead to isolation of populations, and He et al. (2010) are able to show an example where the genetic structure of a species, Banksia hookeriana, is not solely dependent on the structure of a landscape, in this case where the population is located on sand dune crests physically separated by uninhabitable hollows. Occasional long-distance dispersal of seeds or movement of individuals from one population to another maintains connectivity within the species and prevents isolation. In contrast, Nomura et al. (2010) provide insight into the phylogeny and implications of habitat diversity. Farfugium (Asteraceae) is a monophyletic group associated with a wide range of habitats, including forest understorey (sciophytes), coastal crags (heliophytes) and riverbeds (rheophytes) in an archipelago in east Asia. They conclude that isolation on islands and subsequent parallel adaptation events followed migration over Quaternary land-bridges along the distribution range. Uninformative DNA sequence variation coupled with highly divergent morphologies suggest that adaptive diversification was rapid.
The other four papers make conclusions related to the genetic diversification and selection seen in crop plants. The Tehuacán Valley in Mexico provides a remarkable ‘natural laboratory’ for study of human selection effects on plants, because there are well over 100 native plant species where artificial selection is being practiced and these silvicultural and cultivated populations co-exist with wild populations. Parra et al. (2010) study the cactus Stenocereus puinosus and find that despite selection for larger and sweeter fruit, there are high levels of gene flow that have promoted morphological divergence and moderate genetic structure between wild and managed populations, while conserving genetic diversity. Hence, despite strong selection, there is no evident genetic bottleneck that might limit breeders of the fruit in future, unlike that seen in many other domesticated species.
As noted above, hybridization or polyploidy – speciation by whole-genome duplication – can lead to new, and reproductively isolated, species in a single event. Evidence of evolutionarily recent polyploidy events is seen in half of all plants, and contributes significantly to plant biodiversity. Shi et al. (2010) look at ancient events, or paleopolyploidy, that may be inferred from genomic data and their analysis of the nuclear genomes of kiwi fruit (Actinidia) and related Ericales shows evidence for at least two paleopolyploidy events. Their results provide evidence that gene-family methods are able to reliably uncover ancient polyploid speciation events.
Soybean, Glycine max, is an important tetraploid crop, but there are still gaps in its domestication history. Guo et al. (2010) carry out an extensive study of the diversity of soybean from its South China centre of origin using molecular markers, and propose a single origin with a moderately severe genetic bottleneck during domestication. Wild soybeans in this region have an unexploited and valuable gene pool for future breeding, but, unlike the situation in Stenocereus, it will require careful study and extensive crossing with selection to introduce this diversity into the germplasm pool available to plant breeders. The final paper in the Highlight presents an important example of how diversity from a wild species can be used in one of the world’s three most important grain crops. Rice, Oryza sativa, requires fertilization to set seed, but the temperatures experienced during hot weather (over 32–36 °C) induce sterility. Considering that such temperatures are rarely reached in the early morning, Ishimaru et al. (2010) introgressed an early-morning flowering (EMF) trait from wild rice, O. officinalis, where anthesis occurs soon after sunrise. Although the temperature effect on sterility itself was similar in the two rice species, the avoidance of high temperatures by a few hours caused by the early-morning flowering trait leads to significantly increased fertility in the line with introgression of the EMF trait.
Together, these seven papers add considerably to our understanding of genetics in a broad evolutionary context. The results are of significance for wild species, with implications for whole ecosystems, and indeed the species used as examples in these papers are those of coastal, island and duneland systems that are particularly threatened by changes including urban ‘development’, sea-level alterations, storm frequencies and temperature. The crop papers show how knowledge of the mechanisms of evolution and associated genes can impact on our exploitation of biodiversity in crops and their wild relatives.

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Tetrad shape and aperture pattern ontogeny in pollen

Tetrad shape and aperture pattern ontogeny in pollen
Tetrad shape and aperture pattern ontogeny in pollen

Patterns of male cytokinesis are suspected to play a role in the diversity of aperture patterns found in pollen grains of angiosperms. By comparing two eudicots, Epilobium roseum and Paranomus reflexus, that exhibit intra-individual variation in aperture number, Abert et al. demonstrate that the positions of apertures are determined by the way additional callose is deposited once the cytoplasms are severed in cytokinesis. The recorded variation in tetrad shape is correlated with variations in aperture pattern, demonstrating the role of cell partitioning in aperture pattern ontogeny.

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Hopefully I’m running out of wrong ways to issue a press release

Farming a Gray Ghost Organ Pipe Cactus

Farming a Gray Ghost Organ Pipe Cactus. Credit F. Parra.

We have a new press release out, this time on biodiversity and indigenous farming in Mexico. As you can see the photo is stunning, so it’s a bit of a shame that it didn’t go out with the text for some reason. You can download the massive version of the photo here (right-click or cmd-click and ‘Save as…’. I shall have a go at blogging this tonight because there’s some interesting context I had to cut from the press release.

In the spirit of making lemonade from lemons, I shall pretend this was a gimmick to announce the release of a new issue. The paper is part of a Genes in Evolution section in the September issue of Annals of Botany that went online today.

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Evolution of mycoheterotrophy from mixotrophic ancestors

Evolution of mycoheterotrophy from mixotrophic ancestors
Evolution of mycoheterotrophy from mixotrophic ancestors

Nutritional changes associated with the evolution of achlorophyllous, mycoheterotrophic plants have not been inferred within a robust phylogenetic framework. Motomura et al. examine variations in heterotrophy in association with the evolution of leaflessness using a chlorophyllous/achlorophyllous species pair in Cymbidium (Orchidaceae) and demonstrate that mycoheterotrophy evolved after the establishment of mixotrophy rather than through direct shifts from autotrophy to mycoheterotrophy. This may be one of the principal patterns in the evolution of mycoheterotrophy.

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Evolution of long scapes in Drosera

Evolution of long scapes in <i>Drosera</i>
Evolution of long scapes in Drosera

Conventional wisdom is that long scapes in insectivorous plants have evolved to provide spatial separation between flowers and traps, preventing pollinators from being captured. However, Anderson studies two sympatric species with identical pollinators, Drosera cistiflora, with an upright growth form but a short scape, and D. pauciflora with a basal rosette of traps and a very long scape, and finds that no pollinators are trapped by either species. Manipulation of flower height in D.cistiflora suggests that long scapes probably evolved to attract pollinators.

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Don’t Be So Cerebral?

Bob Blumer - Surreal Gourmet. Photo by Roland Tanglao.
Is the way to someone’s heart through their gut? Photo Bob Blumer – Surreal Gourmet by Roland Tanglao.

I’m following my introduction to Don’t Be Such a Scientist with a look at the first chapter of the book. It opens with Randy Olson’s four organs model of communication based on the Head, Heart, Gut and Sex Organs. The Head is rational and responds to facts. It’s the organ that scientists respond to, at least in an ideal world. Olson argues that to connect with most people you have to move communication from the Head to the Heart so that it’s a matter of feeling. Ideally you should even move into the Gut a less rational place that’s about what you instinctively know, even if it’s wrong. If you really want a connection the goal is the Sex Organs an utterly chaotic region ruled by desire. I have a couple of problems with this.

One is that I don’t like this model. If Olson’s right then if change is going to happen then it’s not going to happen through Humanity collectively acting rationally. No matter what side of the political spectrum you sit on, you’d almost certainly like decisions to be made on an intelligent basis. I might know this intellectually, but to act on it as fact feels like a surrender. Of course whether or not I like it doesn’t make it true or false. It does prime my defences against his argument.

The second problem is that it’s demonstrably false. Rational fact-based argument doesn’t work? Well it does for me, and for most of the people I know. So clearly he’s simply wrong.

Almost.

The fact-based communication strategy might work for me, but my belief it works is based on personal experience. Even bringing people I know into account doesn’t work because an awful lot of people I know work in the university. “It works for me” is a Heart or Gut-based argument in Olson’s model, not Head-based. Even if it does work for me, it doesn’t follow this one approach, or any one approach, will work for everyone. A difficulty for me at the moment is that if I’m writing a press release then I do have just the one shot.

Another argument against Head-based writing, if you’re targeting a mass audience, is that you have to look at how scientific training works. Degrees spend at least three years teaching scientific processes and another one or two years at M-level before you can start your PhD. Digesting knowledge in that way is a skill, and scientists can still be ignorant of what makes a compelling argument in fields outside of their own expertise. So should a good press release (or blog) for a general audience take this into account or take the view that if people really want the information they should work for it. The latter approach is probably safer. If I do that I can say any failure is down to the shallowness of the media and make a virtue of “refusing to dumb down”.

I’ve decided that the experts on the papers in Annals of Botany are the people who wrote them. It’s a pretty obvious conclusion. If I were to try to replicate that kind of writing, not only would I be duplicating their efforts, but also I’d be duplicating them badly. That means thinking more about writing, and Olson’s model is a good place to start thinking from. I had a nibble at moving the writing to the heart and sex organs in this release on Sundews. Fortunately the editors have been clear that they’re after people between Botanical students to research scientists, so falling short and writing too cerebrally isn’t a disaster. If I go too far in the other direction there’s plenty of people who’ll let me know.

See also Don’t be so cerebral on Uncommon Ground.

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Mixed mating and colonization potential of a fern

Mixed mating and colonization potential of a fern
Mixed mating and colonization potential of a fern

Environmental change leads to increasing selection pressure on the capacity of plants to colonize new areas. Wubs et al. show that the colonization success of the fern Asplenium scolopendrium is linked to its mating system, with selfing rates varying greatly among genotypes. Single-spore establishment of new populations requires selfing genotypes, but later immigrants are more successful if they are outcrossing. The results provide further evidence against the overly simple dichotomous distinction of fern species as either selfing or outcrossing.

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