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Archive for the ‘Pollination biology’ Category

Evolving specialized pollination, where you eventually develop a complete dependence to a single pollinator species, is both a risky bet and a win-win path to success. That is, dependence is critical to your reproduction, since you will only succeed to make seeds when your pollinating pet lives around. Mind you, this is not only tricky  because you need to adjust to its needs and way of life, it’s also that you’ll only be able to expand within its own ecological niche.

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It’s so hard to just say « no! », when you happen to be a pollinator.

Because, you know, nectar is not only food. It is not only highly sweet, nor just energetic like corn syrup. Because of its high sugar contents (many oses at many doses), nectar also happens to make the delight of microbes that made the trip to the flower via insect transportation. For this reason, nectar is often getting fermented.

In other words, don’t trust pollinators when then assure you it’s just « feeding » behaviour.  They constantly understate their actual need for nectar. It’s making little lights in their reward limbic system. They’re irremediably addicted, but they would never acknowledge it.

But would it be so true as to classify some pollinators as junkies?

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Okay, so it’s the beginning of the first round of Application Time here, and because of teaching crazziness I’m quite late with regard to paper writing, so I fear I’ll have to let Seeds Aside further swamped into the slowing down spiral. Meanwhile, I’m happy to learn my latest paper is available on the interthing so I tell you as well… (Though if I want to get more now, I’m left with writing, and I do):

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Just published this month. But this is a small case of self promotion, since I got a somewhat low rank in authorship… But hey, that’s still counting, isn’t it?* :-p

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Here is the my BBB 2008 ‘report’ for insects and arachnids during a short bioblitz at the Black Gate Woods.

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Orchids have the strangest and most fascinating blooms. Not that gardeners care. Not only that Darwin was right. But because orchids have their share of evolutionary master tricks. When it comes to reproduction, orchids always strike. You may remember how Epipactis helleborine produces a deceiving caterpillar scent to get its pollination service from wasps. Or the most widespread orchidean reproductive strategy: a flower mimicking their pollinator’s female (visually, but also via scenty insect sexual pheromones) and luring those poor male bees and wasps that desparately try to mate with a flower (usually reproducing the orchid, but not their own kind…).

Thus, many orchid flowers are just plain porn (to hymenoptera, I mean). But how far can the little critters be deceived in their mating attempt? In the Australian tongue orchids (Cryptostylis species) [1], the lure is working so far as to have their pollinators ejaculating on the flowers, and thus wasting precious gametes that would have otherwise well served them to an actual reproduction. One has to realise the cost of wasp porn… (though the abused wasps usually don’t get tricked twice).

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Epipactis helleborineAttracting pollinators is not only about being colourful but to produce a decent scent. With decent, it is not necessarily meant a perfume-like odour, but something attracting a pollinator. This may be a highly specific task, because when you aim to attract specific pollinators, you decrease the odds that it will disperse your precious gametes to any other plant. If you succeed to make it loyal and visit your own kind next, it will prove highly rewarding because you have some hope to sire offspring instead of wasting pollen…

Epipactis atrorubens

 And that’s what Epipactis helleborine (left) is doing. It’s producing a scent that attracts a rather specific pollinator (well, “specific” with regard to its pollinating behaviour at least), common wasps. This scent is similar to compounds emitted by herbivore-damaged plants. Wasps are thus lured into thinking they will find some fleshy caterpillar, and go their way to the orchid. Hereafter, they still obtain a somewhat interesting reward (a sweet nectar), that may lead to the wasp further visiting Epipactis helleborine. But it’s still a lure, not a fair game. Apparently, a closely related species also mainly pollinated by wasps, Epipactis purpurata, is using the same strategy, while another species within the Genus, Epipactis atrorubens (right), doesn’t (it is specialized on being pollinated by bees, which are contributing to the flower scent too, but for another reason ;).

Read the complete story at Not exactly Rocket Science (but still with rocking posts) here

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That may not be news (the study in question* was published in 1992), but this is a rather interesting result… Bees are able to detect if flowers have been visited by another bee, and more readily leave those that have recently been. This behaviour is not difficult to explain: you better have to move if there is less to forage (don’t waste your time where reward is probably lower). Direct cues to assess nectar availability can be used by bees (when nectar content of a flower can be seen, or smelled), but this way isn’t always possible with any flower morphology and requires some level of inspection, i.e. there is a time cost. But bees are making the process easier by marking the flowers they visit with a special scent.

The effect of the scent was here experimentally reduced in the study (with artificial flowers) via an air extractor. When on, flower rejection dramatically decreased, flower inspection and visit time were also increased, while the number of visits was unchanged between the two experimental conditions. I find it amazing how far and finely tuned behaviours have evolved in these insects…

But we may also notice that the experimental flowers were still providing a great reward even after they were visited. This means bees in the experiment were stuck into their innate foraging method and losing resources aside. This probably means there is no such thing as a continuously rewarding flower in nature… :-)


M. Giurfa and J.A. Nunez (1992).Honeybees mark with scent and reject recently visited flowers. Oecologia 89: 113-117.

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Brenne_20080428_051Just back from a wonderful area, La Brenne, which is a natural regional park (more here) constituted of hundreds of lakes and wet meadows. Since the time is rainy at spring, and leaves are just , it’s been an amazing bath in acute greeny greens…

Moreover, since spring almost never comes alone, we’ve been gratified by many good surprises (plants of course, but not only, so you can keep reading… ;).

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A recurrent argument in favor of protecting nature is of course that new drugs and cures may hide behind biodiversity, so that we may best protect to our best, with the hope we are buying in the right tombola ticket (whenever we can’t save everything). Of course this is of importance (even though we overlooked the simple fact that recreational and cultural values of biodiversity should be enough to convince protecting is still the best we have to do), but translating the effort into the actual benefit is a very long enterprise. There are examples of interests but they are way too scarce.

But today, I’d like to investigate yet another aspect of biodiversity (variation within species instead of the more general “species richness” that we mean when speaking about biological diversity), and how the biodiversity thing can be more directly of importance with regard to health issues than finding the new cure to everything. [picture of olive tree courtesy of Luigi Rosa]

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