Odd pollinators

by Matthew Cobb

Insects and plants are intimately linked in terms of their ecology and evolution. Insects and vascular plants both first appear in the fossil record around 400 MY ago, at the beginning of the Devonian, as terrestrial ecology changed to allow the colonization of the land.

Then about 20 MY later, the first arboreal plants appear, and insects developed wings (probably from ancestral gills – the same genes are now involved in the development of arthropod gills and insect wings). However, things really went crazy in the middle of the Carboniferous, when seed plants first appeared, and the insects underwent a massive diversification, or “radiation” as paleontologists call it.

In this period, all of the major insect groups appeared, with only one (the Palaeodictyopterida – they looked a bit like dragonflies) disappearing between then and now. Insects even breezed through the end-Permian mass extinctions around 248 MY ago, when around 95% of marine species disappeared, profiting from the changed ecosystem to undergo a further wave of radiation.

By the time the flowering plants (“angiosperms”) appeared around 100 MY ago (flowers are a relatively recent invention), the insects were established as one of the dominant features of the terrestrial ecosystem, and quickly took advantage of the new plant arrivals. Although insects (and their larvae) munch through plants, the relation can also be mutually beneficial, especially with regard to pollination. Flowering plants generally provide a sucrose reward (nectar) for insect visitors, which in turn inadvertently carry off pollen to other plants of the same species, spreading the genes about. This mutually beneficial relation is shown by the parallel radiation of angiosperms and lepidopterans (butterflies and moths).

Darwin famously predicted that the comet orchid, which has an amazingly long “nectar spur” (the structure holding the nectar – it can be over 30cm long), must be pollinated by an insect with an equally long proboscis. He was right – it turned out to be the nocturnal hawk moth, with a 35cm long proboscis.

But what happened before there were flowers? Did insects simply eat the gymnosperms and ginkos that covered the Earth, or were they still involved in pollination – and how? Were all plants simply wind-pollinated?

Two recent discoveries give some insight into this. First, back in November, a stunning set of fossils was described in Science, showing in exquisite detail the mouthparts of some Mecopterans – scorpion flies. Nowadays they are a pretty insignificant bunch of around 600 species (and, of course, they are not flies…) [see comment #3 below!].

Source: Science

The fossils (and contemporaneous amber specimens) showed long, flexible probosces, and sucky ends that the insects could have used to suck up nectar-like substances produced by gynmosperms. The authors, led by Dong Ren of Capital Normal University, Beijing, conclude:

The presence of scorpionfly taxa suggests that siphonate proboscides fed on gymnosperm pollination drops and likely engaged in pollination mutualisms with gymnosperms during the mid-Mesozoic, long before the similar and independent coevolution of nectar-feeding flies, moths, and beetles on angiosperms.

Now another insight into unusual pollinators has come from Reunion Island, down in the south Indian Ocean, next to Mauritius (despite its distance from Europe, Reunion is part of France). Writing in the Annals of Botany, Claire Micheneau describes how she set out to find out how an unusual orchid,Angraecum cadetii (related to Darwin’s star orchid), was pollinated. [See also this BBC page.] They discovered that the animal responsible was an unusual – and unnamed – cricket with unusually long antennae:

These crickets, which are nocturnal foragers, reached flowers by climbing up leaves of the orchid or jumping across from neighbouring plants and probed the most ‘fresh-looking’ flowers on each plant.

They even provide a video, which should be visible below (although perhaps not to readers outside the UK; try here if not):Vodpod videos no longer available.

This is the first time that a cricket has been described as a pollinator, but it gives some indication of the variety of ways that pollination could have taken place even before flowers.  Orthopterans (crickets and grasshoppers) appeared at the same time as the gymnosperms; although people generally assumed the insects would have eaten the plants, the example of the scorpion flies suggests they might also have played a role in pollination.

[First posted at z-letter.com]

5 Comments

  1. Posted January 12, 2010 at 9:40 am | Permalink

    Isn’t that like saying that spiders in the past might have been vegetarian because one largely vegetarian species has now been found?

    Anything’s possible, it’s the best inference that matters.

    The scorpionflies do look like good pollinators, by contrast, and yet as I recall that one caveat to the conclusion that they were is that none of the specimens in amber had any pollen on them. Which seems unlikely, but still possible.

    Glen Davidson
    http://tinyurl.com/mxaa3p

  2. TheBlackCat
    Posted January 12, 2010 at 9:47 am | Permalink

    It isn’t like we lack insect-pollinated gymnosperms today. Welwitschia comes to mind. I am getting mixed messages about what specifically pollinates it, some sources say flies and other wasps. Both of which are known to pollinate other plants, if I recall correctly, so it isn’t really an odd pollinator, although the pollinated certainly is very odd 😛

  3. Matthew Cobb
    Posted January 12, 2010 at 10:43 am | Permalink

    I have only just noticed this great post on Boreids, a kind of Mecopteran, over at the excellent Catalogue of Organisms:

    http://catalogue-of-organisms.blogspot.com/2010/01/name-bug-boreus.html

    Chris Taylor also nuances my suggestion that Mecopterans are not flies by pointing out that flies might be Mecopterans…

  4. Dr.John R. Vokey
    Posted January 12, 2010 at 9:53 pm | Permalink

    How about: “way cool!” As not one of the cognoscenti, I found the piece fascinating.

  5. MadScientist
    Posted January 14, 2010 at 7:39 am | Permalink

    So the answer to “how is this orchid pollinated” is: By Jiminy!


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