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The Planet of the Insects

By Dave Armstrong - 28 Aug 2014 14:15:1 GMT
The Planet of the Insects

The blue dasher, Pachydiplax longipennis, is a North American skimmer dragonfly, illustrating in this article how successful his wings were. Later the folding of wings and the evolution of an even more complex life cycle helped the insects towards their enormously successful diversity in so many niches; Blue dasher image; Credit: © Shutterstock

The incredible diversity of the insects is often displayed on our Facebook page. Classifying most of them is still a nightmare. The innovations employed by this 50% of the whole animal kingdom include the critical evolution of the wing, wing-folding and the caterpillar/grub/maggot/larva of a complete metamorphosis system. Our dragonfly above is possibly the earliest example of this insect evolutionary innovation, here used to indicate environmental conditions within its two habitats in - Dragonflies as Indicators. These developmental marvels are found in other animals but never completed so successfully as in the familiar Holometabola or endopterygote, 4 stage life cycle.

David B. Nicholson, Andrew J. Ross and Peter J. Mayhew of the University of York and the National Museum of Scotland located first and last occurrences of fossil forms in early insects such as the dragonflies illustrate higher origination and extinction rates than wingless groups. The rates slowed in the insects with complete metamorphosis. Other insects have a current constant but low rate of diversification, indicating a great influence on our rich insect fauna by the possession of wings and the type of life history. The paper can be found in Proc.Roy.Soc.B as - Fossil evidence for key innovations in the evolution of insect diversity.

Species-rich groups are a bit like biodiverse regions of the earth. They contain many more types of organism than other species-poor groups. The insects are an example of this in themselves, but this analysis of their groups reveals a lot more than you would think. This dataset uses past relationships to show up connections that are impossible to see in the living insects.

It is the ecological mechanisms of specialisation, escape from competition or deceasing the likelihood of extinction that can be imagined influencing evolution of a new species. Fossil evidence can uniquely show how new species could have evolved in these ways. Early records of a group show the most rapid origins (with some extinctions) of its members. This happened most recently for many insects particularly the Holometabola (complete metamorphosis) in the Eocene (at 56-34mya)

This recent evolutionary acceleration would be in beetles, flies, Hymenoptera and Lepidoptera. They have inherited, in some cases, these high rates of diversification. This seems to be due to the key evolutionary change in their life-cycle. To put this in perspective, there is also evidence that they have slowed down their rates of origination and extinction, once they, "have attained considerable richness." The beetles evolution of wing-folding is yet another example of an important cause of such evolutionary acceleration that "experiment" certainly paid off for most extant beetles, but some will have become extinct too.

The insects of the Holometabola therefore seem to have achieved more than any other group, with their key innovation of a 4-stage life history. They reached their limit, it seems, but have such diversity that present speciations are still more likely than in less well-endowed animals. Now to find out how that splendid life helps these creatures to survive in so many land habitats. Their successes result from their 2 active phases, feeding up as a larva, then breeding and dispersing as a winged adult. This ecological double-life must have many hidden advantages, even though it must have caused many extinctions!