Thursday, July 12, 2012

A Bug's World

Here is a link to an abstract documenting insect/plant interaction from the Middle-Upper Triassic Madygen Formation of southwestern Kyrgyzstan. The plant in question is a lycopsid (specifically a quillwort), an ancient order of plants today represented by Lycopodiaceae (club mosses), Selaginellaceae (spike mosses) and Isoetaceae (quillworts). In modern ecosystems they are typically rather ephemeral components of the groundcover, epiphytic or aquatic. In the Carboniferous some types reached heights of 50 meters and formed the basis for the coal deposits in America.


Damselfly w/closeup of ovipositor
The insect in question is of the extinct suborder Archyzigoptera which belongs to the order Odonatoptera (dragonflies and damselflies). The interaction in question consists of ovipositor induced damage in the host plant tissue. One of the chief distinguishing features between dragonflies and damselflies is the presence of an ovipositor in damselflies used to pierce into plant tissue and lay eggs. Although both damselfly and dragonfly nymphs are aquatic predators the authors suggest the Archyzigoptera nymphs used the plants as a direct food source (damselflies inject their eggs into plants to prevent dessication of the eggs from dropping water levels). I don't know how they interpret this suborder as herbivorous but if any one out there finds something let me know.

What can be taken from this though is that we should not outright assume that interactions between pre-angiosperm plants (nonflowering plants) and ancient insects were no less complicated, involved, or implicit than the well documented coevolutionary history of many modern insects and plants.

* While on the subject of dragonfly type insects an interesting study was recently published online which argues that although atmospheric oxygen levels controlled insect size up until the Upper Jurassic, it was the advent of birds in the later Mesozoic and later bats in the Cenozoic that suppressed insect size.

The seeming lack of aerial insect predators through out most of the Mesozoic was always a bone of contention fo me. Of course you have the anuragonathids and presumably baby pterosaurs may have concentrated on insects but all in all pterosaurs show an ecological bias towards terrestrial carnivory. So it appears that dragonfly type insects would actually have been the dominant aerial insectivores until the advent of birds.



Lycopsid-arthropod associations and odonatopteran oviposition on Triassic herbaceous Isoetites

Environmental and biotic controls on the evolutionary history of insect size

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