Elke Buschbeck

The functional organization and evolution of a novel insect visual system


In our investigation of the functional organization of the insect visual systems, we have come across one which appears to be different from any other insect previously reported: that of the twisted-wing insect Xenos peckii (Strepsiptera). Strepsiptera have been placed into their own insect order, and nearly nothing is known of their neurobiology, despite the fact that they are rather unusual in nearly every respect. While the Xenos eye superficially looks like a compound eye it in fact functions as an assemblage of separate, small, image forming single eyes. Whereas all other insect and crustacean eyes (as far as known) follow a rigid blueprint, the strepsipteran eye is organized in a drastically different manner. Instead of units consisting of long narrow channels each conveying a single point in space (all other insects), the Xenos eye is characterized by a series of pigmented cups with extended retinae, each representing a “chunk” of the visual environment. Naturally such changes in the peripheral organization also result in profound changes in the neural centers for vision and imply major evolutionary changes. Thus far we have established the general mode of function of the Xenos eye. We now propose to extend our analysis. In terms of a broader impact our findings will contribute to the larger field of biomimicry. There are three main objectives to this proposal:

  1. To deepen our understanding of the functional organization of the eye of Xenos peckii. We will use ophthalmoscopy to determine the level of lateral spread within the retinae, and the degree of overlap between neighboring units, both of which influence the neural function of the eye profoundly. Because Xenos lacks the typical neuropil cartridges of all other insects, we plan to use immunohistochemistry and light, as well as electron microscopy, to establish the framework for spatial resolution within the neuropils. We also plan to use microspectrophotometry and electrophysiology to investigate the chromatic sensitivity of the strepsipteran eye.

  2. To investigate selected developmental stages of the Strepsiptera, Xenos peckii. The origin of Strepsiptera’s unusual eye has been much debated and it has been suggested that the adult eye represents a pedomorphic stage. An anatomical investigation of different developmental stages will shed some light on that question. Furthermore, if (as has been suggested), the Xenos eye indeed evolved from a regular compound eye, it will be interesting to find out to what degree there are parallels to the development of compound eyes.

  3. To investigate the evolutionary origin of the eye of Xenos peckii. It is conceivable that the Xenos eye evolved because of visual limitations of a nocturnal ancestor. Such an ancestor could be the most basal family of Strepsiptera, Mengenillidae, which are indeed nocturnal. Thus, we plan to investigate the functional organization of the eye of Mengenillidae, and possibly other Strepsiptera and put our findings into an evolutionary framework.