This essay is the first of a monthly series I plan to write about the cricket cercal system. This a well-studied system that is still revealing many mysteries. I plan to range over a multitude of issues as I would like to find out about all aspects of the insect. As an amateur I don’t have a lab or a university post but I have the vast resources of the web and can review the literature and use various modeling tools to explore the structure and computational mathematics of this particular stimulus/response system. At the very least I can gain knowledge of current problems and avenues of research and perhaps even add some insight. These essays will be supplemented by an open source educational resource called Moodle. This site, which I call Short Labs, will have a copy of each essay with citations linked to a resource and term glossary, a pdf copy, and various data that I have found and collected, including neuron structural models and NEURON simulations. I have a glossary resource that now contains over 430 citations with abstracts and I am taking notes and categorizing each paper as I read it. I have provided access to pdf copies of the open source papers and links to the paywall papers. I also have a term glossary that now contains over 60 categorized terms, including the names and pictures of the many species I have encountered. These two glossaries will continue to grow and be major resources in themselves. In addition, most formulae besides an important few will reside on the Short Labs version of the essay. This is because Moodle provides better math typesetting.
Insects perceive the world through a variety of receptors distributed over the surface of the body; hairs, bristles, and bumps which provide the insect with specific and general information about it’s immediate environment. Most insects have two appendages projecting from either side of the terminal abdominal segment. This organ is called the cercus or cercal appendage (singular: cerci). Cerci length varies from barely visible to several body lengths. This organ has a generalized usage with receptors for mechanical stress, gravity, sound, vibration, wind and defense in addition to various sex specific usages. In Orthoptera and Blattodea (there seems to be some confusion as to whether Blattodea is in Orthoptera or not, although Tree of Life Web puts them in separate orders) each cerci is covered with receptors in which the number and type vary widely (Desutter-Grandcolas, et. al., 2010). Both orders have wind-sensitive filliform hairs, but in crickets, the most striking feature is their length, greater than 1000 μ (Edwards & Palka, 1974). Orthoptera and Blattodea are two of the oldest orders of insects, going back to the Carboniferous. Fossils of Orthoptera clearly show cerci (Riek, 1954). Spiders (Barth, 2000) and other arthropods also have wind response hairs and locusts and stick insects have wind-sensitive hairs associated with flight response (Hustert & Klug, 2009). Aquatic arthropods also have water-flow sensitive hairs (Koehl, 1993), the most studied being crayfish (Herberholz, et. al., 2004). These hairs and the evolution, ecology, life history, development, behavior, and sensory to response pathways of crickets in relation to these hairs will be the subject of this series of essays.
The insect nervous system is distributed along a nerve cord running the length of the body. Swellings in this nerve cord, called ganglia, occur in each body segment. These ganglia fuse together in different combinations as the different segments have combined in different orders of insects (Mendenhall & Murphey, 1974). These regions are semi-autonomous and one disturbing feature is that if you remove the head capsule an insect will still preform many behaviors including sex (Dingle & Fox, 1966). Thus the ‘brain’ is not as integrated as in vertebrates. The major axons do connect to the brain and there are axons running back down into the nerve cord creating feedback loops, but they aren’t necessary for many behaviors. Another difference from vertebrates is that some invertebrate neurons are monopolar, the soma is attached to a neurite that contains both the dendrite root and the axon root. Thus the computations taking place between the dendrites and the firing of the axon is in the neurite while the soma is not electronically active. The sensory neurons however, are bipolar (Kell, 1997). The sensory neurons are connected to interneurons in the ganglia, the axons of some of the abdominal interneurons being quite large. These have axons reaching up through the different ganglia, connecting to other interneurons or to motoneurons which enervate the muscles. Developmentally, the sensory neurons are afferent, the axons grow inward to connect with the interneurons, while the motoneurons are efferent, the axons grow outward to enervate and actually grow the muscles.
Crickets are hemimetabolous. Northern climate crickets have a two year life history and diapause as an egg in the ground and as a nymph. Southern Crickets only have a one year life history. On hatching, the first form, called a vermiform larvae, has a membrane covering the legs and it must wiggle up through the soil to the surface. The membrane dries off and the miniature crickets grow through 8 or 9 instars (Gabbutt, 1959). During juvenile growth the cercal appendages can be damaged or even lost and will grow back the next instar and recover completely by the second instar (Murphey, et. al, 1976). Crickets are a major food source of a variety of creatures from birds and bats, to frogs and lizards, to wolf spiders and parasitic wasps (Gnatzy & Kämper, 1990). Predator activity has been found to be a major adaptive force modifying the behavior, nervous system and structure of the cercus in crickets (Desutter-Grandcolas, et. al., 2010). Study of this system took off in the 70s with the advent of different staining techniques and the electron microscope (Murphey, 1973). Presently there is enough knowledge of the system so that a loose model can be constructed, from stimulus to response. I am presently gathering all available resources and reviewing them in historical order to better understand how thinking has changed and deepened through the last 4 decades.
Finally, this series of essays intend to be an experiment in themselves. Is it really possible to be an amateur in neuroscience? What form should I use to publish my results. I would like to eventually have a paper but feel I’m a ways from that. So in the spirit of open science I intend to document my journey and hope to bring in comments and contacts.
- How to catch the wind: spider hairs specialized for sensing the movement of air.
Barth FG. 2000.
Naturwissenschaften 87(2), 51–58.
- Evolution of the cercal sensory system in a tropical cricket clade (Orthoptera: Grylloidea: Eneopterinae): a phylogenetic approach
Laure Desutter-Grandcolas, Elodie Blanchet, Tony Robillard, Christelle Magal, Fabrice Vannier And Olivier Dangles
The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 614–631
- The cerci and abdominal giant fibers of the house cricket Acheta domesticus. I. Anatomy and physiology of normal adults
J. S. Edwards & J. Palka 1974
Proceedings of the Royal Society of London, Series B, Biological Sciences, Vol 185, No. 1978, 83-103
- Response to cercal stimulation recorded in the cricket brain.
Dingle H, Fox SS. 1966.
Nature. 210, 1050 – 1051.
- Further Triassic insects from Brookvale, New South Wales (orders Orthoptera Saltatoria, Protorthoptera, Perlaria).
Riek, E. F., 1954.
Records of the Australian Museum 23(4): 161–168, plate xi.
- Hairy Little Legs: Feeding, Smelling, and Swimming At Low Reynolds Number
Contemporary mathematics, Vol 141, 1993
- Escape behavior and escape circuit activation in juvenile crayﬁsh during prey/predator interaction.
Herberholz, J., Sen, M. M. & Edwards, D. H. 2004.
Journal of Experimental Biology, 207, 1855e1863.
- Digger wasp against crickets. II. An airborne signal produced by a running predator.
Gnatzy W, Kämper G. 1990.
Journal of comparative Physiology A 167: 551–556.
- The Bionomics of the Wood Cricket, Nemobius sylvestris (Orthoptera: Gryllidae)
Peter D. Gabbutt 1959
Journal of Animal Ecology Vol. 28, No. 1, pp. 15-42
- Characterization of an insect neuron which cannot be visualized in situ.
Murphey, R.K. 1973
In: Intracellular staining in neurobiology.
Kater, S.B., Nicholson, C. (eds), pp. 135-150. Berlin, Heidelberg, New York: Springer
- Recovery from deafferentation by cricket interneurons after reinnervation by their peripheral field.
Murphey, R. K., S. G. Matsumoto, and B. Mendenhall. 1976.
J Comp Neurol 169:335–346.
- The morphology of cricket giant interneurons.
Mendenhall, B. & Murphey, R. K. (1974).
J. Neurobiol. 5, 565-580.
- Functional morphology of insect mechanoreceptors.
Keil TA. 1997.
Microsc Res Tech. 39(6):506-31.
- Evolution of a new sense for wind in flying phasmids? Afferents and interneurons
Reinhold Hustert, Rebecca Klug. 2009.
Naturwissenschaften 96(12): 1411–1419.