MOTOR SYSTEMS Fect Orexactlytheoppositeeffect

MOTOR SYSTEMS Fect Orexactlytheoppositeeffect

Outside JEB iv the brain and anterior regions of the leech Keeping track of the literature intact, while simultaneously recording from isnʼt easy, so Outside JEB is a E21 and motor nerves involved in monthly feature that reports the swimming. The front part of the leech was most exciting developments in placed in sensory environments ranging experimental biology. Short from deep water (to enhance swimming) to articles that have been selected solid substrate (to stimulate crawling). In and written by a team of active the watery environment, E21 went back to research scientists highlight the enhancing swim episodes exclusively. But papers that JEB readers canʼt when the animal was faced with solid afford to miss. ground, E21 activation initiated and enhanced crawling. This suggests that instead of rigidly commanding downstream circuits to do a single behavior, E21 cells are commanding motor circuits to do an appropriate behavior based on sensory cues. MOTOR SYSTEMS This effect was completely masked in isolated preparations lacking brains. LEECH BRAIN ADDS FLEXIBILITY TO COMMAND How does the presence of the brain add NEURON OUTPUT flexibility to the circuits called into play by Spinal cords and equivalent structures in E21? The team measured how descending invertebrates (nerve cords) often generate inputs from the brain affect the strength of rhythmic motor patterns without inputs a synapse between E21 and a downstream from sensory systems or the brain. cell type known to ‘gate’ swimming. Gating Preparations that generate such ‘fictive cell activity is required to maintain swim rhythms’ have been used to uncover episodes, so when the E21-to-gating cell properties of motor circuits in many synapse is weak, triggered swim episodes animals. The (largely untested) assumption are shortened. In the absence of the brain, has always been that circuits in these E21 strongly excites gating cells; however, preparations are fundamentally the same when the brain is present, the connecting with or without the brain. However, Olivia synapses are weaker and show increased B Mullins and Otto Friesen at the University variability. The mechanism remains of Virginia recently decided to see whether mysterious, but it is possible that the this assumption is true in the leech Hirudo modulation of this synapse by descending E verbena. inputs accounts for much of the variability seen when E21 is stimulated in brain- In previous work, Mullins and Friesen attached preparations. J identified a neuron (E21) that, in the absence of the brain, appears to be a The work of Mullins and Friesen is ‘command-like’ neuron. When stimulated, it important because it shows that a long-held initiates and enhances fictive swimming assumption in motor systems research is not exclusively. The team wanted to see how always true. Motor circuits can indeed be E21’s ability to drive swimming would be fundamentally different in the absence of e modulated when the brain was intact. To do the brain, and so we need to be careful how this, they dissected out the brain and nerve we interpret data from ‘brain-less’ cord and put them in a dish. Then they preparations. Paradoxically, the team’s work evoked fictive swim episodes by shocking a also highlights how useful it is to begin d motor nerve. During swim bouts, they with such isolated preparations and then stimulated E21 and measured any resulting progressively add complexity back into i effects on fictive motor patterns. them. At the end of the day, this simple Surprisingly, the duo found that with the approach may be the best way to really brain attached, E21’s actions within the grasp how flexibility is generated in motor swim circuit were wildly variable. In some systems. s preparations, stimulating the cell enhanced fictive swimming, but in others, stimulation 10.1242/jeb.064253 Mullins, O. J. and Friesen, W. O. (2012) The brain t had no effect or exactly the opposite effect. matters: effects of descending signals on motor The presence of the brain clearly added control. J. Neurophysiol. doi: 10.1152/jn.00107.2012. flexibility to what was thought at first to be a very rigid command circuit. Stefan Pulver u Janelia Farm Research Campus Leeches swim in water but crawl on land [email protected] and the motor programs underlying each behavior are very different. The team wanted to see whether E21 activation can O drive locomotor rhythms tailored for these two behavioral states. To this end, they kept THE JOURNAL OF EXPERIMENTAL BIOLOGY Outside JEB v relationship between dewlap size and bite force. They predicted that if the handicap hypothesis is correct, and the cost of maintaining the bright dewlap maintains the honesty of the signal, then food restriction should limit both dewlap size and bite force. The question is, when the times are tough, do the lizards stay honest? To answer this question, the authors captured juvenile male green anoles and raised them to sexual maturity in the laboratory, under either food-restricted or plentiful diets. At the end of the study, both dewlap size and bite force were measured. The authors discovered that while lizards COMMUNICATION with plenty of food developed the typically CRYOPROTECTION honest relationship between dewlap size WHEN THE TIMES GET TOUGH, and bite force, the food-restricted males FRUIT FLIES ON ICE THE LIZARDS START LYING developed the bright dewlaps without The ability to survive freezing comes For the most part, it seems that animals developing the corresponding bite force. naturally to a select group of insects. These communicate honestly with one another. Therefore, food-deprived lizards were not cold-adapted insect species live in areas Individuals use various signals such as as honest as their resource-rich where they might experience sub-zero elaborate colours or ornaments to convey counterparts. Moreover, it appears that for temperatures for at least some of the year. information to others about their fighting green anoles, bite force itself is more costly But Drosophila melanogaster, the favourite ability or potential value as a mate. Signals than the bright dewlap signal. fly of researchers from several life sciences are useful, and communication can save disciplines, is better known for its time and energy. For example, mismatched As the cost of a bright dewlap doesn’t keep preference for the warmth of human rivals can avoid a risky dual if they can the lizards honest, what factors maintain kitchens and is injured by cold – even at communicate their fighting ability, and the dewlap size? The authors suggest several temperatures above freezing. Scientists weaker opponent cede to the stronger. explanations, including the possibility that would love to know how to successfully social feedback might play an important put these flies into suspended animation The lingering puzzle of animal role. In this study, lizards were raised in using cryopreservation to maintain their communication is why animals are honest individual cages, and did not interact with valuable stocks of laboratory-modified D. with one another. On the surface, it would one another. However, in the wild, melanogaster lines. In recent work seem beneficial to embellish exaggerating about bite force with a bright published in Proceedings of the National communication signals. What animal would dewlap might land a lizard in a fight where Academy of Sciences, Vladimir Koštál and not want to appear stronger and more he is overmatched and could be injured. colleagues from the Czech Republic show attractive? The classic explanation is the While more research is necessary to fully that with a few simple tricks picked up ‘handicap hypothesis’, or the hypothesis understand the factors that maintain honest from a freeze-tolerant cousin, it is possible that the cost of communication signals communication signals, it seems that, for to convert the chill-susceptible D. maintains the honesty of these signals. One lizards, honesty is still the best policy. melanogaster into a fly that can survive common example is the tail of the peacock. freezing. This lavish adornment is so cumbersome 10.1242/jeb.064246 that only strong males can haul around an Lailvaux, S. P., Gilbert, R. L. and Edwards, J. R. Earlier work by Koštál and his colleagues (2012). A performance-based cost to honest signalling impressive tail and still escape from in male green anole lizards (Anolis carolinensis). Proc. showed that Chymomyza costata, a predators. R. Soc. B doi: 10.1098/rspb.2011.2577. drosophilid fly closely related to D. melanogaster, has two requirements to Simon Lailvaux, Rebecca Gilbert and Constance M. OʼConnor survive freezing: (1) it must be in Jessica Edwards from the University of McMaster University developmental arrest (called diapause) New Orleans put the handicap hypothesis to [email protected] during an overwintering stage, and (2) it the test in a unique way using green anole must accumulate large quantities of the free lizards (Anolis carolinensis). The green amino acid proline. The authors thought a anole is an excellent subject for such a similar protocol might work for D. study, as male green anoles signal to one melanogaster. First, the team reared larvae another with a brightly coloured dewlap – a at either room temperature or a relatively flap of skin beneath the jaw that they can low temperature for D. melanogaster extend and retract – and the size of this (15°C) until they reached the final larval dewlap is an honest signal of their bite stage. Then, they subjected the larvae to force, an essential trait for fighting. temperatures that fluctuated between 6°C Importantly for the study, the dewlap is and 11°C for 3days to induce a type of developmentally unrelated to the muscles diapause. In addition, some of the insects surrounding the jaw that generate bite force, were fed diets rich in known so it is possible for the two traits to vary cryoprotectants: glycerol, proline or independently of one another.

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    3 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us