Article

Stress-induced accumulation of glycerol in the flesh fly, Sarcophaga bullata: evidence indicating anti-desiccant and cryoprotectant functions of this polyol and a role for the brain in coordinating the response.

Department of Biology, Wittenberg University, Springfield, OH 45501, USA.
Journal of Insect Physiology (Impact Factor: 2.5). 03/2006; 52(2):202-14. DOI: 10.1016/j.jinsphys.2005.10.005
Source: PubMed

ABSTRACT Nondiapausing larvae of the flesh fly, Sarcophaga bullata, responded to several forms of short-term environmental stress (low temperature, anoxia and desiccation) by accumulating glycerol. Elevation of this polyol, regardless of the type of stress that induced accumulation, conferred cold resistance: larvae with high glycerol levels were 3-4 times more tolerant of a 2h exposure to -10 degrees C than unstressed larvae. Protection against low temperature injury, as well as dehydration, was also attained by injection of exogenous glycerol into third instar larvae. This artificially induced cold hardiness was only temporary: when glycerol-injected larvae were exposed to -10 degrees C immediately after injection, survival was high, but none survived if they were injected and then held at 25 degrees C for 2 days before the -10 degrees C exposure. Larvae ligated behind the brain immediately after low temperature exposure failed to accumulate glycerol, but glycerol did accumulate in larvae ligated 6-24h after cold treatment, thus implying a critical role for the brain in initiating glycerol production. Interestingly, a much shorter exposure (2h) to low temperature was sufficient to reduce the maximum rate of water loss. Collectively, these observations suggest that multiple pathways may be exploited in response to stress: one pathway is most likely associated with rapid cold hardening (RCH) which generates immediate protection, and a second pathway remains activated for a longer period to enhance the initial protection afforded by glycerol.

0 Bookmarks
 · 
64 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: 1. Early-season flooding and ice entrapment at sub-zero temperatures pose significant challenges to any polar terrestrial invertebrate.2. The chironomid midge, Eretmoptera murphyi, is native to the sub-Antarctic island of South Georgia and has been introduced to the maritime Antarctic (Signy Island). While the majority of its 2-year life cycle is spent as a terrestrial larva, it is found in habitats potentially exposed to prolonged flooding.3. The current study explored the tolerance of the larvae to extended submergence, demonstrating survival for at least 28 days, underlain by their ability to respire (oxy-regulate) whilst submerged. To date, this ability is not known to be shared by any other terrestrial midge. Larvae also demonstrated notable anoxia tolerance whilst encased in ice, surviving for up to 28 days.4. These data indicate a capacity to survive ecologically relevant periods of submergence and/or ice entrapment, such as may be experienced in their natural habitats.
    Ecological Entomology 10/2014; · 1.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Insects cope with thermal stressors using mechanisms such as rapid cold hardening and acclimation. These mechanisms have been studied in temperate insects, but little is known about their use by tropical insects in response to cold stress. Here, we investigated whether cold stress (1 × 8 h and 3 × 8 h at 4 °C) triggers a metabolic response in the Madagascar cockroach Gromphadorhina coquereliana. We examined the effects of cold on the levels of selected metabolites in the fat body tissue of G. coquereliana. After cold exposure, we found that the quantity of total protein increased significantly in the insect fat body, whereas glycogen decreased slightly. Using antibodies, we observed upregulation of AQP-like proteins and changes in the HSP70 levels in the fat body of G. coquereliana when exposed to cold. We also examined the content and nature of the free sugars in the G. coquereliana hemolymph and discovered an increase in the levels of polyols and glucose in response to cold stress. These results suggest an important role of the fat body tissue of tropical insects upon cold exposure.
    Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 01/2015; 183.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: After taking vertebrate blood, female mosquitoes quickly shed excess water and ions while retaining and concentrating the mostly proteinaceous nutrients. Aquaporins (AQPs) are an evolutionary conserved family of membrane transporter proteins that regulate the flow of water and in some cases glycerol and other small molecules across cellular membranes. In a previous study, we found six putative AQP genes in the genome of the yellow fever mosquito, Ae. aegypti, and demonstrated the involvement of three of them in the blood meal-induced diuresis. Here we characterized AQP expression in different tissues before and after a blood meal, explored the substrate specificity of AQPs expressed in the Malpighian tubules and performed RNAi-mediated knockdown and tested for changes in mosquito desiccation resistance. We found that AQPs are generally down-regulated 24 hrs after a blood meal. Ae. aegypti AQP 1 strictly transports water, AQP 2 and 5 demonstrate limited solute transport, but primarily function as water transporters. AQP 4 is an aquaglyceroporin with multiple substrates. Knockdown of AQPs expressed in the MTs increased survival of Ae. aegypti under dry conditions. We conclude that Malpighian tubules of adult female yellow fever mosquitoes utilize three distinct AQPs and one aquaglyceroporin in their osmoregulatory functions.
    Scientific reports. 01/2015; 5:7795.