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Effects of ammonia loading on the loach Misgurnus anguillicaudatus
$96
Abstracts / ComparativeBiochemistryand Physiology, PartB 126 (2000) $1-S108
Effects of ammonia loading on the loach M i s g u r n u s anguiUicaudatus K. N. T. Tsui 1, Y. Jin 1, K. H. Lee l, S. F. Chew 2, D. J. Randall 3 and Y. K. Ip 1 1Department o f Biological Sciences, National University o f Singapore2Biology Division, N a n y a n g Technological University, National Institute o f Education Singapore and 3Department o f Zoology, UBC, Vancouver The loach Misgurnus anguillicaudatus inhabits the dee field in Southern China. It encounters drought during s~nnmer and ammonia loading during agricultu~l fertilization. When M. anguillicaudatus is exposed to ammonia loading condition, ammonia is not detoxified to urea or glutamine. Upon exposure to 30 mM NH4CI, alanine level increases transieraly after 12 h and returns to the control level thereatter. This indicates that M. anguitlicaudtrtus resorts to partial amino acid catabolism in the beginning to slow down the rate of internal ammonia production. Two major strategies are deployed by this loach to avoid ammonia intoxication. One strategy is to tolerate the high level of ammonia built up in its tissues, and the plasma ammonia level is the highest among fishes. Presumably, the high plasma ammonia level would revert the NH3 gradient to slow down the penetration of ammonia in the ambient medium, and might even facilitate the excretion of internally produced ammonia. Another strategy adopted by this loach is to excrete proton equivalents to lower the pH of the external medium. It is capable of lowering the pH of the external medium containing NI-I4CIwithin a short period of time. Such a strategy of "environmental ammonia detoxication" is superior as it would lower the NH3 concentration in the medium and slow down its penetration. At the same time, it would facilitate the excretion of internally produced ammonia as the ammonia level in the plasma builds up.
C R I T I C A L T H E R M A L M A X I M U M OF T I l E A F R I C A N A N T , O C Y M Y R M E X S P . : P O S S I B I L I T Y OF A N E W R E C O R D P R O M P T S A R E V I E W OF M E T H O D O L O G I E S .
Turner, R.*, Lightort, J.R.*, Turner, J.S. D *University o f N e v a d a Las Vegas, nState University o f N e w
York
In a desert, the extreme stresses of heat load and water deficit join with those of predation and competition to define the functional foraging niche of its species. Competition and predation can be diminished by utilizing a thermal window that more physiologically limited species avoid. Those that can, do well. harvesting for themselves potential ,,heatfall." Insects exhibit the highest heat tolerance among animals; of those insects studied, the ant is championed for the honor of ,,most thetmo-toierant" by Wchner, Marsh and others. Several African and a few Australian species have been studied to determine the ,critical thermal maximmn" (CTms~) and tolerance ranges for each species. Other studies indicate biochemical mechanisms which may drive such behavioral strategies as they publish the rectal-to-date of the most heat tolerant animal. Although the desert ant is diverse in kind and broad in geographic distribution, the physiological, data accumulated on its thermal traits is sparse, neglecting a field of New World, Old World and as yet un-typed candidates. In this study, thermal perameters of a heretofore unstudied Kalahari Desert Myrmicine, Ocymyrmex sp. [probable typespecimen: R. Snelling, pers. com.] were measured. The question of induction of heat tolerance was tested but the data acquired was insufficient to imply its presence or absence. The CTm~ of this species at 55 °C equals or surpasses the record noted for the Saharan species Cataglyphis bombycina or its Australian Formicine cousin, Melophorus spp. In order to examine such a declaration, a comparative synthesis of thermal data within the taxon is presented. Distinctions in the methodology and criteria used in various studies to determine arthropod C T ~ are discussed, stressing the need to develop a more standardized approach for the measurement of a critical adaptation.
Abstracts / ComparativeBiochemistryand Physiology, PartB 126 (2000) $1-S108
Effects of ammonia loading on the loach M i s g u r n u s anguiUicaudatus K. N. T. Tsui 1, Y. Jin 1, K. H. Lee l, S. F. Chew 2, D. J. Randall 3 and Y. K. Ip 1 1Department o f Biological Sciences, National University o f Singapore2Biology Division, N a n y a n g Technological University, National Institute o f Education Singapore and 3Department o f Zoology, UBC, Vancouver The loach Misgurnus anguillicaudatus inhabits the dee field in Southern China. It encounters drought during s~nnmer and ammonia loading during agricultu~l fertilization. When M. anguillicaudatus is exposed to ammonia loading condition, ammonia is not detoxified to urea or glutamine. Upon exposure to 30 mM NH4CI, alanine level increases transieraly after 12 h and returns to the control level thereatter. This indicates that M. anguitlicaudtrtus resorts to partial amino acid catabolism in the beginning to slow down the rate of internal ammonia production. Two major strategies are deployed by this loach to avoid ammonia intoxication. One strategy is to tolerate the high level of ammonia built up in its tissues, and the plasma ammonia level is the highest among fishes. Presumably, the high plasma ammonia level would revert the NH3 gradient to slow down the penetration of ammonia in the ambient medium, and might even facilitate the excretion of internally produced ammonia. Another strategy adopted by this loach is to excrete proton equivalents to lower the pH of the external medium. It is capable of lowering the pH of the external medium containing NI-I4CIwithin a short period of time. Such a strategy of "environmental ammonia detoxication" is superior as it would lower the NH3 concentration in the medium and slow down its penetration. At the same time, it would facilitate the excretion of internally produced ammonia as the ammonia level in the plasma builds up.
C R I T I C A L T H E R M A L M A X I M U M OF T I l E A F R I C A N A N T , O C Y M Y R M E X S P . : P O S S I B I L I T Y OF A N E W R E C O R D P R O M P T S A R E V I E W OF M E T H O D O L O G I E S .
Turner, R.*, Lightort, J.R.*, Turner, J.S. D *University o f N e v a d a Las Vegas, nState University o f N e w
York
In a desert, the extreme stresses of heat load and water deficit join with those of predation and competition to define the functional foraging niche of its species. Competition and predation can be diminished by utilizing a thermal window that more physiologically limited species avoid. Those that can, do well. harvesting for themselves potential ,,heatfall." Insects exhibit the highest heat tolerance among animals; of those insects studied, the ant is championed for the honor of ,,most thetmo-toierant" by Wchner, Marsh and others. Several African and a few Australian species have been studied to determine the ,critical thermal maximmn" (CTms~) and tolerance ranges for each species. Other studies indicate biochemical mechanisms which may drive such behavioral strategies as they publish the rectal-to-date of the most heat tolerant animal. Although the desert ant is diverse in kind and broad in geographic distribution, the physiological, data accumulated on its thermal traits is sparse, neglecting a field of New World, Old World and as yet un-typed candidates. In this study, thermal perameters of a heretofore unstudied Kalahari Desert Myrmicine, Ocymyrmex sp. [probable typespecimen: R. Snelling, pers. com.] were measured. The question of induction of heat tolerance was tested but the data acquired was insufficient to imply its presence or absence. The CTm~ of this species at 55 °C equals or surpasses the record noted for the Saharan species Cataglyphis bombycina or its Australian Formicine cousin, Melophorus spp. In order to examine such a declaration, a comparative synthesis of thermal data within the taxon is presented. Distinctions in the methodology and criteria used in various studies to determine arthropod C T ~ are discussed, stressing the need to develop a more standardized approach for the measurement of a critical adaptation.