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Znari, M., Hichami, N., Hamidy, M. E., Namous, S., & Naimi, M. , Osmotic responses of the souss valley tortoises (testudo graeca soussensis) to the effects of chronic drought in an arid area of west central morocco. Unpublished paper presented at World Congress of Herpetology. 
Added by: Sarina Wunderlich (06 Jul 2014 16:17:32 UTC)
Resource type: Conference Paper
BibTeX citation key: Znari2012c
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Categories: General
Keywords: Emydidae, Habitat - habitat, Malaclemys terrapin, Nordafrika - Northern Africa, Schildkröten - turtles + tortoises
Creators: Hamidy, Hichami, Naimi, Namous, Znari
Collection: World Congress of Herpetology
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Abstract     
Testudinidae The Souss Valley tortoises, Testudo graeca soussensis , occupies various habitats in west central Morocco, including arid environments where they are frequently confronted to unpredictable chronic droughts. These can affect their water and osmotic balances due to the lack of water and high salt concentrations in food plants. Seasonal patterns of osmoregulation were investigated during different periods between 2002 and 2012 in an arid area of West central Morocco. From April 2011 to March 2012, plasma osmolality in free ranging tortoises remained relatively constant across seasons, but not urine osmolality which showed significant seasonal changes due to variation in water availability related to chronic drought and occurrence of rainfall events. Dehydrated adult tortoises (9 males and 8 females) which experienced 6-8 weeks of drought during 2008, were captured, weighed, bleeded (100 to 300 μl) and, occasionally, their voided urinary fluid collected. They were then kept in captivity and rehydrated while provided with a mixture of fresh vegetables and lucerne and water ad libitum for two weeks. They were then reweighed, rebleeded, and voided urinary fluids taken 24h before and after an acute KCl overloading. The plasma and urinary fluid osmolalities, electrolytes‘ (sodium, potassium and chlorine) and total nitrogen concentrations were measured. The urinary fluid/plasma osmolality ratio, approaching isotonicity, in both dehydrated and potassium overloaded tortoises was much higher than in rehydrated ones (respectively 0.80 and 0.86 vs. 0.24). These were indicative of an advanced dehydration condition in free-living tortoises the urinary electrolytes‘ concentrations of which were relatively higher and comparable to those in potassium overloaded tortoises. These showed a relatively higher urine total nitrogen concentration. Implications for conservation are discussed with respect of the PEP (Potential Excretion of Potassium) hypothesis (Oftedal, 2002) according to which plants high in water and/or proteins, but low in potassium should be selected in favorable periods.
Added by: Sarina Wunderlich  
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