Comparative short-term variation of urine concentration among three sigmodontine rodent species from contrasting habitats

We compared urine concentration capacity among three phylogenetically closed sigmodontine rodent species that occur in two distinct habitats: Necromys lasiurus (xeric), Akodon cursor and Akodon lindberghi (mesic). Water conservation ability was evaluated in 30 h-trials, with urine collected every 6 h. A control (I- water and food ad libitum) and a test (II- food and water deprivation) were conducted for each species. Body mass loss (BML), urine volume (UV), urine relative volume (UVr) and urine concentration (UC) were compared between experiments I and II for each species and among species. Changes in urine osmolality between experiments were modeled using exponential and sine functions. Circadian variation of urine concentration was obtained by sine functions fit to the experiments I. Best fit was achieved for sine functions with an accumulation term for experiments II, showing that even in stressful conditions the circadian variation is still present. Highest UC and lowest BML were obtained from Necromys lasiurus individuals, which achieved them at faster rates. The lowest UC with highest BML were obtained for A. cursor individuals at slower rates and values than A. lindberghi, which were intermediate. Necromys lasiurus is more adapted for xeric habitats achieving higher urine concentration in shorter time and faster rate than species of genus Akodon.