Hummingbirds arrest their kidneys at night: diel variation in glomerular filtration rate in Selasphorus platycercus.
Small nectarivorous vertebrates face a quandary. When feeding, they must eliminate prodigious quantities of water; however, when they are not feeding, they are susceptible to dehydration. We examined the role of the kidney in the resolution of this osmoregulatory dilemma. Broad-tailed hummingbirds (Selasphorus platycercus) displayed diurnal variation in glomerular filtration rate (GFR). During the morning, midday and evening, GFRs were 0.9+/-0.6, 1.8+/-0.4 and 2.3+/-0.5 ml h(-1), respectively. At midday, GFR increased linearly with increased water intake. During the evening, hummingbirds decreased renal fractional water reabsorption linearly with increased water intake. Broad-tailed hummingbirds appeared to cease GFR at night (-0.1+/-0.2 ml h(-1)) and decreased GFR in response to short-term ( approximately 1.5 h) water deprivation. GFR seems to be very responsive to water deprivation in hummingbirds. Although hummingbirds and other nectarivorous birds can consume astounding amounts of water, a phylogenetically explicit allometric analysis revealed that their diurnal GFRs are not different from the expectation based on body mass.
Bakken
Bradley Hartman
BH
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
McWhorter
Todd J
TJ
Tsahar
Ella
E
Del Rio
Carlos Martínez
CM
D000704:Analysis of Variance; D000818:Animals; D001717:Birds / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology; D005919:Glomerular Filtration Rate / Q000502:physiology*; D007668:Kidney / Q000502:physiology*; D008954:Models, Biological; D010802:Phylogeny; D014867:Water / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
D014867:Water