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Environmental and physiological influences to isotopic ratios of N and protein status in a Montane ungulate in winter.

Gustine DD, Barboza PS, Adams LG, Wolf NB - PLoS ONE (2014)

Bottom Line: Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction.The δ 15N of the body protein pool varied by 4‰ and 46% of the variance was associated with year.Conservation of body protein in caribou is the result of active exchange among diet and body N pools.

View Article: PubMed Central - PubMed

Affiliation: United States Geological Survey, Alaska Science Center, Anchorage, Alaska, United States of America.

ABSTRACT
Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction. Nitrogen (N) isotopes in blood fractions can be used to track the use of body proteins in northern and montane ungulates. We studied 113 adult female caribou for 13 years throughout a series of severe winters that reduced population size and offspring mass. After these severe winters, offspring mass increased but the size of the population remained low. We devised a conceptual model for routing of isotopic N in blood in the context of the severe environmental conditions experienced by this population. We measured δ15N in three blood fractions and predicted the relative mobilization of dietary and body proteins. The δ 15N of the body protein pool varied by 4‰ and 46% of the variance was associated with year. Annual variation in δ15N of body protein likely reflected the fall/early winter diet and winter locations, yet 15% of the isotopic variation in amino acid N was due to body proteins. Consistent isotopic differences among blood N pools indicated that animals tolerated fluxes in diet and body stores. Conservation of body protein in caribou is the result of active exchange among diet and body N pools. Adult females were robust to historically severe winter conditions and prioritized body condition and survival over early investment in offspring. For a vagile ungulate residing at low densities in a predator-rich environment, protein restrictions in winter may not be the primary limiting factor for reproduction.

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The a) isotopic ratios of nitrogen (δ15N in ‰) in the red blood cells (δ15NRBC), serum proteins (δ15NProteins), and serum amino acids (δ15NAAs) and the b) differences between δ15NRBC and δ15NProteins (ΔRBC-Proteins) and δ15NRBC and δ15NAAs (ΔRBC-AAs) in adult female caribou from Denali National Park and Preserve, March 1993–2007.Shading denotes winters with above average snowfall.
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pone-0103471-g005: The a) isotopic ratios of nitrogen (δ15N in ‰) in the red blood cells (δ15NRBC), serum proteins (δ15NProteins), and serum amino acids (δ15NAAs) and the b) differences between δ15NRBC and δ15NProteins (ΔRBC-Proteins) and δ15NRBC and δ15NAAs (ΔRBC-AAs) in adult female caribou from Denali National Park and Preserve, March 1993–2007.Shading denotes winters with above average snowfall.

Mentions: Isotopic N varied by 4‰ within each fraction of blood across the study period (Fig. 5a, b). The δ15NRBC (n = 155) averaged 2.1±0.90‰ and ranged from 0.18 to 4.72‰. Similarly, the δ15NProteins (n = 140) appeared to track the annual variation in δ15NRBC (2.3±0.81‰, range = 0.69 to 4.98‰), while the δ15NAAs (n = 137) was consistently lower than δ15NRBC and δ15NProteins (−2.1±0.99‰, range = −5.97 to 0.58‰). Indeed, these observations at the population level were consistent with comparisons within individual caribou (Fig. 5b) because the ΔRBC-Proteins (n = 127) was similar to zero (−0.21±0.71‰, range = −1.51 to 2.41‰) while the ΔRBC-AAs (n = 125) was always greater than zero (4.3±1.03‰, range = 1.12 to 7.91‰).


Environmental and physiological influences to isotopic ratios of N and protein status in a Montane ungulate in winter.

Gustine DD, Barboza PS, Adams LG, Wolf NB - PLoS ONE (2014)

The a) isotopic ratios of nitrogen (δ15N in ‰) in the red blood cells (δ15NRBC), serum proteins (δ15NProteins), and serum amino acids (δ15NAAs) and the b) differences between δ15NRBC and δ15NProteins (ΔRBC-Proteins) and δ15NRBC and δ15NAAs (ΔRBC-AAs) in adult female caribou from Denali National Park and Preserve, March 1993–2007.Shading denotes winters with above average snowfall.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4125309&req=5

pone-0103471-g005: The a) isotopic ratios of nitrogen (δ15N in ‰) in the red blood cells (δ15NRBC), serum proteins (δ15NProteins), and serum amino acids (δ15NAAs) and the b) differences between δ15NRBC and δ15NProteins (ΔRBC-Proteins) and δ15NRBC and δ15NAAs (ΔRBC-AAs) in adult female caribou from Denali National Park and Preserve, March 1993–2007.Shading denotes winters with above average snowfall.
Mentions: Isotopic N varied by 4‰ within each fraction of blood across the study period (Fig. 5a, b). The δ15NRBC (n = 155) averaged 2.1±0.90‰ and ranged from 0.18 to 4.72‰. Similarly, the δ15NProteins (n = 140) appeared to track the annual variation in δ15NRBC (2.3±0.81‰, range = 0.69 to 4.98‰), while the δ15NAAs (n = 137) was consistently lower than δ15NRBC and δ15NProteins (−2.1±0.99‰, range = −5.97 to 0.58‰). Indeed, these observations at the population level were consistent with comparisons within individual caribou (Fig. 5b) because the ΔRBC-Proteins (n = 127) was similar to zero (−0.21±0.71‰, range = −1.51 to 2.41‰) while the ΔRBC-AAs (n = 125) was always greater than zero (4.3±1.03‰, range = 1.12 to 7.91‰).

Bottom Line: Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction.The δ 15N of the body protein pool varied by 4‰ and 46% of the variance was associated with year.Conservation of body protein in caribou is the result of active exchange among diet and body N pools.

View Article: PubMed Central - PubMed

Affiliation: United States Geological Survey, Alaska Science Center, Anchorage, Alaska, United States of America.

ABSTRACT
Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction. Nitrogen (N) isotopes in blood fractions can be used to track the use of body proteins in northern and montane ungulates. We studied 113 adult female caribou for 13 years throughout a series of severe winters that reduced population size and offspring mass. After these severe winters, offspring mass increased but the size of the population remained low. We devised a conceptual model for routing of isotopic N in blood in the context of the severe environmental conditions experienced by this population. We measured δ15N in three blood fractions and predicted the relative mobilization of dietary and body proteins. The δ 15N of the body protein pool varied by 4‰ and 46% of the variance was associated with year. Annual variation in δ15N of body protein likely reflected the fall/early winter diet and winter locations, yet 15% of the isotopic variation in amino acid N was due to body proteins. Consistent isotopic differences among blood N pools indicated that animals tolerated fluxes in diet and body stores. Conservation of body protein in caribou is the result of active exchange among diet and body N pools. Adult females were robust to historically severe winter conditions and prioritized body condition and survival over early investment in offspring. For a vagile ungulate residing at low densities in a predator-rich environment, protein restrictions in winter may not be the primary limiting factor for reproduction.

Show MeSH
Related in: MedlinePlus