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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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Projected differences in isotopic ratios of N (δ15N in ‰) between red blood cells and serum fractions in relation to gain or loss of body protein; the gradient of shading indicates the light (low δ15N) to heavy N (high δ15N).
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pone-0103471-g002: Projected differences in isotopic ratios of N (δ15N in ‰) between red blood cells and serum fractions in relation to gain or loss of body protein; the gradient of shading indicates the light (low δ15N) to heavy N (high δ15N).

Mentions: Isotopes of nitrogen (N) can be used to assess the mobilization of body proteins in northern and montane ungulates because the isotope ratio of heavy 15N to light 14N (δ15N) is typically higher in body proteins than in dietary proteins [29]. Isotopically light N is preferentially incorporated in metabolic processes and excreted, thereby leaving body tissues with more of the heavy isotope [30]. Nitrogen in dietary proteins is digested and absorbed as amino acids and those amino acids can be incorporated into body tissues as protein. If the dietary amino acids are used for energy, glucogenesis, or lipogenesis, the N is removed and excreted as urea (Fig. 1) [31]. Thus, increasing δ15N ratios in serum amino acids indicate that an increasing proportion of the associated N is derived from body proteins [18]. As amino acids are reused in the body, the δ15N of serum proteins rises above cellular proteins (e.g., red blood cells), so δ15N in serum protein provides an additional indicator of N conservation in wintering ungulates (Fig. 2). While δ15N of bulk serum samples may occasionally correspond to protein status [29], [32], bulk isotopic values obscure the complexities of N dynamics within pools of N in the blood of wintering ungulates. Therefore, δ15N of blood fractions (i.e., red blood cells, serum proteins, and serum amino acids) and relative changes therein (Fig. 1, 2) provide a conceptual blood-based system for evaluating protein status and allocation of maternal proteins in wintering ungulates [33].


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)

Projected differences in isotopic ratios of N (δ15N in ‰) between red blood cells and serum fractions in relation to gain or loss of body protein; the gradient of shading indicates the light (low δ15N) to heavy N (high δ15N).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0103471-g002: Projected differences in isotopic ratios of N (δ15N in ‰) between red blood cells and serum fractions in relation to gain or loss of body protein; the gradient of shading indicates the light (low δ15N) to heavy N (high δ15N).
Mentions: Isotopes of nitrogen (N) can be used to assess the mobilization of body proteins in northern and montane ungulates because the isotope ratio of heavy 15N to light 14N (δ15N) is typically higher in body proteins than in dietary proteins [29]. Isotopically light N is preferentially incorporated in metabolic processes and excreted, thereby leaving body tissues with more of the heavy isotope [30]. Nitrogen in dietary proteins is digested and absorbed as amino acids and those amino acids can be incorporated into body tissues as protein. If the dietary amino acids are used for energy, glucogenesis, or lipogenesis, the N is removed and excreted as urea (Fig. 1) [31]. Thus, increasing δ15N ratios in serum amino acids indicate that an increasing proportion of the associated N is derived from body proteins [18]. As amino acids are reused in the body, the δ15N of serum proteins rises above cellular proteins (e.g., red blood cells), so δ15N in serum protein provides an additional indicator of N conservation in wintering ungulates (Fig. 2). While δ15N of bulk serum samples may occasionally correspond to protein status [29], [32], bulk isotopic values obscure the complexities of N dynamics within pools of N in the blood of wintering ungulates. Therefore, δ15N of blood fractions (i.e., red blood cells, serum proteins, and serum amino acids) and relative changes therein (Fig. 1, 2) provide a conceptual blood-based system for evaluating protein status and allocation of maternal proteins in wintering ungulates [33].

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