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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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Winter and late winter locations of adult female caribou in Denali National Park and Preserve (Denali NPP), Alaska; blood was collected (n = 168) for isotopic analyses at late winter locations during March 1993–2007.
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pone-0103471-g003: Winter and late winter locations of adult female caribou in Denali National Park and Preserve (Denali NPP), Alaska; blood was collected (n = 168) for isotopic analyses at late winter locations during March 1993–2007.

Mentions: We used a conceptual model of isotopic routing of N (Fig. 1) to assess potential correlates to characteristics of isotopic N and to evaluate protein dynamics in adult female caribou of the Denali herd through the winters of 1993–2002, 2004–2005, and 2007. The Denali herd is a low density (≤0.3 caribou km−2) population that resides in a multi-predator multi-prey system within Denali National Park and Preserve (Fig. 3) that is largely insulated from anthropogenic influences [38]. Adult females are large bodied (Fig. 4d) and experience high neonatal losses to predation [38], [39]. The Denali herd increased from 2,500 to 3,200 in 1989 and then declined abruptly, to approximately 2,000 caribou, during 6 consecutive years of above-average winter snowfall (1988–1994) with the winter of 1992–93 the harshest winter on record (Fig. 4a, b) [40]. The period of severe winter conditions resulted in increased calf and adult mortality [38]–[40]; reduced birth masses of calves (Fig. 4c) [7]; and reduced lactational investment in offspring [6]. We used blood samples and female characteristics (age, mass, and winter location) in late winter to evaluate the long-term patterns and sources of variation in δ15N. We employed our conceptual model of isotopic N in blood fractions from late-winter collections to assess protein status of females through a wide range of winter severity. We predicted that the δ15N of serum proteins and amino acids would enrich with snowfall, thus, the δ15N of serum proteins would rise above the δ15N of red blood cells while δ15N of serum amino acids would approach the δ15N of red blood cells.


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)

Winter and late winter locations of adult female caribou in Denali National Park and Preserve (Denali NPP), Alaska; blood was collected (n = 168) for isotopic analyses at late winter locations during March 1993–2007.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0103471-g003: Winter and late winter locations of adult female caribou in Denali National Park and Preserve (Denali NPP), Alaska; blood was collected (n = 168) for isotopic analyses at late winter locations during March 1993–2007.
Mentions: We used a conceptual model of isotopic routing of N (Fig. 1) to assess potential correlates to characteristics of isotopic N and to evaluate protein dynamics in adult female caribou of the Denali herd through the winters of 1993–2002, 2004–2005, and 2007. The Denali herd is a low density (≤0.3 caribou km−2) population that resides in a multi-predator multi-prey system within Denali National Park and Preserve (Fig. 3) that is largely insulated from anthropogenic influences [38]. Adult females are large bodied (Fig. 4d) and experience high neonatal losses to predation [38], [39]. The Denali herd increased from 2,500 to 3,200 in 1989 and then declined abruptly, to approximately 2,000 caribou, during 6 consecutive years of above-average winter snowfall (1988–1994) with the winter of 1992–93 the harshest winter on record (Fig. 4a, b) [40]. The period of severe winter conditions resulted in increased calf and adult mortality [38]–[40]; reduced birth masses of calves (Fig. 4c) [7]; and reduced lactational investment in offspring [6]. We used blood samples and female characteristics (age, mass, and winter location) in late winter to evaluate the long-term patterns and sources of variation in δ15N. We employed our conceptual model of isotopic N in blood fractions from late-winter collections to assess protein status of females through a wide range of winter severity. We predicted that the δ15N of serum proteins and amino acids would enrich with snowfall, thus, the δ15N of serum proteins would rise above the δ15N of red blood cells while δ15N of serum amino acids would approach the δ15N of red blood cells.

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