Use of stable-carbon and -nitrogen isotopes to assess weaning and fasting in female polar bears and their cubs

Authors: Polischuk S.C.; Hobson K.A.; Ramsay M.A.

Source: Canadian Journal of Zoology, Volume 79, Number 3, March 2001 , pp. 499-511(13)

Publisher: NRC Research Press

Abstract:

In some species, stable-isotope techniques can provide insights into dietary regimens where there are temporal shifts in trophic level or feeding frequency. We determined stable carbon (¹³C) and nitrogen (¹⁵N) isotope values for plasma and milk proteins and ¹³C values for milk lipids from female polar bears (Ursus maritimus) and cubs to (i) ascertain whether cubs are at a higher trophic level than their mothers as a result of nursing and whether we can determine when weaning occurs, and (ii) determine the impact of seasonal fasting on ¹³C and ¹⁵N values. The plasma ¹³C values for mothers and cubs were similar to milk-protein ¹³C values and were significantly enriched in ¹³C compared with those for milk lipid. Plasma from cubs of the year (COYs) in spring, when milk was their only diet, was isotopically enriched in ¹⁵N by 1.0 over that of their mothers (¹⁵N = 21.5 ± 0.8 (mean ± SD) for cubs and 20.5 ± 0.5 for mothers) and depleted in ¹³C by 0.8 (¹³C = –19.6 ± 0.5 for cubs and –18.8 ± 0.8 for mothers). For bears who fasted between summer and fall (3–4 months), plasma became depleted in ¹³C by 0.5 and in ¹⁵N by 1. Plasma from females, who had fasted from summer to spring (7–8 months) and given birth to cubs, became enriched in ¹³C by 0.7 and in ¹⁵N by 2. By using stable-isotope analyses we were able to show that (i) young cubs were at a higher trophic level than their mother when milk was their only food source, and (ii) seasonal fasting influenced ¹³C and ¹⁵N values. However, we were not able to use stable-isotope analyses to determine the exact time of weaning.

Chez certaines espèces, les techniques basées sur les isotopes stables peuvent renseigner sur les régimes alimentaires là où il y a des variations temporelles du niveau trophique ou de la fréquence des repas. Nous avons déterminé la valeur des isotopes de carbone (¹³C) et d'azote (¹⁵N) stables dans le plasma et les protéines du lait et les valeurs de ¹³C dans les lipides du lait de femelles de l'Ours blanc (Ursus maritimus) et chez leurs petits dans le but (i) de vérifier si les oursons sont à un niveau trophique plus élevé que leurs mères à cause de l'allaitement et s'il est possible de déterminer à quel moment a lieu le sevrage et (ii) d'évaluer l'impact d'un jeûne saisonnier sur les mesures de ¹³C et de ¹⁵N. Les valeurs de ¹³C du plasma chez les mères et leurs petits étaient semblables aux valeurs de ¹³C des protéines du lait et significativement plus riches en ¹³C que les lipides du lait. Le plasma des oursons de l'année (COYs) au printemps, moment où ils ne consomment que du lait, était plus riche de 1,0 en isotopes ¹⁵N que celui de leurs mères (¹⁵N = 21,5 ± 0,8 (moyenne ± écart type) chez les

Language: English

Document Type: Research article

Publication date: 2001-03-01

• Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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