Nitrogen allocation to offspring and milk production in a capital breeder

Abstract

Nitrogen (N) is a limiting nutrient for many herbivores, especially when plant availability and N content are low during the period of maternal investment, which is common for arctic ungulates. We used natural abundance of N isotopes to quantify allocation of maternal nitrogen to neonatal calves and milk in wild migratory caribou (Rangifer tarandus). We contrasted female-calf pairs from two herds in northern Quebec/Labrador, Canada: Rivière-George herd (RG; low population size with heavy calves) and the Rivière-aux-Feuilles herd (RAF; high population size and small calves). We assessed whether females of both herds relied on body protein or dietary N to produce the neonatal calf and milk at calving and weaning. Female caribou of both herds relied mostly on body N for fetal development. RAF females allocated less body N to calves than did RG females (92% vs. 95% of calf N), which was consistent with the production of calves that were 8% smaller in RAF than in RG. Allocation of body N to milk was also high for both herds, similar at calving for RAF and RG females (88% vs. 91% of milk N, respectively), but lower in RAF than RG females (95% vs. 99% of milk N) at weaning, which was consistent with a small but significantly greater reliance on dietary N supplies to support milk production at weaning. Female caribou used body protein stores to ensure a constant supply of N for fetal growth and milk production that minimized the effects of trophic mismatches on reproduction. The combination of migration and capital investment may therefore allow females to produce calves and attenuate the effects of both temporal and spatial mismatches between vegetation green-up and calf growth, which ultimately would reduce trophic feedbacks on population growth. Our data suggest that small changes in maternal allocation of proteins over the long period of gestation produce significant changes in calf mass as females respond to changes in resources that accompany changes in the size and distribution of the population.

Environmental and Physiological Influences to Isotopic Ratios of N and Protein Status in a Montane Ungulate in Winter

“…The evolving picture of δ 15 N RBC within the literature shows that, although varied, estimates generally fall within 1–4‰ with means that are remarkably similar for widely distributed caribou populations. For example, large populations of migratory caribou in Alaska (Western Arctic: 1.5±0.3‰, 32, Central and Western Arctic: 2.2±1.6‰) [54] and Québec ( n  = 60, 2.6±0.5‰) [33] were similar to sedentary, montane populations in central Alaska (this study: 2.1±0.92‰) and the Wrangell-St. Elias Mountains (Chisana: 2.7±0.7‰) [55] as well as north central British Columbia (Pink Mountain: 2.3±0.5‰) [56]. Notwithstanding the similarities among these herds, the substantial inter-annual variance in δ 15 N RBC remains unexplained.…”

“…Some northern and alpine ungulates, such as muskoxen ( Ovibos moschatus ) [18], mountain goats ( Oreamnos americanus ) [19], [20], and bighorn sheep ( Ovis canadensis ) [17] rely solely on stored capital for production of young. Alternatively, others, such as caribou ( R. tarandus ) use primarily capital and some income to meet nutrient demands throughout a reproductive event [21], [22], whereas roe deer ( Capreolus capreolus ) rely exclusively on income to produce offspring [12].…”

“…Therefore, δ 15 N 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].…”

Observed and predicted effects of climate change on Arctic caribou and reindeer

“…Both Veiberg et al (2016) and Gustine et al (2017) noted that because caribou and reindeer are capital breeders (Taillon et al 2013), it is expected that the influence of spring phenology should be less important than that of maternal winter body condition on reproductive success. Reliance on maternal body stores for foetal development rather than dietary income may mitigate negative effects of changing phenologies (Stephens et al 2009;Veiberg et al 2016;Gustine et al 2017).…”

Assessing the Impacts of Summer Range on Bathurst Caribou’s Productivity and Abundance since 1985

“…Despite well documented effects of habitat nutrition on individual animal performance and nutritional strategies of caribou and reindeer [42]- [45], few studies have been able to link nutrition and population demographics in a quantitative fashion. By determining the upper envelope curve between summer range indicator and caribou productivity, we suggest that an assessment can be made of when the summer range conditions could become limiting.…”