Influence of Reproduction on Stable-Isotope Ratios: Nitrogen and Carbon Isotope Discrimination between Mothers, Fetuses, and Milk in the Fin Whale, a Capital Breeder

Abstract

In mammals, the influence of gestation and lactation on the tissue stable-isotope ratios of females, fetuses, and milk remains poorly understood. Here we investigate the incidence of these events on δ(13)C and δ(15)N values in fin whales sampled off northwestern Spain between 1983 and 1985. The effect of gestation on tissue stable-isotope ratios was examined in the muscle of pregnant females (n = 13) and their fetuses (n = 10) and that of lactation in the muscle of nursing females (n = 21) and their milk (n = 25). Results suggest that fetuses are enriched compared to their mothers in both (15)N (Δ(15)N = 1.5‰) and (13)C (Δ(13)C =1.1‰), while, compared to muscle, milk is enriched in (15)N (Δ(15)N = 0.3‰) but depleted in (13)C (Δ(13)C = -0.62‰). This pattern is consistent with that previously observed for other species that, like the fin whale, rely on endogenous energy during reproduction, and it substantiates a general difference in the physiological processing of nitrogen and carbon balances between income and capital breeders. These findings are relevant to the understanding of the energetic balance of mammals during gestation and lactation and are central when inferences on trophic ecology are drawn from isotopic values of reproductive females.

Temporal variability in stable isotope ratios of C and N in the vibrissa of captive and wild adult South American sea lions Otaria byronia: More than just diet shifts

“…, Borrell et al . ), probably because fasting and lactogenesis have opposing effects of the stable isotope ratios of the female.…”

“…Enrichment in 13 C is expected to be particularly intense in lactating female otariids, as they produce milk with high fat contents and thus depleted in 13 C when compared with female tissues (Newsome et al 2006). The situation is different in female phocids and other capital breeders, which fast through lactation (Polischuck et al 2001, Ducatez et al 2008, Habran et al 2010, Borrell et al 2016, probably because fasting and lactogenesis have opposing effects of the stable isotope ratios of the female.…”

“…On the other hand, pregnancy has been reported to modify the nitrogen balance of females, and hence TDF (Fuller et al 2004). Furthermore, the stable isotope values of milk differ from those of the mother's tissues (Jenkins et al 2001, Habran et al 2010, Borrell et al 2016, indicating that lactation might result in major changes in the stable isotope values of lactating females, although to our knowledge no experimental evidence exists. All this suggests that confounding factors associated with metabolically induced changes in TDF during the annual breeding cycle may exist in mammals and may interfere with the interpretation of stable isotope ratios in inert tissues.…”

“…, Borrell et al . ), indicating that lactation might result in major changes in the stable isotope values of lactating females, although to our knowledge no experimental evidence exists. All this suggests that confounding factors associated with metabolically induced changes in TDF during the annual breeding cycle may exist in mammals and may interfere with the interpretation of stable isotope ratios in inert tissues.…”

The Utility of Combining Stable Isotope and Hormone Analyses for Marine Megafauna Research

“…Second, animals undergoing nutritional stress must rely on their own tissue catabolism or other mechanisms to maintain function (see Elia et al, 1999;Aguilar et al, 2014;Borrell et al, 2016), and these adaptations to resource limitation or starvation can vary in their effect on the δ 13 C and δ 15 N values in tissues. Much evidence points to an increase in the δ 15 N values of tissues for animals undergoing protein catabolism when they are starving (Hobson et al, 1993;Polischuk et al, 2001;Cherel et al, 2005;Lohuis et al, 2007;Newsome et al, 2010;Bowes et al, 2014).…”