Nitrogen- and carbon-isotope fractionation between mothers and offspring in red-backed voles (Clethrionomys gapperi)

Abstract

Small mammals are income breeders, but the degree to which females draw from maternal reserves and partition nutrients to the mammary glands in the wild is not known. This study examined stable-nitrogen and stablecarbon isotopes in red-backed vole, Clethrionomys gapperi (Vigors, 1830), hair to determine mother-offspring trophic relationships and to consider the extent to which voles rely on maternal reserves during lactation. Both dependent and independent young showed isotopic enrichment in 15 N and depletion of 13 C in their hair relative to mothers. We suggest that growing offspring, both dependent and independent, may catabolize body reserves to support both growth and moult. We propose that the nitrogen-and carbon-isotope compositions of hair may be more useful indicators of metabolic rate than mother-offspring trophic relationships in small mammals. Résumé :Les petits mammifères utilisent leurs apports énergétiques quotidiens (revenu) pour se reproduire; on connaît cependant mal dans quelle mesure les femelles en nature puisent dans leurs réserves maternelles et allouent des nutriments aux glandes mammaires. Notre étude examine les isotopes stables d'azote et de carbone dans le poil des campagnols à dos roux de Gapper, Clethrionomys gapperi (Vigors, 1830), afin de déterminer les relations trophiques mère-petits et évaluer dans quelle mesure les campagnols utilisent leurs réserves maternelles durant l'allaitement. Tant chez les petits dépendants qu'indépendants, il y a un enrichissement isotopique en 15 N et un appauvrissement en 13 C dans le poil, par comparaison à leur mère. Nous croyons que les rejetons en croissance, tant dépendants qu'indépendants, peuvent cataboliser leurs réserves corporelles pour alimenter la croissance et la mue. Nous croyons que la composition isotopique d'azote et de carbone du poil chez les petits mammifères est un indicateur plus fiable du taux métabolique que de la relation trophique mère-petits.[Traduit par la Rédaction] Sare et al. I 716

Stable nitrogen and carbon isotope discrimination between juveniles and adults in an income-breeding small mammal (Peromyscus maniculatus)

“…Average 13 C tissue-diet of Ten mammal species j −2.1 (0.9) Blood plasma 0 0 −0.2 (0.8) a Current study. b Sare et al (2005b). c Polischuk et al (2001).…”

“…Such studies show that dependent offspring are generally enriched in 15 N by approximately 1-3‰ relative to adults. The one such study to date of mammals weighing less than 50 g found that hair from juvenile Clethrionomys gapperi (red-backed voles) was enriched in 15 N by 1.9‰ relative to their mothers (Sare et al 2005b).…”

Growth velocity and weaning δ15N “Dips” during ontogeny in Macaca mulatta

“…Catabolism of endogenous tissue reserves as in wasting (Fuller et al, 2005;Hatch, 2012;Hobson et al, 1993) or as is the case for income breeders who draw off endogenous reserves to meet the reproductive demands (Hinde et al, 2009;Sare et al, 2005) and protein synthesis during fasting in anabolic states (Lee et al, 2012), leads to higher d…”

Longitudinal differences in 15N between mothers and offspring during and after weaning in a small cooperative mammal, the meerkat (Suricata suricatta)

“…6 Since lactating offspring physiologically consume their mother, 15 N may be used to explore lactation patterns in mammalian females. 7 Consequently, 15 N has been used to investigate lactation patterns both in extinct 8 and in extant 9,10 mammal populations. Such studies have mainly focused on the timing of weaning 11,12 or confounding effects for diet reconstruction.…”

“…13 However, 15 N measurements can also be used to explore tactics of energy acquisition for lactation, since it is possible to generate testable predictions regarding different levels of 15 N enrichment in offspring from capital versus income breeding mothers. 7,10 In capital breeders, differences in 15 N between mothers and their offspring should reflect one trophic level at parturition and two trophic levels during peak lactation. The incorporation of female reserves into embryonic tissue should cause the trophic enrichment at parturition, i.e.…”