• bioenergetics – lecithotrophy – life-history evolution – reproductive ecology – stable isotopes

Reproductive allocation strategies have been historically described as lying on a continuum between capital and income breeding. Capital breeders have been defined as species that allocate stored reserves to reproduction, whereas income breeders have been defined as species that allocate relatively recently-ingested food resources to reproduction. Snakes are considered capital breeders because they efficiently store large amounts of nutrients and energy, potentially enough to support an entire reproductive bout without feeding. We examined the abilities of five viviparous snake species to allocate income to follicles during vitellogenesis. We fed 15N-labelled L-leucine to experimental females of each species during vitellogenesis, whereas control females were fed unlabelled meals. After ovulation, we measured yolk 15N p.p.m. using mass spectrometry. Maternal scale samples taken before labelling were used to estimate endogenous 15N concentrations, which should represent ‘capital’. Scale samples taken at ovulation were used to determine whether snakes assimilated 15N-labelled-leucine from labelled diets. Yolks and post-ovulatory scales of labelled females were significantly more enriched in 15N than those of unlabelled females in all species, indicating significant assimilation and allocation of income-derived amino acids to the yolk during vitellogenesis. The lack of among-species differences suggests that all species allocated income amino acids to vitellogenesis. The results obtained in the present study suggest that proportional utilization of income or capital depends on the frequency and timing of foraging success during reproductive events. Therefore, capital and income breeding may be consequences of both life-history and environmental constraints on foraging success, rather than strategies of reproductive allocation. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 390–404.