Parent-offspring conflicts are likely to occur when resources are limiting either at pre- or postnatal stages due to intergenerational trade-offs over resources. Current theory posits that such conflicts may influence the evolution of parental allocation as well as reproductive modes. While energy allocation to the offspring has received considerable attention, the distribution of water – another potentially limited vital resource to both the mother and offspring – and the resulting outcomes remain grossly understudied. Here, we explored the intergenerational trade-off related to water resources in the viviparous aspic viper (Vipera aspis) by examining the effects of water deprivation on female physiology (body mass, haematocrit, and osmolality), water transfer to developing embryos, and reproductive performance. As a result of water deprivation, females became dehydrated, with the effects more pronounced in pregnant compared to non-reproductive females. Among pregnant females, the impacts of water deprivation on water balance were correlated with fecundity. In contrast, water deprivation had no effect on water transfer to the offspring or on reproductive performance. Our results demonstrate that, under water-constraining conditions, female water balance is compromised in favour of the developing embryos, highlighting a significant intergenerational trade-off for water. Although ectothermic reptiles are particularly tolerant in water balance perturbations, our results suggest that, like energy, water can be a conflicting resource between mother and offspring. Parent-offspring conflict over water should therefore be further investigated to better understand reproductive modes and reproductive trade-offs in terrestrial organisms.

Female physiology and reproductive performance datasheetFile containing measurements of female physiology and reproductive performanceFemale physiology and reproductive performance.txtNeonate morphologyFile containing measurements of neonate morphologyneonate morphology.txt