Senescence is an intricate, multifaceted process that can vary among populations, individuals, and traits within individuals. However, the relative importance of factors generating observed differences in senescence patterns remains poorly understood. In particular, there is a lack of studies that quantify both age-dependent and state dependent components of senescence, and do so across different environmental conditions. Also, few studies have explicitly tested cumulative reproductive costs, or how early-life conditions like maternal age and state at offspring birth affect offspring adult phenotypes and senescence trajectories. I use individual-based long-term data from wild yellow-bellied marmots, to quantify chronological (age-dependent) and biological (state-dependent) senescence in female reproductive success and season-specific body mass across two different elevational environments. Since previous reproductive history could influence biological age, I also estimate costs of previous short-term and cumulative long-term reproduction on females' current reproductive success. Finally, I test whether maternal age and state at daughter birth affect daughter reproduction and senescence. I demonstrate complex senescence patterns in body mass and reproductive success. First, senescence in body mass has both age-dependent and state-dependent components, and effects are greater at lower elevation than higher elevation and greater in late summer than in spring. Second, at both elevations, females that reproduced frequently and weaned large litters in previous years have reduced current reproductive probability, while there are no short-term effects of previous reproduction. Finally, higher chronological age and closer proximity to death of the mother have positive environment-dependent effects on daughter reproductive trajectories. Overall, my findings reveal the need to investigate senescence patterns across multiple environments and over long time periods to allow capturing certain intra-individual and inter-generational effects. The persistence of maternal effects into daughters' adult lives highlights the complexity of life-history trade-offs, and calls for more studies that consider such long-term transgenerational effects when studying life-history variation and senescence in wild populations.

When to reproduce for the first time is a key question in evolutionary ecology. Indeed, age at first reproduction has clear impacts on population dynamics and fitness. Breeding early in life may impair survival due to a resource allocation trade-off between survival, growth, and reproduction. Postponing reproduction, however, reduces reproductive opportunities and increases the chances of dying before reproducing. Here, I investigate the consequences of age at first reproduction on both survival and lifetime reproductive success by using long-term monitoring data of a population of yellow-bellied marmots (Marmota flaviventer) at the Rocky Mountain Biological Laboratory (Colorado, USA). Mixed models were employed to analyze the relationships between age at first reproduction in females and their lifetime reproductive success, as well as three survival components: longevity, the number of years after first reproduction, and annual survival probability. The results showed that postponing reproduction until 2 years of age increased longevity, but delaying it beyond 2 years did not yield additional survival benefits. Females reproducing for the first time after 3 years exhibited high rates of actuarial senescence. Furthermore, delaying first reproduction beyond 3 years old did not lead to a compensatory increase in lifetime reproductive success that would offset the reduction in survival associated with postponing first reproduction. These results suggest that the optimal age at first reproduction, in terms of survival and reproductive success, is 2 years. The reproductive strategy might be governed by body condition or environmental factors. These findings shed light on the trade-offs between early reproduction and survival, as well as reproductive success, illustrating the complexity of reproductive strategies in relation to individual fitness.