Differences in Reproductive Success in Young and Old Females of a Long-Lived Species

SIMPLE SUMMARY: A central goal of life history studies is documenting traits related to reproduction. In long-lived species, older individuals might have traits that enhance reproductive success. However, survivorship at young life stages is usually unknown, which blurs the basic understanding of how female traits influence recruitment and the relevance of climate variation. Our study, which was based on the spur-thighed tortoise, demonstrated that (i) maternal age and climatic conditions influence the recruitment, (ii) older females have greater offspring numbers, greater survival and smaller size and mass than younger females and (iii) severe climatic conditions—low rainfall and temperature—reduce the number of surviving offspring despite their increased size. We discuss deeply how the maternal age and climatic conditions might affect population dynamics of long-lived species and recommended long-term studies of reproductive parameters and appropriate conservation actions. ABSTRACT: Long-lived species are particularly interesting for investigation of trade-offs that shape reproductive allocation and the effective contribution to the next generations. Life history theory predicts that these species will buffer environmental stochasticity via changes in the reproductive investment, while maintaining high adult survival rates. The spur-thighed tortoise was selected as a case study in order to investigate the relationship between the linked maternal characteristics (size and age) and related traits in their hatchlings. We tracked naturally emerging hatchlings from young and old females under semi-natural conditions to test variations in hatchling numbers, body mass, size and survival over two years. We used linear mixed-effect models to analyze variations in hatchling body mass and size, and a mark–release–recapture framework to model their survival. Our study illustrates that old females of long-lived species have greater offspring numbers, greater survival and smaller size when compared with those of young females. The interannual variability evidenced the reduced offspring number and survival in the lower autumn rainfall and spring mean temperature year. Our results highlight the role of maternal age and climatic conditions in the population dynamics and the need for long-term studies of reproduction traits for designating adequate conservation strategies.