Conceptual Revision and Synthesis of Proximate Factors Associated with Age‐Related Improvement in Reproduction

Abstract

Improvement in reproductive performance with age, up to the point of senescence, is a predominant pattern among vertebrates. Predictions from life‐history theory provide a powerful framework for understanding the evolutionary basis of these patterns. However, based on the growing number of publications on this topic, there is increased interest in understanding the proximate causes of age‐related improvements in reproductive performance (ARIRP). A formal conceptual framework through which factors related to ARIRP can be examined is lacking. Here, we establish hypotheses with testable predictions for social and ecological factors, including resource quality, mate fidelity, site fidelity, prior breeding experience, and changes in ability to attract mates. We use this conceptual framework to review 55 empirical studies published (between 1900 through 2013) on avian species as birds have the greatest representation in empirical studies of ARIRP. Our synthesis revealed that tests of the breeding experience hypothesis are most prevalent in the literature, whereas tests of the site fidelity hypothesis are least prevalent. Overall, the role of increased mate attraction with age seems to be an important predictor of ARIRP, whereas changes in resource quality with age show the least support among published studies. Because many studies suffered from small sample sizes and did not control for confounding variables, we suggest experimental methodologies for teasing apart hypotheses in empirical investigations and offer statistical approaches for longitudinal datasets. From an ultimate perspective, we also highlight the role of life‐history variation, in shaping within‐individual improvements. Future work should employ a standardized framework to study patterns of ARIRP, as set forward here, to allow for more quantitative comparison of results across studies.

DNA methylation levels in candidate genes associated with chronological age in mammals are not conserved in a long-lived seabird

“…Whilst ageing and senescence have now been observed in many wild animals, the rate of reproductive and functional decline varies [ 2 , 3 ]. The effect of increasing chronological age is associated with key ecological characteristics including reproductive maturity [ 4 – 6 ], reproductive frequency [ 7 ], and mortality [ 8 ]. Given that many species lack measurable external changes with age, estimating chronological age is often difficult.…”

Communication Value of Mistakes in Dark-Eyed Junco Song

“…Older males sang three types of atypical songs less frequently (atypical syllables, multitype songs, and alternating a song type without repetition), which could be due to either improved singing with age and/or increased survival of better singers. In either case, these atypical songs give an indication of age, which is an important aspect of male quality because it may indicate parental ability or investment (reviewed by Forslund andPärt 1995 andBradley andSaffran 2014;in the junco: Reed et al 2006). The relation between atypical songs and age agrees with the view that these are singing or develop- interval from the best model; number indicated in parentheses beside each type of mistake), and relations with reproductive success used the best model (AICc criterion).…”

Multiple song features are related to paternal effort in common nightingales

“…In our study, the orderliness of male song sequencing indicated increased paternal investment. Given that song orderliness is also associated with male age [ 47 ], females choosing an orderly singing male might benefit from a male who signals viability and experience with the breeding grounds (factors significantly enhancing reproductive success in birds [ 57 , 58 ]) and his willingness to care for the offspring. Together these findings support the idea that the sequential ordering of birdsong carries relevant information during communication which may be directed to female listeners and thus, may have evolved by female choice [ 59 ].…”