Life‐history trade‐offs and senescence in plants

Abstract

1. An increasing number of studies have shown that senescence, the functional decline in traits and increased risk of mortality with increasing age, occurs in organisms in wild populations, but there is a wide range of diversity in the patterns of senescence across species.2. The antagonistic pleiotropy and the disposable soma theories of senescence predict that there will be life-history trade-offs between performance at early-and late-life stages. Plants show variation in senescence patterns and thus provide an opportunity to evaluate life-history trade-offs and senescence. Many plant species can be easily followed demographically and their environments, resources and allocation to reproduction can be manipulated, which makes them particularly good models to address these questions. 3. We compared the results from 22 studies of plant senescence in the wild and compiled 20 examples of life-history trade-offs in plants. Some of the unique features of plants that may influence senescence patterns and trade-offs in the wild are highlighted through the results.4. We found all three age-specific patterns: age decline, age improvement and no change with age for plants in the wild. Most species showed an age-dependent decline in at least one trait but, even within a species, the age-specific patterns of traits varied. Results also showed that trade-offs vary across environments and that plants can manipulate their resource pool through increases in photosynthesis, which will influence the manifestation of trade-offs.5. We conclude that aspects of plant biology including dynamic resource pools, the impact of size, dormancy and below-ground storage may influence both the patterns of senescence and life-history trade-offs. The diversity of plant life forms and life cycles provide a wealth of opportunities to experimentally study senescence in the context of life-history trade-offs.

An integrative view of senescence in nature

“…Indeed, negative actuarial senescence (i.e. decrease in mortality with age) does not preclude the occurrence of reproductive senescence, and vice-versa (Roach & Smith, 2020), which suggests that asynchronous senescence patterns might be common in plants, as recently observed in animals Hayward et al, 2015).…”

“…Based on a compilation of age-specific changes in iteroparous perennials plants, Roach and Smith (2020) reveal that age-specific mortality can increase with age, stay constant or even decrease with age (i.e. negative senescence, sensu Vaupel, Baudisch, Dölling, Roach, & Gampe, 2004), as observed in the long-lived herb, Borderea pyrenaica (Roach & Smith, 2020). This diversity in senescence patterns is not only observed between species but also occurs within species, which emphasize the importance of considering multiple traits when it comes to study senescence.…”

“…Such a diversity of demographic senescence patterns appears to be even more noticeable in plants. Based on a compilation of age-specific changes in iteroparous perennials plants, Roach and Smith (2020) reveal that age-specific mortality can increase with age, stay constant or even decrease with age (i.e. negative senescence, sensu Vaupel, Baudisch, Dölling, Roach, & Gampe, 2004), as observed in the long-lived herb, Borderea pyrenaica (Roach & Smith, 2020).…”

“…In particular, a special focus will be given to plants, insects and ectotherms. Roach and Smith (2020) review age-specific changes in plant traits and demonstrate a larger than expected diversity of these patterns. Although they are the taxonomic group that includes by far the greatest number of extant species, insects have been particularly overlooked in senescence studies in the wild.…”

The effects of age on the demography of a perennial plant depend on interactions with size and environment

“…In addition, high fecundity and rapid growth is expected in unpredictable environments with high frequency of disturbance (Ellis et al., 2009; Kirkwood & Austad, 2000). Analogously, we could expect trade‐offs to affect ageing patterns (Roach & Smith, 2020), and any possible negative effects of age on individual survival to be lower in resource‐poor versus resource‐rich environments as well as being higher in unpredictable versus predictable environments, while fecundity and growth would be affected in the opposite direction. Tendencies of such patterns in survival were detected by Dahlgren et al.…”