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Age, growth and size interact with stress to determine life span and mortality

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... herbàcies perennes han demostrat que hi ha un efecte de l'edat sobre la mortalitat (Laurenroth & Adler, 2008;Roach, 2012), però això no ha estat observat en l'herbàcia perenne no clonal més longeva registrada fins a l'actualitat, B. pyrenaica . Estudis comparatius realitzats en la planta herbàcia Plantago lanceolata, en condicions controlades i en condicions naturals, mostren que la longevitat màxima de l'espècie es redueix significativament en condicions naturals. ...
... Estudis comparatius realitzats en la planta herbàcia Plantago lanceolata, en condicions controlades i en condicions naturals, mostren que la longevitat màxima de l'espècie es redueix significativament en condicions naturals. A més a més, en condicions controlades els estressos ambientals provoquen un augment de la mortalitat en els individus més vells (Roach et al., 2009;Roach, 2012). En condicions naturals els patrons d'envelliment depenen de les condicions de l'individu, és a dir, qualsevol factor de mortalitat interactua amb l'estat fisiològic de l'individu, el qual pot incrementar la seva mortalitat. ...
Thesis
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One of the most accepted theories of ageing in animals and humans is the free radical theory of ageing, which describes that oxidative stress increases with age. Unfortunately, there are very few studies that test this theory in plants, and none in long-lived perennial plants. In this thesis, we choose two models of long-lived perennial plants to investigate the processes of ageing and the importance of oxidative stress, along with the role of protection mechanisms such as vitamin E, in the ageing process in plants under natural climatic conditions. With this aim, we explored the effects of age (ranging from 1 to 280 years) in the extent of lipid peroxidation, photoprotection mechanisms and other oxidative stress markers in leaves and tubers (perennial organ) in the longest-lived perennial – not clonal – herb registered to date, Borderea pyrenaica. The other species used in the study, Vellozia gigantea, is an endemic plant of Brazil in which it is not possible estimate its age, but it is considered to live more than 500 years. In this species, we evaluated the effect of size on various oxidative stress markers and evaluated the ecophysiological response to seasonal variations in water availability (rainy and dry season) in plants grown in their natural habitat. Results show that neither age nor size have a negative effect on plant physiological processes related to oxidative stress, thus suggesting that the free radical theory of ageing is not universal in perennials plants. B. pyrenaica showed absence of physiological deterioration with aging as indicated by oxidative stress markers, at least until the studied age (280 years), showing that the oldest females display a greater photoprotection than males of the same age and juveniles (negative senescence). The perennial organ that growsunderground in B. pyrenaica (tubers) seems to be the secret of its long life, considering its unique growth strategy together with its efficient antioxidant protection mechanism (vitamin E), whose levels increased with age. V. gigantea also shows absence of physiological deterioration with ageing (mature individuals of various sizes were examined), which was also associated with increasing vitamin E levels in the oldest individuals, suggesting therefore a case of negligible senescence. In this plant species, tocotrienols were found in leaves (this is the first documented study showing tocotrienols in leaves of higher plants), which might have an important role to protect against photo-oxidative stress, along with tocopherols. Water deficit conditions during the dry season led V. gigantea to activate an efficient protection mechanism based on abscisic acid-induced stomatal closure to prevent water loss and presumably increase vitamin E biosynthesis. In this thesis, it is concluded that perennials plants are highly resistant organisms to stress and ageing, as shown by their protective mechanisms to maintain adequate physiological functions until very advanced ages, so that neither age nor size cause any functional decline in the organism.
... A larger size generally leads to higher vital rates (Obeso, 2002;Vaupel et al., 2004). Moreover, studies assessing effects of both age and size have found that size is more important than age (Mencuccini et al., 2005;García et al., 2011, but see Lauenroth & Adler, 2008, but Roach (2012) found that age, size and growth can interact when the environment is stressful. Few studies have investigated interactive effects of age and size but if effects of being bigger are generally positive on vital rates, we would expect that larger plants would also be less adversely affected by age than smaller plants. ...
... Large plants were positively affected by age, and young large plants were more likely to grow less or to shrink in size than old large plants. Shrinkage in plants has been suggested as a general adaptive response of weak plants to survive adverse environmental conditions(Morris & Doak, 1998;Salguero-Gómez & Casper, 2010), and previous studies with P. lanceolata have shown such shrinkage to be more prevalent in plants in the few years before their death(Roach, 2012;Shefferson & Roach, 2013). We did not investigate whether shrinkage prior to death unrelated to age occurred. ...
Article
Age‐dependence of the demographic rates survival, fecundity and individual growth is a fundamental aspect of population biological theory. Knowledge about plant ageing can also be important for conservation and agriculture as it will improve the accuracy of population viability assessments and long‐term performance assessments in perennial crops. Recent studies show age effects on demographic rates for several plant species, yet much remains to be learned about the patterns and mechanisms of plant ageing, particularly about how age effects interact with the environment and with plant size. We collected age‐and‐size‐based demographic data, as well as individual‐based environmental data, for the perennial herb Plantago lanceolata in Denmark over three annual transitions (four years). We combined frequent field monitoring of carefully mapped individuals with the underused technique of root histology to determine age of herbaceous plants. We used generalized linear mixed effects models to assess how age, soil properties, and year influenced survival, growth, and reproduction. Our results show no strong evidence of consistent age declines, rather, we found mostly positive effects of age on vital rates. For all vital rates, i.e. survival, growth, flowering, and reproductive output, age effects also differed significantly among years. Additionally, we detected an interactive effect of age and size in the growth model. Size, and temporal and spatial environmental variation also affected vital rates independently of age. Synthesis: Our study shows that age‐dependence of demographic rates can depend both on individual size and environmental variation. These results suggest that a consideration of potential age‐interactions may improve the accuracy of comparative studies of ageing and population projections. Moreover, this study shows that much is still unknown about how plant ageing can be affected by the environment.
... However, plants in eastern Australia have a lifespan of 1-2 years (i.e. they are annuals or biennials) (PlantNET, NSW Government). An assessment of the age-mortality relationship in a field experiment suggests mortality increases significantly by the first or second year following the initiation of reproduction, particularly under stressful conditions (Roach 2012). P. lanceolata has a basal rosette growth form with an inflorescence borne on each flowering stalk. ...
... This suggests life histories that involve early high reproduction may be adaptive in the rangeedge environment, and may be beneficial for adaptation to even more stressful habitats further inland. Given that early mortality is high for P. lanceolata under stressful conditions (Roach 2012), a loss of the buffering effects of developmental plasticity may inhibit adaptation to more stressful environments away from the edge (Nicotra et al. 2010) and may be responsible for the formation of the edge. Adaptation to environmental change is believed to occur quicker in plants with fast life histories (Sultan 2000;Smith & Donoghue 2008); the evolution of a fixed slow life history in secondary invasion plants may be inhibiting further adaptation. ...
Article
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Adaptation to changing environments is a fundamental process occurring throughout a species’ range, particularly under novel and stressful conditions at the range edges of invasive species. However, the evolutionary consequences associated with adaptation are still poorly understood. Secondary invasion into stressful areas may incur fitness costs that could limit range expansion. In addition, developmental plasticity is predicted to be lost under strong selection in stressful habitats. We assessed populations across a range transect of an invasive plant (Plantago lanceolata L.) for a loss of developmental plasticity and for adaptation costs, where there was prior expansion inland into stressful and novel areas from relatively benign areas closer to the coast. In the glasshouse, we grew plants from seed originating from two secondary invasion locations (near-edge and edge), and from the range centre location representing the area of primary invasion. Plants were exposed to high or low nutrient treatment, and novel copper stress and control (no copper) treatment to assess adaptation costs associated with secondary invasion. In addition, we compared the costs in near-edge and edge plants. Developmental plasticity in life-history traits was lost for secondary invasion plants compared to plants from the range centre. Plants from secondary invasion locations expressed a slower life-history under both nutrient treatments. In contrast, range-centre plants were able to switch to a faster life-history under high nutrient treatment. Our copper treatment had only slight effects on plants, where they expressed intermediate specific leaf area (SLA) under copper treatment. Near-edge plants had the lowest plant size and reproduction. The loss of plasticity associated with secondary invasion may have implications on evolution in range edge populations. Phenotypic plasticity may have initially mediated ecological adaptation to stressful habitats; however adaptation to stressful conditions can also have the consequence of inhibiting further range expansion in invasive species.
... Interestingly, there were no carryover effects of the stress in these years, with respect to survival and reproduction (see also little shift in size distribution across the years Online Appendix Fig. S2). This lack of carryover is particularly interesting given that small, and in particular small, old, individuals died at high rates during this stressful time 23 . ...
... Models that included only age and year, or age and sires (not shown) did not lead to qualitatively different results. Previous studies using this data 17,[22][23][24] revealed that survival dropped significantly in 2003 for all cohorts or ages 22 . A model comprising ageand-year-and-sire combinations could not be fit here because of lack of sample size; moreover, such a complex model would be difficult to interpret biologically. ...
Article
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Simple demographic events, the survival and reproduction of individuals, drive population dynamics. These demographic events are influenced by genetic and environmental parameters, and are the focus of many evolutionary and ecological investigations that aim to predict and understand population change. However, such a focus often neglects the stochastic events that individuals experience throughout their lives. These stochastic events also influence survival and reproduction and thereby evolutionary and ecological dynamics. Here, we illustrate the influence of such non-selective demographic variability on population dynamics using population projection models of an experimental population of Plantago lanceolata. Our analysis shows that the variability in survival and reproduction among individuals is largely due to demographic stochastic variation with only modest effects of differences in environment, genes, and their interaction. Common expectations of population growth, based on expected lifetime reproduction and generation time, can be misleading when demographic stochastic variation is large. Large demographic stochastic variation exhibited within genotypes can lower population growth and slow evolutionary adaptive dynamics. Our results accompany recent investigations that call for more focus on stochastic variation in fitness components, such as survival, reproduction, and functional traits, rather than dismissal of this variation as uninformative noise.
... The relationship between age-dependent expression of traits and the environment is shown in a study with Plantago lanceolata, where, during high mortality, aging plants had a higher risk of death (Roach et al., 2009) and decreased in size, while growing plants grew in size (Roach, 2012). Two possible sources of stress that can affect the expression of age dependence in plants are competition and seasonal stress. ...
Article
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Plants hold all records in longevity. Their aging is a complex process. In the presented review, we analyzed published data on various aspects of plant aging with focus on any inferences that could shed a light on aging in animals and help to fight it in human. Plant aging can be caused by many factors, such as telomere depletion, genomic instability, loss of proteostasis, changes in intercellular interaction, desynchronosis, autophagy, epigenetic changes and others. Plants have developed a number of mechanisms to increase lifespan. Among these mechanisms are gene duplication (“genetic backup”), the active work of telomerases, abundance of meristematic cells, capacity of maintaining the meristems permanently active and continuous activity of phytohormones. Plant aging usually occurs throughout the whole perennial life, but could be also seasonal senescence. Study of causes for seasonal aging can also help to uncover the mechanisms of plant longevity. The influence of different factors such as microbiome communities, glycation, alternative oxidase activity, mitochondrial dysfunction on plant longevity was also reviewed. Adaptive mechanisms of long-lived plants are considered. Further comparative study of the mechanisms underlying longevity of plants is necessary. This will allow us to reach a potentially new level of understanding of the aging process of plants.
... This is likely to occur in wild populations in which differential mortality is determined by abiotic conditions and/or biotic pressures of predation, disease, and competition (Abrams 1993, Williams & Day 2003. Condition-dependent aging has been found in the black-brown albatross (Pardo et al. 2013a), snail kites (Reichert et al. 2010), the common gull (Brommer et al. 2010), and a plant species Plantago lanceolata (Roach 2012, Roach et al. 2009), and at high densities for Soay sheep (Coulson et al. 2001). This increased susceptibility of older individuals can change how selection acts on traits, and life span might evolve to be longer under some conditions (Abrams 1993, Descamps et al. 2008, Williams & Day 2003. ...
Article
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Empirical studies reveal aging occurs in wild populations. Consideration of the ecological and evolutionary consequences of these findings is critical for many areas of research, including life-history evolution, sexual selection, behavior, and applied ecology. Variation in the patterns of age-dependent declines of phenotypic traits has been found both within and among individuals, and this raises future questions aimed at understanding what determines these trajectories across traits and across the tree of life. The presence of older, aging, individuals in populations can have transgenerational effects on offspring and can influence how individuals interact. In some species older individuals in populations can have positive impacts, influencing knowledge and leadership, postreproductive care, and population cycle stabilization. Aging and long life span also need to be recognized in an applied ecology context including management plans, vector-borne disease transmission, and ecotoxicology.
... We have shown that a system without evidence of actuarial senescence may still exhibit evidence of physiological senescence suggestive of the accumulation of damage with age. Actuarial senescence has been noted in a number of iteroparous herbaceous perennial species (Silvertown, Franco & Perez-Ishiwara 2001), but patterns in Plantago have been more complex to expose (Roach 2012), requiring further cohorts and periods of stress to identify Roach, Ridley & Dudycha 2009). We encourage further research on age-determinate vs. age-indeterminate factors at work in senescence, particularly in plants and other organisms in which they have not been well documented. ...
Article
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4 synthesis: The hypothesis that plants escape senescence generally assumes that plants can continue to grow larger and increase reproduction as they get older. The results here show that size and reproduction decline with age and the rates of these declines toward death are lifespan- and age-dependent. Further research is needed to delineate the importance of age-determinate vs. age-indeterminate factors in senescence patterns across species.
... They use innovative methodological approaches to analyse remarkable data sets in the plant kingdom and yield valuable and novel insights into the biology of ageing. Several recent publications have highlighted the need for a better understanding of the causes of senescence (García, Dahlgren & Ehrl en 2011; Baudisch & Vaupel 2012; Roach 2012). The contribution by Morales et al. (2013) takes the recent report of negative senescence in the dioecious, herbaceous perennial Borderea pyrenaica (Garc õa, Dahlgren & Ehrl en 2011) one step further. ...
Article
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1. Senescence, the physiological decline that results in decreasing survival and/or reproduction with age, remains one of the most perplexing topics in biology. Most theories explaining the evolution of senescence (i.e. antagonistic pleiotropy, accumulation of mutations, disposable soma) were developed decades ago. Even though these theories have implicitly focused on unitary animals, they have also been used as the foundation from which the universality of senescence across the tree of life is assumed.2. Surprisingly, little is known about the general patterns, causes and consequences of whole-individual senescence in the plant kingdom. There are important differences between plants and most animals, including modular architecture, the absence of early determination of cell lines between the soma and gametes, and cellular division that does not always shorten telomere length. These characteristics violate the basic assumptions of the classical theories of senescence and therefore call the generality of senescence theories into question.3. This Special Feature contributes to the field of whole-individual plant senescence with five research articles addressing topics ranging from physiology to demographic modelling and comparative analyses. These articles critically examine the basic assumptions of senescence theories such as age-specific gene action, the evolution of senescence regardless of the organism's architecture and environmental filtering, and the role of abiotic agents on mortality trajectories.4. Synthesis. Understanding the conditions under which senescence has evolved is of general importance across biology, ecology, evolution, conservation biology, medicine, gerontology, law and social sciences. The question ‘why is senescence universal or why is it not?’ naturally calls for an evolutionary perspective. Senescence is a puzzling phenomenon, and new insights will be gained by uniting methods, theories and observations from formal demography, animal demography and plant population ecology. Plants are more amenable than animals to experiments investigating senescence, and there is a wealth of published plant demographic data that enable interpretation of experimental results in the context of their full life cycles. It is time to make plants count in the field of senescence.
... In natural populations, mortality is greatly influenced by the environment (Picó and Retana, 2008), and C. albidus plants usually die due to natural causes (Roy and Sonié, 1992), for example due to competition for water during drought years or biotic causes. Age, size, and growth can also interact with the environment to influence mortality and life span when the environment is stressful (Roach, 2012). Stress also had an effect on the plants in this study as observed with the correlation of the perimeter of the trunk and the age of the plant: individuals growing in natural conditions with similar ages to those in the Experimental Fields had smaller trunks ( Supplementary Fig. S5). ...
Article
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The question of whether or not perennial plants senesce at the organism level remains unresolved. The aim of this study was to unravel whether or not plant age can influence the production and composition of seeds. Flower and seed production was examined in 3-, 8-, and 13-year-old Cistus albidus plants growing in experimental plots corresponding to the F2, F1, and F0 generations of the same population. Furthermore, the phytohormone, fatty acid, and vitamin E content of the seeds was evaluated, and their viability was examined. Whether or not age-related differences in seed quality were observed in a natural population in the Montserrat Mountains (NE Spain) was also tested. The results indicate that under controlled conditions, the oldest plants not only produced fewer flowers, but also had higher rates of embryo abortion in mature seeds. However, germination capacity was not negatively affected by plant ageing. Seeds of the oldest plants contained significantly higher salicylic acid, jasmonic acid, and vitamin E levels compared with those from younger plants. Despite vigour (in terms of plant growth) being severely reduced due to harsh environmental conditions in the natural population, the oldest individuals produced seeds with no decline in viability. Seed biomass was instead positively correlated with seed viability. In conclusion, increased plant size may explain the loss of seed viability in the experimental field, but older smaller individuals in natural populations can escape senescence in terms of seed viability loss.
... For example, Silvertown et al. [23] documented an increase in the mortality rates with age in about half of the 65 perennial plant species in their study. Similar age-specific mortality patterns have been found in experimental populations of the nonclonal perennial herb Plantago lanceolata [34][35][36], including higher mortality rates and reduced lifespan in plants under stress. Demographic evidence for senescence has also been found for number of perennial grasses and forbs [37]. ...
Article
The evolution of senescence (the physiological decline of organisms with age) poses an apparent paradox because it represents a failure of natural selection to increase the survival and reproductive performance of organisms. The paradox can be resolved if natural selection becomes less effective with age, because the death of postreproductive individuals should have diminished effects on Darwinian fitness [1 • Rose M. • Charlesworth B. A test of evolutionary theories of senescence.Nature. 1980; 287: 141-142 • Crossref • PubMed • Scopus (212) • Google Scholar , 2 • Monaghan P. • Charmantier A. • Nussey D.H. • Ricklefs R.E. The evolutionary ecology of senescence.Funct. Ecol. 2008; 22: 371-378 • Crossref • Scopus (196) • Google Scholar ]. A substantial body of empirical work is consistent with this prediction for animals, which transmit their genes to progeny via an immortal germline. However, such evidence is still lacking in plants, which lack a germline and whose reproduction is diffuse and modular across the soma. Here, we provide experimental evidence for a genetic basis of senescence in the short-lived perennial plant Silene latifolia. Our pedigree-based analysis revealed a marked increase with age in the additive genetic variance of traits closely associated with fitness. This result thus extends to plants the quantitative genetic support for the evolutionary theory of senescence.
... For example, Silvertown et al. [23] documented an increase in the mortality rates with age in about half of the 65 perennial plant species in their study. Similar age-specific mortality patterns have been found in experimental populations of the nonclonal perennial herb Plantago lanceolata [34][35][36], including higher mortality rates and reduced lifespan in plants under stress. Demographic evidence for senescence has also been found for number of perennial grasses and forbs [37]. ...
Article
In adaptation studies, approaches in genomics investigate the genetic, cellular and biochemical mechanisms involved in adaptation using model organisms. In study systems such as Arabidopsis, the demand is high to test for the effect of genes which polymorphism is known on the ability of plants to cope with adverse environmental conditions. In evolutionary ecology, understanding how selection and environmental heterogeneity shape the diversity of organisms is crucial. In that regard, tools to decipher how the architecture of standing genetic variation affects the evolutionary potential of plants to adapt are required. Quantitative genetics provide a range of statistical methods that could be used to study those questions but are generally neglected as a consequence of their scary name, as for example for the pedigree based random regression method used in our approach. Here, we provide a practical guide for researchers from multiple domains who would like to use such methods. We begin by providing an overview of some of the challenges in plant sciences, such as understanding the role of regulatory genes in adaptation that could gain from using such approach. We then illustrate the “how to” of the method by applying it to an imaginary example. We also provide a complete tutorial in the supplementary online material under the form of a protocol and data that can be used to train researchers and students by replicating entirely our approach. We conclude by highlighting the advantages and limits of such approach.
... For example, Chu and Adler (2014) found that, compared to models that included only size, models that took into account both age and size generated better estimates of survival in perennial grasses. Similarly, Roach (2012) found that size, age, and environmental factors determine mortality patterns in Plantago lanceolata (Linnaeus Fig. 2. Trace and posterior density plots for each parameter estimated with the Bayesian model on age-and size-specific mortality on a simulated dataset. The traces show the convergence for the four parallel runs of the model. ...
Article
Full-text available
Mortality in organisms that grow indefinitely, known as indeterminate growers, is thought to be driven primarily by size. However, a number of ageing mechanisms also act as functions of age. Thus, to explain mortality in these species, both size and age need to be explicitly modelled. Here we developed a model that treats age- and size-specific mortality as a bivariate process. This method facilitates the exploration of the underlying (unobserved) contributions of age and size to mortality. We show that, in theory, a population can show declining mortality with age and size while the underlying contribution of age, as a proxy for chronological deterioration, is of typical senescence; while a seemingly senescent population can have underlying age-related negative senescence, which is, however, overcome by negative underlying size effects. We show how inference about these unobserved processes can be made using a simple Bayesian model, and how all of the mortality parameters are accurately retrieved. We then apply the methods to published datasets on water pythons and freshwater mussels and test different hypotheses regarding the effects of age and size on mortality. In both cases we found age-dependent senescent mortality, with size having only negligible effects. The methods we present here can help to improve the demographic models commonly applied to a vast number of species of commercial and conservation importance such as fish, trees or bivalves, among many other, for which both age and size are relevant. In addition, the application of these methods can help to shed light on the existence of processes such as negative senescence, and contribute to our understanding of the evolutionary mechanisms of senescence in species that do not fit the established theories.
... the individual probability of survival that is expected in the case senescence was nevertheless found to be common in perennial plant species (Silvertown et al., 2001). Furthermore, longitudinal demographic surveys show that demographic senescence can occur in wild plant populations (Picó and Retana, 2008;Roach et al., 2009;Roach, 2012). Whether the demographic assumptions underlying Hamilton's claim apply to most plants is still debated. ...
Article
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Senescence, the deterioration of morphological, physiological, and reproductive functions with age that ends with the death of the organism, was widely studied in plants. Genes were identified that are linked to the deterioration of cells, organs and the whole plant. It is, however, unclear whether those genes are the source of age dependent deterioration or get activated to regulate such deterioration. Furthermore, it is also unclear whether such genes are active as a direct consequence of age or because they are specifically involved in some developmental stages. At the individual level, it is the relationship between quantitative genetic variation, and age that can be used to detect the genetic signature of senescence. Surprisingly, the latter approach was only scarcely applied to plants. This may be the consequence of the demanding requirements for such approaches and/or the fact that most research interest was directed toward plants that avoid senescence. Here, I review those aspects in turn and call for an integrative genetic theory of senescence in plants. Such conceptual development would have implications for the management of plant genetic resources and generate progress on fundamental questions raised by aging research.
... As observed in Table 6, this study further proves that seed sources, the age of mother stands, and the interaction of the two have a significant effect on teak seed germination rate [34]. [8] also confirm that local environmental conditions present where the mother stands grew could largely influence germination timing and success. ...
Article
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Teak (Tectona grandis L. f.) plantations developers in Ghana have difficulty in selecting teak seeds from ecological sources and maternal ages that could guarantee optimum germination rates. To fill this knowledge gaps and contribute knowledge on germination characteristics of teak seeds in Ghana, we studied the effects of age of the maternal tree, the ecological zone of the mother tree, and the combination of the two on germination rates of teak seeds. We collected teak seeds from 10, 15, and 20-year-old healthy teak stands in the Savannah Zone (SZ), Transitional Zone (TZ), and the High Forest Zone (HFZ) of Ghana for this study. Fifty seeds from each maternal age for each ecological source were pretreated and sown in nine replicates using a completely randomized design in a factorial experiment with 2-factor treatment combination (age and ecological source). Our findings show that germination rate of seeds from the three maternal ages in the SZ was not different. The SZ also recorded the lowest overall germination rate among the three ecological zones studied. In the TZ, germination rate was not different between 10 years (47.33%) and 15 years (45.33%) maternal stands but both were significantly (p<0.01) higher than 20 years old (34.22%) maternal stands. The TZ recorded intermediate overall germination rates, which are higher than SZ but lower than HFZ. Germination rate was not different between 15 years old (88.00%) and 20 years old (94.44%) in the HFZ but was significantly (p<0.05) higher than 10 years old (41.56%). Moreover, the HFZ recorded the highest overall germination rate among the three ecological zones studied. Our findings further show that seed source (ecological zone), the age of the maternal teak tree, and the interaction of both, have significant (p<0.01) effects on germination rate of teak seeds. More importantly, the effects of age of maternal tree on germination rate was found to be dependent on the ecological zone in which it is located as same maternal age trees recorded different germination rates in different ecological zones. Interaction plot of age and the ecological zone of maternal teak plant produced the highest germination rate at the combination of HFZ with 15 and 20-year-old teak stands. We recommend that teak plantation developers in Ghana select teak seeds from 15 years and above in the High Forest Zone for optimum germination rates.
... In this study, we investigated how climate and non-lethal harvesting of wild plants for non-timber forest products affect age-specific mortality patterns. Studies on the age-specific mortality of plants are rare (Roach et al., 2009;Roach, 2012). This is partly due to difficulties in estimating individual plant age. ...
Article
Environmental and anthropogenic stressors can interact (e.g., drought, harvest or herbivory) to shape plant demography and evolutionary strategies with implications for sustainable resource management plans. Harvest or recurrent biomass removal can act as a selective force. However, our understanding of how harvest and changes in climate can synergistically shape plant evolutionary strategies is limited. We used age-from-stage matrix modeling to investigate how chronic anthropogenic disturbance (severe foliage and bark harvest) affects age-specific mortality trajectories of a tropical tree, Khaya senegalensis in two contrasting climatic regions (dry versus moist) in West Africa. We then developed a stochastic model to test if changes in disturbance regime and the environmental conditions in which a cohort is born may alter stochastic age-specific mortality rates. The effect of harvest on age-specific mortality trajectories was modest and only noticeable in the moist region. Age-specific mortality trajectories differed significantly between regions. In the moist region, mortality rates decreased with age for the first 30 years of life to a minimum rate and then increased gradually after to reach an old age mortality plateau. In the dry region, mortality rates decreased with age to reach a plateau asymptotically. This difference in age-specific mortality trajectory is due to a greater delay in reaching reproductive size/age in the dry region. Our findings underscore intraspecific variation in age-specific mortality schedules and indicate that climatic effect may override the impact of anthropogenic activities on plant demography. Harvest, by favoring fast life stage transition to reproductive stages, can buffer the effect of drought.
... We discussed similarities in coefficient of variation across different level in complexity among organisms and across levels of control that suggest that our result is not exceptional. Promising attempts to overcome the unknown genetics of individuals in natural populations have been made by releasing hundreds or thousands of genetically known crossed individuals into the wild and then tracked throughout their lives (Roach 2012, Travis et al. 2014. Evidence of such experiments suggests that levels of within cross heterogeneity is substantial compared to among cross heterogeneity. ...
Article
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Identifying what drives individual heterogeneity has been of long interest to ecologists, evolutionary biologists and biodemographers, because only such identification provides deeper understanding of ecological and evolutionary population dynamics. In natural populations one is challenged to accurately decompose the drivers of heterogeneity among individuals as genetically fixed or selectively neutral. Rather than working on wild populations we present here data from a simple bacterial system in the lab, Escherichia coli. Our system, based on cutting-edge microfluidic techniques, provides high control over the genotype and the environment. It therefore allows to unambiguously decompose and quantify fixed genetic variability and dynamic stochastic variability among individuals. We show that within clonal individual variability (dynamic heterogeneity) in lifespan and lifetime reproduction is dominating at about 82–88%, over the 12–18% genetically (adaptive fixed) driven differences. The genetic differences among the clonal strains still lead to substantial variability in population growth rates (fitness), but, as well understood based on foundational work in population genetics, the within strain neutral variability slows adaptive change, by enhancing genetic drift, and lowering overall population growth. We also revealed a surprising diversity in senescence patterns among the clonal strains, which indicates diverse underlying cell-intrinsic processes that shape these demographic patterns. Such diversity is surprising since all cells belong to the same bacteria species, E. coli, and still exhibit patterns such as classical senescence, non-senescence, or negative senescence. We end by discussing whether similar levels of non-genetic variability might be detected in other systems and close by stating the open questions how such heterogeneity is maintained, how it has evolved, and whether it is adaptive.
... We discuss similarities in coefficient of variation across different level in complexity among organisms and across levels of control that suggest that our results might not be so special. Promising attempts to overcome the unknown genetics of individuals in the wild have been made by releasing hundreds or thousands of genetically known crossed individuals into the wild and then tracked throughout their lives (Roach 2012, Travis et al. 2014. Evidence of such experiments suggests that levels of within cross heterogeneity is substantial compared to among cross heterogeneity, indicating substantial levels of neutral variability. ...
Preprint
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Identifying what drives individual heterogeneity has been of long interest to ecologists, evolutionary biologists and biodemographers, because only such identification provides deeper understanding of ecological and evolutionary population dynamics. In natural populations one is challenged to accurately decompose the drivers of heterogeneity among individuals as genetically fixed or selectively neutral. Rather than working on wild populations we present here data from a simple bacterial system in the lab, Escherichia coli. Our system, based on cutting-edge microfluidic techniques, provides high control over the genotype and the environment. It therefore allows to unambiguously decompose and quantify fixed genetic variability and dynamic stochastic variability among individuals. We show that within clonal individual variability (dynamic heterogeneity) in lifespan and lifetime reproduction is dominating at about 82-88%, over the 12-18% genetically (adaptive fixed) driven differences. The genetic differences among the clonal strains still lead to substantial variability in population growth rates (fitness), but, as well understood based on foundational work in population genetics, the within strain neutral variability slows adaptive change, by enhancing genetic drift, and lowering overall population growth. We also revealed a surprising diversity in senescence patterns among the clonal strains, which indicates diverse underlying cell-intrinsic processes that shape these demographic patterns. Such diversity is surprising since all cells belong to the same bacteria species, E. coli , and still exhibit patterns such as classical senescence, non-senescence, or negative senescence. We end by discussing whether similar levels of non-genetic variability might be detected in other systems and close by stating the open questions how such heterogeneity is maintained, how it has evolved, and whether it is adaptive. Data deposition The processed image analysis data, R code, as well as the Leslie matrices will be archived at Dryad.org.
... Empirical evidence has shown various survivorship curves (Harper, 1967), and the chance to survive may even rise with age (Lauenroth & Adler, 2008;Baudisch et al., 2013). More recent studies have shown that age may positively and negatively influence the vital rates, i.e. survival, growth, and fecundity, of plant individuals in herbaceous species (Roach, 2012;Baudisch et al., 2013;Baden et al., 2021). ...
Article
1. Identifying to what degree inherent characteristics of plant species and their variation in response to their environment regulate the temporal stability of plant populations is important to understand patterns of species coexistence and the stability of ecosystems. Longevity is a key characteristic of plant‐life history and an important component of demographic storage, but age is usually unknown for herbaceous species. 2. In a 12‐year old biodiversity experiment (Jena Experiment) comprising 80 grassland communities with six levels of plant species richness (1, 2, 4, 8, 16 and 60 species) and four levels of functional groups richness (1, 2, 3 and 4 functional groups), we studied populations of 38 dicotyledonous forb species (N = 1,683 plant individuals). The sampled individuals represented three plant functional groups (legumes, small herbs, tall herbs) and two different growth forms (species with long‐lived primary roots, or clonal species with rhizomes/stolons). We assessed the age of plant individuals by means of growth ring analysis and related the age of plant populations to their temporal stability in terms of peak biomass production. 3. On average, plant species richness did not affect the mean age of the populations or the maximum age of individuals found in a population. Age of herbs with taproots increased and age of herbs with clonal growth decreased with increasing species richness, cancelling out each other when growth forms were analyzed together. Mean population age was lowest for small herbs and highest for tall herbs, while legumes had an intermediate population age. Herbs with a taproot were on average older than herbs with a rhizome. Across all species‐richness levels, populations with older individuals were more stable in terms of biomass production over time. 4. Synthesis. Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species.
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Both demographic and physiological senescence have been demonstrated to occur in various organisms. However, indeterminate growers, such as some animals and most perennial plants, seem to escape the wear and tear of aging. Indeed, most angiosperms show no signs of senescence, and both negligible and negative senescence (improved physiological performance with aging) have been reported in perennial plants growing in their natural habitat. In this opinion article, I review recent developments in the study of senescence in perennial plants and propose that continuous growth prevents senescence. I also address the question whether senescence is a universal process.
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Longevity is a key demographic characteristic of herbaceous plants, but often unknown. While root or rhizome growth ring analysis may allow assessment plant longevity directly and conveniently, so far it has only been used in a few case studies of herbaceous dicotyledonous species. To evaluate whether growth ring analysis is applicable to a large spectrum of herbaceous dicotyledonous plant species, we used plant communities of varying species richness in a 12-year-old grassland biodiversity experiment (Jena Experiment). Cross-sections of the oldest available part of the plants were analysed for all available dicotyledonous perennial herb species (S = 37), which represented three functional groups: legumes, small herbs and tall herbs. We studied 1664 individuals representing the genet in clearly distinguishable plant individuals, and the ramet in clonally growing plant species.
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Plant scientists, conservationists, and land managers have expressed a need for more research into causal mechanisms behind whole-plant senescence and mortality, especially where increased rates and incidence of forest decline are projected owing to climate change. However, these disciplines use the terminology of senescence in different ways, and this impedes communication between them. We highlight three common difficulties with senescence terminology as used in the ecological literature and propose some solutions. Specifically, we recommend (1) distinguishing between physiological and demographic senses of the term "senescence"; (2) discarding the qualifiers "exogenous" and "endogenous" as applied to disturbances that can contribute to senescence; and (3) using care in attributing mortality of individual woody perennials to senescence.
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Senescence is a puzzling phenomenon. Few convincing studies of senescence in perennial herbaceous plants exist. While ramets senesce apparently, whether the senescence of bunchgrasses actually occurs is not clear. In this study, we grew a set of plants of Elymus excelsus, a bunchgrass, to examine plant size, sexual reproduction and bud formation in individual plants in relation to their gradual ageing, intending to determine whether E. excelsus experiences senescence. We collected data in two consecutive years (2009 and 2010) from field samples of plants which were one to five years old. Using regression models we performed age‐related analyses for growth and reproduction parameters. Overall, our results showed that individual plant size (plant diameter, individual plant biomass), total biomass of ramets, number and biomass of reproductive ramets, percentage of ramets that were reproductive, reproductive allocation, over‐wintering buds and juvenile ramets all declined with age. However, the vegetative growth (number and biomass of vegetative ramets) did not decrease with age. Those plants which had survived dwindled in size as they aged. The plants did not shift their resource allocation from growth to reproduction as they aged, so such a shift in allocation could not account for their dwindling size. This article is protected by copyright. All rights reserved.
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Little is known about plant age‐dependent trait expression and how environmental conditions might affect aging in the wild. This study evaluates age variation in multiple traits of a short‐lived perennial herb using a manipulative field experimental design. Two different‐aged cohorts were followed in a field plot for over a year to evaluate trait expression in response to a competition treatment and seasonal stress. Traits measured included size, mortality, reproduction, and physiology, including photosynthetic efficiency and chlorophyll content (SPAD). We hypothesized that the stress of competition and seasonal changes would accentuate age‐dependent trait declines in older plants. The results highlight consistent age differences in plant size, mortality, and seed size with older plants being smaller, more likely to die, and producing smaller seeds. Some of the aging declines were sensitive to environmental conditions such that it was only during certain seasons when older plants had higher mortality, lower photosynthetic efficiency, and lower chlorophyll content than young plants. Age‐dependent trait expression also varied in response to competition such that age differences in size were only present in the ‘no competition treatment,’ and old individuals in the competition treatment had a higher mortality than all other age‐environment combinations. Synthesis. These findings show that aging in plants is a complex phenotype where declines in traits are uncoordinated and can be, but are not always, sensitive to environmental conditions. This study shows age‐dependent maternal effects on offspring quality which, together with the decline in performance of older individuals, may have impacts on an individual's fitness and on natural population demography. This article is protected by copyright. All rights reserved.
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Our goal was to elucidate the population dynamics of the perennial understory herb Calathea ovandensis in a rain forest in southern Mexico using matrix projection model analysis. We emphasize the magnitude and consequences of spatiotemporal variation in (1) basic demographic parameters (growth, survival, and reproduction) (2) asymptotic demographic properties of a given environment (the asymptotic population growth rate and the associated stable-stage distribution and reproductive values) and (3) demographic sensitivities associated with a given environment (sensitivity and elasticity). We obtained 6 yr (1982-1987) of empirical data from four study plots (differing in substrate, light, and density) from which we used the first 5 yr (1982-1986) to construct 16 plot-year and 1 pooled population projection matrices. This stage-structured population was characterized by a long-lived seed bank, temporally variable seedling recruitment (10-fold variability among years), high mortality of seedlings (>90%), very low mortality of reproductives (usually
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Methodological problems in describing patterns of senescence in wild populations have until recently impeded progress in understanding the evolution of a process that decreases individual fitness, We investigated age- and sex-specific survival in five populations of three species of ungulates (roe deer, Capreolus capreolus; bighorn sheep, Ovis canadensis; and isard, Rupicapra pyrenaica), using recent statistical developments of capture-mark-recapture models and long-term (12 to 22 yr) data on marked individuals. The yearly survival of females aged 2-7 yr was remarkably similar and very high (92-95%) in all five populations. Survival of adult males varied among species and populations. Survival decreased from 8 yr onward for both sexes in all populations, suggesting that senescence was a common phenomenon. Male survival was lower than female survival, and the gender difference increased with age. The extent of sex differences in survival was related neither to sexual dimorphism in mass nor to the level
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We applied four tests to detect evidence of the evolution of senescence in life tables and fecundity schedules for 65 species of iteroparous perennial plants. Test 1 determined the pattern of variation in age-specific mortality with age (µ x). Fifty-five percent of species showed an increase in, or maximum value of, µ x at the end of life. In test 2, we tried to separate mortality into initial or baseline mortality and senescent mortality by fitting the survival data of these 65 species to Weibull functions. Unlike published results with animals, the rate of senescence was inde-pendent of initial mortality rate. However, a positive relationship was found between rate of senescence and reproductive lifespan, suggesting increasing risk of death with successive repro-ductive events. It has been suggested that a decline in reproductive value with age is a better diagnostic of senescence, but (in test 3) this occurred in only 9% of species (6/65). Our fourth test detected a positive correlation between age at first reproduction (α) and mean reproductive lifespan (L α), as predicted by the theory that senescence is due to a trade-off between adult survival and reproduction. Comparing species within the two largest families present in the data set, we found a correlation between α and L α among the Liliaceae, which was largely represented by ramet life tables, but not among the Poaceae, which was largely represented by genet life tables. Clonal growth, which is common in plants, is a necessary but not a sufficient condition to prevent the evolution of senescence. We predict that clones that fragment are more likely to escape the evolution of senescence at the genet level than clones that remain physiologically integrated.
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1. Plant demographers using matrix tools have paid special attention to vital rates of reproduction, growth and survival. The demographic implications of plants regressing in size, or shrinking, have been overlooked. Shrinkage has either been ignored during demographic censuses or lumped with other demographic processes such as stasis or growth under the assumption that they have similar demographic effects. 2. We carried out a comparative prospective analysis using classical vital rate elasticities in size-based projection matrices of 80 herbaceous perennial species. We analysed the correlations of the elasticities of each demographic vital rate with the demographic life-history traits (life span, population growth rate, etc.). 3. We also conducted a comparative loop analysis to understand the effects of shrinkage on demographic parameters linked to size plasticity. We classified loops into ‘recruitment’ (growth that contributes to reproduction), ‘size plasticity’ (where individuals fluctuate in size) and ‘size rigidity’ (no change in size class), and used them as the basis to explain ecological characteristics of the species. 4. Our results with classical vital rates demonstrate that considering shrinkage as a separate vital rate increases our understanding of factors that contribute to demographic equilibrium (e.g. minimized departure from population growth rate at equilibrium) and buffering (e.g. higher speed of recovery after disturbance), and to reproductive strategies (e.g. mean age of parents of offspring). 5. The loop analysis results support the findings with vital rate analyses and also reveal new patterns: high growth rates are not exclusively dominated by high elasticities of recruitment, but also by size-plastic loops, and long-lived species experience a marginal increase in the demographic importance of size plasticity. 6.Synthesis. This study illustrates the necessity for exploring individual demographic vital rates, as opposed to grouping them, to advance our understanding of how different biological processes affect population dynamics. Shrinkage is demographically important because it aids in demographic buffering, increases survival and is related to maintenance–reproduction trade-offs. However, shrinkage cannot be fully explored only with traditional elasticity approaches; because shrinkage for some species is a fundamental plastic trait, its importance is more appropriately captured with loop analyses.
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The theory of evolution via natural selection predicts that the genetic composition of wild populations changes over time in response to the environment. Different genotypes should exhibit different demographic patterns, but genetic variation in demography is often impossible to separate from environmental variation. Here, we asked if genetic variation is important in determining demographic patterns. We answer this question using a long-term field experiment combined with general linear modeling of deterministic population growth rates (lambda), deterministic life table response experiment (LTRE) analysis, and stochastic simulation of demography by paternal lineage in a short-lived perennial plant, Plantago lanceolata, in which we replicated genotypes across four cohorts using a standard breeding design. General linear modeling showed that growth rate varied significantly with year, spatial block, and sire. In LTRE analysis of all cohorts, the strongest influences on growth rate were from year x spatial block, and cohort x year x spatial block interactions. In analysis of genetics vs. temporal environmental variation, the strongest impacts on growth rate were from year and year x sire. Finally, stochastic simulation suggested different genetic composition among cohorts after 100 years, and different population growth rates when genetic differences were accounted for than when they were not. We argue that genetic variation, genotype x environment interactions, natural selection, and cohort effects should be better integrated into population ecological studies, as these processes should result in deviations from projected deterministic and stochastic population parameters.
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1. The effects of environment experienced during early development on phenotype as an adult has started to gain vast amounts of interest in various taxa. Some evidence on long-term effects of juvenile environment is available, but replicated experimental studies in wild animals are still lacking. 2. Here we report the first replicated experiment in wild mammals which examines the long-term effects of juvenile and adult environments on individual fitness (reproduction, survival and health). The early development of bank vole (Myodes glareolus) individuals took place in either food-supplemented or un-supplemented outdoor enclosures. After the summer, adult individuals were reciprocally changed to either a similar or opposite resource environment to overwinter. 3. Adult environment had an overriding effect on reproductive success of females so that females overwintering in food-supplemented enclosures had a higher probability of breeding and advanced the initiation of breeding. However, the characteristics of their litters were determined by juvenile environment: females initially grown in food-supplemented conditions subsequently produced larger litters with bigger pups and a male-biased sex ratio. 4. In males, individuals growing in un-supplemented conditions had the highest survival irrespective of adult environment during winter, whereas in females, neither the juvenile nor adult environments affected their survival significantly. The physiological condition of voles in spring, as determined by haematological parameters, was also differentially affected by juvenile (plasma proteins and male testosterone) and adult (haematocrit) environments. 5. Our results suggest that (i) life-history trajectories of voles are not strictly specialized to a certain environment and (ii) the plastic life-history responses to present conditions can actually be caused by delayed effects of the juvenile environment. More generally, the results are important for understanding the mechanisms of delayed life-history effects as well as recognizing their population dynamic consequences.
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1. There is a growing number of empirical reports of environmental change simultaneously influencing population dynamics, life history and quantitative characters. We do not have a well-developed understanding of links between the dynamics of these quantities. 2. Insight into the joint dynamics of populations, quantitative characters and life history can be gained by deriving a model that allows the calculation of fundamental quantities that underpin population ecology, evolutionary biology and life history. The parameterization and analysis of such a model for a specific system can be used to predict how a population will respond to environmental change. 3. Age-stage-structured models can be constructed from character-demography associations that describe age-specific relationships between the character and: (i) survival; (ii) fertility; (iii) ontogenetic development of the character among survivors; and (iv) the distribution of reproductive allocation. 4. These models can be used to calculate a wide range of useful biological quantities including population growth and structure; terms in the Price equation including selection differentials; estimates of biometric heritabilities; and life history descriptors including generation time. We showcase the method through parameterization of a model using data from a well-studied population of Soay sheep Ovis aries. 5. Perturbation analysis is used to investigate how the quantities listed in summary point 4 change as each parameter in each character-demography function is altered. 6. A wide range of joint dynamics of life history, quantitative characters and population growth can be generated in response to changes in different character-demography associations; we argue this explains the diversity of observations on the consequences of environmental change from studies of free-living populations. 7. The approach we describe has the potential to explain within and between species patterns in quantitative characters, life history and population dynamics.
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Theory suggests that iteroparity may confer greater fitness than semelparity in situations in which temporal environmental variation is high and unpredictable. Variable age-specific mortality, density dependence, and other factors may also favor iteroparity over semelparity. Here, we empirically test the adaptive benefits of greater numbers of reproductive years in a study of reproductive schedules in an experimental population of a short-lived polycarpic perennial, Plantago lanceolata. A large experimental population was established that included four cohorts with similar genetic structure. Individuals were censused for mortality, size, and reproduction for seven years. Plants experienced variable numbers of reproductive years, but one or two years were most common (approximately 46.7% of the population reproduced only once). The probability of flowering at least once prior to death was determined strongly by extrinsic, environmental or intrinsic but environmentally influenced variables, including early-life size, cohort, and block, but also varied with a number of interactions involving paternal lineage. Maternal effects explained small but significant components of the variance in the number of reproductive years among individuals in each cohort, while paternal effects were significant in only two cohorts. Number of reproductive years contributed significantly to fitness in this system, more so than all other variables tested, although most of the variation in relative fitness may be attributed ultimately to environmental influences. We suggest that the high proportion of each cohort composed of plants reproducing only once may be due to environmental constraints on either growth or size. Such environmental influences, particularly on early life size, may result in small but important indirect effects on fitness.
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It is generally assumed for most species that mortality rates increase monotonically at advanced ages. Mortality rates were found to level off and decrease at older ages in a population of 1.2 million medflies maintained in cages of 7,200 and in a group of approximately 48,000 adults maintained in solitary confinement. Thus, life expectancy in older individuals increased rather than decreased with age. These results cast doubt on several central concepts in gerontology and the biology of aging: (i) that senescence can be characterized by an increase in age-specific mortality, (ii) that the basic pattern of mortality in nearly all species follows the same unitary pattern at older ages, and (iii) that species have absolute life-span limits.
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Advances in our knowledge of age-associated diseases have far outpaced advances in our understanding of the fundamental ageing processes that underlie the vulnerability to these pathologies. If we are to increase human life expectancy beyond the fifteen-year limit that would result if today's leading causes of death were resolved, more attention must be paid to basic research on ageing. Determination of longevity must be distinguished from ageing to take us from the common question of why we age to a more revealing question that is rarely posed: why do we live as long as we do? But if the ability to intervene in ageing ever becomes a reality, it will be rife with unintended and undesirable consequences.
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Accurate measures of age-dependent mortality are critical to life-history analysis and measures of fitness, yet these measures are difficult to obtain in natural populations. Age-dependent mortality patterns can be obscured not only by seasonal variation in environmental conditions and reproduction but also by changes in the heterogeneity among individuals in the population over time due to selection. This study of Plantago lanceolata uses longitudinal data from a field study with a large number of individuals to develop a model to estimate the shape of the baseline hazard function that represents the age-dependent risk of mortality. The model developed here uses both constant (genetics, spatial location) and time-varying (temperature, rainfall, reproduction, size) covariates not only to estimate the underlying mortality pattern but also to demonstrate that the risk of mortality associated with fitness components can change with time/age. Moreover, this analysis suggests that increasing size after reproductive maturity may allow this plant species to escape from demographic senescence.
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Classical theories for the evolution of senescence predict that organisms that experience low mortality rates attributable to external factors, such as disease or predation, will evolve a later onset of senescence. Here we use patterns of senescence in guppies derived from natural populations that differ in mortality risk to evaluate the generality of these predictions. We have previously found that populations experiencing higher mortality rates evolve earlier maturity and invest more in reproduction, as predicted by evolutionary theory. We report here that these same populations do not have an earlier onset of senescence with respect to either mortality or reproduction but do with respect to swimming performance, which assesses neuromuscular function. This mosaic pattern of senescence challenges the generality of the association between decreased extrinsic mortality and delayed senescence and invites consideration of more derived theories for the evolution of senescence.
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Why do individuals stop reproducing after a certain age, and how is this age determined? The antagonistic pleiotropy theory for the evolution of senescence predicts that increased early-life performance should be accompanied by earlier (or faster) senescence. Hence, an individual that has started to breed early should also lose its reproductive capacities early. We investigate here the relationship between age at first reproduction (AFR) and age at last reproduction (ALR) in a free-ranging mute swan (Cygnus olor) population monitored for 36 years. Using multivariate analyses on the longitudinal data, we show that both traits are strongly selected in opposite directions. Analysis of the phenotypic covariance between these characters shows that individuals vary in their inherent quality, such that some individuals have earlier AFR and later ALR than expected. Quantitative genetic pedigree analyses show that both traits possess additive genetic variance but also that AFR and ALR are positively genetically correlated. Hence, although both traits display heritable variation and are under opposing directional selection, their evolution is constrained by a strong evolutionary tradeoff. These results are consistent with the theory that increased early-life performance comes with faster senescence because of genetic tradeoffs. • evolutionary tradeoff • genetic correlation • heritability • mute swan • aging
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Because environments vary with both predictable patterns and with unpredictable but recurring events, ecologists have long been interested in the ecological adaptations that organisms use to survive periods in which the environment may be exceptionally harsh. In the north-east Pacific, one example of this is periodic warming episodes. Here, we demonstrate for the first time that krill (Euphausia pacifica Hansen), which is a centrally important species in coastal-upwelling systems, can survive periods of abnormally high temperatures by shrinkage between molts, even if food is plentiful. In addition, we demonstrate that there is a high amount of individual variation in growth rates of krill. Krill are centrally important within pelagic foodwebs both worldwide and within the north-east Pacific, thus we explore the potential ecological consequences of such shrinkage for both krill and their predators.
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1 Lefkovitch transition matrices were used to determine vital demographic rates of a natural population of Taraxacum officinale in Morgantown, WV, USA. Separate size transition matrices were calculated for each of four seasons, October-January, January--April, April--July, and July--October, to test if demographic rates vary as a function of season and if size-specific rates vary differentially among seasons. Season-dependent demography was also compared for four phenotype classes segregated by cluster analysis of leaf morphology. 2 The finite rate of increase for the entire population was largest in autumn (October-January) and declined throughout the rest of the year. Overall, there was a small reduction in the population size. Size-specific probabilities of survival, growth and fertility varied dramatically among seasons. Sensitivity analyses showed that small individuals were particularly important to population growth from autumn to spring. Larger individuals were more important during summer. 3 Highly season-dependent demographic rates have large implications for population distribution and persistence since increased vulnerability to perturbation during particular seasons may constrain population growth and stability. Although T. officinale is a long-lived perennial, annual censuses may mask the importance of certain individuals or life history traits for maintenance of genetic variability and population viability. 4 Seasonal and annual finite rates of increase also varied as a function of phenotype class. Of two phenotype classes which had identical annual growth rates, one grew better in cool seasons while the second performed better in warm seasons. Direct competition for resources should be reduced by such inverse patterns of demography across seasons. 5 If phenotype classes are to some degree genetically determined, the differential responses observed here suggest that temporal variation in the environment could explain the maintenance of genetic diversity within populations.
Article
The major starting point to life history analysis is the schedule of reproduction and mortality; hence, knowledge of age-specific demographic dynamics is needed. The key ingredients to studies on age-specific demography must include large cohorts of individuals of known age, an accurate accounting of all individuals, and an experimental design to facilitate a separation of age-dependent and age-independent dynamics. In this study with Plantago lanceolata, multiple, large cohorts were planted over four successive years, and the individuals were censused monthly for nearly five years. Longitudinal analysis showed seasonal variation in demography that was correlated with maximum temperature and cumulative precipitation. Cross-sectional analysis of the different cohorts showed variation across cohorts in age-specific demography. The cohort with the lowest juvenile mortality had the highest adult mortality and the lowest fecundity, suggesting that there is an interdependence of demographic patterns across life stages and that the history of mortality within a cohort may be critical to late-age demographic patterns.
Article
Trade-offs involving life span are important in the molding of plant life histories. However, the empirical examination of such patterns has so far been limited by the fact that information on life span is mainly available in terms of discrete categories; annuals, semelparous perennials and iteroparous perennials. We used transition matrix models to project continuous estimates of conditional life spans from published information on size- or stage-structured demography for 71 perennial plant species. The projected life span ranged from 4.3 to 988.6 years and more than half of the species had a life span of more than 35 years. Woody plants had on average a projected life span more than four times as long as non-woody plants. Life spans were higher in forests than in open habitats and individuals of non-clonal species tended to have a longer life span than ramets of clonal species. Self-incompatible plants on average lived longer than self-compatible plants. There were no clear relations between life span and geographical region, dispersal syndrome, pollination mode, seed size or the presence of a seed bank. We conclude that accurate estimates of life span are central to understand how longevity is correlated to other traits within the group of perennial plants.
Article
Examines the variation in an individual's phenotype contributed by the maternal parent beyond the equal chromosomal contribution expected from each parent. Cytoplasmic genetic, endosperm nuclear and maternal phenotypic effects are distinguished. Such maternal influences are especially pronounced in the seed (size, mineral composition, dormancy and germination), but can also be evident at the seedling and adult stages (eg in yield components and male sterility).-P.J.Jarvis
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The author calls this book a compilation, because he has brought together the findings and thoughts of many scientists on the nature and measurement of senescence, its distribution in man, animal life and protozoa, the influence of genetic factors, the role of growth and rate of living, senescence in cells and in the endocrines. A great deal of factual information is still needed before senescence will be really understood. 733-item bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
Evidence from wildlife and human populations indicates that conditions during early development can have marked effects on the subsequent performance of individuals and cohorts. Likewise, the effects of maternal and, more generally, parental environments can be transferred among individuals between generations. These delayed life-history effects are found consistently and suggestions have been made that they can be one source of both variability and of delayed density dependence in population dynamics. Assessments of several different time series indicate that population variability and delayed density dependence are common and that understanding the mechanisms giving rise to them is crucial for the interpretation and application of such models to basic and applied research. Therefore, it is necessary to assess the different ways in which history in the life history might give rise to variability and delayed density dependence in population dynamics. Here, we build on recent appraisals of the pervasive influence of past environmental conditions on current and future fitness and link the details of these life-history studies to classic features of population dynamics.
Article
1. Understanding how vital rates and reproductive value change with age is fundamental to demography, life history evolution and population genetics. The universality of organism senescence has been questioned on both theoretical and empirical grounds, and the prevalence and strength of senescence remain a controversial issue. Plants are particularly interesting for studies of senescence since individuals of many species have been reported to reach very high ages. 2. In this study, we examined whether the herb Borderea pyrenaica, known to reach ages of more than 300 years, experiences senescence. We collected detailed demographic information from male and female individuals in two populations over 5 years. An unusual morphological feature in this species enabled us to obtain exact age estimates for each of the individuals at the end of the demographic study. 3. We used restricted cubic regression splines and generalized linear models to determine nonlinear effects of age and size on vital rates. We then incorporated the effects of age and size in integral projection models of demography for determining the relationship between age and reproductive value. As the species is dioecious, we performed analyses separately for males and females and examined also the hypothesis that a larger reproductive effort in females comes at a senescence cost. 4. We found no evidence for senescence. Recorded individuals reached 260 years, but growth and fecundity of female and male individuals did not decrease at high ages, and survival and reproductive value increased with age. The results were qualitatively similar also when accounting for size and among-individual vital rate heterogeneity, with the exception that male flowering probability decreased with age when accounting for size increases. 5.Synthesis. Overall, our results show that performance of both male and female plants of B. pyrenaica may increase rather than decrease at ages up to several centuries, and they support the notion that senescence may be negligible in long-lived modular organisms. This highlights the need to explore mechanisms that enable some species to maintain high reproductive values also at very high ages and to identify the evolutionary reasons why some organisms appear to experience no or negligible senescence.
Article
We analyzed and modeled the demography of Eryngium cuneifolium, an herbaceous species endemic to the fire-prone Florida scrub, using 10 annual censuses (1990– 1999) of 11 populations at Archbold Biological Station. Nearly every aspect of the de-mography of this plant is affected by time since fire. Year, time since fire, life history stage, and plant age affected survival, growth, and fecundity of E. cuneifolium, but time since fire and life history stage had the most consistent effects. Survival, flowering stem pro-duction, and early seedling survival were highest in recently burned sites. Long-term sur-vival, growth, and fecundity were highest for yearling cohorts recruiting recently after fire, with the largest contrast between plants recruiting two years postfire and those recruiting more than a decade postfire. Prior (historical) stage also affected individual plant fates. For example, plants with prior stasis or regression in stage subsequently died in greater numbers than plants with prior advancement in stage. Historical analyses did not suggest any cost associated with the initiation of flowering. We used a matrix selection approach to explicitly model Eryngium cuneifolium popu-lation viability in relation to fire. This simulation strategy included preserving observed data and variances within projection matrices formed for individual combinations of pop-ulation and year. We built 54 of these matrices, each with six stages (seed bank, yearlings, vegetative plants, and three reproductive stages). Each of these matrices also represented a specific time since fire. In building matrices, we minimized the use of pooled data while retaining specific matrices whenever possible. In this way, we preserved both the correlation structure within individual matrices (populations, years) and protected patterns among ma-trices across the time-since-fire gradient. To deal with less-detailed data on recruitment processes, we evaluated 13 fertility and seed bank scenarios that bracketed a range of outcomes. All scenarios were similar in showing the positive effects of fire on the demography of E. cuneifolium. The scenario with high seed bank survival (0.5) and low germination rates (0–0.005) was the best predictor of observed postfire years of peak aboveground population size (8 yr) and aboveground population disappearance (30–34 yr), and also did a good job of reproducing observed population trajectories. Finite rates of increase () were 1 only during the first decade postfire but then declined beyond a decade postfire. Although prior (historical) stage affected most individual de-mographic parameters, it did not significantly influence finite rates of increase. Elasticities were highest for stasis and germination from the seed bank. Elasticities for survival in-creased with time since fire, while growth and fertility elasticities decreased. In historical models (those with information on stage from the second-to-last year), the elasticities for stasis were higher and the elasticities for growth lower, compared to models without this history. Bootstrapping suggested small standard errors for several types of model output. Most matrix elements were positively correlated, suggesting that favorable conditions affect many life history stages similarly, and that simulations using element selection would provide a less conservative risk assessment than the matrix selection technique used. We used a stochastic simulation program to simulate changing demography with time since fire, with various fire-return intervals, and for various initial population sizes. We obtained estimates of extinction risk and probability of population decline. Even populations as large as thousands of individuals will become extinct in the absence of fire. Fire-return intervals of 15 yr or less are necessary for E. cuneifolium persistence at individual sites. Fires at intervals longer than 20 yr create substantial extinction risks, and intervals longer than 12 yr produce declining populations. Cycles of widely divergent, alternating short and long fire-return intervals caused slightly higher chances of extinction compared to regular fire-return intervals. Although shrub regrowth is implicated in the decreased viability of E. cuneifolium populations under regimes of infrequent fire, aboveground fuel increases are often too slow 1 to allow frequent burning in Florida rosemary scrub. If E. cuneifolium's rosemary scrub habitat burns less often than every 20 yr, local extinctions and metapopulation dynamics may be the norm. Other rosemary scrub specialists (e.g., Hypericum cumulicola) thrive with less frequent fires and persist in smaller gaps among the regrowing shrubs. Therefore, we suggest that temporal variation in fire-return intervals and spatial variation in fire intensity and patchiness (pyrodiversity) will allow coexistence of all Florida scrub species and hedge against local extinctions of specialists like E. cuneifolium.
Article
1Survival, life expectancy and life span are key demographic parameters that are essential for understanding life-history evolution and forecasting population dynamics, but empirical data on these parameters is extremely limited for herbaceous species.2We used long-term data from annually mapped permanent quadrats in a Kansas, USA, grassland to estimate survival, life expectancy and life span for 29 perennial forbs (herbaceous dicots) and 11 perennial grasses. In the cases of both forbs and grasses, they were the most common species at the research site.3We developed computer programs to track the identity of individual genets based on their spatial locations in the permanent quadrats. The programs distinguished between new recruits and surviving individuals, and calculated the ages and life spans of the survivors.4Most herbaceous perennials die young; life expectancy at age 1 year ranged from 0.6 to 6.5. However, forbs are more likely to die young than grasses. Survival from age 1 to 2 years for forbs ranged from 0.11 to 0.49 with an average of 0.30, whereas for grasses it ranged from 0.30 to 0.63 with an average of 0.44. Maximum observed life spans ranged from 3 to 25 years for forbs and 5 to 39 years for grasses.5All species tended towards Type III survivorship curves, but grasses were more strongly Type III while many forbs had relatively constant survival rates with age. Therefore, population models must account for increasing survival with age, especially for grasses.6Age was a better predictor of grass survival than size, raising questions about the use of size-based methods to indirectly estimate survival and life span.7Maximum observed life span was positively and significantly related with species importance.8Synthesis. The higher survival, life expectancy and life span of grasses compared to forbs may provide a demographic explanation for community-level differences in the dominance and turnover of these two functional groups in grassland plant communities.
Article
Summary 1. Classical evolutionary theory states that senescence should arise as a consequence of the declining force of selection late in life. Although the quantitative genetic predictions of hypotheses derived from this theory have been extensively tested in laboratory studies of invertebrate systems, relatively little is known about the genetics of ageing in the wild. 2. Data from long-term ecological studies is increasingly allowing quantitative genetic approaches to be used in studies of senescence in free-living populations of vertebrates. We review work to date and argue that the patterns are broadly consistent with theoretical predictions, although there is also a clear need for more empirical work. 3. We argue that further advances in this field of research might be facilitated by increased use of reaction norm models, and a decreased emphasis on attempting to discriminate between mutation accumulation and antagonistic pleiotropy models of senescence. We also suggest a framework for the better integration of environmental and genetic effects on ageing. 4. Finally, we discuss some of the difficulties in applying quantitative genetic models to studies of senescence outside the laboratory. In particular we highlight the problems that viability selection can cause for an accurate estimation of parameters used in the prediction of age-trajectory evolution.
Article
Biodemography is increasingly focused on the large and persistent differences between individuals within populations in fitness components (age at death, reproductive success) and fitness-related components (health, biomarkers) in humans and other species. To study such variation we propose the use of dynamic models of observable phenotypes of individuals. Phenotypic change in turn determines variation among individuals in their fitness components over the life course. We refer to this dynamic accumulation of fitness differences as dynamic heterogeneity and illustrate it for an animal population in which longitudinal data are studied using multistate capture-mark-recapture models. Although our approach can be applied to any characteristic, for our empirical example we use reproduction as the phenotypic character to define stages. We indicate how our stage-structured model describes the nature of the variation among individual characteristics that is generated by dynamic heterogeneity. We conclude by discussing our ongoing and planned work on animals and humans. We also discuss the connections between our work and recent work on human mortality, disability and health, and life course theory.
Article
Conditions experienced during early development affect survival and reproductive performance in many bird and mammal species. Factors affecting early development can therefore have an important influence both on the optimization of life histories and on population dynamics. The understanding of these evolutionary and dynamic consequences is just starting to emerge.
Article
The mixed-model factorial analysis of variance has been used in many recent studies in evolutionary quantitative genetics. Two competing formulations of the mixed-model ANOVA are commonly used, the "Scheffe" model and the "SAS" model; these models differ in both their assumptions and in the way in which variance components due to the main effect of random factors are defined. The biological meanings of the two variance component definitions have often been unappreciated, however. A full understanding of these meanings leads to the conclusion that the mixed-model ANOVA could have been used to much greater effect by many recent authors. The variance component due to the random main effect under the two-way SAS model is the covariance in true means associated with a level of the random factor (e.g., families) across levels of the fixed factor (e.g., environments). Therefore the SAS model has a natural application for estimating the genetic correlation between a character expressed in different environments and testing whether it differs from zero. The variance component due to the random main effect under the two-way Scheffe model is the variance in marginal means (i.e., means over levels of the fixed factor) among levels of the random factor. Therefore the Scheffe model has a natural application for estimating genetic variances and heritabilities in populations using a defined mixture of environments. Procedures and assumptions necessary for these applications of the models are discussed. While exact significance tests under the SAS model require balanced data and the assumptions that family effects are normally distributed with equal variances in the different environments, the model can be useful even when these conditions are not met (e.g., for providing an unbiased estimate of the across-environment genetic covariance). Contrary to statements in a recent paper, exact significance tests regarding the variance in marginal means as well as unbiased estimates can be readily obtained from unbalanced designs with no restrictive assumptions about the distributions or variance-covariance structure of family effects.
Article
Survival and fecundity are basic components of demography and therefore have a strong influence on population dynamics. These two key parameters and their relationship are crucial to understand the evolution of life histories. It remains, however, to be empirically established how life span, fecundity, and population dynamics are linked in different organism groups. We conducted a comparative study based on demographic data sets of 55 populations of 23 perennial herbs for which structured demographic models and among-year natural variation in demographic attributes were available. Life span (from 4 to 128 yr old), estimated by using an algorithm, was inversely correlated with the deviance of the population growth rate from equilibrium as well as with among-year population fluctuations. Temporal variability was greater for short-lived species than for the long-lived ones because fecundity was more variable than survival and relatively more important for population dynamics for the short-lived species. The relationship between life span and population stability suggests that selection for longevity may have played an important role in the life history evolution of plants because of its ability to buffer temporal fluctuations in population size.
Article
Many important questions in ecology and evolutionary biology can only be answered with data that extend over several decades and answering a substantial proportion of questions requires records of the life histories of recognisable individuals. We identify six advantages that long-term, individual based studies afford in ecology and evolution: (i) analysis of age structure; (ii) linkage between life history stages; (iii) quantification of social structure; (iv) derivation of lifetime fitness measures; (v) replication of estimates of selection; (vi) linkage between generations, and we review their impact on studies in six key areas of evolution and ecology. Our review emphasises the unusual opportunities and productivity of long-term, individual-based studies and documents the important role that they play in research on ecology and evolutionary biology as well as the difficulties they face.
Article
1. Understanding the evolution of life histories requires an assessment of the process that generates variation in life histories. Within-population heterogeneity of life histories can be dynamically generated by stochastic variation of reproduction and survival or be generated by individual differences that are fixed at birth. 2. We show for the kittiwake that dynamic heterogeneity is a sufficient explanation of observed variation of life histories. 3. The total heterogeneity in life histories has a small contribution from reproductive stage dynamics and a large contribution from survival differences. We quantify the diversity in life histories by metrics computed from the generating stochastic process. 4. We show how dynamic heterogeneity can be used as a null model and also how it can lead to positive associations between reproduction and survival across the life span. 5. We believe our approach to identifying the nature of among-individual heterogeneity yields important insights into the forces that generate within-population variation of life-history traits. It provides an alternative to claims that fixed individual differences are a major determinant of heterogeneity in life histories.
Article
We know very little about aging (senescence) in natural populations, and even less about plant aging. Demographic aging is identified by an increasing rate of mortality following reproductive maturity. In natural populations, quantifying aging is often confounded because changes in mortality may be influenced by both short- and long-term environmental fluctuations as well as age-dependent changes in performance. Plants can be easily marked and monitored longitudinally in natural populations yet the age-dependent dynamics of mortality are not known. This study was designed to determine whether a plant species, Plantago lanceolata, shows demographic aging in its natural environment. A large, multiple-cohort design was used to separate age-independent and age-dependent processes. Seven years of results show environmental influences on mortality as evidenced by synchronous changes in mortality across four cohorts over time. Age-dependent mortality was found through an age-by-environment interaction when the oldest cohorts had significantly higher mortality relative to the younger cohorts during times of stress. Neither size nor quantity of reproduction could explain this variation in mortality across cohorts. These results demonstrate demographic senescence in a natural population of plants.
Article
Longitudinal data on natural populations have been analysed using multistage models in which survival depends on reproductive stage, and individuals change stages according to a Markov chain. These models are special cases of stage-structured population models. We show that stage-structured models generate dynamic heterogeneity: life-history differences produced by stochastic stratum dynamics. We characterize dynamic heterogeneity in a range of species across taxa by properties of the Markov chain: the entropy, which describes the extent of heterogeneity, and the subdominant eigenvalue, which describes the persistence of reproductive success during the life of an individual. Trajectories of reproductive stage determine survivorship, and we analyse the variance in lifespan within and between trajectories of reproductive stage. We show how stage-structured models can be used to predict realized distributions of lifetime reproductive success. Dynamic heterogeneity contrasts with fixed heterogeneity: unobserved differences that generate variation between life histories. We show by an example that observed distributions of lifetime reproductive success are often consistent with the claim that little or no fixed heterogeneity influences this trait. We propose that dynamic heterogeneity provides a 'neutral' model for assessing the possible role of unobserved 'quality' differences between individuals. We discuss fitness for dynamic life histories, and the implications of dynamic heterogeneity for the evolution of life histories and senescence.
Article
Experimental systems that are amenable to genetic manipulation can be used to address fundamental questions about genetic and nongenetic determinants of longevity. Analysis of large cohorts of ten genotypes of Drosophila melanogaster raised under conditions that favored extended survival has revealed variation between genotypes in both the slope and location of age-specific mortality curves. More detailed examination of a single genotype showed that the mortality trajectory was best fit by a two-stage Gompertz model, with no age-specific increase in mortality rates beyond 30 days after emergence. These results are contrary to the limited life-span paradigm, which postulates well-defined, genotype-specific limits on life-span and brief periods of intense and rapidly accelerating mortality rates at the oldest age.
Article
Recent observations of a levelling of the death rate in extreme old age, in both experimental species and humans, are posing difficult problems for evolutionary biologists, in particular about the evolution of the post-reproductive period.
Article
Changes in bone metabolism enable these adult lizards to reversibly alter their length.
Article
Nutritional conditions during key periods of development, when the architecture and modus operandi of the body become established, are of profound importance in determining the subsequent life-history trajectory of an organism. If developing individuals experience a period of nutritional deficit, they can subsequently show accelerated growth should conditions improve, apparently compensating for the initial setback. However, recent research suggests that, although compensatory growth can bring quick benefits, it is also associated with a surprising variety of costs that are often not evident until much later in adult life. Clearly, the nature of these costs, the timescale over which they are incurred and the mechanisms underlying them will play a crucial role in determining compensatory strategies. Nonetheless, such effects remain poorly understood and largely neglected by ecologists and evolutionary biologists.
Article
Ageing (senescence) has never been demonstrated convincingly in any insect in the wild, where mean lifespans are probably much shorter than in the laboratory, and most evidence for senescence in other wild animals (such as mammals) is limited to their reduced survival with age. Here we show that ageing is detectable in wild populations of a very short-lived insect, the antler fly (Protopiophila litigata), and causes debilitating and costly effects that force a decline not only in survival probability, but also in the reproductive rate of males. Our findings argue against the possibility of a trade-off between fitness components, whereby survival may decline without senescence if investment in reproduction increases with age, and indicate that ageing rates are subject to intense selection in the wild.
Article
Life-history theory predicts vital rates that on average make large contributions to the annual multiplication rate of a lineage should be highly buffered against environmental variability. This prediction has been tested by looking for a negative correlation between the sensitivities (or elasticities) of the elements in a projection matrix and their variances (or coefficients of variation). Here, we show by constructing random matrices that a spurious negative correlation exists between the sensitivities and variances, and between the elasticities and coefficients of variation, of matrix elements. This spurious correlation arises in part because size transition probabilities, which are bounded by 0 and 1, have a limit to their variability that often does not apply to matrix elements representing reproduction. We advocate an alternative analysis based on the underlying vital rates (not the matrix elements) that accounts for the inherent limit to the variability of zero-to-one vital rates, corrects for sampling variation, and tests for a declining upper limit to variability as a vital rate's fitness contribution increases. Applying this analysis to demographic data from five populations of the alpine cushion plant Silene acaulis, we provide evidence of stronger buffering in the vital rates that most influence fitness.
Article
A central prediction of classical theories of senescence states that environments posing a high risk of mortality favor the evolution of rapid intrinsic deterioration, or ageing. Although widely cited as being largely corroborated by existing data, empirical support for this prediction has been mixed. Recent theory suggests that this expectation should only be realized under particular circumstances, and this could account for the equivocal empirical findings. Here, we highlight the salient features of some of the recent developments in this field and suggest some ways in which progress might be made. We argue that it is necessary to move beyond the simplistic classical expectation and to take a more comprehensive and precise approach to studies of senescence, both theoretically and empirically.
Article
Stage-based demographic data are now available on many species of plants and some animals, and they often display temporal and spatial variability. We provide exact formulas to compute age-specific life expectancy and survivorship from stage-based data for three models of temporal variability: cycles, serially independent random variation, and a Markov chain. These models provide a comprehensive description of patterns of temporal variation. Our formulas describe the effects of cohort (birth) environmental condition on mortality at all ages, and of the effects on survivorship of environmental variability experienced over the course of life. This paper complements existing methods for time-invariant stage-based data, and adds to the information on population growth and dynamics available from stochastic demography.
Article
1. Three hypotheses have been advanced to account for age-related improvement in performance: the selection hypothesis predicts improved due to the loss of lower quality phenotypes, the constraint hypothesis predicts individuals improve function, and the restraint hypothesis predicts younger individuals forego or reduce effort because of mortality risks. A decline in age-related performance (i.e. senescence) is predicted by mutation accumulation, antagonistic pleiotropy and disposable soma (wear and tear) hypotheses. 2. Using five measures of performance - birth rate, maternal and pup birth mass, pup weaning mass, weaning success and lactation length - we tested these hypotheses concerning age-related change in reproduction in 279 female grey seals (Halichoerus grypus), ages 4-42 years, over a 23-year period between 1983 and 2005 on Sable Island, Nova Scotia. These females produced 2071 pups. 3. Although body mass of primiparous females increased with age (4-7 years) birth mass of their pups did not, but pup weaning mass did. Second- and third-parity females of the same age as primiparous females gave birth to and weaned heavier pups. However, parity and age were dropped from models when maternal body mass was included. 4. The proportion of females giving birth varied significantly with maternal age, increasing in young females and then declining late in life. Weaning success rate also increased rapidly to about 8 years and subsequently declined in females > 32 years. 5. Generalized additive models indicated nonlinear changes in 3 day body mass (i.e. approximately birth mass) and weaning mass of pups as a function of maternal age, after accounting statistically for the effects of maternal body mass. Mixed-effects, repeated-measures models fitted to longitudinal data further supported the conclusion that pup birth mass and weaning mass vary nonlinearly with maternal age and indicated nonlinear changes in lactation duration. 6. We found some support for the constraint hypothesis, but our findings were not consistent with the selection hypothesis or the restraint hypothesis as the basis for improvement in reproductive performance. 7. Senescence was evident in multiple female and offspring traits, indicating the degeneration in function of several physiological systems as predicted by the disposable soma hypothesis.
Article
Phenotypic development is the result of a complex interplay involving the organism's own genetic make-up and the environment it experiences during development. The latter encompasses not just the current environment, but also indirect, and sometimes lagged, components that result from environmental effects on its parents that are transmitted to their developing offspring in various ways and at various stages. These environmental effects can simply constrain development, for example, where poor maternal condition gives rise to poorly provisioned, low-quality offspring. However, it is also possible that environmental circumstances during development shape the offspring phenotype in such a way as to better prepare it for the environmental conditions it is most likely to encounter during its life. Studying the extent to which direct and indirect developmental responses to environmental effects are adaptive requires clear elucidation of hypotheses and careful experimental manipulations. In this paper, I outline how the different paradigms applied in this field relate to each other, the main predictions that they produce and the kinds of experimental data needed to distinguish among competing hypotheses. I focus on birds in particular, but the theories discussed are not taxon specific. Environmental influences on phenotypic development are likely to be mediated, in part at least, by endocrine systems. I examine evidence from mechanistic and functional avian studies and highlight the general areas where we lack key information.
Article
The process of ageing, or senescence, is an important focus of current research, but our knowledge of the factors influencing ageing rates in naturally occurring populations remains poor [1]. A growing number of studies of wild vertebrate and human populations has shown that environmental conditions early in life can have long-term effects on fitness-correlated traits [2,3]. However, the consequences of early-life environment for ageing rates remain unknown [4]. Using data collected over 35 years from a wild population of red deer (Cervus elaphus), we show that females experiencing high levels of resource competition during early life showed faster rates of senescence as adults. Our results suggest that rather than inducing adaptive shifts in developmental trajectories, harsh early-life conditions may constrain development and ultimately exacerbate the ageing process.
Article
Aging, or senescence, defined as a decline in physiological function with age, has long been a focus of research interest for evolutionary biologists. How has natural selection failed to remove genetic effects responsible for such reduced fitness among older individuals? Current evolutionary theory explains this phenomenon by showing that, as a result of the risk of death from environmental causes that individuals experience, the force of selection inevitably weakens with age. This in turn means that genetic mutations having detrimental effects that are only felt late in life might persist in a population. Although widely accepted, this theory rests on the assumption that there is genetic variation for aging in natural systems, or (equivalently), that genotype-by-age interactions (GxA) occur for fitness. To date, empirical support for this assumption has come almost entirely from laboratory studies on invertebrate systems, most notably Drosophila and C. elegans, whereas tests of genetic variation for aging are largely lacking from natural populations. By using data from two wild mammal populations, we perform quantitative genetic analyses of fitness and provide the first evidence for a genetic basis of senescence to come from a study in the natural environment. We find evidence that genetic differences among individuals cause variation in their rates of aging and that additive genetic variance for fitness increases with age, as predicted by the evolutionary theory of senescence.
Article
Density-independent and density-dependent processes affect plant mortality. Although less well understood, age-specific mortality can also play an important role in plant mortality. The goal of this study was to analyse several factors accounting for mortality in the Mediterranean short-lived perennial herb Lobularia maritima. We followed three cohorts of plants (from emergence to death) during 4 years in field conditions. We collected data on plant mortality of the effect of biotic agents (moth larvae and mycoplasma-like organisms, MLOs) and environmental variables. We also estimated density-dependent relationships affecting the fate of seedlings and adults. Results show that cohorts differed in their survival curves and ageing significantly increased mortality risk. Seedling mortality was density-dependent whereas adult mortality was not affected by density. MLO infection led to higher plant mortality whereas moth larvae attack did not affect plant mortality. In general, seedlings and adult plants experienced the highest mortality events in summer. We found, however, weak relationships between weather records and plant mortality. Age and size structures were not correlated. Overall, this study provides a comprehensive review of age-specific, density-dependent and density-independent factors that account for mortality of L. maritima plants throughout their life cycle in field conditions, highlighting the fact that age is an important factor in determining plant population dynamics.
Marine iguanas shrink to survive El Nino. Changes in bone metabolism enable these adult lizards to reversibly alter their length
  • M Wilelski
  • C Thom
Wilelski, M., Thom, C., 2000. Marine iguanas shrink to survive El Nino. Changes in bone metabolism enable these adult lizards to reversibly alter their length. Nature 403, 37-38.
Early growth conditions, phenotypic development and environmental change
  • P Monaghan
Monaghan, P., 2008. Early growth conditions, phenotypic development and environmental change. Philos. Trans. R. Soc. B. 363, 1635-1645.