Testing evolutionary models of senescence in a natural population: age and inbreeding effects on fitness components in song sparrows

Mutation accumulation (MA) and antagonistic pleiotropy (AP) have each been hypothesized to explain the evolution of 'senescence' or deteriorating fitness in old age. These hypotheses make contrasting predictions concerning age dependence in inbreeding depression in traits that show senescence. Inbreeding depression is predicted to increase with age under MA but not under AP, suggesting one empirical means by which the two can be distinguished. We use pedigree and life-history data from free-living song sparrows (Melospiza melodia) to test for additive and interactive effects of age and individual inbreeding coefficient (f) on fitness components, and thereby assess the evidence for MA. Annual reproductive success (ARS) and survival (and therefore reproductive value) declined in old age in both sexes, indicating senescence in this short-lived bird. ARS declined with f in both sexes and survival declined with f in males, indicating inbreeding depression in fitness. We observed a significant agexf interaction for male ARS (reflecting increased inbreeding depression as males aged), but not for female ARS or survival in either sex. These analyses therefore provide mixed support for MA. We discuss the strengths and limitations of such analyses and therefore the value of natural pedigreed populations in testing evolutionary models of senescence.     

Longitudinal age changes in a fishermen population of West Bengal

The longitudinal anthropological age changes in a sample of coastal fishermen in West Bengal are discussed. The results show that some traits follow the trends observed in ageing of Western populations, for instance nasal length and breadth continue to increase throughout life in both sexes. Stature follows also the trend generally observed: a decrease occurs indeed from 35 years of age in both sexes, the decline is becoming higher with increasing age. The typical ecological conditions of our population influence the rate of change in other traits, such as weight and biacromial diameter. Weight is known to be influenced by the nutritional status and the way of life. It explains that in our study of males an early increase of weight and biacromial diameter is observed first and a decrease afterwards. In females, however, a decrease is observed already from 35 years of age. This kind of analysis was only possible with the help of longitudinal data and in a well defined population: only longitudinal data is free from the effect of secular changes and of selective death.     

Ecology and mode-of-life explain lifespan variation in birds and mammals

Maximum lifespan in birds and mammals varies strongly with body mass such that large species tend to live longer than smaller species. However, many species live far longer than expected given their body mass. This may reflect interspecific variation in extrinsic mortality, as life-history theory predicts investment in long-term survival is under positive selection when extrinsic mortality is reduced. Here, we investigate how multiple ecological and mode-of-life traits that should reduce extrinsic mortality (including volancy (flight capability), activity period, foraging environment and fossoriality), simultaneously influence lifespan across endotherms. Using novel phylogenetic comparative analyses and to our knowledge, the most species analysed to date (n = 1368), we show that, over and above the effect of body mass, the most important factor enabling longer lifespan is the ability to fly. Within volant species, lifespan depended upon when (day, night, dusk or dawn), but not where (in the air, in trees or on the ground), species are active. However, the opposite was true for non-volant species, where lifespan correlated positively with both arboreality and fossoriality. Our results highlight that when studying the molecular basis behind cellular processes such as those underlying lifespan, it is important to consider the ecological selection pressures that shaped them over evolutionary time.     

Consequences of heterogeneity in survival probability in a population of Florida scrub-jays

1. Using data on breeding birds from a 35-year study of Florida scrub-jays Aphelocoma coerulescens (Bosc 1795), we show that survival probabilities are structured by age, birth cohort, and maternal family, but not by sex. Using both accelerated failure time (AFT) and Cox proportional hazard models, the data are best described by models incorporating variation among birth cohorts and greater mortality hazard with increasing age. AFT models using Weibull distributions with the shape parameter > 1 were always the best-fitting models. 2. Shared frailty models allowing for family structure greatly reduce model deviance. The best-fitting models included a term for frailty shared by maternal families. 3. To ask how long a data set must be to reach qualitatively the same conclusions, we repeated the analyses for all possible truncated data sets of 2 years in length or greater. Length of the data set affects the parameter estimates, but not the qualitative conclusions. In all but three of 337 truncated data sets the best-fitting models pointed to same conclusions as the full data set. Shared frailty models appear to be quite robust. 4. The data are not adequate for testing hypotheses as to whether variation in frailty is heritable. 5. Substantial structured heterogeneity for survival exists in this population. Such structured heterogeneity has been shown to have substantial effects in reducing demographic stochasticity.     

Longevity differs among sexes but is not affected by repeated immune activation in voles (Microtus arvalis)

Investment of resources in immune defences, despite obvious short-term benefits, may be detrimental to long-term maintenance and thus decrease longevity in absence of parasites. In addition, females and males may differ in immune investment and intrinsic longevity because they are subjected to different degrees of sexual competition and extrinsic mortality. In order to test if sex-specific investment in mounting an immune response reduced longevity, we compared the longevity of captive male and female common voles Microtus arvalis regularly challenged with keyhole limpet haemocyanin, an antigen which elicits the production of antibodies, to the longevity of voles injected with the corresponding antigen-free buffer (phosphate-buffered saline). Injections were repeated every 28 days to mimic a chronic infection. The magnitude of immune response did not vary between males and females and did not affect longevity. Overall, females lived longer than males, independently of the immune challenge. Thus, the long-term costs of immunity seem small in voles. The longevity pattern is consistent with the prediction that male-biased predation or parasitism in the wild causes reduced intrinsic lifespan, but this reduction is not mediated by a decrease in male immunity.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 328–333.     

Fine-scale population structure, inbreeding risk and avoidance in a wild insect population

The ecological and evolutionary importance of fine-scale genetic structure within populations is increasingly appreciated. However, available data are largely restricted to wild vertebrates and eusocial insects. In addition, there is the expectation that most insects tend to have such large- and high-density populations and are so mobile that they are unlikely to face inbreeding risks through fine-scale population structuring. This has made the growing body of evidence for inbreeding avoidance in insects and its implication in mating systems evolution somewhat enigmatic. We present a 4-year study of a natural population of field crickets. Using detailed video monitoring combined with genotyping, we track the movement of all adults within the population and investigate genetic structure at a fine scale. We find some evidence for relatives being found in closer proximity, both across generations and within a single breeding season. Whilst incestuous matings are not avoided, population inbreeding is low, suggesting that mating is close to random and the limited fine-scale structure does not create significant inbreeding risk. Hence, there is little evidence for selective pressures associated with the evolution of inbreeding avoidance mechanisms in a closely related species.     

A comparative analysis of senescence in adult damselflies and dragonflies (Odonata)

Any population whose members are subject to extrinsic mortality should exhibit an increase in mortality with age. Nevertheless, the prevailing opinion is that populations of adult damselflies and dragonflies do not exhibit such senescence. Here, we challenge this contention by fitting a range of demographic models to the data on which these earlier conclusions were based. We show that a model with an exponential increase in age-related mortality (Gompertz) generally provides a more parsimonious fit than alternative models including age-independent mortality, indicating that many odonates do indeed senesce. Controlling for phylogeny, a comparison of the daily mortality of 35 odonate species indicates that although male and female mortalities are positively correlated, mortality tends to be higher in males of those species that exhibit territoriality. Hence, we show for the first time that territoriality may impose a survivorship cost on males, once the underlying phylogenetic relationships are accounted for.     

Dispersal as a source of variation in age-specific reproductive strategies in a wild population of lizards

Dispersal syndromes describe the patterns of covariation of morphological, behavioural, and life-history traits associated with dispersal. Studying dispersal syndromes is critical to understanding the demographic and genetic consequences of movements. Among studies describing the association of life-history traits with dispersal, there is anecdotal evidence suggesting that dispersal syndromes can vary with age. Recent theory also suggests that dispersive and philopatric individuals might have different age-specific reproductive efforts. In a wild population of the common lizard (Zootoca vivipara), we investigated whether dispersive and philopatric individuals have different age-specific reproductive effort, survival, offspring body condition, and offspring sex ratio. Consistent with theoretical predictions, we found that young dispersive females have a higher reproductive effort than young philopatric females. Our results also suggest that the early high investment in reproduction of dispersive females trades-off with an earlier onset of senescence than in philopatric females. We further found that young dispersive females produce smaller offspring in lower body condition than do young philopatric females. Overall, our results provide empirical evidence that dispersive and philopatric individuals have different age-specific life-history traits.     

Sociality, age at first reproduction and senescence: comparative analyses of birds

Evolutionary theories of senescence suggest that aging evolves as a consequence of early reproduction imposing later viability costs, or as a consequence of weak selection against mutations that act late in life. In addition, highly social species that live in sites that are protected from extrinsic mortality due to predation should senesce at a slower rate than solitary species. Therefore, species that start reproducing late in life should senesce at a slower rate than species that start reproducing early. In addition, social species should senesce more slowly than solitary species. Here I investigate the rate of senescence using an extensive data set on longevity records under natural field conditions to test predictions about the evolution of senescence among 271 species of birds. Longevity records increased with sampling effort and body mass, but once these confounding variables were controlled statistically, there was a strongly positive relationship between relative longevity and relative adult survival rate. Relative longevity after controlling statistically for sampling effort, body mass and adult survival rate, increased with age at first reproduction, but not with degree of breeding sociality. These findings suggest that the evolution of senescence is related to timing of first reproduction, but that the evolution of breeding sociality has played a negligible role in the evolution of senescence.     

Diet‐dependent female evolution influences male lifespan in a nuptial feeding insect

Theory predicts that lifespan will depend on the dietary intake of an individual, the allocation of resources towards reproduction and the costs imposed by the opposite sex. Although females typically bear the majority of the cost of offspring production, nuptial feeding invertebrates provide an ideal opportunity to examine the extent to which reproductive interactions through gift provisioning impose a cost on males. Here we use experimental evolution in an Australian ground cricket to assess how diet influences male lifespan and how the costs of mating evolve for males. Our findings show that males had significantly shorter lifespans in populations that adapted to a low‐quality diet and that this divergence is driven by evolutionary change in how females interact with males over reproduction. This suggests that the extent of sexual conflict over nuptial feeding may be under‐realized by focusing solely on the consequences of reproductive interactions from the female’s perspective.     

Consequences of mating and predation risk for longevity in a freshwater snail: abstinence makes the heart beat longer

Senescence is not a static property of an individual or population, but rather it is a dynamic process that may be influenced by environmental conditions. This can occur in at least two ways: in the long‐term across multiple generations, and in the short‐term via phenotypic plasticity. The former has attracted a lot of attention, both theoretically and empirically; the latter has lagged behind. To determine whether two important environmental variables (predation risk and mate availability) affect the pattern of actuarial senescence (i.e. the increase in mortality with age), we reared 30 full‐sib families of the simultaneously hermaphroditic freshwater snail Physa acuta under four different environmental conditions and tracked individuals until death. Individuals were reared in a 2×2 factorial experiment that manipulated the nonlethal presence of chemical cues from predatory crayfish (presence/absence) and the opportunity to mate with an unrelated partner (mated/not mated). Snails that receive a partner reproduce by outcrossing, whereas those that remain in isolation can reproduce by self‐fertilization. We compared the cumulative survival curves to test for an effect of predation risk and mating. The hazard ratio (HR) for the predation risk comparison was 1.042 indicating no significant difference between the curves. However, the HR for the mating comparison was 4.021, reflecting a significant reduction in survival probability for mated snails relative to isolated snails. As such, mating resulted in a much shorter lifespan, an outcome that we interpret in terms of shifting resource allocation.     

Self-reported dry mouth in Swedish population samples aged 50, 65 and 75 years

doi: 10.1111/j.1741‐2358.2010.00420.x Self‐reported dry mouth in Swedish population samples aged 50, 65 and 75 years Background: Reduced salivary flow may have a negative impact on general well‐being, quality of life and oral health. Objectives: To examine xerostomia in 50‐, 65‐ and 75‐year‐olds, background factors and effect on Oral Impacts on Daily Performances (OIDP). Methods: In 1992, a questionnaire was sent to all 50‐year‐old persons (n = 8888) in two Swedish counties. In 2007, the same questionnaire was sent to all 65‐year‐olds (n = 8313) in the two counties and to all 75‐year‐olds (n = 5195). Response rate was for the 50, 65 and 75 year olds 71.4, 73.1 and 71.9%, respectively. Results: Xerostomia was higher in women than in men in all age groups. There was higher prevalence of xerostomia with increasing age in both sexes and it was more frequent at night than during daytime. ‘Often mouth dryness’ was 2.6–3.4 times more prevalent in those who reported an impact from OIDP. The highest odd ratios were for daytime xerostomia and for the variables burning mouth (17.1), not feeling healthy (4.5), daily smoking (4.4), and medication (4.1). Conclusions: The dramatic increase of xerostomia between age 50 and 75, especially amongst women, needs to be considered in the management of this age group.     

Identification and management of a single large population of wild dromedary camels

The dromedary camel (Camelus dromedarius) is a significant invasive species in Australia. It is an unusual pest species that is of large body size with relatively low fecundity compared with other pest species. Camels are highly adapted to the arid regions that characterize a large proportion of Australia and occupy an almost completely undisturbed area of ≥3 million km². They have no history of invasion elsewhere in the world. Despite this, their population has been expanding at approximately 80,000 camels per annum, with the most recent estimate of population size around 1,000,000 individuals. We employed a landscape-genetic approach to evaluate the population structure and molecular ecology of Australian camels. We combined mitochondrial control region sequence (n = 209 animals) with 18 microsatellite markers to profile over 800 adult camels to identify the presence of a single panmictic population. We showed that demographically defined neighborhoods for wild camels are about 200 km; this value was supported by home range estimates. Distances greater than this display no pattern of isolation by distance across the Australian continent. The result is the largest single geographical population so far recorded for an invasive species in Australia. This pattern may be explained by the impressive and near-nomadic dispersal pattern of camels, in combination with an unpredictable environment virtually devoid of barriers to movement and predatory suppression. Although it is technically feasible, the reality is that it would not be economically or politically viable to have continental eradication of wild camels in Australia because of the vast size and movement dynamics of the camel population. As such, we advocate a change away from an expensive solution to an intractable reduction program (that is almost entirely focused on protection of biological refugia) and moves to include cultural, economic, and biodiversity asset protection for the management of this most unorthodox of invasive species. © 2012 The Wildlife Society.     

Conserving genetic variability of a wild insect population under laboratory conditions

Drosophila melanogaster (Meigen) was used to test the power of isofemale lines in preserving genetic variability. We performed experiments in two ways. One series consisted of measuring the genetic variability for three enzymatic loci in 32 isofemale lines, in the first and 23^rd generations of culture. In the second series, we tested the capacity of the larvae to eliminate a parasitoid by encapsulation after eight years of laboratory breeding. In general, individual isofemale lines appeared to change during the 23 generations of the study, but the global frequency of these alleles among the 32 isofemale lines stayed relatively unchanged. The only rare allele observed was also conserved. Changes in allozyme frequencies at any one locus were independent of those at other loci. Genetic variation of a biological trait, the capacity of the larvae to encapsulate a parasitoid, also changed, but it could be restored to a level close to that of the starting population by mass hybridizing together individuals of each line.

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Résumé D. melanogaster (Meigen) a été utilisé pour tester la capacité des lignées isofemelles à conserver la variabilité génétique d'une population naturelle. Deux types d'expériences ont été réalisées. L'une a consisté à déterminer la variabilité génétique de 3 locus enzymatiques pour 32 lignées isofemelles à la première et à la 23^ème génération d'élevage au laboratoire. L'autre a consisté à tester la capacité des larves à éliminer un parasito?de par le processus d'encapsulation après 8 années d'élevage au laboratoire. D'une fa?on générale, certaines lignées isofemelles perdent de la variabilité durant les 23 générations de l'étude. Mais la fréquence globale des allèles reste inchangée si l'on considère l'ensemble des 32 lignées. Le seul allèle rare observé a également été conservé. Les modifications des fréquences allèliques à chacun des locus ont lieu de fa?on indépendante les unes des autres. La variabilité génétique d'un caractère biologique, la capacité des larves à encapsuler le parasito?de, a également varié, mais elle a pu être restaurée à un niveau proche de la population initiale en rassemblant plusieurs individus de chacune des lignées.

     

Assessing changes in oral health‐related quality of life and its factors in community‐dwelling older Brazilians

doi: 10.1111/j.1741‐2358.2012.00656.x Assessing changes in oral health‐related quality of life and its factors in community‐dwelling older Brazilians Objective: To describe changes in oral health‐related quality of life and to evaluate the associations of these changes in community‐dwelling older people. Materials and methods: In this longitudinal study a representative sample of 872 older people, living in Brazil, was evaluated during 2004. The follow‐up was carried out during 2008, with 587 older persons evaluated. A questionnaire assessing socio‐demographic information, health history, oral health‐impact profile and number of natural teeth was used. Changes in oral health‐related quality of life were categorized as improvement or deterioration. Data analysis was performed using a hierarchical approach based in a conceptual framework. A hierarchal approach was carried out using Poisson regressions. Results: Older persons living in rural areas, those who reported brushing once a day or less and older persons with fewer natural teeth had an increased chance of reporting deterioration in oral health‐related quality of life. Women and participants who received a minimum wage of less than US$219.50 were more likely to report improvement in oral health‐related quality of life. Conclusion: The results of this study suggest that changes in the oral health‐related quality of life are influenced by many of the variables that were included in the conceptual framework.     

Trans‐generational effects on ageing in a wild bird population

Ageing, long thought to be too infrequent to study effectively in natural populations, has recently been shown to be ubiquitous, even in the wild. A major challenge now is to explain variation in the rates of ageing within populations. Here, using 49 years of data from a population of great tits (Parus major), we show that offspring life‐history trajectories vary with maternal age. Offspring hatched from older mothers perform better early in life, but suffer from an earlier onset, and stronger rate, of reproductive senescence later in life. Offspring reproductive lifespan is, however, unaffected by maternal age, and the different life‐history trajectories result in a similar fitness payoff, measured as lifetime reproductive success. This study therefore identifies maternal age as a new factor underlying variation in rates of ageing, and, given the delayed trans‐generational nature of this effect, poses the question as to proximate mechanisms linking age‐effects across generations.     

Genotypic and phenotypic diversity of a baculovirus population within an individual insect host

It is becoming increasingly apparent that many pathogen populations, including those of insects, show high levels of genotypic variation. Baculoviruses are known to be highly variable, with isolates collected from the same species in different geographical locations frequently showing genetic variation and differences in their biology. More recent studies at smaller scales have also shown that virus DNA profiles from individual larvae can show polymorphisms within and between populations of the same species. Here, we investigate the genotypic and phenotypic variation of an insect baculovirus infection within a single insect host. Twenty four genotypically distinct nucleopolyhedrovirus (NPV) variants were isolated from an individual pine beauty moth, Panolis flammea, caterpillar by in vivo cloning techniques. No variant appeared to be dominant in the population. The PaflNPV variants have been mapped using three restriction endonucleases and shown to contain three hypervariable regions containing insertions of 70-750 bp. Comparison of seven of these variants in an alternative host, Mamestra brassicae, demonstrated that the variants differed significantly in both pathogenicity and speed of kill. The generation and maintenance of pathogen heterogeneity are discussed.