Reproductive effort accelerates actuarial senescence in wild birds: an experimental study

Optimality theories of ageing predict that the balance between reproductive effort and somatic maintenance determines the rate of ageing. Laboratory studies find that increased reproductive effort shortens lifespan, but through increased short‐term mortality rather than ageing. In contrast, high fecundity in early life is associated with accelerated senescence in free‐living vertebrates, but these studies are non‐experimental. We performed lifelong brood size manipulation in free‐living jackdaws. Actuarial senescence – the increase in mortality rate with age – was threefold higher in birds rearing enlarged‐ compared to reduced broods, confirming a key prediction of the optimality theory of ageing. Our findings contrast with the results of single‐year brood size manipulation studies carried out in many species, in which there was no overall discernible manipulation effect on mortality. We suggest that our and previous findings are in agreement with predictions based on the reliability theory of ageing and propose further tests of this proposition.     

Social life histories: jackdaw dominance increases with age,terminally declines and shortens lifespan

Behaviour may contribute to changes in fitness prospects with age, for example through effects of age-dependent social dominance on resource access. Older individuals often have higher dominance rank, which may reflect a longer lifespan of dominants and/or an increase in social dominance with age. In the latter case, increasing dominance could mitigate physiological senescence. We studied the social careers of free-living jackdaws over a 12 year period, and found that: (i) larger males attained higher ranks, (ii) social rank increased with age within individuals, and (iii) high-ranked individuals had shorter lifespan suggesting that maintaining or achieving high rank and associated benefits comes at a cost. Lastly, (iv) social rank declined substantially in the last year an individual was observed in the colony, and through its effect on resource access this may accelerate senescence. We suggest that behaviour affecting the ability to secure resources is integral to the senescence process via resource effects on somatic state, where behaviour may include not only social dominance, but also learning, memory, perception and (sexual) signalling. Studying behavioural effects on senescence via somatic state may be most effective in the wild, where there is competition for resources, which is usually avoided in laboratory conditions.     

Soil quality as affected by tillage-residue management in a wheat-maize irrigated bed planting system

There is a clear need to develop conservation agriculture technologies appropriate for surface irrigated conditions, and the adoption by small-scale farmers. The objective of this paper is to evaluate the effect on soil quality of five different tillage-crop residue management systems (conventionally tilled raised beds [CTB] with residue incorporated and permanent raised beds [PB] with residue burned, removed, partly retained or fully retained). Data were collected in a long-term trial established in 1992 with a wheat-maize rotation under irrigated, arid conditions in north-western Mexico. Three groups of tillage-straw systems with different characteristics in relation to the soil environment were distinguished: PB-straw burned, CTB-straw incorporated, and PB-straw not burned. The PB-straw burned had high electrical conductivity, Na concentration and penetration resistance and low soil resilience and aggregation, showing that the combination of PB with the burning of residues is not a sustainable management option. The CTB-straw incorporated was distinguished from the PB practices by the soil physical variables, especially the low direct infiltration and aggregate stability, indicating degradation of physical soil quality in this system. The practice of PB, where all or part of the residue is retained in the field, seems to be the most sustainable option for this cropping system.     

An appraisal of how the vitamin A‐redox hypothesis can maintain honesty of carotenoid‐dependent signals

The vitamin A‐redox hypothesis provides an explanation for honest signaling of phenotypic quality by carotenoid‐dependent traits. A key aspect of the vitamin A‐redox hypothesis, applicable to both yellow and red coloration, is the hypothesized negative feedback of tightly regulated Vitamin A plasma levels on the enzyme responsible for sequestering both Vitamin A and carotenoids from the gut. We performed a meta‐analysis and find that vitamin A levels are positively related to carotenoid plasma levels (r = 0.50, P = 0.0002). On the basis of this finding and further theoretical considerations, we propose that the vitamin A‐redox hypothesis is unlikely to explain carotenoid‐dependent honest signaling.     

No important role for genetic variation in the Chibby gene in monogenic and complex obesity

Chibby (CBY) has been identified as a potent proadipogenic factor required for adipocyte differentiation. It has been shown that CBY inhibits the canonical Wnt pathway, and therefore promotes the development of new fat cells. Our objective therefore is to investigate the contribution of rare and common genetic variation in CBY to the development of human obesity. A mutation analysis was performed on a total of 566 obese patients and 432 lean individuals. To investigate the involvement of CBY in complex obesity, we performed a genetic association analysis of the entire CBY gene region on 1,011 obese individuals and 523 control samples. Four rare, novel variants were identified in either obese patients or lean control subjects, among which two non-synonymous variations and one frameshift mutation. In addition, four previously reported CBY variants were found. In the association analysis, logistic and linear regression showed no association between common genetic variation in CBY and obesity parameters. Several novel variations were found, but no definite role in the pathogenesis of obesity could be confirmed. Results from the association analysis suggest that common variation in CBY is not a cause for obesity in the Belgian population.     

A silver spoon for a golden future: long-term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)

1. Long-term effects of conditions during early development on fitness are important for life history evolution and population ecology. Using multistrata mark-recapture models on 20 years of data, we quantified the relation between rearing conditions and lifetime fitness in a long-lived shorebird, the oystercatcher (Haematopus ostralegus). We addressed specifically the relative contribution of short- and long-term effects of rearing conditions to overall fitness consequences. 2. Rearing conditions were defined by differences in natal habitat quality, in which there is a clear dichotomy in our study population. In the first year of life, fledglings from high-quality natal origin had a 1.3 times higher juvenile survival. Later in life (age 3-11), individuals of high-quality natal origin had a 1.6 times higher adult prebreeder survival. The most striking effect of natal habitat quality was that birds that were reared on high-quality territories had a higher probability of settling in high-quality habitat (44% vs. 6%). Lifetime reproductive success of individuals born in high-quality habitat was 2.2 times higher than that of individuals born in low-quality habitat. This difference increased further when fitness was calculated over several generations, due to a correlation between the quality of rearing conditions of parents and their offspring. 3. Long-term effects of early conditions contributed more to overall fitness differences as short-term consequences, contrary to common conceptions on this issue. 4. This study illustrates that investigating only short-term effects of early conditions can lead to the large underestimation of fitness consequences. We discuss how long-term consequences of early conditions may affect settlement decisions and source-sink population interactions.     

Role of the AMP-activated protein kinase (AMPK) signaling pathway in the orexigenic effects of endogenous ghrelin

Ghrelin, released from the stomach, stimulates food intake through activation of the ghrelin receptor (GHS-R) located on neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons in the hypothalamus. A role for the energy sensor AMP-activated protein kinase (AMPK) and its downstream effector uncoupling protein 2 (UCP2) in the stimulatory effect of exogenous ghrelin on NPY/AgRP expression and food intake has been suggested. This study aimed to investigate whether a rise in endogenous ghrelin levels is able to influence hypothalamic AMPK activity, pACC, UCP2 and NPY/AgRP expression through activation of GHS-R. An increase in endogenous ghrelin levels was established by fasting (24h) or by induction of streptozotocin(STZ)-diabetes (15 days) in GHS-R(+/+) and GHS-R(-/-) mice. GHS-R(+/+) mice showed a significant increase in AgRP and NPY mRNA expression after fasting, which was not observed in GHS-R(-/-) mice. Fasting did not affect AMPK activity nor ACC phosphorylation in both genotypes and increased UCP2 mRNA expression. The hyperghrelinemia associated with STZ-induced diabetes was accompanied by an increased NPY and AgRP expression in GHS-R(+/+) but not in GHS-R(-/-) mice. AMPK activity and UCP2 expression in GHS-R(+/+) mice after induction of diabetes were decreased to a similar extent in both genotypes. Exogenous ghrelin administration tended to decrease hypothalamic AMPK activity. In conclusion, an increase in endogenous ghrelin levels triggered by fasting or STZ-induced diabetes stimulates the expression of AgRP and NPY via interaction with the GHS-R. The changes in AMPK activity, pACC and UCP2 occur independently from GHS-R suggesting that they do not play a major role in the orexigenic effect of endogenous ghrelin.     

Metabolic ageing in individual zebra finches

Oxidative stress is suggested as a contributor to the ageing process. Knowledge of the relationship between age and energy expenditure may contribute to our understanding of ageing patterns, due to the link between oxygen consumption and free radical production. However, studies on basal metabolic rate (BMR) and age have generally been cross-sectional, which may confound estimates of the age effect due to disproportionate mortality (also known as 'selective disappearance'). We therefore performed a longitudinal study of BMR using captive zebra finches (Taeniopygia guttata) up to 5 years of age. BMR declined with age in individuals of both sexes when body mass was controlled for. Males gained mass with age while females did not. There was no evidence for disproportionate mortality with respect to BMR in either sex. To our knowledge, this is the first longitudinal study of avian BMR over such a long proportion of the lifespan of the study species.