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.

Nestling telomere shortening, but not telomere length, reflects developmental stress and predicts survival in wild birds.

Developmental stressors often have long-term fitness consequences, but linking offspring traits to fitness prospects has remained a challenge. Telomere length predicts mortality in adult birds, and may provide a link between developmental conditions and fitness prospects. Here, we examine the effects of manipulated brood size on growth, telomere dynamics and post-fledging survival in free-living jackdaws. Nestlings in enlarged broods achieved lower mass and lost 21% more telomere repeats relative to nestlings in reduced broods, showing that developmental stress accelerates telomere shortening. Adult telomere length was positively correlated with their telomere length as nestling (r = 0.83). Thus, an advantage of long telomeres in nestlings is carried through to adulthood. Nestling telomere shortening predicted post-fledging survival and recruitment independent of manipulation and fledgling mass. This effect was strong, with a threefold difference in recruitment probability over the telomere shortening range. By contrast, absolute telomere length was neither affected by brood size manipulation nor related to survival. We conclude that telomere loss, but not absolute telomere length, links developmental conditions to subsequent survival and suggest that telomere shortening may provide a key to unravelling the physiological causes of developmental effects on fitness.

Stochastic modeling of length-dependent telomere shortening in Corvus monedula.

It was recently shown that, within individuals, longer telomeres shorten at a higher rate. This explorative study deals with a mathematical model of this process. It is a nonlinear differential equation describing length-dependent decrease that can be linked to a Poisson process. The model also takes in account telomere shortening due to the end replication problem. Parameters are fitted using data from samples of red blood cells of free-living juvenile corvids. The Poisson process can be related to oxidative stress causing DNA strand breaks. The shortest telomeres in a genome are the best predictors of survival, and one can therefore hypothesize on functional grounds that short telomeres should be better protected by some control mechanism in the cellular system. However, the present study shows that such a mechanism is not required to explain length-dependent telomere shortening: agents of telomere shortening such as oxidative stress with a certain strength modeled by a Poisson process with an appropriately chosen parameter suffice to generate the observed pattern.

Telomere shortening and survival in free-living corvids.

Evidence accumulates that telomere shortening reflects lifestyle and predicts remaining lifespan, but little is known of telomere dynamics and their relation to survival under natural conditions. We present longitudinal telomere data in free-living jackdaws (Corvus monedula) and test hypotheses on telomere shortening and survival. Telomeres in erythrocytes were measured using pulsed-field gel electrophoresis. Telomere shortening rates within individuals were twice as high as the population level slope, demonstrating that individuals with short telomeres are less likely to survive. Further analysis showed that shortening rate in particular predicted survival, because telomere shortening was much accelerated during a bird's last year in the colony. Telomere shortening was also faster early in life, even after growth was completed. It was previously shown that the lengths of the shortest telomeres best predict cellular senescence, suggesting that shorter telomeres should be better protected. We test the latter hypothesis and show that, within individuals, long telomeres shorten faster than short telomeres in adults and nestlings, a result not previously shown in vivo. Moreover, survival selection in adults was most conspicuous on relatively long telomeres. In conclusion, our longitudinal data indicate that the shortening rate of long telomeres may be a measure of 'life stress' and hence holds promise as a biomarker of remaining lifespan.

Metabolic adjustments to increasing foraging costs of starlings in a closed economy.

Knowledge of the physiological consequences of variation in food availability may be essential for understanding behavioural and life history responses to such variation. To study the physiological consequences of food availability animals are generally subjected to caloric restriction or starvation, thereby reducing the upper limit to the energy budget. The relevance of this approach to free-living animals is questionable, however, because under natural conditions low food availability often results in higher foraging costs, and everything else remaining equal this results in a higher energy budget. We manipulated food availability by varying the foraging costs and studied effects on daily energy expenditure (DEE) and energy allocation of captive starlings Sturnus vulgaris. Birds in a closed economy earned their food by flying between two perches 5 m apart. The probability of a reward was set at three different levels, thereby creating a 'poor', 'intermediate' and 'rich' environment. Compared with the rich environment, birds flew 4 times more (2.3 h per day) in the poor environment, and increased DEE by 43% to 220 kJ day-1 (3.7xBMR), within the range of free-living parents rearing young. To our knowledge this is the first study to show an increase in DEE with decreasing food availability. Body mass, basal metabolic rate (BMR) and pectoral muscle size were reduced in the poor environment. Nocturnal energy expenditure was further reduced by reaching BMR earlier in the night. Calculations show that the energy demands in the poor environment could not be met with the flight costs of 20.5 W that we measured previously in a rich environment. Flight costs derived indirectly from the energy budget were lower, at 17.5 W, probably due to lower body mass. By reducing body mass by 20%, and economising during sleep, the birds achieved savings of 37% in their DEE. Without these savings, a DEE substantially higher than measured in free-living parents rearing young would be required to remain in energy balance. Surprisingly little data exist to verify whether free-living animals use the same tactics to survive periods with low food availability.

Nitric oxide and gallbladder motility in prairie dogs.

In this study we evaluated the role of nitric oxide (NO) on gallbladder motility in the normal prairie dog by 1) immunohistochemistry, 2) an enzymatic assay for NO synthase (NOS), and 3) an in vivo model to measure whole gallbladder tone and contractility. NOS was localized to gallbladder mucosal cells by NADPH-diaphorase and polyclonal antibodies to a constitutive brain NOS. Gallbladder mucosal homogenates demonstrated total NOS activity in the range of 578 +/- 115 pmol x mg protein(-1) x 30 min(-1). Blockade of NOS activity in vivo using N(omega)-nitro-L-arginine methyl ester resulted in an up to 80% increase in gallbladder tone from basal. A 40% increase in tone was seen with methylene blue, suggesting that tone was maintained by both NO activation of guanylate cyclase and possibly direct effects on Ca2+ channels. An exogenous nitrosothiol, S-nitroso-N-acetyl-cysteine, abolished cholecystokinin (CCK) octapeptide and bethanechol-stimulated gallbladder contraction. We conclude that the prairie dog gallbladder contains constitutive NOS and synthesizes NO, which is important for the maintenance of basal gallbladder tone and is an inhibitor of the contractile response of the gallbladder to agonists such as CCK and bethanechol.

Whole blood and plasma water in health and disease: longitudinal and transverse observations and correlations with several different hematological and clinicochemical parameters.

In a healthy reference population, hemoglobin (Hgb) and hematocrit (Hct) have been proposed as surrogate markers for whole blood water (WBW). We have extended this study under different physiological and pathological conditions in two longitudinal series, viz. (1) acute hyper- and hypohydration experiments in a healthy individual and (2) three athletes running 5 km each, and in three transverse series, viz. (3) a young reference population (n = 97, 49 females), (4) an old reference population (n = 37, nine females) consisting of inhabitants of a nursing home and (5) cardiac, hematological and renal patients including severe anaemia, polycythaemia and abnormal protein levels (n = 50, 25 females) with suspected hydration disturbances. The only sex difference found was a lower WBW in males in the young reference group. The percentage change of PW was less than that of WBW. In all five groups together (n = 293) WBW correlated closely (P < 0.0001) with Hgb and Hct (both r = -0.95) and with erythrocyte count (r = -0.85), whereas PW correlated with total protein (Tprot) (r = -0.84). In the longitudinally studied groups (1) and (2) WBW also correlated (P < 0.0001) with cholesterol, Ca, Tprot, albumin, platelets, globulin and white blood cells (r +/- 0.98-0.37), while PW correlated (P < 0.0001) not only with the same clinicochemical parameters but also with Hct, Hgb and red blood cells (r +/- 0.98-0.44). The homeostasis of PW is more narrowly regulated than that of WBW. Hgb, Hct and erythrocyte count reflect WBW and Tprot reflects PW also under disease conditions. WBW (mass%) can be calculated from Hgb and Hct using the formulae: -0.09 x Hgb (g/l) + 91.7 and -28.6 x Hct (v/v) + 91.8 and PW (mass%) from Tprot using the formula: -0.09 x Tprot (g/l) + 97.6. Other correlations were observed only in a longitudinal setting and presumably are due to concentration and dilution.