Endocrine and haemodynamic stress responses to an arithmetic cognitive challenge.

OBJECTIVE: We aimed at developing and validating a simple, highly repeatable computer-based tool, which could be employed to simulate the effects of an acute mental stress on endocrine and haemodynamic stress responses. METHODS: Fifteen subjects underwent a mental cognitive challenge, employing an ad hoc designed web tool (available at http://bagame.altervista.org) that proposed a series of random arithmetic operations (addictions or subtractions) between one- to three-digit numbers for 10 minutes. We measured plasma epinephrine, norepinephrine, cortisol, and ACTH, in addition to heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure throughout the test. RESULTS: The arithmetic mental challenge promptly activated the sympatho-adrenomedullary axis (epinephrine +112±24%, p<0.05; norepinephrine +37±13%, p<0.004) and the hypothalamic-pituitary-adrenocortical axis (cortisol +25±7%, p<0.008; ACTH +97±44%, p<0.008), which in turn exerted stimulatory effects on the cardiovascular system (HR +18±4%, p<0.05; SBP +112±24%, p<0.05; DBP +34±8%, p<0.05) in all subjects, without any symptoms and regardless of the individuals' mental arithmetic ability. CONCLUSIONS: We developed and validated a computer-based tool that is effective for simulating endocrine and haemodynamic responses to an acute mental stress. This novel tool is easy-to-use, freely-accessible, and it can be employed to further investigate stress-related pathophysiological mechanisms and their role in cardiovascular diseases.

Effects of corticosteroids on oxidative damage and circulating carotenoids in captive adult kestrels (Falco tinnunculus).

Birds control body homeostasis through the secretion of corticosterone. This hormone is the end-product of the hypothalamic-pituitary-adrenal (HPA) axis response to stressors. High levels of corticosterone may be associated with low individual fitness and may affect balance between pro-oxidants and antioxidants. Given these points, chronic stress modulated by hormones could undermine individual fitness by increasing oxidative tissue damage. In this study, we administered corticosteroids by diet (20 mg/kg of diet) to captive adult kestrels (Falco tinnunculus) over a 14-day period to evaluate the effects of a simulated chronic stress modulated by corticosteroids. We found that dietary administration of corticosterone caused a 32% increase of reactive oxygen metabolites, but did not impair total serum antioxidant capacity, serum carotenoids or body mass. Oxidative stress had a 64% increase in treated birds compared to 30% in controls. The two groups did not differ in the total serum antioxidant capacity, which showed a significant decrease over the study period. In contrast, circulating carotenoids and body mass increased in both groups. These results suggest that stress hormones, such as corticosterone, may also act as modulators of oxidative stress in birds.

Carotenoid availability does not limit the capability of nestling kestrels (Falco tinnunculus) to cope with oxidative stress.

It is recognized that carotenoids are useful anti-oxidants in embryo and hatchling avian models. However, recent evidence suggests that the anti-oxidant role of carotenoids in nestling or adult birds may not be as important as previously thought. The aim of the present work was to investigate if supplemental carotenoids decreased the level of oxidative damage (by reactive oxygen metabolites, ROMs) and increased the serum anti-oxidant capacity (OXY) in nestling Eurasian kestrels Falco tinnunculus. Circulating carotenoids in supplemented nestlings increased about 1.5-fold compared to the control and pre-treatment levels at the end of the supplementation period. There was no effect on ROMs, OXY or the level of oxidative stress (ratio between ROMs and OXY), however, or on body mass or body condition of nestlings. ROMs and OXY decreased with age, but this pattern varied across the nests. Our results show that (i) in general, younger nestlings actually have to cope with a high free radical production, and (ii) the ability of wild nestling kestrels to cope with oxidative stress is not affected by carotenoid availability.

Male-biased predation of western green lizards by Eurasian kestrels.

Selective predation can be an important force driving the evolution of organisms. In particular, sex-biased predation is expected to have implications for sexual selection, sex allocation and population dynamics. In this study, we analysed sex differences in the predation of the western green lizard (Lacerta bilineata) by the Eurasian kestrel (Falco tinnunculus) during the reproductive season. In addition, we investigated whether the rate of predation differed during the 8-year study period and among the three habitats studied. We collected lizard remains from nest boxes of kestrels. Freshly killed lizards were sexed by visual inspection, whilst the sex of head remains was assigned by analysing the cephalic scale morphology using geometric morphometrics. Our results show that the risk of being predated by a kestrel in our population was overall about 3.55 times higher for males than for females. To our knowledge this is the first study showing a male-biased predation in a lizard species. The selective predation of males was consistent between years over the 8-year study period (1999-2006) and also consistent between the three types of kestrel hunting habitat. Overall predation rates on lizards differed between habitats, depending on the year. We propose that the observed sex-biased predation is mainly due to sex differences in lizard behaviour.

Effects of carotenoid supplementation on colour expression, oxidative stress and body mass in rehabilitated captive adult kestrels (Falco tinnunculus).

Carotenoids are considered a limited resource for animals because they are not synthesised by the body. Birds use carotenoids, mainly xanthophylls, for physiological functions, such as anti-oxidant activity, and for colour expression; hence, they need to shunt carotenoids between competitive demands. Recent studies suggest that the anti-oxidant role of xanthophylls might not be as important as previously thought and that at high concentrations they may, in fact, acquire pro-oxidant properties. In this work, we studied the effects of a moderate xanthophyll supplementation (115 mg of carotenoids/kg diet/day; 4 weeks) on serum carotenoids, serum concentration of reactive oxygen metabolites (ROMs), serum anti-oxidant capacity (OXY), the degree of oxidative stress (OS; ROMs/OXY x 1,000), body mass, and skin colour, in rehabilitated captive adult Eurasian kestrels (Falco tinnunculus). The supplementation caused increased levels of serum carotenoids (approximately 90%), ROMs (approximately 82%), OS (approximately 115%) and an immediate loss of body mass (approximately 6.2%), but it did not affect OXY and tarsi skin hue. The red (approximately 16%) and yellow (approximately 15%) colorimetric components were increased after the first week of supplementation and the effect persisted during the rest of the experiment. Two months after the end of supplementation, serum carotenoids, OS and ROMs returned to baseline levels, however the body mass did not. Our findings suggest that, above a certain physiological threshold, carotenoids can cause detrimental effects. This is relevant for the trade-off between expression of sexual signals and the costs of maintaining/producing them.

Patterns of serum carotenoid accumulation and skin colour variation in kestrel nestlings in relation to breeding conditions and different terms of carotenoid supplementation.

Carotenoids are pigments synthesised by autotrophic organisms. For nestlings of raptorial species, which obtain carotenoids from the consumption of other heterotrophic species, the access to these pigments can be crucial. Carotenoids, indeed, have fundamental health maintenance functions, especially important in developing individuals as nestling kestrels. The aim of this study was to investigate how body carotenoid levels and skin pigmentation vary in kestrel nestlings (Falco tinnunculus) in relation to nesting parameters. Furthermore, we experimentally altered carotenoid availability (short- medium- and long-term) for nestlings and investigated skin and serum variance. The skin colour variance of 151 nestlings was explained by nest of origin, age and by the body condition (body mass corrected by age), older nestlings with higher body condition being redder. No difference in skin colour was detected between sexes. Differences in hue (skin "redness") between treatments did not emerge during the first week, but did occur 15 days after administration between long-term supplemented and control chicks. In contrast, the serum carotenoid concentration showed a treatment-dependent increase after 5 days from the first carotenoid administration and at least after two supplemented feedings. In general, hue but not serum carotenoids, was correlated with the body condition of nestlings. Based on the increased skin pigmentation of nestling kestrels in the long-term experimental group, we suggest carotenoid availability to be limited for colour expression. The small increase of serum carotenoids due to supplementation is consistent with the hypothesis that there is a physiological constraint on these pigments, as well as an environmental limitation. The presented results are useful for the understanding of carotenoid uptake and accumulation by a wild raptorial species, located at the top of the food web, highlighting that carotenoids are a limited resource for kestrel nestlings.

Correlates of oxidative stress in wild kestrel nestlings (Falco tinnunculus).

The fitness of an organism can be affected by conditions experienced during early development. In light of the impact that oxidative stress can have on the health and ageing of a bird species, this study evaluated factors accounting for the variation in oxidative stress levels in nestlings of the Eurasian kestrel (Falco tinnunculus) by measuring the serum concentration of reactive oxygen metabolites and the serum antioxidant barrier against hypochlorite-induced oxidation. The ratio between these two variables was considered as an index of oxidative stress, with higher values meaning higher oxidative damage. Six-chick broods showed the highest level of oxidative stress, while no effect of sex was found. Age showed an inverse relationship with the oxidants and the levels of oxidative stress, with younger birds having higher levels. Hatching date, body condition, body mass and carotenoid concentration did not show any relationship with oxidants, antioxidants or degree of oxidative stress. These findings suggest that intrabrood sibling competition could play a role in determining oxidative stress, and that in carnivorous birds other antioxidant molecules could be more important than carotenoids to reduce oxidative stress.