Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 34
Filtrar
1.
Nano Lett ; 23(19): 8940-8946, 2023 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-37733604

RESUMO

A fundamental capability needed for any transmissive optical component is anti-reflection, yet this capability can be challenging to achieve in a cost-effective manner over longer infrared wavelengths. We demonstrate that Mie-resonant photonic structures can enable high transmission through a high-index optical component, allowing it to function effectively over long-wavelength infrared wavelengths. Using silicon as a model system, we demonstrate a resonant metasurface that enables a window optic with transmission up to 40% greater than that of unpatterned Si. Imaging comparisons with unpatterned Si and off-the-shelf germanium optics are shown as well as modulation transfer function measurements, showing excellent performance and suitability for imaging applications. Our results show how resonant photonic structures can be used to improve optical transmission through high-index optical components and highlight their possible use in infrared imaging applications.

2.
Nano Lett ; 22(2): 594-601, 2022 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-35014534

RESUMO

The Breakthrough Starshot Initiative aims to send a gram-scale probe to our nearest extrasolar neighbors using a laser-accelerated lightsail traveling at relativistic speeds. Thermal management is a key lightsail design objective because of the intense laser powers required but has generally been considered secondary to accelerative performance. Here, we demonstrate nanophotonic photonic crystal slab reflectors composed of 2H-phase molybdenum disulfide and crystalline silicon nitride, highlight the inverse relationship between the thermal band extinction coefficient and the lightsail's maximum temperature, and examine the trade-off between minimizing acceleration distance and setting realistic sail thermal limits, ultimately realizing a thermally endurable acceleration minimum distance of 23.3 Gm. We additionally demonstrate multiscale photonic structures featuring thermal-wavelength-scale Mie resonant geometries and characterize their broadband Mie resonance-driven emissivity enhancement and acceleration distance reduction. More broadly, our results highlight new possibilities for simultaneously controlling optical and thermal response over broad wavelength ranges in ultralight nanophotonic structures.

3.
Nano Lett ; 22(1): 90-96, 2022 01 12.
Artigo em Inglês | MEDLINE | ID: mdl-34939817

RESUMO

We argue that light sails with nanometer-scale thicknesses that are rapidly accelerated to relativistic velocities by lasers must be significantly curved in order to reduce their intrafilm mechanical stresses and avoid tears. Using an integrated opto-thermo-mechanical model, we show that the diameter and radius of curvature of a circular light sail should be comparable in magnitude, both on the order of a few meters, in optimal designs for gram-scale payloads. Moreover, we demonstrate that, when sufficient laser power is available, a sail's acceleration length decreases as its curvature increases. Our findings provide critical guidance for emerging light sail design programs, which herald a new era of interstellar space exploration to destinations such as the Oort cloud, the Alpha Centauri system, and beyond.


Assuntos
Lasers
4.
Ecol Evol ; 11(10): 5111-5120, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-34025995

RESUMO

Trait differences among plant species can favor species coexistence. The role that such differences play in the assembly of diverse plant communities maintained by frequent fires remains unresolved. This lack of resolution results in part from the possibility that species with similar traits may coexist because none has a significant fitness advantage and in part from the difficulty of experimental manipulation of highly diverse assemblages dominated by perennial species. We examined a 65-year chronosequence of losses of herbaceous species following fire suppression (and subsequent encroachment by Pinus elliottii) in three wet longleaf pine savannas. We used cluster analysis, similarity profile permutation tests, and k-R cluster analysis to identify statistically significant functional groups. We then used randomization tests to determine if the absence of functional groups near pines was greater (or less) than expected by chance. We also tested whether tolerant and sensitive species were less (or more) likely to co-occur by chance in areas in savannas away from pines in accordance with predictions of modern coexistence theory. Functional group richness near pines was lower than expected from random species extirpations. Wetland perennials with thick rhizomes and high leaf water content, spring-flowering wetland forbs (including Drosera tracyi), orchids, Polygala spp., and club mosses were more likely to be absent near pines than expected by chance. C3 grasses and sedges with seed banks and tall, fall-flowering C4 grasses were less likely to be absent near pines than expected by chance. Species sensitive to pine encroachment were more likely to co-occur with other such species away from pines at two of the three sites. Results suggest that herb species diversity in frequently burned wet savannas is maintained in part by a weak fitness (e.g., competitive) hierarchy among herbs, and not as a result of trait differences among co-occurring species.

5.
Cureus ; 12(7): e9428, 2020 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-32864254

RESUMO

A 77-year-old male with a history of cataract extraction and intraocular lens placement 5.5 years prior, was referred for idiopathic corneal edema of the right eye. Six months prior to initial consult with a Cornea specialist, the patient presented with acute onset cystoid macular edema (CME) and later developed anterior chamber (AC) cell. The cornea became diffusely edematous and decompensated on topical steroids and hypertonic drops. During the Descemet's membrane endothelial keratoplasty (DMEK) procedure, a sequestered retained lens fragment (RLF) migrated out of the posterior chamber and was aspirated. The remainder of the surgery and post-operative period was unremarkable. This case is the first reported in which a significantly delayed onset of inflammatory reaction from a sequestered RLF led to full corneal decompensation requiring keratoplasty. This case highlights the importance of RLF suspicion in delayed presentation, even when RLFs are not visible via slit-lamp or on gonioscopic view.

6.
ACS Appl Mater Interfaces ; 12(39): 44156-44162, 2020 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-32877159

RESUMO

The adaptation of colloidal quantum dots loaded within a polymer for use in nondestructive testing can be used as an optical strain gauge due to the nanomaterial's strain sensing properties. In this paper, we utilized InP/ZnS colloidal quantum dots loaded within a polymer matrix applied onto the surface of a dog-bone foil precoated with an epoxy. By employing an empirical formula and a calibration factor, there is a propinquity between both the calculated optical strain and mechanical stress-strain reference data. Fluctuations are observed, which may be due to both additional strain responses not seen by the mechanical data and quantum dot blinking. These results and methods show the applied use of this novel optical nondestructive testing technique for a variety of structures, especially for structures that operate in harsh environments.

7.
Appl Opt ; 58(25): 6834-6840, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31503653

RESUMO

Phase retrieval is an attractive approach for sensor-less adaptive optics (AO) because of its relatively simple implementation. Recently, random phase diversity has shown fast convergence for phase retrieval algorithms. In this study, design optimization using random phase diversity is discussed with respect to a sensor-less AO system using a liquid-crystal-on-silicon (LCoS) spatial light modulator. The extrinsic phase disturbances studied are due to Kolmogorov turbulence. Simulation analysis shows that the size of super-pixel segments of the random phase patterns on the LCoS and the cropped image area of the phasorgrams are determined by Fried's parameter for high-Strehl-ratio and low-iteration-number reconstruction. AO experiments with an LCoS spatial light modulator confirm the simulation results.

8.
Ecol Evol ; 7(12): 4377-4389, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28649349

RESUMO

The factors responsible for maintaining diverse groundcover plant communities of high conservation value in frequently burned wet pine savannas are poorly understood. While most management involves manipulating extrinsic factors important in maintaining species diversity (e.g., fire regimes), most ecological theory (e.g., niche theory and neutral theory) examines how traits exhibited by the species promote species coexistence. Furthermore, although many ecologists focus on processes that maintain local species diversity, conservation biologists have argued that other indices (e.g., phylogenetic diversity) are better for evaluating assemblages in terms of their conservation value. I used a null model that employed beta-diversity calculations based on Raup-Crick distances to test for deterministic herbaceous species losses associated with a 65-year chronosequence of woody species encroachment within each of three localities. I quantified conservation value of assemblages by measuring taxonomic distinctness, endemism, and floristic quality of plots with and without woody encroachment. Reductions in herb species richness per plot attributable to woody encroachment were largely stochastic, as indicated by a lack of change in the mean or variance in beta-diversity caused by woody encroachment in the savannas studied here. Taxonomic distinctness, endemism, and floristic quality (when summed across all species) were all greater in areas that had not experienced woody encroachment. However, when corrected for local species richness, only average endemism and floristic quality of assemblages inclusive of herbs and woody plants were greater in areas that had not experienced woody encroachment, due to the more restricted ranges and habitat requirements of herbs. Results suggest that frequent fires maintain diverse assemblages of fire-dependent herb species endemic to the region. The stochastic loss of plant species, irrespective of their taxonomic distinctness, to woody encroachment suggests that the relevance of niche partitioning or phylogenetic diversity to the management of biodiversity in wet pine savannas is minimal.

10.
Br J Sports Med ; 49(1): 3-6, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25263651

RESUMO

While the research base is limited, studies have consistently reported poor oral health in elite athletes since the first report from the 1968 Olympic Games. The finding is consistent both across selected samples attending dental clinics at major competitions and more representative sampling of teams and has led to calls from the International Olympic Committee for more accurate data on oral health. Poor oral health is an important issue directly as it can cause pain, negative effects on appearance and psychosocial effects on confidence and quality of life and may have long-term consequences for treatment burden. Self-reported evidence also suggests an impact on training and performance of athletes. There are many potential challenges to the oral health of athletes including nutritional, oral dehydration, exercise-induced immune suppression, lack of awareness, negative health behaviours and lack of prioritisation. However, in theory, oral diseases are preventable by simple interventions with good evidence of efficacy. The consensus statement aims to raise awareness of the issues of oral health in elite sport and recommends strategies for prevention and health promotion in addition to future research strategies.


Assuntos
Desempenho Atlético/fisiologia , Saúde Bucal/normas , Consenso , Desidratação/fisiopatologia , Comportamento Alimentar/fisiologia , Comportamentos Relacionados com a Saúde , Conhecimentos, Atitudes e Prática em Saúde , Promoção da Saúde , Humanos , Doenças da Boca/etiologia , Doenças da Boca/fisiopatologia , Fatores de Risco
11.
Res Sports Med ; 22(4): 425-37, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25295479

RESUMO

Goal line officials (GLO) are exposed to extreme environmental conditions when employed to officiate in professional European soccer cup competitions. The present study aimed to investigate the effect of such environments on GLO decision-making ability. Thirteen male participants were exposed to three conditions: cold (-5°C, 50% relative humidity (RH)); temperate (18°C, 50% RH); and hot (30°C, 50% RH) for 90 min per condition, with a 15 min half-time break after 45 min. Decision-making ability was assessed throughout the 90 min exposure. Core and skin temperatures were recorded throughout. Decision making was improved during exposure to the temperate condition when compared with the cold (mean difference = 12.5%; 95% CI = 1.1%, 23.9%; P = 0.031). Regression analysis indicated that as skin temperature increases so does decision-making ability. Exposure to cold conditions diminished the decision-making ability of GLO.


Assuntos
Temperatura Baixa , Tomada de Decisões , Temperatura Alta , Umidade , Futebol , Temperatura Corporal , Humanos , Masculino , Testes Neuropsicológicos , Adulto Jovem
12.
Front Physiol ; 5: 185, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24904425

RESUMO

Soccer referees enforce the laws of the game and the decisions they make can directly affect match results. Fixtures within European competitions take place in climatic conditions that are often challenging (e.g., Moscow ~ -5°C, Madrid ~30°C). Effects of these temperatures on player performance are well-documented; however, little is known how this environmental stress may impair cognitive performance of soccer referees and if so, whether exercise exasperates this. The present study aims to investigate the effect of cold [COLD; -5°C, 40% relative humidity (RH)], hot (HOT; 30°C, 40% RH) and temperate (CONT; 18°C, 40% RH) conditions on decision making during soccer specific exercise. On separate occasions within each condition, 13 physically active males; either semi-professional referees or semi-professional soccer players completed three 90 min intermittent treadmill protocols that simulated match play, interspersed with 4 computer delivered cognitive tests to measure vigilance and dual task capacity. Core and skin temperature, heart rate, rating of perceived exertion (RPE) and thermal sensation (TS) were recorded throughout the protocol. There was no significant difference between conditions for decision making in either the dual task (interaction effects: FALSE p = 0.46; MISSED p = 0.72; TRACKING p = 0.22) or vigilance assessments (interaction effects: FALSE p = 0.31; HIT p = 0.15; MISSED p = 0.17) despite significant differences in measured physiological variables (skin temperature: HOT vs. CONT 95% CI = 2.6 to 3.9, p < 0.001; HOT vs. COLD 95% CI = 6.6 to 9.0, p < 0.001; CONT vs. COLD 95% CI = 3.4 to 5.7, p < 0.01). It is hypothesized that the lack of difference observed in decision making ability between conditions was due to the exercise protocol used, as it may not have elicited an appropriate and valid soccer specific internal load to alter cognitive functioning.

13.
J Strength Cond Res ; 28(12): 3416-24, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24910953

RESUMO

Precooling lowers skin (Tsk) and core temperature (Tre) and can improve performance in hot conditions, but has predominantly been studied in males. This study investigated the effects of precooling on self-paced 2,000-m rowing performance, within females, in hot, humid conditions. Eight physically active females (19.9 ± 1.5 years, 66.8 ± 3.1 kg, 30.0 ± 5.0% body fat) performed 2,000-m rows in a randomized order within 3 conditions {control (CONT) (20° C, 40% relative humidity [RH]); hot (HOT) (35° C, 60% RH); precooling (PREC) (35° C, 60% RH, preceded by precooling)}. The precooling condition consisted of 20-minute precooling with a cold water shower, followed by a 2,000-m row. In contrast, CONT and HOT consisted of 20-minute passive rest in place of precooling. Tre, Tsk, and power output were recorded every 100 m of the rows. Muscle temperature (Tmu) was recorded at baseline, after 20-minute passive rest/precooling and post-row. No differences were observed between conditions for performance time (CONT, 8.89 ± 0.45 minutes; HOT, 9.01 ± 0.55 minutes; PREC, 8.87 ± 0.48 minutes; p = 0.42). Mean Tre during the row was not different between conditions (CONT, 37.8 ± 0.2° C; HOT, 37.7 ± 0.3° C; PREC, 37.5 ± 0.2° C; p = 0.12; main effect), although lower Tre was observed at 1,600 and 1,800 m in PREC compared with HOT (p ≤ 0.05). Tmu was significantly reduced after precooling (p = 0.03). Precooling did not enhance 2,000-m rowing performance, despite differences in Tre, Tsk, and Tmu. The lack of observed improvement in rowing performance after cold shower precooling may have been due to the short exercise time. An improvement in performance may have been observed using an alternate method of precooling, which has been shown to be ergogenic in other sports.


Assuntos
Desempenho Atlético/fisiologia , Temperatura Corporal , Temperatura Baixa , Esportes/fisiologia , Adolescente , Feminino , Temperatura Alta , Humanos , Umidade , Músculo Esquelético/fisiologia , Distribuição Aleatória , Temperatura Cutânea , Adulto Jovem
14.
Int Immunopharmacol ; 15(2): 282-8, 2013 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-23333630

RESUMO

Avian thymic hormone (ATH) is a ß-parvalbumin produced by epithelial cells in the thymic cortex and in the eyes of chickens. Chicken parvalbumin 3 (CPV3) is a homologous protein produced in the thymus and in hair cells of the chicken ear. ATH circulates in the blood on a five-day cycle and stimulates cell-mediated immunity when administered to young chickens. We report the identification of target cells for ATH and CPV3 and the immunophenotype of target cells for ATH. Newly hatched chicks were injected intracoelomically with ATH and killed 5, 10, 15 or 20 min later. Naïve chickens also were killed at 1, 7 and 14 days of age. Various tissues were examined by EM for the presence of either ATH or CPV3 using colloidal gold labeling. Gold particles were initially present on plasma membranes of lymphocytes in T cell areas of spleen and cecal tonsils from the chicks injected with ATH, internalized within 10 min, and accumulated in nuclei by 20 min. Immunofluorescence staining also identified the presence of ATH in T cell areas of spleen and cecal tonsils. Target cells labeled for ATH were immunophenotyped by double labeling. They were positive for CD3, CD8 and the lymphocyte receptor TCR-1, a phenotype characteristic of cytotoxic γδ T cells. Some of the target cells in the spleen were TCR-3 positive. Targeting of lymphocytes by CPV3 indicated that it may also be an immunomodulating hormone.


Assuntos
Proteínas Aviárias/metabolismo , Calreticulina/metabolismo , Núcleo Celular/metabolismo , Galinhas/imunologia , Células Epiteliais/metabolismo , Parvalbuminas/metabolismo , Linfócitos T/imunologia , Transporte Ativo do Núcleo Celular , Animais , Proteínas Aviárias/imunologia , Citotoxicidade Imunológica , Células Epiteliais/ultraestrutura , Olho/ultraestrutura , Coloide de Ouro , Imunidade Celular , Imunofenotipagem , Especificidade de Órgãos , Parvalbuminas/imunologia , Receptores de Antígenos de Linfócitos T gama-delta/metabolismo , Timo/patologia
15.
Eur J Appl Physiol ; 113(1): 109-15, 2013 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22592455

RESUMO

Heat acclimation (HA) can improve thermoregulatory stability in able-bodied athletes in part by an enhanced sweat response. Athletes with spinal cord lesion are unable to sweat below the lesion and it is unknown if they can HA. Five paralympic shooting athletes with spinal cord lesion completed seven consecutive days HA in hot conditions (33.4 ± 0.6 °C, 64.8 ± 3.7 %rh). Each HA session consisted of 20 min arm crank exercise at 50 % [Formula: see text] followed by 40 min rest, or simulated shooting. Aural temperature (T (aur)) was recorded throughout. Body mass was assessed before and after each session and a sweat collection swab was fixed to T12 of the spine. Fingertip whole blood was sampled at rest on days 1 and 7 for estimation of the change in plasma volume. Resting T (aur) declined from 36.3 ± 0.2 °C on day 1 to 36.0 ± 0.2 °C by day 6 (P < 0.05). During the HA sessions mean, T (aur) declined from 37.2 ± 0.2 °C on day 1, to 36.7 ± 0.3 °C on day 7 (P < 0.05). Plasma volume increased from day 1 by 1.5 ± 0.6 % on day 7 (P < 0.05). No sweat secretion was detected or changes in body mass observed from any participant. Repeated hyperthermia combined with limited evaporative heat loss was sufficient to increase plasma volume, probably by alterations in fluid regulatory hormones. In conclusion, we found that although no sweat response was observed, athletes with spinal cord lesion could partially HA.


Assuntos
Aclimatação , Regulação da Temperatura Corporal , Exercício Físico , Traumatismos da Medula Espinal/fisiopatologia , Esportes , Adulto , Temperatura Alta , Humanos
16.
J Inorg Biochem ; 111: 187-94, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22437160

RESUMO

In the presence of magnesium, enolase catalyzes the dehydration of 2-phospho-d-glycerate (PGA) to phosphoenolpyruvate (PEP) in glycolysis and the reverse reaction in gluconeogensis at comparable rates. The structure of human neuron specific enolase (hNSE) crystals soaked in PGA showed that the enzyme is active in the crystals and produced PEP; conversely soaking in PEP produced PGA. Moreover, the hNSE dimer contains PGA bound in one subunit and PEP or a mixture of PEP and PGA in the other. Crystals soaked in a mixture of competitive inhibitors tartronate semialdehyde phosphate (TSP) and lactic acid phosphate (LAP) showed asymmetry with TSP binding in the same site as PGA and LAP in the PEP site. Kinetic studies showed that the inhibition of NSE by mixtures of TSP and LAP is stronger than predicted for independently acting inhibitors. This indicates that in some cases inhibition of homodimeric enzymes by mixtures of inhibitors ("heteroinhibition") may offer advantages over single inhibitors.


Assuntos
Fosfopiruvato Hidratase/química , Fosfopiruvato Hidratase/metabolismo , Multimerização Proteica , Estrutura Quaternária de Proteína , Ligação Competitiva , Cristalografia por Raios X , Inibidores Enzimáticos/química , Inibidores Enzimáticos/metabolismo , Inibidores Enzimáticos/farmacologia , Ácidos Glicéricos/química , Ácidos Glicéricos/metabolismo , Humanos , Cinética , Modelos Moleculares , Estrutura Molecular , Fosfoenolpiruvato/química , Fosfoenolpiruvato/metabolismo , Fosfopiruvato Hidratase/genética , Ligação Proteica , Estrutura Terciária de Proteína , Subunidades Proteicas/química , Subunidades Proteicas/metabolismo , Proteínas Recombinantes/antagonistas & inibidores , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Especificidade por Substrato , Tartronatos/química , Tartronatos/metabolismo , Tartronatos/farmacologia
17.
FEBS Lett ; 584(5): 979-83, 2010 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-20102712

RESUMO

We determined the kinetics of the reaction of human neuronal enolase and yeast enolase 1 with the slowly-reacting chromophoric substrate D-tartronate semialdehyde phosphate (TSP), each in tris (tris (hydroxymethyl) aminomethane) and another buffer at several Mg2+ concentrations, 50 or 100 microM, 1 mM and 30 mM. All data were biphasic, and could be satisfactorily fit, assuming either two successive first-order reactions or two independent first-order reactions. Higher Mg2+ concentrations reduce the relative magnitude of the slower reaction. The results are interpreted in terms of a catalytically significant interaction between the two subunits of these enzymes.


Assuntos
Fosfopiruvato Hidratase/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Tartronatos/metabolismo , Humanos , Cinética , Magnésio/metabolismo , Ligação Proteica , Especificidade por Substrato
18.
Gen Comp Endocrinol ; 166(1): 19-24, 2010 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-19699742

RESUMO

Vertebrates respond to perceived stressors through increased plasma concentrations of glucocorticoids. However, there is considerable variation within and across species in the circumstances and degree to which glucocorticoid levels are elevated. We measured baseline and acute stress-induced levels of corticosterone of free-living, black-legged kittiwake chicks (Rissa tridactyla) across four consecutive breeding seasons in the northern Gulf of Alaska to determine the effect of hatching order and brood size on corticosterone levels of chicks. We sampled 12- to 15-day-old chicks from intact broods (i.e., no brood reduction) at three colonies from 2002-2005 (n=164). Baseline and stress-induced levels of corticosterone did not vary by hatching order or brood size. These results suggest that the adrenocortical function of kittiwake chicks from broods that survive intact through 12-15 days is not affected by either hatching order or brood size.


Assuntos
Animais Recém-Nascidos/sangue , Charadriiformes , Corticosterona/sangue , Comportamento de Nidação , Alaska , Animais , Animais Selvagens , Estresse Fisiológico
19.
Protein Pept Lett ; 15(5): 516-20, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18537743

RESUMO

Measurements of [theta](222) of E. coli phosphatase on heating from 20 degrees to 90 degrees and subsequent cooling to 20 degrees shows a gradual increase in [theta](222) on heating, while cooling shows a symmetric transition centered at 45 degrees . Reheating and cooling shows the same phenomenon. Enzyme heated and cooled once is fully active. The activity of the enzyme depends on its storage conditions (buffer and pH for example), but such changes are least to some extent reversible, especially by heating in different solvents. We conclude the enzyme exists in several forms which are in slow equilibrium with each other, so that the enzyme responds slowly when heated and hence is not at equilibrium during heating/cooling experiments.


Assuntos
Fosfatase Alcalina/química , Escherichia coli/enzimologia , Fosfatase Alcalina/metabolismo , Temperatura Baixa , Estabilidade Enzimática , Temperatura Alta , Desnaturação Proteica , Termodinâmica
20.
Gen Comp Endocrinol ; 156(2): 361-8, 2008 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-18308320

RESUMO

Over the last decade, field endocrinologists have explored the efficacy of using plasma corticosterone concentrations of breeding seabirds as an indicator of food availability and predictor of breeding success. However, studies have been predominately confined to adults and the results have been inconsistent. We examined the relationship between the productivity of black-legged kittiwakes (Rissa tridactyla) and the baseline and stress-induced corticosterone levels of 12-15 day-old kittiwake chicks in a multi-year study in Chiniak Bay, Kodiak, Alaska. We predicted that corticosterone levels would negatively correlate with productivity. Productivity decreased across years from relatively high levels in 2002, to very low levels in 2004 and 2005. Baseline corticosterone levels of the chicks did not increase consistently across years. Stress-induced corticosterone levels were statistically indistinguishable in high productivity years but increased significantly in low productivity years. The decline in kittiwake productivity coincided with warming ocean conditions, which, historically, are linked to declines in forage abundance for kittiwakes. Inconsistent changes in baseline corticosterone levels suggest some adult kittiwakes were able to buffer their chicks from poor foraging conditions. However, large increases in stress-induced corticosterone levels during the low productivity years indicate chicks were physiologically stressed for some period prior to sampling. Our results suggest that stress-induced corticosterone levels of kittiwake chicks are effective indicators of productivity in poor years, whereas the changes in baseline corticosterone levels across years are not as pronounced and therefore may not be as reliable.


Assuntos
Glândulas Suprarrenais/fisiologia , Aves/fisiologia , Charadriiformes/fisiologia , Estações do Ano , Animais , Peso Corporal/fisiologia , Corticosterona/sangue , Feminino , Masculino , Reprodução/fisiologia , Estresse Psicológico/metabolismo
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...