An increase in both vascular circumferential tension and shear stress in the developing vasculature of the chicken embryo has been hypothesized to stimulate angiogenesis in the developing peripheral circulation chorioallantoic membrane (CAM). To test this hypothesis, angiogenesis in the CAM, development, and growth were measured in the early chicken embryo, following acute and chronic topical application of the purely bradycardic drug ZD7288. At hour 56, ZD7288 reduced heart rate (f(H)) by ~30% but had no significant effect on stroke volume (~0.19 ± 0.2 μL), collectively resulting in a significant fall in cardiac output (CO) from ~27 ± 3 to 18 ± 2 μL min(-1). Mean f(H) at 72 h of development was similarly significantly lowered by acute ZD7288 treatment (250 μM) to 128 ± 0.3 beats min(-1), compared with 174.5 ± 0.3 and 174.7 ± 0.8 beats min(-1) in control and Pannett-Compton (P-C) saline-treated embryos, respectively. Chronic dosing with ZD7288-and the attendant decreases in f(H) and CO-did not change eye diameter or cervical flexion (key indicators of development rate) at 120 h but significantly reduced overall growth (wet and dry body mass decreased by 20%). CAM vessel density index (reflecting angiogenesis) measured 200-400 μm from the umbilical stalk was not altered, but ZD7288 reduced vessel numbers-and therefore vessel density-by 13%-16% more distally (500-600 μm from umbilical stalk) in the CAM. In the ZD7288-treated embryos, a decrease in vessel length was found within the second branch order (~300-400 μm from the umbilical stock), while a decrease in vessel diameter was found closer to the umbilical stock, beginning in the first branch order (~200-300 μm). Paradoxically, chronic application of P-C saline also reduced peripheral CAM vessel density index at 500 and 600 μm by 13% and 7%, respectively, likely from washout of local angiogenic factors. In summary, decreased f(H) with reduced CO did not slow development rate but reduced embryonic growth rate and angiogenesis in the CAM periphery. This study demonstrates for the first time that different processes in the ontogeny of the early vertebrate embryo (i.e., hypertrophic growth vs. development) have differential sensitivities to altered convective blood flow.

Mammals use five main, mutually nonexclusive mechanisms to balance energy budgets: torpor, metabolic compensation, change in activity patterns, change in ingested energy, and/or variability in digestive efficiency. Bats, as small and actively flying mammals, have a high mass-specific energy demand; therefore, balancing mechanisms should be pronounced in this group. We found that male Myotis daubentonii exhibited marked variation in the relative importance of these different mechanisms during their period of seasonal activity in response to extrinsic (ambient temperature, insect abundance) and intrinsic (reproduction, body condition) factors. Cold ambient temperatures in spring facilitated long and frequent daily torpor bouts, whereas in early summer, increased energy intake was the dominant factor in energy balancing. Intake was further increased in late summer, when insect abundance was highest, and daily torpor bouts were shorter and less frequent than in early summer. In autumn, males used metabolic compensation to reduce their resting metabolic rate in addition to daily torpor. Metabolic compensation might be one of the mechanisms that allow males to maintain high body temperature during the day while decreasing the need for foraging time at night, thus maximizing their opportunities to mate.

Abstract Despite host defense against parasites and pathogens being considered a costly life-history trait, relatively few studies have assessed the energetic cost of immune responsiveness. Knowledge of such energetic costs may help to understand the mechanisms by which trade-offs with other demanding activities occur. The time course and associated metabolic costs of mounting a primary and secondary humoral immune response was examined in little ringed plovers Charadrius dubius challenged with sheep red blood cells. As was expected, the injection with this antigen increased the production of specific antibodies significantly, with peaks 6 d postinjection in both primary and secondary responses. At the peak of secondary antibody response, the antibody production was 29% higher than that observed during the primary response, but the difference was nonsignificant. Mounting the primary response did not significantly increase the resting metabolic rate (RMR) of birds, whereas the secondary response did by 21%, suggesting that the latter was more costly in terms of RMR. In spite of the fact that the primary response did not involve an increase in RMR, birds significantly decreased their body mass. This could imply an internal energy reallocation strategy to cope with the induced immune challenge. Last, we found that RMR and antibody production peaks were not coupled, which could help to conciliate the variable results of previous studies. Collectively, the results of this study support the hypothesis that humoral immunity, especially the secondary response, entails energetic costs that may trade-off with other physiological activities.

Previous studies have related levels of plasma corticosterone (CORT) of seabirds to variation in foraging conditions during the breeding period, but it is unclear whether similar relationships between foraging conditions and baseline CORT exist during other life stages. We validated methods for identifying baseline CORT of lethally sampled birds and assessed variation in baseline CORT relative to winter habitat conditions. We collected free-living white-winged scoters (Melanitta fusca) at four wintering sites during December and February. We found increasing CORT values beyond 3 min after time since flush (the duration between initial flush and death), presumably reflecting acute stress responses. Our results demonstrate that it is possible to obtain baseline CORT from lethally sampled birds if the time from initial flush until death is measured. Our study sites varied appreciably in exposure to wind and waves, predation danger, diving depths, and the fraction of preferred foods in scoter diets. Despite these habitat differences, baseline CORT did not vary across sites or winter periods. We interpret this lack of variation as evidence that birds select wintering areas where they can successfully manage site-specific costs and maintain physiological homeostasis.

Permanent offspring modification through maternal hormone transfer is thought to be a tool for mothers to influence life-history trajectories of individual offspring. In birds, yolk hormones influence numerous aspects of the offspring's physiology, including antioxidant status, an important physiological measure that is linked to growth, reproductive effort, and survival. While it is evident that yolk hormones can affect antioxidant status of nestlings, it is not known whether their effect extends beyond the nestling stage. In this study, we use the zebra finch (Taeniopygia guttata) to test experimentally whether exposure to elevated yolk testosterone (T) levels can result in long-term effects on antioxidant status and traits likely to be associated with this measure. Our data show a significant but sex-specific effect with respect to a period from fledging to the age of 7 mo; T males had higher antioxidant status than control males, whereas antioxidant levels did not differ among females and were intermediate compared with the two male groups. Bill color, a trait associated with carotenoids (a specific group of antioxidants) and known to be under the control of circulating levels of T, was not affected by our yolk T manipulation. Bill color (alone or in covariation with egg treatment or sex) did not predict immune responsiveness or antioxidant status. Moreover, there was only weak evidence that antioxidant status predicted the strength of different immune responses. Antioxidant status (in covariation with egg treatment and sex) predicted levels of circulating total antibody levels but did not predict the strength of cell-mediated and humoral immune responses. Our results suggest that yolk T affects antioxidant status independently of these other traits.

Testosterone has been implicated as a developmental mechanism involved in the organization and expression of sexually dimorphic traits, such as plumage coloration, in birds. Although research findings relating testosterone levels to plumage expression is equivocal, few studies have investigated how testosterone may influence the expression of structurally based plumage coloration. Here, we use experimental and correlational evidence to test the hypothesis that testosterone influences the development and maintenance of structurally based plumage coloration in a wild-breeding population of eastern bluebirds (Sialia sialis). First, we experimentally manipulated yolk testosterone and measured the effect on the development of plumage coloration of nestlings. Second, we implanted juvenile bluebirds with testosterone and measured the effect on nestling growth, body condition, and plumage coloration of nestlings. Third, we measured covariation between circulating testosterone and plumage coloration of breeding males. Yolk testosterone injections had no significant effect on nestling plumage coloration. Testosterone implantation, however, caused a reduction in plumage brightness, elevated corticosterone, and slower growth in nestlings. Finally, in breeding adult males we found no significant relationship between structural coloration and testosterone; however, males with higher testosterone levels exhibited duller chestnut (melanin-based) plumage. Our observations lead us to reject the hypothesis that testosterone increases structural plumage coloration in male eastern bluebirds.

The carotenoid trade-off hypothesis states that diet-derived carotenoids are traded off among competing physiological demands, but this statement is rarely tested in ornamented females. In this study, reverse sexually dimorphic convict cichlids (Amantitlania nigrofasciata) were fed diets containing carotenoid supplementation at three biologically relevant levels for 12 wk. This treatment was followed by spectral, microscopic, and chemical analysis to determine how females allocated the pigments to tissues and how those decisions affected their ventral patch coloration. Yellow coloration of the integument increased with carotenoids in the diet, as did carotenoids deposited in ovaries, but diet did not change carotenoid allocation to skin. The results of this study suggest that females have the ability to modulate their expression of yellow coloration via an alternative coloration strategy. Gonadosomatic index and tank environment were also related to ventral patch color, supporting previous behavioral work highlighting the importance of social selection in reinforcing signal honesty.

Behavioral responses of elasmobranch fishes to weak electric fields have been well studied. These studies typically employ a stimulator that produces a dipole electric field intended to simulate the natural electric field of prey items. However, the characteristics of bioelectric fields have not been well described. The magnitude and frequency of the electric field produced by 11 families of marine organisms were quantified in this study. Invertebrate electric potentials ranged from 14 to 28 μV and did not differ from those of elasmobranchs, which ranged from 18 to 30 μV. Invertebrates and elasmobranchs produced electric potentials smaller than those of teleost fishes, which ranged from 39 to 319 μV. All species produced electric fields within the frequency range that is detectable by elasmobranch predators (<16 Hz), with the highest frequencies produced by the penaeids (10.3 Hz) and the gerreids (4.6 Hz). Although voltage differed by family, there was no relationship between voltage and mass or length of prey. Differences in prey voltage may be related to osmoregulatory strategies; invertebrates and elasmobranchs are osmoconformers and have less ion exchange with the surrounding seawater than teleosts species, which are hyposmotic. As predicted, voltage production was greatest at the mucous membrane-lined mouth and gills, which are sites of direct ion exchange with the environment.

Visual temporal resolution and spectral sensitivity of three coastal teleost species (common snook [Centropomus undecimalis], gray snapper [Lutjanus griseus], and pinfish [Lagodon rhomboides]) were investigated by electroretinogram. Temporal resolution was quantified under photopic and scotopic conditions using response waveform dynamics and maximum critical flicker fusion frequency (CFFmax). Photopic CFFmax was significantly higher than scotopic CFFmax in all species. The snapper had the shortest photoreceptor response latency time (26.7 ms) and the highest CFFmax (47 Hz), suggesting that its eyes are adapted for a brighter photic environment. In contrast, the snook had the longest response latency time (36.8 ms) and lowest CFFmax (40 Hz), indicating that its eyes are adapted for a dimmer environment or nocturnal lifestyle. Species spectral responses ranged from 360 to 620 nm and revealed the presence of rods sensitive to dim and twilight conditions, as well as multiple cone visual pigments providing the basis for color and contrast discrimination. Collectively, our results demonstrate differences in visual function among species inhabiting the Indian River Lagoon system, representative of their unique ecology and life histories.

Stress-induced increases in glucocorticoids (GCs) modulate behavior and are key in directing energy reserves. The capture-restraint protocol was developed to experimentally stimulate and quantify the magnitude of the acute stress response by comparing baseline GC levels with those collected after restraining a subject for a period of time, typically 30 min. This protocol has been used extensively in the field and lab, yet few studies have investigated whether it parallels hypothalamic-pituitary-adrenal (HPA) activation under natural acute stressors. We examined the hypothesis that acute stress from the capture-restraint protocol accurately mimics the adrenocortical response induced by a natural acute stressor. Using wild-caught rock pigeons Columba livia in a repeated-measures design, we compared plasma corticosterone (CORT) concentrations at baseline, after exposure to acute capture-restraint (30 min in a cloth bag), after tethering in a harness (30 min), and after a real but nonlethal attack by a predatory raptor. As found in previous studies, the capture-restraint treatment significantly increased CORT levels of pigeons compared with baseline. However, we also found that when pigeons were exposed to an attack by a raptor, their CORT levels were more than twice as high compared with the capture-restraint treatment. Our results provide evidence that an authentic acute stressor can activate the HPA axis to a greater extent than the capture-restraint protocol and also suggest that real predation attempts can have a significant effect on acute stress levels of wild birds.