Gary Burness

INTERINDIVIDUAL VARIABILITY IN BODY COMPOSITION AND RESTING OXYGEN CONSUMPTION RATE IN BREEDING TREE SWALLOWS, TACHYCINETA BICOLOR

Basal metabolic rate is one of the most widely measured physiological traits. Previous studies on lab mice and field‐caught lizards suggest that individuals with relatively high basal metabolic rates or standard metabolic rates have relatively large masses of metabolically active tissues (e.g., heart, kidney, liver). As these are energetically expensive organs, there may be variability between breeding seasons dependent on, for example, availability of prey and capacity for energy intake. We present data from breeding tree swallows (Tachycineta bicolor) collected over two successive seasons. There was no difference between years in resting oxygen consumption rates, although there were significant interannual differences in the masses of all organs and tissues except the pectoralis. Interindividual differences in the masses of the kidney and small intestine explained 21% of the variation in oxygen consumption rates. Although individuals with relatively high resting oxygen consumption rates had relatively large, metabolically active kidneys, they had relatively small intestines and pectoral muscles. This is in contrast to all previous studies on mammals and to the single interspecific study of birds. Oxygen consumption rate also correlated positively with hematocrit. Our results suggest that assumptions of consistent positive relationships between resting oxygen consumption rate and organ masses cannot be extended intraspecifically for birds.

Juveniles exposed to embryonic corticosterone have enhanced flight performance

Exposure to maternally derived glucocorticoids during embryonic development impacts offspring phenotype. Although many of these effects appear to be transiently ‘negative’, embryonic exposure to maternally derived stress hormones is hypothesized to induce preparative responses that increase survival prospects for offspring in low-quality environments; however, little is known about how maternal stress influences longer-term survival-related performance traits in free-living individuals. Using an experimental elevation of yolk corticosterone (embryonic signal of low maternal quality), we examined potential impacts of embryonic exposure to maternally derived stress on flight performance, wing loading, muscle morphology and muscle physiology in juvenile European starlings (Sturnus vulgaris). Here we report that fledglings exposed to experimentally increased corticosterone in ovo performed better during flight performance trials than control fledglings. Consistent with differences in performance, individuals exposed to elevated embryonic corticosterone fledged with lower wing loading and had heavier and more functionally mature flight muscles compared with control fledglings. Our results indicate that the positive effects on a survival-related trait in response to embryonic exposure to maternally derived stress hormones may balance some of the associated negative developmental costs that have recently been reported. Moreover, if embryonic experience is a good predictor of the quality or risk of future environments, a preparative phenotype associated with exposure to apparently negative stimuli during development may be adaptive.

Is there an energetic-based trade-off between thermoregulation and the acute phase response in zebra finches?

SUMMARY There has been recent interest in understanding trade-offs between immune function and other fitness-related traits. At proximate levels, such trade-offs are presumed to result from the differential allocation of limited energy resources. Whether the costs of immunity are sufficient to necessitate such energy reallocation remains unclear. We tested the metabolic and behavioural response of male zebra finches (Taeniopygia guttata) to the combined effects of thermoregulation and generation of an acute phase response (APR). The APR is the first line of defence against pathogens, and is considered energetically costly. We predicted that at cold temperatures zebra finches would exhibit an attenuated APR when compared with individuals at thermoneutrality. We challenged individuals with bacterial lipopolysaccharide (LPS), an immunogenic compound that stimulates an APR. Following LPS injection, we measured changes in food intake, body mass, activity, and resting and total energy expenditure. When challenged with LPS under ad libitum food, individuals at both temperatures decreased food intake and activity, resulting in similar mass loss. In contrast to predicted energetic trade-offs, cold-exposed individuals injected with LPS increased their nocturnal resting energy expenditure more than did individuals held at thermoneutrality, yet paradoxically lost less mass overnight. Although responding to LPS was energetically costly, resulting in a 10% increase in resting expenditure and 16% increase in total expenditure, there were few obvious energetic trade-offs. Our data support recent suggestions that the energetic cost of an immune response may not be the primary mechanism driving trade-offs between immune system function and other fitness-related traits.

Morphological and behavioural responses of frog tadpoles to perceived predation risk: A possible role for corticosterone mediation? 1

Abstract: Predators can have an important influence on prey survival and fitness, and many prey species exhibit morphological or behavioural responses to perceived predation risk. Although basic characteristics of anti-predator responses have been well documented, physiological pathways underlying such responses are poorly understood. We sought evidence for a role of corticosterone, a major stress hormone in amphibians, in the behavioural and morphological anti-predator responses of leopard frog tadpoles (Rana pipiens) exposed to caged dragonfly nymphs (Aeshna spp.). By superimposing a metyrapone treatment (corticosteroid synthesis inhibitor) over chronic predator exposure in a 2 × 2 factorial design, we evaluated if tadpole anti-predator responses were mediated by corticosterone. Tadpoles were less active and more likely to exhibit a startle response when exposed to perceived predation risk, but direct and interactive effects of the metyrapone treatment on behaviour were negligible. Predator-exposed tadpoles grew larger and had deeper tail fins, whereas the metyrapone treatment resulted in smaller tadpoles with shallower tail fins. Tadpoles simultaneously exposed to metyrapone treatment and predation risk had reduced tail-fin depth and increased body:tail ratio compared to steroid-normal animals. Because both traits are implicated in tadpole vulnerability to predation, these results suggest that the corticosteroid pathway may mediate tadpole morphological response to perceived predation risk. We provide evidence supporting a possible role for corticosterone in anti-predator responses of amphibians specifically in terms of morphological responses. Our results suggest that corticosteroid adjustment may impact prey survival through phenotypic change upon exposure to predation risk and thereby suggest a possible functional role of this hormonal pathway in amphibian physiological ecology. Nomenclature : Hillis, 1988.

Carotenoid-Based Ornaments of Female and Male American Goldfinches (Spinus tristis) Show Sex-Specific Correlations with Immune Function and Metabolic Rate

Conspicuous ornamentation has been linked to immunological and physiological condition in males of many species. In species where both sexes are ornamented, it is unclear whether the signal content of ornaments differs between males and females. We examined the immunological and physiological correlates of carotenoid-based bill and plumage ornamentation in American goldfinches Spinus tristis, a species in which bright orange bills are sexually monomorphic but yellow plumage is sexually dimorphic during the breeding season. Because bill color is dynamic over short periods while plumage color is static over longer time frames, we tested whether these signals have the potential to provide temporal information about immunity and condition. In both sexes, bill color (but not plumage color) was negatively related to leukocyte differential, a measure of recent stress, while plumage color (but not bill color) was positively related to resting metabolic rate. In females, bill color also positively correlated with immunoglobulin Y, a component of acquired immunity, while plumage color positively predicted natural antibody levels, a component of innate immunity. In males, neither bill color nor plumage color predicted immune function, suggesting that the mechanisms underlying these signals vary with sex. Our results demonstrate that dynamic signals such as bill coloration do not merely reflect the same information provided by static signals but that these two classes of signal provide information about different temporal aspects of phenotypic quality. Furthermore, our results indicate that a signal expressed in both sexes has the potential to provide different information depending on the sex of the bearer.

Intraspecific Variation in Thermal Tolerance and Acclimation Capacity in Brook Trout (Salvelinus fontinalis): Physiological Implications for Climate Change*

Cold-water fishes are becoming increasingly vulnerable as changing thermal conditions threaten their future sustainability. Thermal stress and habitat loss from increasing water temperatures are expected to impact population viability, particularly for inland populations with limited adaptive resources. Although the long-term persistence of cold-adapted species will depend on their ability to cope with and adapt to changing thermal conditions, very little is known about the scope and variation of thermal tolerance within and among conspecific populations and evolutionary lineages. We studied the upper thermal tolerance and capacity for acclimation in three captive populations of brook trout (Salvelinus fontinalis) from different ancestral thermal environments. Populations differed in their upper thermal tolerance and capacity for acclimation, consistent with their ancestry: the northernmost strain (Lake Nipigon) had the lowest thermal tolerance, while the strain with the most southern ancestry (Hill’s Lake) had the highest thermal tolerance. Standard metabolic rate increased following acclimation to warm temperatures, but the response to acclimation varied among strains, suggesting that climatic warming may have differential effects across populations. Swimming performance varied among strains and among acclimation temperatures, but strains responded in a similar way to temperature acclimation. To explore potential physiological mechanisms underlying intraspecific differences in thermal tolerance, we quantified inducible and constitutive heat shock proteins (HSP70 and HSC70, respectively). HSPs were associated with variation in thermal tolerance among strains and acclimation temperatures; HSP70 in cardiac and white muscle tissues exhibited similar patterns, whereas expression in hepatic tissue varied among acclimation temperatures but not strains. Taken together, these results suggest that populations of brook trout will vary in their ability to cope with a changing climate.

Logging affects fledgling sex ratios and baseline corticosterone in a forest songbird.

Silviculture (logging) creates a disturbance to forested environments. The degree to which forests are modified depends on the logging prescription and forest stand characteristics. In this study we compared the effects of two methods of group-selection (“moderate” and “heavy”) silviculture (GSS) and undisturbed reference stands on stress and offspring sex ratios of a forest interior species, the Ovenbird (Seiurus aurocapilla), in Algonquin Provincial Park, Canada. Blood samples were taken from nestlings for corticosterone and molecular sexing. We found that logging creates a disturbance that is stressful for nestling Ovenbirds, as illustrated by elevated baseline corticosterone in cut sites. Ovenbirds nesting in undisturbed reference forest produce fewer male offspring per brood (proportion male = 30%) while logging with progressively greater forest disturbance, shifted the offspring sex ratio towards males (proportion male: moderate = 50%, heavy = 70%). If Ovenbirds in undisturbed forests usually produce female-biased broods, then the production of males as a result of logging may disrupt population viability. We recommend a broad examination of nestling sex ratios in response to anthropogenic disturbance to determine the generality of our findings.

Post-hatch heat warms adult beaks: irreversible physiological plasticity in Japanese quail

Across taxa, the early rearing environment contributes to adult morphological and physiological variation. For example, in birds, environmental temperature plays a key role in shaping bill size and clinal trends across latitudinal/thermal gradients. Such patterns support the role of the bill as a thermal window and in thermal balance. It remains unknown whether bill size and thermal function are reversibly plastic. We raised Japanese quail in warm (30°C) or cold (15°C) environments and then at a common intermediate temperature. We predicted that birds raised in cold temperatures would develop smaller bills than warm-reared individuals, and that regulation of blood flow to the bill in response to changing temperatures would parallel the bills role in thermal balance. Cold-reared birds developed shorter bills, although bill size exhibited ‘catch-up’ growth once adults were placed at a common temperature. Despite having lived in a common thermal environment as adults, individuals that were initially reared in the warmth had higher bill surface temperatures than cold-reared individuals, particularly under cold conditions. This suggests that blood vessel density and/or the control over blood flow in the bill retained a memory of early thermal ontogeny. We conclude that post-hatch temperature reversibly affects adult bill morphology but irreversibly influences the thermal physiological role of bills and may play an underappreciated role in avian energetics.

DIRECT AND INDIRECT CONSEQUENCES OF MINK PRESENCE IN A COMMON TERN COLONY

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A new procedure for transmitter attachment : effects on brood attendance and chick feeding rates by male common terns

A transmitter crystal and battery were covered with epoxy and wired to a size 2 USFWS aluminum leg band. The male partners of 10 Common Tern (Sterna hirundo) pairs were captured during late incubation at a Port Colbome, Ontario tern colony and the transmitter units fixed to their legs. The total package weighed an average 1.08 g more than the usual mass of a single band. The brood attendance patterns and feeding frequency rates of transmittered-males and of their female partners were contrasted over a 20-day period with those of non-transmittered males and their partners. No differences were found. Advantages of the attachment procedure are speed of attachment, light mass, rapid loss of antennae following battery exhaustion, and lack of adverse effect on parental behavior.