Lee B. Astheimer

Interactions of corticosterone with feeding, activity and metabolism in passerine birds

Corticosterone (B) may play a direct role in the promotion of feeding behavior under conditions of nutritional stress. However, effects of exogenous B and nutritional stress in passerines indicate a complex relationship of fed state, perceived or anticipated nutritional stress, and previous history. In a series of investigations on caged White-crowned Zonotrichia leucophrys and Song Sparrows Z. melodia, foraging behaviors and feeding rates were unaffected by exogenous B in fed birds. When food was returned, birds implanted with B refed for longer and with greater intensity following the 24 hour fast. Additionally, B-implanted birds showed lower activity (perch hopping) than controls when fed ad libitum, but when fasted this trend reversed with B-implanted birds showing increased activity and apparent escape behavior. In a second study, small flocks of Pine Siskins Carduelis pinus and Darkeyed Juncos Junco hyemalis held in aviaries and fasted for 24 hours had higher plasma levels of B than similar flocks that had been allowed to refeed for 1 hour after fasting. However, the highest levels of B in fasted birds were still lower than in free-living conspecifics exposed to capture stress. This low amplitude modulation of plasma B levels in relation to fed state was corroborated by results from free-living Pine Siskins and Lapland Longspurs Calcarius lapponicus captured during snow storms. In spite of unusually high feeding intensities during the storm, individuals of only some Pine Siskins and no Lapland Longspurs had elevated circulating levels of B. In the latter species, serial samples revealed very high levels of B within 15 minutes of capture suggesting enhanced adrenal secretory activity as a result of the storm. Finally, in White-crowned Sparrows, exogenous B substantially reduced overnight metabolic expenditure by reducing the frequency and amplitude of arousal bouts during the night. This suggested a possible energy savings effect of B during the hours when foraging was impossible and, possibly, insurance that the individual will retain sufficient resources to seek food the following day. Taken together, our data suggest that B may be important for initiation of food-searching during periods of food deprivation. Only small increases in B secretion appear to be required thus facilitating a rapid return to homeostasis after food is located. Although under prolonged nutritional stress the basal levels of B remained low, adrenal potential to secrete B in response to further stress increased dramatically.

The Key Importance of Soy Isoflavone Bioavailability to Understanding Health Benefits

Research over the past two decades has provided significant epidemiological and other evidence for the health benefits of the consumption of soy-based foods. A large number of dietary intervention studies have examined the effects of soy isoflavones on risk factors for cardiovascular disease and hormone-dependent cancers. However, these report large variability in outcome measures, very limited reproducibility between studies, and in some cases, controversy between the results of clinical trials using dietary soy or soy protein and isoflavone supplementation. This highlights a major gap in our understanding of soy isoflavone uptake, metabolism, distribution, and overall bioavailability. There are many potential factors that may influence bioavailability and a better knowledge is necessary to rationalize the inconsistencies in the intervention and clinical studies. This review focuses attention on our current state of knowledge in this area and highlights the importance of metabolism of the parent soy isoflavones and the critical role of gut microbiota on the bioavailability of these compounds and their metabolites.

Testosterone is involved in acquisition and maintenance of sexually selected male plumage in superb fairy-wrens, Malurus cyaneus

Abstract Testosterone has been proposed as a physiological link between the level of sexual signalling and male condition. Bright plumage is one of the most noticeable sexual signals and is often used by females as a basis for mate choice. Yet bright male plumage is not necessarily testosterone dependent. We investigated the role of testosterone in the moult into seasonal nuptial plumage in male superb fairy-wrens. Early pre-nuptial moult is under intense intersexual selection and males can acquire the bright plumage any time between autumn and the next spring. Testosterone was always undetectable or very low in males in dull eclipse plumage. During the pre-nuptial moult, both the number of males with detectable testosterone and average testosterone levels increased sharply. High testosterone was more correlated with nuptial plumage than with presence of the cloacal protuberance (indicative of sperm storage). Subcutaneous testosterone implants always induced the pre-nuptial moult within 2–3 weeks after implantation, even well outside the natural time range of moulting. Moreover, removal of the implants before the nuptial plumage was completed, arrested the moult process. The evidence suggests that development of the nuptial plumage is testosterone dependent, although we cannot exclude that testosterone exerts its action after conversion to a metabolite such as oestrogen. Once the nuptial plumage was completed, all males maintained substantially elevated testosterone, sometimes months before the onset of breeding. These high levels could be necessary to maintain the plumage, and/or are involved in courtship displays. The results are discussed with respect to potential costs involved in acquiring and maintaining the nuptial plumage.

Frequency-dependent physiological trade-offs between competing colour morphs

Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and black-headed male morphs of the Gouldian finch (Erythrura gouldiae). Red-headed males are highly sensitive to changes in the social environment, especially towards the relative density of their own aggressive morph, exhibiting high stress responses and immunosuppression in socially competitive environments. In contrast, the non-aggressive black-headed males follow a more passive strategy that appears to buffer them against social stresses. The differential effect of hormones on aggressive behaviour and immune performance reinforces the contrasting behavioural strategies employed by these colour morphs, and highlights the importance of the social environment in determining the individual basis of behavioural and physiological responses.

Corticosterone treatment has no effect on reproductive hormones or aggressive behavior in free-living male tree sparrows, Spizella arborea

We examined the effect of corticosterone on plasma levels of reproductive hormones (testosterone, dihydrotestosterone, and luteinizing hormone) and territorial defense behavior in male tree sparrows, Spizella arborea. Birds receiving Silastic implants filled with corticosterone (B) had significantly higher plasma levels of B than control birds, which received empty implants, and exhibited pectoral muscle wastage and a decrease in body mass. We evaluated the hormonal and agonistic responses of the two implanted groups of birds using a simulated territorial intrusion (STI) 2 to 4 days after they were implanted. Corticosterone-treated and control birds did not differ in their circulating levels of reproductive hormones or in their behavioral responses to STI (latency to respond to intrusion, number of songs, and closest approach to a decoy and tape recording). Unlike previous studies of north temperate passerines, high physiological levels of exogenous B had no effect either on circulating levels of reproductive hormones or on territorial behaviors associated with breeding. Nonetheless, untreated tree sparrows do mount a robust adrenocortical response, having a two- to fourfold increase in plasma B levels during a 1-h period of capture. Thus, adrenocortical responsiveness is maintained in these birds, but elevated levels of glucocorticoids do not suppress reproductive hormones or associated behaviors. We believe that this hormonal and behavioral refractoriness to glucocorticoids-or uncoupling of the stress response from the reproductive axis-may be advantageous for species having extreme temporal constraints on their breeding schedules.

The annual testosterone profile in cooperatively breeding superb fairy-wrens, Malurus cyaneus, reflects their extreme infidelity

Abstract. Superb fairy-wrens are cooperatively breeding birds that combine stable, socially monogamous pair bonds and high levels of paternal care, with extreme levels of extra-pair mating and high levels of sexual competition. Our aim was to determine which testosterone correlates would prevail in such a life history that combines features that are conventionally associated with divergent hormone profiles. Unlike the situation in other species with monogamous pair bonds and high levels of paternal care, testosterone was elevated for a very long period of several months. During breeding there was a broad peak in testosterone followed by a gradual decline: this resembles the profile found in polygynous and promiscuous species. We found that three factors correlated with testosterone: development of the sexually selected nuptial plumage, social status and extra-group mating opportunities. Testosterone started increasing months prior to breeding, when the males that are later preferred as extra-group sires develop their nuptial plumage. Although these males did not have higher testosterone levels during breeding, they sustained high testosterone for much longer, and this might lend reliability to this sexual signal. Dominant males in groups had higher testosterone than pair-dwelling males and subordinate helpers. This was not due to differences in age, reproductive capability or mating opportunities, but was presumably associated with the assertion of dominance. In contrast to findings in other species, male testosterone level was not correlated with whether the resident female was fertile or had dependent nestlings. However, testosterone was strongly correlated with the total number of fertile females in the population, and hence with the opportunities for extra-group mating.

Limited Lipid-lowering effects of regular consumption of whole soybean foods

Aim: To examine cardiovascular health benefits of foods containing a whole soybean extract. Methods: The study design was a randomized, placebo-controlled crossover trial of consuming soy-based milk and yoghurt (treatment) or equivalent dairy products (control) for 5 weeks each. Twenty-six mildly hypercholesterolaemic and/or hypertensive volunteers were recruited from the community as study volunteers, of which 23 completed. Main outcome measures included clinic and ambulatory blood pressure, arterial compliance, lipids, fatty acids and isoflavones in fasted blood and 24-hour urinary isoflavone excretion. Nutrient intakes were assessed initially and after each 5-week period. Multiple regression analyses were used to determine predictor variables in statistical models; order effects were tested by repeated measures ANOVA. Changes in Lp(a) were determined by Wilcoxon signed ranks tests; other differences between treatment and control were assessed by t tests. Results: Plasma and urinary isoflavones were markedly increased by whole soy supplementation but there were no overall differences in plasma lipids, blood pressure or arterial compliance between the soy and dairy diets. However, in 8 equol-positive subjects (equol detected in either plasma or urine), retrospective analysis revealed significant reductions in total cholesterol (8.5%), LDL cholesterol (10%), LDL:HDL ratio (13.5%), plasma triglycerides (21%) and lipoprotein(a) (11%) with the soy diet. These reductions were independent of changes in polyunsaturated fat and other macronutrient intakes. Conclusions: Regular consumption of whole soybean milk and yogurt products had no effect on plasma lipids, blood pressure or arterial compliance in at-risk subjects, despite substantially increasing isoflavone levels in blood and urine. Retrospective analysis suggests that improvement of plasma lipids may have been limited to equol-positive subjects.

Dietary combination of soy with a probiotic or prebiotic food significantly reduces total and LDL cholesterol in mildly hypercholesterolaemic subjects

Objective:We hypothesized that a dietary combination of soy with either a probiotic (yoghurt) or a prebiotic (resistant starch) would result in enhanced lipid-lowering effects compared with a control soy diet, possibly via improvements in isoflavone bioavailability.Subjects:Mildly hypercholesterolaemic subjects (men and post-menopausal women) older than 45 years were recruited via the local media. Thirty-six subjects commenced the study; five withdrew.Results:Soy+probiotic significantly decreased total cholesterol (4.7±2.0%; P=0.038) and soy+prebiotic significantly decreased total and low-density lipoprotein cholesterol (5.5±1.6%; P=0.003 and 7.3±2.2%; P=0.005, respectively). The bioavailabilities of daidzein, genistein or equol were not affected by probiotic or prebiotic consumption or associated with lipid changes.Conclusion:Dietary combination of soy with either a probiotic or a prebiotic resulted in significant lipid lowering, not related to isoflavone bioavailability.

Afternoon t: Testosterone level is higher in red than yellow male polychromatic lizards.

Recent work on within-species polymorphism across a broad range of taxa has renewed and considerably increased the attention to this classic evolutionary area, notably in lizard species where colors covary with reproductive strategies. We demonstrate elsewhere that red-headed males beat yellow-headed males in staged contests for females in the Australian painted dragon lizard Ctenophorus pictus. This morph difference in behaviour is linked to what appears to be a convention of red dominance in male-male interactions set very early in ontogeny, long before coloration has developed. In the current note, we investigate the relationship between time of day, which is directly linked to vigilance time in territorial males, and plasma levels of testosterone and corticosterone. We show that red males have higher testosterone levels in late afternoon following a day of territory patrolling and a non-significant trend in plasma corticosterone levels that decline with time of day. In conclusion, there are significant differences in testosterone profile between the two color morphs, providing a potential proximate link to the behavioural differences between them.

Effects of sublethal fenitrothion ingestion on cholinesterase inhibition, standard metabolism, thermal preference, and prey-capture ability in the Australian central bearded dragon (Pogona vitticeps, agamidae)

The central bearded dragon (Pogona vitticeps) is a medium-sized lizard that is common in semiarid habitats in Australia and that potentially is at risk of fenitrothion exposure from use of the chemical in plague locust control. We examined the effects of single sublethal doses of this organophosphate (OP; low dose = 2.0 mg/kg; high dose = 20 mg/kg; control = vehicle alone) on lizard thermal preference, standard metabolic rate, and prey-capture ability. We also measured activities of plasma total cholinesterase (ChE) and acetylcholinesterase before and at 0, 2, 8, 24, 120, and 504 h after OP dosing. Predose plasma total ChE activity differed significantly between sexes and averaged 0.66 +/- 0.06 and 0.45 +/- 0.06 micromol/min/ml for males and females, respectively. Approximately 75% of total ChE activity was attributable to butyrylcholinesterase. Peak ChE inhibition reached 19% 2 h after OP ingestion in the low-dose group, and 68% 8 h after ingestion in high-dose animals. Neither OP doses significantly affected diurnal body temperature, standard metabolic rate, or feeding rate. Plasma total ChE levels remained substantially depressed up to 21 d after dosing in the high-dose group, making this species a useful long-term biomonitor of OP exposure in its habitat.