962 research outputs found
Individual Quality and Double-brooding in a Highly Synchronous Songbird Population
Multiple brooding, the production of more than one set of offspring per breeding season, is a life history trait potentially doubling or tripling fecundity, but the factors responsible for variation in occurrence of multiple brooding within species remain poorly understood. We investigated the potential causes and consequences of double-brooding in the highly-synchronously breeding European starlings (Sturnus vulgaris), where we predicted that âdateâ (clutch initiation) would have little effect on double-brooding propensity compared to individual âqualityâ. Double-brooding effectively doubled annual fecundity in European starlings (based on annual number of chicks fledged), but on average only 38% of individual females was double-brooded. Furthermore, 39% of females that initiated a second clutch experienced total failure of their second brood, thus accrued no fecundity advantage from their decision to double-brood. As we predicted variation in propensity for, and success of double-brooding was independent of laying date, but also of other putative measures of individual âqualityâ (clutch size, egg mass, relative age, and provisioning rate). However, we found no evidence of a cost of double-brooding; double-brooded females had significantly higher return rate, and similar breeding productivity in the year after double-brooding compared with single-brooding females. Thus, a small proportion (~20%) of âhigh qualityâ female European starlings effectively double their potential breeding productivity through double-brooding without apparently paying a cost or experiencing simple trade-offs
The Adaptive Value of StressâInduced Phenotypes: Effects of Maternally Derived Corticosterone on SexâBiased Investment, Cost of Reproduction, and Maternal Fitness.
The question of why maternal stress influences offspring phenotype is of significant interest to evolutionary physiologists. Although embryonic exposure to maternally derived glucocorticoids (i.e., corticosterone) generally reduces offspring quality, effects may adaptively match maternal quality with offspring demand. We present results from an interannual field experiment in European starlings (Sturnus vulgaris) designed explicitly to examine the fitness consequences of exposing offspring to maternally derived stress hormones. We combined a manipulation of yolk corticosterone (yolk injections) with a manipulation of maternal chickârearing ability (feather clipping of mothers) to quantify the adaptive value of corticosteroneâinduced offspring phenotypes in relation to maternal quality. We then examined how corticosteroneâinduced âmatchingâ within this current reproductive attempt affected future fecundity and maternal survival. First, our results provide support that lowâquality mothers transferring elevated corticosterone to eggs invest in daughters as predicted by sex allocation theory. Second, corticosteroneâmediated sexâbiased investment resulted in rapid maleâbiased mortality resulting in brood reduction, which provided a better match between maternal quality and brood demand. Third, corticosteroneâmediated matching reduced investment in current reproduction for lowâquality mothers, resulting in fitness gains through increased survival and future fecundity. Results indicate that the transfer of stress hormones to eggs by lowâquality mothers can be adaptive since corticosteroneâmediated sexâbiased investment matches the quality of a mother to offspring demand, ultimately increasing maternal fitness. Our results also indicate that the branding of the proximate effects of maternal glucocorticoids on offspring as negative ignores the possibility that shortâterm phenotypic changes may actually increase maternal fitness
Shifts in Metabolic Demands in Growing Altricial Nestlings Illustrate Context-Specific Relationships between Basal Metabolic Rate and Body Composition
Basal metabolic rate (BMR) in animals is interpreted as reflecting the size and metabolic intensity of energy-consuming tissues. However, studies investigating relationships between the mass of specific organs and interindividual variation in BMR have produced inconsistent patterns with regard to which organs have the largest impact on BMR variation. Because of the known flexibility in organ mass and metabolic intensity within individual organs, relationships between BMR and body-composition variables are bound to be context specific. Altricial nestlings are excellent models to illustrate this phenomenon because of the extreme variation in body composition occurring during growth. Using European starlings at three age classes, we studied changes in body composition together with its effect on variation in resting metabolic rate (RMR) in order to highlight the context-specific nature of these relationships. Our data suggest a transition in metabolic costs during growth in starling nestlings. During the linear phase of growth, energy is mainly consumed by tissue-synthesis processes, with fast-growing organs having a large influence on RMR. In the plateau phase of growth, the energy expenditure is transferred to functional costs, with high-intensity organs having a predominant effect on RMR variation. Our data illustrates the context-specific nature of organ mass-metabolic rate correlations, which complicates inter- and intraspecific comparisons of BMR. In the future, such comparisons must be done while taking the physiological state of the study animal into account
Uncoupling clutch size, prolactin, and luteinizing hormone using experimental egg removal
Clutch size is a key avian fitness and life history trait. A physiological model for clutch size determination CSD), involving an anti-gonadal effect of prolactin (PRL) via suppression of luteinizing hormone (LH),was proposed over 20 years ago, but has received scant experimental attention since. The few studies looking at a PRL-based mechanistic hypothesis for CSD have been equivocal, but recent experiments utilizing a pharmacological agent to manipulate PRL in the zebra finch (Taeniopygia guttata) found no
support for a role of this hormone in clutch size determination. Here, we take a complementary approach
by manipulating clutch size through egg removal, examining co-variation in PRL and LH between two breeding attempts, as well as through experimentally-extended laying. Clutch size increased for egg removal females, but not controls, but this was not correlated with changes in PRL or LH. There were also no differences in PRL between egg removal females and controls, nor did PRL levels during early, mid- or late-laying of supra-normal clutches predict clutch size. By uncoupling PRL, LH and clutch size in our study, several key predictions of the PRL-based mechanistic model for CSD were not supported. However,a positive correlation between PRL levels late in laying and days relative to the last egg (clutch completion) provides an alternative explanation for the equivocal results surrounding the conventional PRL-based physiological model for CSD. We suggest that females coordinate PRL-mediated incubation
onset with clutch completion to minimize hatching asynchrony and sibling hierarchy, a behavior that
is amplified in females laying larger clutches
SexâSpecific Variability in the Immune System across LifeâHistory Stages.
Organisms theoretically manage their immune systems optimally across their life spans to maximize fitness. However, we lack information on (1) how the immune system is managed across lifeâhistory stages, (2) whether the sexes manage immunity differentially, and (3) whether immunity is repeatable within an individual. We present a withinâindividual, repeatedâmeasures experiment examining lifeâhistory stage variation in the inflammatory immune response in the zebra finch (Taeniopygia guttata). In juveniles, ageâdependent variation in immune response differed in a sexâ and contextâspecific manner, resulting in no repeatability across stages. In adults, females displayed little stageâdependent variation in immune response when laying while receiving a highâquality (HQ) diet; however, laying while receiving a lowâquality (LQ) diet significantly reduced both immune responses and reproductive outputs in a manner consistent with a facultative (resourceâdriven) effect of reproduction on immunity. Moreover, a reduced immune response in females who were raising offspring while receiving an HQ diet suggests a residual effect of the energetic costs of reproduction. Conversely, adult males displayed no variation in immune responses across stages, with high repeatability from the nonbreeding stage to the eggâlaying stage, regardless of diet quality (HQ diet, ; LQ diet, ). Females displayed high repeatability when laying while receiving the HQ diet (); however, repeatability disappeared when individuals received the LQ diet. Highâresponse females receiving the HQ diet had greater immune flexibility than did lowâresponse females who were laying while receiving the LQ diet. Data are consistent with immunity being a highly plastic trait that is sexâspecifically modulated in a contextâdependent manner and suggest that immunity at one stage may provide limited information about immunity at future stages
Glucocorticoid Manipulations in Free-Living Animals: Considerations of Dose Delivery, Life-History Context, and Reproductive State
1. Experimental glucocorticoid (GC) manipulations can be useful for identifying the mechanisms that drive life history and fitness variation in free-living animals, but predicting the effects of GC treatment can be complicated. Much of the uncertainty about the effects of GC manipulations stems from their multi-faceted role in organismal metabolism, and their variable influence with respect to life-history stage, ecological context, age, sex, and individual variation.
2. Glucocorticoid hormones have been implicated in the regulation of parental care in many vertebrate taxa but in two seemingly contradictory ways, which sets up a potential corticosterone-induced âreproductive conflictâ. GCs mediate adaptive physiological and behavioural responses to stressful events, and elevated levels can lead to trade-offs between reproductive effort and survival (e.g. the current reproduction versus survival hypothesis). The majority of studies examining the fitness effects of GC manipulations extend from this hypothesis. However, when animals are not stressed (likely most of the time) baseline GCs act as key metabolic regulators of daily energy balance, homeostasis, osmoregulation, and food acquisition, with pleiotropic effects on locomotor activity or foraging behaviour. Slight increases in circulating baseline levels can then have positive effects on reproductive effort (e.g. the corticosterone fitness/adaptation hypotheses), but comparatively few GC manipulation studies have targeted these small, non-stress induced increases.
3. We review studies of GC manipulations and examine the specific hypotheses used to predict the effects of manipulations in breeding wildlife. We argue that given the dichotomous function of GCs the current âreproduction versus survivalâ paradigm is unnecessarily restrictive and predicts only deleterious GC effects on fitness. Therefore, a broader set of hypotheses should be considered when testing the fitness effects of GC manipulations.
4. When framing experimental manipulation studies, we urge researchers to consider three key points: life-history context (e.g. long- vs. short-lived, semelparous vs. iteroparous, etc), ecological context, and dose delivery.
 
Glucocorticoid manipulations in free-living animals: Considerations of dose delivery, life-history context and reproductive state
Experimental glucocorticoid (GC) manipulations can be useful for identifying the mechanisms that drive life-history and fitness variation in free-living animals, but predicting the effects of GC treatment can be complicated. Much of the uncertainty stems from the multi-faceted role of GCs in organismal metabolism, and their variable influence with respect to life-history stage, ecological context, age, sex and individual variation. Glucocorticoid hormones have been implicated in the regulation of parental care in many vertebrate taxa but in two seemingly contradictory ways, which sets up a potential GC-induced \u27reproductive conflict\u27. Circulating GCs mediate adaptive physiological and behavioural responses to stressful events, and elevated levels can lead to trade offs between reproductive effort and survival (e.g. the current reproduction vs. survival hypothesis). The majority of studies examining the fitness effects of GC manipulations extend from this hypothesis. However, when animals are not stressed (likely most of the time) baseline GCs act as key metabolic regulators of daily energy balance, homoeostasis, osmoregulation and food acquisition, with pleiotropic effects on locomotor activity or foraging behaviour. Slight increases in circulating baseline levels can then have positive effects on reproductive effort (e.g. the \u27cort\u27 fitness/adaptation hypotheses), but comparatively few GC manipulation studies have targeted these small, non-stress induced increases. We review studies of GC manipulations and examine the specific hypotheses used to predict the effects of manipulations in wild, breeding vertebrates. We argue that given the dichotomous function of GCs the current \u27reproduction vs. survival\u27 paradigm is unnecessarily restrictive and predicts only deleterious GC effects on fitness. Therefore, a broader set of hypotheses should be considered when testing the fitness effects of GC manipulations. When framing experimental manipulation studies, we urge researchers to consider three key points: life-history context (e.g. long vs. short lived, semelparous vs. iteroparous, etc.), ecological context and dose delivery
C4-aldehyde of guaiazulene:synthesis and derivatisation
Guaiazulene is an alkyl-substituted azulene available from natural sources and is a much lower cost starting material for the synthesis of azulene derivatives than azulene itself. Here we report an approach for the selective functionalisation of guaiazulene which takes advantage of the acidity of the protons on the guaiazulene C4 methyl group. The aldehyde produced by this approach constitutes a building block for the construction of azulenes substituted on the seven-membered ring. Derivatives of this aldehyde synthesised by alkenylation, reduction and condensation are reported, and the halochromic properties of a subset of these derivatives have been studied.</p
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