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Sibling Competition (sibling + competition)
Selected AbstractsBrood reduction in the Red-necked Grebe Podiceps grisegenaIBIS, Issue 2 2003Janusz Kloskowski Brood reduction in Red-necked Grebes Podiceps grisegena breeding on fish ponds in south-eastern Poland occurred either through the desertion of the last-laid eggs after partial hatching of the clutch and/or the selective starvation of the smallest chicks. Abandonment of unhatched eggs was not influenced by the number of young already hatched or by the breeding date, but it was more likely in larger clutches and in families suffering chick starvation. Chicks from the largest broods had a higher probability of survival until fledging than those from single-chick broods. Larger chicks obtained food more successfully through better positioning during food delivery. In families that did not suffer brood reduction, chicks were better provisioned with food than in reduced broods. Although allocation of food among chicks in reduced broods was more skewed to the disadvantage of the younger siblings, dominant chicks obtained less food prior to brood reduction than dominant siblings in unreduced broods. Sibling aggression did not differ between unreduced and reduced broods before death of the weakest chicks. Post-laying adjustment of the number of offspring to prevailing feeding conditions occurred at two stages: by parental manipulation of the number of hatched eggs at the time when parents and chicks leave the nest and by competition between chicks. It is suggested that late egg desertion may be an adaptive mechanism of brood-size adjustment, when elimination of the weakest chicks through sibling competition is not very efficient. [source] Maternal clutch reduction in the pied flycatcher Ficedula hypoleuca: an undescribed clutch size adjustment mechanismJOURNAL OF AVIAN BIOLOGY, Issue 6 2006Elisa Lobato During eight years of study of a population of pied flycatchers Ficedula hypoleuca breeding in central Spain, we observed throughout incubation 22 cases of intact eggs being placed on the nest rim and clearly outside of the nest bowl and remaining there, with consequent embryo mortality. We assume that the removal of eggs had been performed by the incubating female. There is no evidence that pied flycatcher parents can detect embryo mortality and eject unhatchable eggs. Maternal egg ejection constitutes a direct mechanism of clutch size adjustment during incubation and before hatching of any young of the brood. This adjustment of clutch size happened when the mean and minimum temperature of the day before ejection were especially low. Also, clutch-reducing females were significantly more prone to show moult-breeding overlap than other females, suggesting a lower disposition to invest in reproduction. Clutch-reducing females were also frequently older than four years and had indications of a lower immunocompetence than females not ejecting eggs. Our results support the hypothesis that adverse conditions can elicit parental family size adjustment at every stage of reproduction without the need to depend on mechanisms of sibling competition. [source] Daytime variation in T-cell-mediated immunity of Eurasian kestrel Falco tinnunculus nestlingsJOURNAL OF AVIAN BIOLOGY, Issue 5 2006Jesús Martínez-PadillaArticle first published online: 15 AUG 200 Host-parasite interactions are central in evolutionary and behavioural ecology. In the last few years, skin injections of the mitogen Phytohaemagglutinin (PHA) have become one of the most important and widely used in-vivo assays of immune function in birds. However, there are no studies of the circadian variation suggesting that care should be taken interpreting results when using this technique. This 3-year study assessed PHA responses as a function of daylight time in 310 Eurasian kestrel Falco tinnunculus nestlings at 24 days of age in Central Spain. I found that T-cell-mediated immunity was positively related to nestling mass and varied among years. Controlling for these variables, I also found that T-cell-mediated immunity decreased with the hour of sampling, and that this pattern was consistent between years. In addition, I found that at the end of the day only, T-cell-mediated immunity decreased with brood size. Parasites seem not to be behind this pattern, but I suggest that the cumulative effect of sibling competition during the day might explain the decrease of cellular immunity with the hour of sampling. Thus, I strongly recommend that future studies of cellular immunity should control for this potential source of variation when nestling self-maintenance is evaluated by the PHA-induced skin-swelling response. [source] Brood size and environmental conditions sex-specifically affect nestling immune response in the European starling Sturnus vulgarisJOURNAL OF AVIAN BIOLOGY, Issue 6 2005Eunice H. Chin In sexually size-dimorphic species, the larger sex can be more sensitive to stressful environmental conditions, often resulting in reduced growth and elevated mortality rates. Development of the immune system is regarded as highly resource dependent, and recent data suggest that nestling passerines experience a possible resource-based trade-off between growth and immunity. Given the hypothesized importance of maximizing growth for the larger sex, the corresponding immune system may also exhibit similar sensitivity to limited resources. To better understand how natural variation in brood size and resources might differentially affect growth and immune function in nestlings of a sexually size-dimorphic species, we examined the relationship between brood size and inter-sexual differences in cell-mediated immunity (CMI) and survival in European starling Sturnus vulgaris nestlings where males are larger in both mass and structural size. We hypothesized that male CMI response should be negatively impacted by increasing sibling competition (brood size), especially during periods of low resource availability. In a year of reduced parental provisioning rates and reduced chick growth rates, male offspring exhibited the predicted negative relationship, whereas female CMI response was unaffected. However, in a year of improved provisioning rates and chick growth, neither sex exhibited a negative relationship between immune response and brood size. Thus, natural variation in brood size can affect sex-specific immunity differently in offspring of a sexually size-dimorphic passerine. However, this relationship appears resource-dependent, suggesting that the hypothesized resource-based trade-off may be compensated for in years of adequate resource abundance. [source] Hatching asynchrony and maternal androgens in egg yolks of House WrensJOURNAL OF AVIAN BIOLOGY, Issue 1 2001Lisa A. Ellis Synchronously and asynchronously hatching clutches of House Wrens Troglodytesaedon usually do not differ in reproductive success. Thus late-hatching nestlings in asynchronously hatching clutches somehow overcome any age- and size-related disadvantages of hatching after their nest-mates. One possible way for them to do this is for female House Wrens to add maternal androgens to the yolk of late-hatching eggs. We tested this hypothesis in a wild population of House Wrens that produces both asynchronously and synchronously hatching clutches. Yolks of eggs from both types of clutches were biopsied and the eggs returned to their nests to hatch. Radioimmunoassays revealed that total androgen levels in the yolk varied within and among clutches. However, total androgen levels in yolks did not vary predictably with egg position in either synchronously or asynchronously hatching clutches. Thus, deposition of androgens in yolk did not follow the expected pattern based on the potential for sibling competition in House Wrens. [source] Hatching asynchrony as a bet-hedging strategy , an offspring diversity hypothesisOIKOS, Issue 3 2004Toni Laaksonen Many birds begin to incubate before their clutch is full, which results in the chicks hatching at different times. I propose that hatching asynchrony could serve as an adaptive parental strategy to produce phenotypic variation in the offspring through asymmetric sibling competition. Producing diverse offspring that follow variable life history strategies might be a risk-spreading strategy in spatially and temporally variable environments. [source] Developmental plasticity varied with sex and position in hatching hierarchy in nestlings of the asynchronous European roller, Coracias garrulusBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010DESEADA PAREJO Allocation rules between ornamental and other functional traits of birds may differ among individuals and vary with environmental conditions. We supplemented roller (Coracias garrulus) nestlings with methionine in a between-nest design to investigate the way in which the sex and position in the hatching hierarchy affect the allocation of resources among growth, immunity, and plumage coloration. Methionine induces the production of lymphocytes at expense of growth; thus, we used it to manipulate growth and immunity, which are two traits likely to compromise plumage coloration. We predicted that late-hatched chicks within a brood (juniors) compared to early-hatched chicks (seniors) should allocate more to traits directly providing fitness than to ornamental traits because juniors are more affected than seniors by sibling competition. The methionine treatment effectively enhanced the production of lymphocytes in experimental broods. This appeared to be at the expense of plumage coloration in junior nestlings because, in supplemented nests, junior males showed a trend to display less greenish bellies than junior males from control nests. However, juniors from supplemented nests maintained wing growth as in control juniors. The plumage coloration of seniors was unaffected by the methionine supplementation, although they paid the costs of lymphocyte production at a level of growth that was reduced compared to senior nestlings in control nests. Hence, sex, and hatching order affected resource allocation among growth, immunity, and plumage coloration of roller nestlings. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 500,511. [source] | ||||||||||