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1.
J Evol Biol ; 21(1): 88-96, 2008 Jan.
Article in English | MEDLINE | ID: mdl-18034804

ABSTRACT

Avian egg size is highly variable on the population level, but is considered inflexible on the individual level. On the basis of 2969 measurements of individual eggs collected during 1981-2005, we analysed heritability, plasticity and selection on egg size in the Ural owl, a long-lived bird that preys on voles. Vole abundance varied in a 3-year cycle, creating varying food supply across the cycle's phases. Ural owl egg size is heritable (h(2) = 60%). Ural owls lay larger eggs in improved food conditions. On the basis of repeated breeding records of 59 females that bred in all vole cycle phases, we show that intra-individual adjustment (plasticity) explained 22.4% of the variation in egg size across phases. Egg size was under stabilizing selection. Extremely small and extremely large eggs had reduced hatchability, and individuals who laid either large or small eggs had lower lifetime fledgling production than the ones laying intermediately sized eggs. Our findings illustrate how maternal investment in egg size can both be heritable and highly responsive to variable environmental conditions, and suggest that variation in the investment in egg size across individuals is canalized.


Subject(s)
Ecosystem , Ovum/physiology , Reproduction/physiology , Selection, Genetic , Strigiformes/physiology , Animals , Body Size/physiology , Female , Male , Reproduction/genetics , Sex Factors , Strigiformes/genetics
2.
J Evol Biol ; 20(6): 2248-52, 2007 Nov.
Article in English | MEDLINE | ID: mdl-17956387

ABSTRACT

Life-history theory centres around trade-offs between current and future reproduction, but we have little understanding of how such trade-offs are mediated. We supplementary fed Ural owls (Strix uralensis) during the nestling period and quantified parents' current and future life-history components as well as their physiological health by monitoring haematocrit, leucocyte profile, intra- and extracellular blood parasites. Feeding led to reduced parental effort but did not improve offspring viability, male parasite defence, or parental survival. Intracellular leucocytozoan infection was reduced in fed females which lasted to the following year's reproductive season (carry-over effect), when fed females also laid larger and earlier clutches. Leucocytozoon infection therefore may mediate the life-history trade-off between current and residual reproduction in this species.


Subject(s)
Animal Nutritional Physiological Phenomena , Strigiformes/physiology , Strigiformes/parasitology , Animals , Eukaryota/isolation & purification , Female , Nesting Behavior , Protozoan Infections, Animal/parasitology , Reproduction , Strigiformes/genetics
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