title: Artificial selection reveals the energetic expense of producing larger eggs.
abstract: BACKGROUND
  The amount of resources provided by the mother before birth has important and long-lasting effects on offspring fitness. Despite this, there is a large amount of variation in maternal investment seen in natural populations. Life-history theory predicts that this variation is maintained through a trade-off between the benefits of high maternal investment for the offspring and the costs of high investment for the mother. However, the proximate mechanisms underlying these costs of reproduction are not well understood. Here we used artificial selection for high and low maternal egg investment in a precocial bird, the Japanese quail (Coturnix japonica) to quantify costs of maternal reproductive investment.
  
  
  RESULTS
  We show that females from the high maternal investment lines had significantly larger reproductive organs, which explained their overall larger body mass, and resulted in a higher resting metabolic rate (RMR). Contrary to our expectations, this increase in metabolic activity did not lead to a higher level of oxidative damage.
  
  
  CONCLUSIONS
  This study is the first to provide experimental evidence for metabolic costs of increased per offspring investment.
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Joel L
authors: JL
authors: Pick
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Pascale
authors: P
authors: Hutter
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Christina
authors: C
authors: Ebneter
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Ann-Kathrin
authors: AK
authors: Ziegler
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Marta
authors: M
authors: Giordano
authors: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Barbara
authors: B
authors: Tschirren
keywords: Cost of reproduction; Egg size; Life history evolution; Maintenance of variation; Maternal investment; Oxidative stress