Incubation temperature as a constraint on clutch size evolution

1. Elucidating factors that limit the number of offspring produced is fundamental to understanding life-history evolution. Here, we examine the hypothesis that parental ability to maintain an optimal physical developmental environment for all offspring constrains clutch size via effects on offspring quality.

2. Experimental laboratory studies of birds have shown that a <1°C difference in average incubation temperature has diverse effects on fitness-related post-hatching offspring phenotypes. Thus, the inability of parents to maintain optimal incubation temperatures could constrain clutch sizes.

3. A fundamental question that has not been sufficiently addressed is whether larger clutch sizes lead to within nest variation in egg temperature that is large enough to produce offspring with different phenotypes within a brood. This could lead to differential survival among offspring, and could create a tradeoff between offspring number and quality.

4. We manipulated clutch size in...