Evol Ecol Res 7: 1077-1088 (2005)     Full PDF if your library subscribes.

The effect of packing constraints on optimal investment in offspring

Christopher W. Beck1* and Robert E. Beck2

1Department of Biology, Emory University, Atlanta, GA 30322 and 2Department of Computing Sciences, Villanova University, Villanova, PA 19085, USA

Author to whom all correspondence should be addressed.
e-mail: christopher.beck@emory.edu


Problem: In some taxa, females retain their entire clutch internally and face a packing constraint, which may lead to a correlation between egg size and total allocation (egg size × clutch size).

Hypotheses: In species with packing constraints (e.g. turtles and copepods), linear measures of egg size will be negatively correlated with total reproductive allocation, but egg volume will be positively correlated with total reproductive allocation. By contrast, in species without packing constraints (e.g. passerine birds), the correlations, if present, can be either positive or negative. However, both will be in the same direction.

Data: Egg length, egg width, egg volume, clutch size and body size in turtles, copepods and North American passerine bird species.

Methods: We calculated independent contrasts separately for each taxonomic group, using composite phylogenies and ignoring branch lengths. We used Smith and Fretwell’s (1974) optimality model of egg size. We modified it by assuming a correlation between total reproductive investment and investment in individual offspring.

Conclusions: The data agreed with the hypotheses. Suppose that total reproductive investment increases rapidly with increases in investment in individual offspring. Then, optimal investment in offspring increases greatly.

Keywords: clutch size, life-history evolution, morphological constraints, optimal egg size, reproductive allocation, reproductive effort, reproductive investment.

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