SREL Reprint #2225

"Grandfather Effects" on offspring size in the eastern mosquitofish, Gambusia holbrooki

Stephen C. Weeks1 and Gary K. Meffe2

1Department of Biology, University of Akron, Akron, Ohio 44325-3908
2Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802

Introduction: Offspring size at birth can be an important determinant of initial offspring success (see reviews in Roff, 1992): larger offspring may have advantages in predator avoidance (Reznick and Endler, 1982; Weeks and Gaggiotti, 1993), growth (Kaplan, 1980), and starvation resistance (Bagenal, 1969; Marsh, 1986). However, the production of larger offspring has a significant energetic cost to the parent (Blaxter, 1969; Sinervo, 1990), and it is commonly assumed that producing larger offspring necessitates the production of fewer overall offspring, resulting in a trade-off between offspring size at birth (hereafter "offspring size") and offspring number (Smith and Fretwell, 1974; McGinley et al., 1987; Winkler and Wallin, 1987).
Several authors have suggested that, within any habitat and specific to any particular species, there will be natural selection for an "optimal" offspring size (Smith and Fretwell, 1974; Morris, 1987; Winkler and Wallin, 1987). This optimum is the size at which the increase in offspring fitness with increased offspring size begins to plateau (Smith and Fretwell, 1974). Producing offspring of this size should balance the benefits to the parent by producing as many offspring as possible, while allocating enough energy to each offspring to provide them a good probability of survival (Morris, 1987). Thus, it is predicted that there should be an identifiable optimal offspring size for an organism living in a particular habitat and that natural populations should be at or near this optimal size because of directional or balancing selection toward this optimum.

SREL Reprint #2225

Weeks, S.C. and G.K. Meffe. 1997. "Grandfather Effects" on offspring size in the eastern mosquitofish, Gambusia holbrooki. Copeia 4:869-874.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).