Meeting Abstract
Identification of the fundamental trade-off between the size and number of offspring has been of enormous value in helping us understand the evolution of life histories. All else being equal, this trade-off leads to the prediction of an optimal offspring size. As we now know, the trade-off function, and thus the optimal offspring size, may show considerable plasticity, and may vary in a context-dependent manner. The plasticity may take surprising forms, such as when females adjust egg size to match male quality (Kindsvater & Alonzo 2014). It is also well documented that in a wide variety of organisms larger females produce larger offspring. Given the logic of the optimality approach, this observation is difficult to explain. If bigger females produce bigger offspring because bigger offspring are better, then smaller females should produce large offspring as well. This female-offspring relationship has been widely studied both theoretically and empirically without full success. Viewing it as a context-dependent phenomenon may offer some help. Roff (1992) predicted that reproductive effort (RE) in iteroparous organisms should increase with female size, producing allometric exponents for RE on body size greater than or equal to unity. If so, this could imply that larger females have “excess” reproductive energy compared to smaller females, which they may spend entirely on increased fecundity, on increased egg size, or on some combination. This may represent a special case of context-dependency in which the context is the size and the comparative amount of reproductive energy of the female herself. Here I explore this possibility using the model system of the threespine stickleback.
