SEQUENTIAL PATTERNS OF SEX ALLOCATION IN SIMULTANEOUS HERMAPHRODITES - DO WE NEED MODELS THAT SPECIFICALLY INCORPORATE THIS COMPLEXITY

Theoretical and empirical studies of sex allocation usually treat sequ ential and simultaneous hermaphroditism as distinct and disparate form s of allocation. However, the sexual patterns of numerous species have both sequential (e.g., size-based) and simultaneous components. In mo st cases, we have drawn from sex allocation theory developed for seque ntial hermaphrodites to explain ontogenetic changes in allocation and from theory developed for simultaneous hermaphrodites to explain the r emaining aspects of these sexual patterns rather than develop a more i ntegrated theory. Here I present the evolutionary stable solution (ESS ) to a dynamic state-variable model that explicitly combines the effec ts of size and simultaneous allocation to male and female function in a dynamic game. The model structure and initial parameter values are b ased on the sexual pattern of the blue-banded goby, Lythrypnus dalli, a simultaneous hermaphrodite. I then compare the natural patterns of s ex allocation in L. dalli with the predictions of the model and with t hose of a dynamic version of the size advantage model. The integrated model predicted variation in allocation, sex-specific size distributio ns, and seasonal sex ratio better than the sequential hermaphroditism model did. Indeed, the sequential model, using L. dalli parameter valu es, predicts a dioecious rather than sequentially hermaphroditic alloc ation pattern. The comparison of these two models illustrates the disa dvantage of drawing from two bodies of theory without a formal integra ted framework. Furthermore, the comparison focuses attention on the ro le of costs of reallocation in the evolution of mixed (or intermediate ) sexual patterns.