How do multiple environmental cycles in combination determine reproductive timing in marine organisms? A model and test

1. Each of the multiple environmental cycles - the light-dark, tidal, semilunar, lunar and seasonal cycles - may have an independent, specific effect on reproductive timings of marine organisms and can alone or in combination produce a variety of temporal reproductive patterns. Assuming that each ecological interaction with these fluctuating environmental cycles generates a unique functional relationship between a component of fitness and the timing of reproduction, a model is proposed that predicts that all fitness components are multiplicative and therefore the reproductive timing is entrained or driven by a cycle(s) having a sharp functional curve of the relevant fitness component. 2. According to this model, many of the reproductive patterns, ranging from diel to lunar, commonly seen in marine organisms were explained by changing relative kurtosis among functional curves of fitness components. Each curve could also differ in its optimum and skewness, making various intermediates and modifications possible. 3. As a model system for the model to be applied, intraspecific variation in the timing of spawning by a puffer, Takifugu niphobles (Jordan & Snyder) was examined. The patterns of daily variation in a day's spawning time within a population and geographical variation in spawning days among populations indicated that (1) the semilunar cycle (i.e. spring-neap tide cycle) has no direct influence on spawning days, (2) a combination between the functional curves of the fitness components associated with the light-dark and tidal cycles produce an apparent biweekly, semilunar spawning rhythm, (3) the curves may be skewed toward earlier and later times, respectively, and (4) their form may differ among populations. 4. This model approach argues that to understand the ecology and evolution of temporal patterns of reproduction, one must properly decouple and evaluate the form of the functional curve of a fitness component associated with each of the multiple environmental cycles.