Some evolutionary arguments about what maintains the pelagic interval in reef fishes

In this paper, we address the question of the nature of evolutionary forces that account for the oceanic planktonic larva period. Putting the emphasis on coral reef fishes, we first present the most common theories and hypotheses, looking at them critically from the standpoint of individual selection and taking into account new data arising from genetic surveys. We concluded that each individual hypothesis based on short term advantages of a larva period cannot convincingly explain by itself the long term maintenance of such a complex life cycle. We then study the impact of the pelagic interval on species dispersal by compiling data sets from the literature. Following simple analysis of this data, we found that duration of the planktonic larva period drives gene flow in the Great Barrier Reef and colonisation throughout the Pacific. In speculating on the real nature of the short term selective forces responsible for the maintenance of the pelagic interval, we acknowledge the fact that long term constraints alone will not withstand erosion if they are not reinforced by some sort of short term mechanism. We tentatively arrive at the conclusion that these short term forces may be different from what could be expected from functional studies of planktonic life.