. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FERTILIZATION AND SPERM MODELS 25 c o '-t-' o N c <D O. 0 20 40 60 80 100 Distance Downstream (m) Figure 5. Predicted effects of depth and vertical separation on pre- dicted fertilization rates. Diffusion parameters as for Figure 3. Sperm release rate (Qs). The phenomenal fertilization success of A. planci can be directly attributed to the ani- mal's high sperm output. By examining the effect of dif- fering sperm outputs, we examined how the spawning of more than one animal, or reduced levels of sperm pro- duction, could
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FERTILIZATION AND SPERM MODELS 25 c o '-t-' o N c <D O. 0 20 40 60 80 100 Distance Downstream (m) Figure 5. Predicted effects of depth and vertical separation on pre- dicted fertilization rates. Diffusion parameters as for Figure 3. Sperm release rate (Qs). The phenomenal fertilization success of A. planci can be directly attributed to the ani- mal's high sperm output. By examining the effect of dif- fering sperm outputs, we examined how the spawning of more than one animal, or reduced levels of sperm pro- duction, could determine the success of external fertiliza- tion. The importance of sperm output level to fertilization success is clearly visible in the comparison of animals from Sesoko Island with those from Davies Reef. When sperm release values in the model were reduced so that they would correspond to those observed for starfish at Sesoko Island, there was a high level of agreement between the predictions and observed fertilization rates (Fig. 6). A group of five spawning male starfish is predicted, using the same model, to be capable of generating fertilization rates in excess of 40% at distances of 100 m or more downstream. Indeed the highest mean fertilization rate we observed for a group of five spawning males was 42% at 100 m (although the mean was much lower, ). If we compare these observations to the predictions of the model based on the gamete release rate of urchins such as Strongylocentrotus (1-3 g, Denny and Shibata. 1989). it becomes apparent why A. planci are capable of fertil- ization at distances much greater than those that are pos- sible for urchins. Sperm release rate can clearly be a major factor determining the outcome of reproductive behavior in a free-spawning marine organism such as Acanthaster. Discussion Free-spawning marine invertebrates can and do achieve high levels of fertilization during normal spawning events. as confirmed by results presented here as
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
