Chapter 3 Spawning

Abstract

Publisher Summary Spawning in most species involves multiple neuro-endocrine pathways that introduce a delay between the perception of the cue and the response to it. An extreme example is the entrainment of internal rhythms by environmental cycles that eventually culminate in spawning. The timing of spawning in invertebrates is independent of prior rhythmic reproductive physiology and that some type of independent stimulus is required to induce gamete release. It might sometimes be impossible to separate the stimuli for gamete production from the actual spawning cue, since the culmination of production may itself stimulate spawning. Indeed, the identification of spawning cues is a major challenge in that it requires three types of evidence: (1) that an environmental change coincides with spawning in the field or precedes it at a fixed interval, (2) that the same change provokes animals to spawn when other conditions are maintained constant, and (3) that other factors can be eliminated as possible spawning cues. The latter point is important because numerous environmental and oceanographic factors vary in parallel. A number of methods, such as gonad indices, histology and microscopic examination of the gonads, oocyte size frequency distributions have been used with various degrees of accuracy to determine the spawning periods of echinoderms, and different interpretations of the factors that control reproduction have been proposed with more or less certainty.