Influence of Sperm and Phytoplankton on Spawning in the Echinoid Lytechinus variegatus

Abstract

The cues triggering large-scale broadcast-spawning events in marine invertebrates are not fully understood. Using the sea urchin Lytechinus variegatus, we tested the effectiveness of a variety of potential spawning cues in eliciting a spawning response. In the laboratory, during two consecutive spawning seasons, about 400 isolated sea urchins were exposed to phytoplankton, sperm, or eggs, singly or in combination. The likelihood of spawning, time to spawning, and spawning behavior were recorded for both sexes. Sperm was most successful at inducing spawning. No response to eggs was noted. Phytoplankton alone did not trigger spawning, but when a phytoplankton cue was followed by the addition of sperm, spawning behavior was induced, the time between addition of sperm and spawning was reduced, and the variance among individuals in the time of spawning initiation was reduced. Males spawned sooner in response to cues than females and rarely spawned spontaneously in phytoplankton or control treatments. A semilunar pattern in the sensitivity to spawning cues was noted. During time periods when sea urchins were less ripe, the ratio of spawning males to spawning females increased. Our results indicate that seasonal and lunar cycles, together with the presence of phytoplankton, increase the sensitivity of these sea urchins to spawning cues and the precision of their responses to conspecific sperm.

The effect of suspended sediment on fertilization success in the urchin Evechinus chloroticus: Analysis of experimental data using hierarchical Bayesian methods

“…However, Gaudette et al (2006) noted that evidence suggesting that phytoplankton trigger spawning in urchins was based only on laboratory studies. Mercier and Hamel (2009) suggested that spawning in urchins is triggered by environmental, temporal and conspecific cues, in agreement with Reuter and Levitan (2010) who proposed that a series of events leads to spawning in urchins including lunar cycles and the presence of phytoplankton. However, it is important to note that phytoplankton alone did not induce urchin spawning (Reuter and Levitan, 2010).…”

“…Mercier and Hamel (2009) suggested that spawning in urchins is triggered by environmental, temporal and conspecific cues, in agreement with Reuter and Levitan (2010) who proposed that a series of events leads to spawning in urchins including lunar cycles and the presence of phytoplankton. However, it is important to note that phytoplankton alone did not induce urchin spawning (Reuter and Levitan, 2010). Therefore, although our work indicates decreased fertilization success with increased suspended sediments, the implications for urchin populations will depend on the environmental conditions found when spawning occurs, or conversely, the cues in the environment that determine when spawning occurs.…”

Environmental and biological cues for spawning in the crown-of-thorns starfish

“…Conversely, flood events associated with phytoplankton blooms are often coupled with significant reductions in salinity [34,35], which may have maladaptive consequences for fertilization success and early development [45]. The role of peak abundance of larval food supply (phytoplankton) on spawning induction in tropical asteroids remains poorly understood [46]. Inter-individual chemical communication through sex pheromones from conspecific gametes has also been proposed in several marine invertebrates [19].…”

“…Spawning by one individual in an aggregation of the sea urchin, Sphaerechinus granularis , induced other conspecifics to spawn [47]. The presence of sperm in the water column has been experimentally demonstrated to induce spawning in sea urchins [42,46] and starfish [48,49]. Further studies suggested a synergistic relationship between sperm and phytoplankton cues, where spawning response depends on whether sea urchins have been in contact with phytoplankton or phytoplankton extracts [50].…”

“…Further studies suggested a synergistic relationship between sperm and phytoplankton cues, where spawning response depends on whether sea urchins have been in contact with phytoplankton or phytoplankton extracts [50]. Conversely, Reuter and Levitan [46] found that phytoplankton alone did not induce spawning, but when a phytoplankton cue was followed by the addition of sperm, response time to sperm was significantly reduced.…”