Mating System and Reproductive Biology of a Temperate Wrasse, Halichoeres semicinctus
The reproductive behavior and mating system of the Rock Wrasse (Halichoeres semicinctus) was recorded and monitored around Big Fisherman Cove, Santa Catalina Island, CA from April 2001 to September 2002. Four sites with different relative densities were visited daily throughout the summer spawning season and once a month throughout the spring and fall. Group spawning was the dominant mating system among smaller individuals (<200 mm) with 8–12 individuals in the spawning aggregations. Large (>200 mm) terminal phase males held territories which were 4–5 m2 and were observed courting on multiple occasions in an attempt to pair spawn, but only three pair spawns were witnessed during the study. Elaborate courtship displays, including vertical rushes and lateral displays by the males within their territory, preceded pair spawning attempts. Spawning occurred primarily in the morning, but aggressive behavior by the territorial males continued throughout the day. The highest level of both group and pair spawning activity occurred at the highest density site, and only group spawning was seen at other sites. Density transect data showed that ratios of initial phase: terminal phase individuals were skewed toward initial phase in late spring and early fall and were skewed toward terminal phase individuals during peak spawning months (July and August) when many aggregations were present. The overall sex ratio in Rock Wrasse from Santa Catalina Island was nearly 1∶1, and histological data suggest that sex-changed individuals made up 38% of studied males. These data suggest that Rock Wrasse utilize a context-dependent, dualistic mating system that may act to increase opportunities for mating and thus, their overall reproductive output.Abstract
Map showing the primary study sites at Santa Catalina Island, California, adjacent to the Wrigley Marine Science Center Marine Reserve. The two high-density sites were Bird Rock and Chalk Cove, and the two low-density sites were Intake Pipes and Blue Cavern.
Stereotypical behavior witnessed during group spawns showing an aggregation composed of a medium sized female being followed by 3–15 males, both initial phase (IP) and mid phase (MP). Males begin bumping female laterally and ventrally. She signals readiness with quick bursts of speed and finally a vertical rush toward the surface. Gametes are released just under the surface of the water, with a large cloud of sperm, indicating many males participating in the spawn.
Stereotypical schematic showing a pair spawn between a territorial terminal phase male and a medium sized female. The male initiates spawning by performing the courtship display of vertical rushes in a circular pattern around the female. If she stays in the territory, he will often perform this rushing behavior several times before approaching her. Upon approach, the male will make lateral contact with the female and nudge her abdomen. She responds by moving up slightly in the water column. He will then lead her in the final vertical spawning rush and both will release gametes just under the water's surface.
Sexual pattern of Rock Wrasse (Halichoeres semicinctus) individuals shown at each of five age classes, indicating the onset of sex-change after the first year and males and females distributed throughout the age classes (n = 99).
Gonadosomatic indices (GSI) for primary and secondary males of Halichoeres semicinctus across the four age classes determined by otolith analysis. GSI was significantly different for primary and secondary males with respect to age class (MANOVA, df = 43, F = 10.35, P = 0.0002).
Gonadosomatic indices (GSI) for primary males and secondary males of Halichoeres semicinctus across standard length, suggesting that males have significantly different GSI as a primary male than as a secondary male (MANOVA, df = 49, F = 10.76, P = 0.0001).
Contributor Notes
Associate Editor: E. Schultz.