Patterns of sexual and asexual reproduction in the brittle star Ophiactis savignyi in the Florida Keys

Abstract

Many plant and animal species reproduce both sexually and asexually. These 2 reproductive modes are both likely to be costly and, in many species, they occur at different times of the year. Here, I present information on the sexual and asexual reproductive biology of the brittle star Ophiactis savignyi (Echinodermata, Ophiuroidea) in the Florida Keys, USA. Small brittle stars (less than 3 mm) are almost always non-mature, and non-mature individuals are more likely to have recently undergone clonal division than mature brittle stars. Males appear to have a lower size threshold for sexual maturity than do females, but the sexes do not differ in the recency of clonal division. The greatest proportion of mature brittle stars was observed in the late summer through fall in all 3 years of the study. The incidence of asexual reproduction increases in the late fall through late winter. It therefore appears that brittle stars are more likely to split after the sexual reproductive season. The onset of cloning as the sexual reproductive season ends may result from differences in the time of year in which each mode confers the greatest fitness benefit or may arise from energetic trade-offs between the 2 modes of reproduction.

Host specialization of an obligate sponge-dwelling brittlestar

“…1). Assuming that larger O. lineata have increased fecundity, which has been demonstrated for other brittlestar species (McGovern 2002), brittlestars in longer tubes may also have greater reproductive output. Enhanced growth in longer tubes could be due to decreased non-lethal predation (arm grazing by fish predators) on O. lineata within larger sponges, a greater surface area for deposit-feeding, or increased larval output of larger sponges.…”

Reproduction and population dynamics of the solitary entoproct Loxosomella plakorticola inhabiting a demosponge, Plakortis sp.

“…Hughes & Cancino (1985) reviewed the alternate sexual and asexual reproduction in many invertebrates. For instance, the annual peaks of the 2 modes of reproduction occur at different times of the year in intertidal sea anemones, Anthopleura elegantissima and A. xanthogrammica, and also in a brittle star, Ophaiactis savignyi (see Sebens 1981, 1982, McGovern 2002. The occurrence of self-division is much lower in the breeding season in the starfish Coscinasterias tenuispina (see Crozier 1920).…”

“…In general, asexual reproduction is advantageous for rapid proliferation, while sexual reproduction is necessary to produce genetic heterogeneity and to disperse over large areas in many benthic, particularly sessile, organisms. However, many studies deal with relatively large, prominent organisms (Sebens 1981, 1982, Uthicke 1997, McGovern 2002, and the reproduction and population dynamics of sessile meiobenthic species is poorly understood. Meiobenthic organisms are often overlooked in the field because of their small (0.2 to 5 mm), transparent bodies, however, they may be common species and have important functions in the marine ecosystem.…”

Bioactive compounds derived from echinoderms

“…68 A minor triterpene glycosides, typicosides A 1 (42), A 2 (43), B 1 (44), C 1 and C 2 (45) were isolated from the sea cucumber Actinocucumis typical. The new glycosides (42)(43)(44)(45), contained a hydroxyl-group in the aglycone side chain, demonstrating rather strong hemolytic and cytotoxic activities. …”