Reproductive biology of four ophiocomid ophiuroids in tropical and temperate Australia – reproductive cycle and oogenic strategies in species with different modes of development

Abstract

The Ophiocomidae, a species-rich family of ophiuroid echinoderms, encompasses a range of developmental modes. We investigated the reproductive biology of four species: Ophiocoma dentata with planktotrophic development and a small egg, and three species with lecithotrophic development and eggs that differ in size (Clarkcoma pulchra, C. canaliculata and O. endeani). Reproduction was investigated by in situ observations, spawning trials and/or gonad histology. Gonad histology of O. dentata from the Northern and Southern Great Barrier Reef indicated that spawning occurs for six to seven months from January to June/July. Gonads of O. endeani, an endemic of subtropical New South Wales, were mature from December to February. In situ observations of two populations of C. pulchra and C. canaliculata in the Sydney region indicated they spawn from December to May. Egg morphology showed modifications in oogenesis associated with the evolution of a large egg, particularly in enhanced deposition of lipid. The eggs of O. dentata, a planktotrophic developer, contained densely packed, strong periodic acid Schiff's þ yolk granules and were negatively buoyant. The eggs of species with lecithotrophic development were dominated by lipid droplets indicating that the evolutionary modification of oogenesis resulted in differences in yolk granule and lipid droplet distribution potentially influenced by selection for egg buoyancy.

Evolution of maternal provisioning in ophiuroid echinoderms: characterisation of egg composition in planktotrophic and lecithotrophic developers

“…In general, the protein content of these eggs is 2-to 3-fold greater than the lipid content (Jaeckle 1995, George 1999. Across the 4 species with small eggs, protein content was particularly high in Ophiocoma dentata, as also indicated by egg protein histochemistry (Falkner et al 2013). Similarly, elevated protein levels are reported in the eggs of another ophiocomid with planktotrophic development, O. alexandri (Whitehill & Moran 2012).…”

“…This difference may be attributed to the high protein content and comparatively high lipid content in the eggs of the only tropical planktotroph studied, Ophiocoma dentata (Falkner et al 2013). Could the increased lipid and protein content in the eggs of this species be a re sponse to a food-poor environment for the developing larvae?…”

Brooding behavior in the shallow‐water brittle star Ophioderma wahlbergii

“…With the evolution of increased parental care, non‐feeding larval forms replaced the ancient, feeding ophiopluteus larva (Selvakumaraswamy & Byrne , ; Byrne & Selvakumaraswamy ; Allen & Podolsky ; Falkner et al. ). At the most extreme end of this continuum, the larvae have lost virtually all pelagic larval features and are retained inside specialized brood chambers.…”