Ecology and functional morphology of Heteropsyllus nunni Coull (Copepoda: Harpacticoida), with a review of diapause in the Cyclopoida, Calanoida and Harpacticoida.

摘要

Heteropsyllus nunni Coull, a meiobenthic harpacticoid, copepod, is the only marine crustacean to undergo a state of diapause within a self-made cyst. A 12 month field population study indicated H. nunni adults reached peak population densities in winter, with nauplii maturing in spring. When the copepodites reach the last developmental stage, become a mature but unmated adult, they begin to encyst. They remain in a state of encystment diapause for three or four months during the summer. Experimental studies on the effects of temperature and photoperiod suggested that these two environmental cues are not crucial for induction into, or termination, of diapause. Cold temperature delayed development, hence time to encystment, while hot temperatures accelerated development, making the time to encystment (reaching the appropriate ontogenetic stage) shorter. H. nunni encyst only as mature, but unmated, adults.; The cysts are spherical and are composed of an amino acid complex similar to collagenous material. The copepod accumulates large stores of wax esters prior to dormancy, which lasts up to four months. Confocal laser micrographical studies of copepods stained with Nile Red dye for lipids showed a visual decline of stored lipid products during the diapause stage. Scanning electron microscopy revealed large cuticular pores on the last urosomal segments and the caudal rami. Light-level histochemistry indicated large storage sites full of cyst-building secretory products fill the lower urosome and these products are extruded via the largest pores, found in the caudal rami. The dorsally located secretory product is proteinaceous in composition while the ventral secretory product is a polysaccharide, as shown by positive reactions to Coomassie Blue (for protein) and periodic acid-Schiff's reagent stain (for polysaccharides). Transmission electron microscopy revealed multicellular glands that secrete the two secretory products. They are located apically to the sites of secretion and storage of the two secretory products.