Site‐specific sperm agglutination and the timed release of a sperm chemo‐attractant by the egg of the leptomedusan, Orthopyxis caliculata

Abstract

In Orthopyxis sperm entry apparently occurs a t the site of emission of the polar bodies. If sperm are present from the time of spawning of the egg, they agglutinate head to head shortly after emission of the second polar body but only a t a point on the egg surface under the second polar body. Since sperm agglutination does not occur elsewhere on the egg, it appears that this part of the surface of the egg of Orthopyxis and probably other hydromedusae is a special membrane patch which causes sperm to bind reversibly both to it, and to each other. The patch develops a t a specific time during egg maturation and ceases function a t or just after fertilization. Concomitant with the appearance of the patch is the production of a species-specific sperm attractant by the egg. These results imply that the egg has strict control not only of the site and timing of sperm penetration but also of the time during which sperm are attracted to the egg.This report presents observations of a complex series of sperm-egg interactions preceding fertilization of the egg of the cnidarian Orthopyxis. Some aspects of the interactions are similar to those reported in the hydromedusa Spirocodon (Dan, '50). However, although Dan provides some evidence for sperm chemotaxis to the germinal vesicle zone, her paper deals mainly with the penetration of the sperm into the egg, rather than the prepenetration events reported here. Not only do the Orthopyxis observations suggest that sperm penetration may result from cooperative sperm behavior a t the egg surface, they also reveal for the first time a close relationship between the timing of animal egg maturation, sperm binding to the egg surface and t o each other, and the onset of production by the egg of a species-specific sperm attractant. MATERIALS AND METHODSMedusae of the hydroid Orthopyxis ( fig. 1) were collected a t dusk as they swim to the surface of the ocean after release from the parent colonies growing under a floating dock. ways released first, with the males appearing some 15 to 20 minutes later. Spawning occurs within 10 t o 15 minutes after release, following which the medusae, lacking stomach or tentacles, swim briefly and then sink to the bottom. The medusae were therefore segregated by sex as soon as possible after they were dipped from the ocean. If the female medusae were brought into the laboratory shortly after collection, spawning still occurred a t the normal time. The eggs were placed on a Siliclad (Clay-Adams, Inc.) treated microscope slide coated over a 2.5 cmz area with albumin to support a large, flat drop of sea water. After the eggs had settled, and the stage of polar body emission confirmed (aided by the tendency of the eggs to rest on their equators), sperm were added some distance from the eggs so that their approach to the eggs and subsequent behavior could be observed. Observations were made using a Zeiss WL microscope with 2.5, 10 and 16 x objectives with dark field illumination. The resulting magnifications were increased 1.2 to 2.0 x using a Zeiss...

Polyspermy prevention in marine invertebrates

“…Sperm can only fuse with the egg at the site of polar body formation. This site develops after second polar body formation and also produces a substance that attracts sperm (Miller, 1978;Freeman, 1982Freeman, , 1987. Eggs begin to produce the chemoattractant after first polar body formation but fertilization will only occur after the second polar body forms (Freeman, 1987).…”

“…To our knowledge, there have been no electrophysiological studies of fertilization in cnidarian eggs. In Orthopyxis, large numbers of sperm described as a "flame" or "clot" are observed at the fertilization site, but polyspermy resistance in these eggs was not investigated (Miller, 1978).…”

Sperm-attractant peptide influences the spermatozoa swimming behavior in internal fertilization in Octopus vulgaris

“…The role of chemotaxis has been explored primarily in cnidarians and echinoderms. In 1978, Miller demonstrated that the eggs of the cnidarian Orthopyxis caliculata not only secrete a chemotactic factor, but also regulate the timing of its release (Miller, 1978). More than 70 sperm-activating peptides (SAPs), with slight differences in their amino acid sequence, have been purified and characterized from the egg jelly of 17 sea urchin species (Suzuki and Yoshino, 1992).…”

The role of cAMP in oocyte maturation and the role of the germinal vesicle contents in mediating maturation and subsequent developmental events in hydrozoans

“…If a mature egg is cut in half, both halves will attract sperm. Eggs continue to attract sperm until they have been fertilized or activated (Freeman 1987;Freeman and Miller 1982;Miller 1978). In the hydrozoan Phialidium, calcium channel function is first initiated about one hour after fertilization or egg activation (Freeman and Ridgway 1987) when first cleavage normally begins.…”