Comparative Studies on the Energy Metabolism in Spermatozoa of Four Closely Related Species of Sea Urchins (Genus Echinometra) in Okinawa

Abstract

Sea urchins of the genus Echinometra are abundant on Okinawa reef flats in southern Japan. The Okinawan Echinometra is designated into four sympatric and closely related species: A, B, C, and D (Ea, Eb, Ec, and Ed). The sperm head size and shape gradually changes to become longer and more slender according to the following order: Ea, Eb, Ec, and Ed. To obtain information regarding speciation in Okinawan Echinometra, this study examined comparatively the energy production system of spermatozoa of Ea, Eb, Ec, and Ed. All spermatozoa contained cholesterol and several kinds of phospholipids. Glycogen, glucose, and triglyceride were present at extremely low levels. After incubation in sea-water, a decrease in the level of phosphatidylcholine (PC) was observed in all spermatozoa concomitantly with activation of motility and respiration. The hydrolysis of PC correlated with the activity of phospholipase A2. Interestingly, the amount of PC consumed, the respiratory rate, and the phospholipase A2 activity in spermatozoa of Ea and Eb were approximately two-fold higher than those of Ec and Ed. Ultrastructural studies showed that lipid bodies within mitochondria were present in the midpieces of all species of spermatozoa. They became small or disappeared after incubation in seawater. Thus, the results obtained strongly suggest that spermatozoa of Ea, Eb, Ec, and Ed all use PC located in the lipid bodies as a substrate for energy metabolism. Also, it seems likely that energy production activities in Ea and Eb spermatozoa are stronger than those in Ec and Ed. The properties of energy metabolism in different species of sea urchin may be related to their habitat.

Effect of temperature on interactions between eggs and spermatozoa in four closely related species of sea urchins of the genusEchinometra

“…As confirming here, sperm head shapes vary among the four species of Echinometra (Arakaki et al, 1998;Mita et al, 2002Mita et al, , 2004. The spermatozoon of Ea, Eb, and Ec each has a head that is longer and more slender than the preceeding species (Fig.…”

“…In view of the substantial differences among the four types, Okinawan types of E. mathaei seem to be four distinct species. In this regard, sperm size and shape were found to differ among the four types (Arakaki et al, 1998;Mita et al, 2002). Furthermore, allozyme analysis (Matsuoka and Hatanaka, 1991) and sequence analysis on mitochondrial DNA Metz et al, 1991) indicate that these types are distinct but closely related species.…”

Speciation in four closely related species of sea urchins (genusEchinometra) with special reference to the acrosome reaction

“…Certainly, the energy metabolism of Ed spermatozoa is only half that of Ea and Eb (Mita et al, 2002), and this is why the size and shape of the sperm head in Ed are quite different from those of Ea, Eb and Ec (Arakaki et al, 1998;Mita et a]., 2002). The long and slender shape of the head in Ed sperm head has been previously reported (Mita et al, 2002), but the reason for this morphological difference remains unclear. Spermatozoa of the sea urchin Colobocentrotus mertensii possess very long and slender heads similar to those of Ed (Uehara, 1990).…”

“…Sperm size and shape vary among the four species of Echinometra (Arakaki et al, 1998;Mita et al, 2002). Three species can be placed in a series according to head shape.…”

Changes in glucose and carnitine levels and their transporters in utero‐tubal junction in relation to sperm storage in the vespertilionid bat, Scotophilus heathi

“…In addition to glucose, mammalian spermatozoa actively utilize lipids for energy source for their motility and metabolism (Mita, , Lenzi et al, ; Mita et al, ). In ovine spermatozoa endogenous fatty acids have been shown to support the metabolic requirement in the absence of glycolytic substrates (Hartree and Mann, ).…”