Changes in motility, ATP content, morphology and fertilisation capacity during the movement phase of tetraploid Pacific oyster (Crassostrea gigas) sperm

Abstract

Changes in sperm features during the movement phase are especially interesting to study in external fertilization species whose sperm duration movement is long because this implies a significant adaptation of moving cells to the external medium. This study describes the changes in tetraploid Pacific oyster sperm characteristics in relation to time post activation. Sperm individually collected on three tetraploid males were activated in seawater. Their features were analysed over a 24h period and compared to a sperm pool collected on three diploid males as a reference. The percentage of motile spermatozoa, the intracellular ATP content, and the fine structure of spermatozoa were studied in relation to time post activation. Furthermore, the fertilisation capacity of sperm individually collected on five diploid males was assessed after 1 and 24h post activation. A forward progressive movement was maintained for at least a 20h duration. Compared to diploid males, the percentage of motile spermatozoa was lower in tetraploid males. The intracellular ATP concentration was higher in spermatozoa from tetraploid males than in spermatozoa from diploid males. A decrease in ATP content was observed in the first 6h post activation and severe alterations were observed in sperm morphology after 24h. Then, a lower fertilisation capacity of sperm from diploid males was observed at the end of the movement phase. The cessation of Pacific oyster sperm motility was unlikely caused by ATP consumption as ATP concentration was still high at the end of sperm movement but rather caused by drastic changes in sperm morphology. Compared to sperm collected on diploid males, the lower quality of sperm from tetraploid males was emphasized by a shorter movement duration and deeper morphological alterations at the end of the movement phase.

Effect of sampling location, release technique and time after activation on the movement characteristics of scallop (Pecten maximus) sperm

“…On the other hand, a higher swimming speed was assessed in black-lip-pearl oysters: 221 ± 12 µm s −1 (Demoy-Schneider et al 2012). The mean intracellular ATP content of scallop sperm is high compared to that measured in different mollusk species (from 4 to 45 nmol × 10 −9 spermatozoa; Suquet et al 2010). However, an even higher ATP content was assessed in black-lip-pearl oysters: 700 nmol × 10 −9 spermatozoa (Demoy-Schneider et al 2012).…”

“…Then, the cessation of scallop sperm movement 8 to 10 h post activation could be caused by a limiting concentration of ATP amounting for a 90 ± 4% loss, as compared to the initial ATP content. On the contrary, 94% of the initial ATP content of Pacific oyster sperm was still assessed at the end of the movement period, suggesting that the cessation of sperm movement was not caused by a low ATP level in this species, but rather by drastic changes in sperm morphology (Suquet et al 2010). The causes of scallop sperm movement cessation will be further explored by testing the ability of spermatozoa to perform a second swimming phase after incubation in a non activating medium, as previously described in turbot (Dreanno 1998).…”

“…Sperm movement period may depend on many factors including animal maturation stage and sperm initial ATP content. Compared to scallop, the progressive movement of Pacific oyster sperm was maintained for a longer duration (20 to 24 h; Suquet et al 2010). The decrease of scallop ATP level is gradual: a decrease of 19 ± 11% of the initial content occurs after one hour post activation, which reaches a 40 ± 25% after 3 h and followed by further decrease from 3 to 10 h post activation.…”

“…Sperm samples of 500 µl were immediately frozen in liquid nitrogen. Intracellular ATP content was measured (triplicates) by bioluminescence (kit ATP lite, Perkin Elmer) using a microplate reader (Biotech Synergy HT) as previously described (Suquet et al 2010). After dilution to 1/500 in 1 µm filtered seawater, sperm concentration was determined by Coulter Counter (duplicates).…”

Motility of sea urchin Paracentrotus lividus spermatozoa in the post-activation phase

“…Sperm motility features may vary widely from one species to another, as a result of the development of different reproductive traits and fertilization strategies (Hassan, Qin & Li, ), reflected in differences in sperm morphology and physiology (Gallego, Pérez, Asturiano & Yoshida, ; Suquet et al., , ). Sea urchin spermatozoa have relatively long‐lasting motility (Au, Lee, Chan & Wu, ; Ohtake, Mita, Fujiwara, Tazawa & Yasumasu, ), and thanks to this feature, they are widely used in laboratory research, from ecotoxicology to molecular biology, being among the best models for developmental and evolutionary studies (D'Adamo et al., ; Kazama & Hino, ; McClay, ).…”