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A newborn brownbanded bamboo shark Chiloscyllium punctatum hatched in the lagoon tank at Steinhart Aquarium in San Francisco—almost four years after its mother was last in contact with a male! This finding is almost twice the previous sperm storage record of days for sharks, which was held by the chain catsharks Scyliorhinus rotifer. This amazing new discovery has added a new wrinkle to the already complicated field of shark reproductive biology.
Ejaculationthe release of sperm cells and seminal plasma from the male reproductive system. Ejaculation takes place in two phases: in the first, or emission, stage, sperm are moved from the testes and the epididymis where the sperm are stored to the beginning of the urethraa hollow tube running through the penis that transports either sperm or urine; in the second stage, ejaculation proper, the semen is moved through the urethra and expelled from the body. Sperm cells that are stored in the male body are not capable of self-movement because of the acidity of the accompanying fluids.
The human male reproductive system contains these parts:. The two testes one of them is called a testis are contained in a bag of skin called the scrotum. The testes have two functions:.
Internal fertilization ensures successful reproduction of tetrapod vertebrates on land, although how this mode of reproduction evolved is unknown. Here, we identified a novel gene encoding sperm motility-initiating substance SMISa key protein for the internal fertilization of the urodele Cynops pyrrhogaster by Edman degradation of an isolated protein and subsequent reverse transcription polymerase chain reaction. No gene with substantial similarity to the SMIS was in the data bank of any model organisms.
For reproduction, most fish species adopt external fertilization: their spermatozoa are delivered in the external milieu marine- or freshwater that represents both a drastic environment and a source of signals that control the motility function. This chapter is an updated overview of the signaling pathways going from external signals such as osmolarity and ionic concentration and their membrane reception to their transduction through the membrane and their final reception at the flagellar axoneme level. Additional factors such as energy management will be addressed as they constitute a limiting factor of the motility period of fish spermatozoa. Modern technologies used nowadays for quantitative description of fish sperm flagella in movement will be briefly described as they are more and more needed for prediction of the quality of sperm used for artificial propagation of many fish species used in aquaculture.
Still others lack the energy to finish the long journey through the female reproductive tract, or they get snared in sticky fluid meant to impede all but the strongest swimmers. For the subset of a subset of spermatozoa that reach their trophy, the final winner would be determined by one last sprint to the end. The exact identity of the sperm was random, and the egg waited passively until the Michael Phelps of gametes finally arrived.
The trajectory of sperm in the presence of background flow is of utmost importance for the success of fertilization, as sperm encounter background flow of different magnitude and direction on their way to the egg. Here, we have studied the effect of an unbounded simple shear flow as well as a Poiseuille flow on the sperm trajectory. In the presence of a simple shear flow, the sperm moves on an elliptical trajectory in the reference frame advecting with the local background flow. The length of the major-axis of this elliptical trajectory decreases with the shear rate.