Sperm motility activation in the critically endangered booroolong frog: the effect of medium osmolality and phosphodiesterase inhibitors.

Effective activation of sperm motility is fundamental to successful artificial fertilisation; however, studies investigating optimal procedures in amphibians are lacking. This study found the optimal osmolality of activation media for sperm motility activation and evaluated the effect of phosphodiesterase (PDE) inhibitors on sperm activation and longevity in the critically endangered booroolong frog, Litoria booroolongensis. To assess the effect of medium osmolality (10, 25, 50, 75, 100 and 200mOsmolkg) and PDE inhibitors (control, 2.5mM caffeine, 5mM caffeine, 2.5mM pentoxifylline, 5mM pentoxifylline, 2.5mM theophylline and 5mM theophylline) on initial activation, percentage sperm motility and sperm velocity were quantified using computer-assisted sperm analysis. To assess the effect of PDE inhibitors (control, 2.5mM caffeine and 2.5mM theophylline) on sperm longevity, percentage motility and velocity were assessed hourly until 10h after activation. High (>60%) percentage motility was achieved in a broad range of activation-medium osmolalities (10-75mOsmolkg). PDE inhibitors did not have an effect on initial sperm motility or velocity, but caffeine and theophylline improved sperm longevity, significantly increasing motility and velocity at 8, 9 and 10h after activation. Data also show that sperm longevity in L. booroolongensis is extreme, with spermatozoa remaining motile more than twice as long as those of any other anuran amphibian.