Temperature-dependent regulation of sperm motility of Ijima's copper pheasants (Syrmaticus soemmerringii ijimae), one of ‘near threatened' species

In order to conserve the copper pheasants, one of the Japanese ‘near threatened' species, the knowledge on the sperm characteristics is the inevitable issue. Therefore, temperature-dependent regulation of copper pheasant sperm motility was investigated in comparison with that of domestic fowl spermatozoa. Motility of intact spermatozoa from both species was markedly affected by temperature. During incubation at 30°C, copper pheasant spermatozoa showed around 60-70% motility, but became almost immotile when the temperature was raised to 40°C. Then, when the temperature of the sperm suspension was subsequently cooled to 30°C, the spermatozoa regained their motility. The motility of domestic fowl spermatozoa showed a similar pattern. Temperature also affected the motility of both demembranated copper pheasant and domestic fowl spermatozoa in the same way. The motility of intact copper pheasant and domestic fowl spermatozoa at 30°C was unaffected following the addition of 2mM CaCl₂, 100nM calyculin A, an inhibitor of protein phosphatase-type 1 (PP1), or 4mM diB-cAMP, respectively, compared with those with no effectors. However, the presence of 10μM ML-7, a selective inhibitor of myosin light chain kinase (MLCK), inhibited motility of spermatozoa from both species. At 40°C, the presence of CaCl₂ or calyculin A restored the motility of spermatozoa from both species, but the addition of diB-cAMP or ML-7 could not prevent the immobilization of spermatozoa. At 30°C in the presence of ATP, the motility of demembranated copper pheasant spermatozoa was over 60% but was inhibited following the addition of 10μM ML-7; a similar pattern was found with demembranated domestic fowl sperm motility. The motility of demembranated spermatozoa from both species was inhibited following the addition of 2mM EGTA to the reactivation medium at 30°C, but restored by the subsequent addition of 4mM CaCl₂. These results suggest that copper pheasant sperm motility might be regulated by similar mechanisms to that of domestic fowl spermatozoa: i.e., the balance of Ca²⁺/MLCK or an MLCK-like protein-dependent phosphorylation and PP1-dependent dephosphorylation. The similarity in physiological regulation of spermatozoa from both species shows that extensive technology developed for artificial breeding of the domestic fowl might be applicable to captive breeding of copper pheasants.