Association of heat shock protein 90 with motility of post-thawed sperm in bulls.

The correlation between the 90 kDa heat-shock protein (HSP90) and sperm quality following the process of freezing-thawing in bulls has not been studied clearly. Therefore, the objective of the present was to clarify the relationship between HSP90 level and semen parameters during the process of cryopreservation in bulls. Semen samples from 5 Holstein bulls were obtained by artificial vagina. Characteristics of these semen at three stages (fresh, after equilibration and frozen-thawed), including motility, plasma membrane integrity and acrosome integrity were evaluated. The mRNA expression level of HSP90 at the three stages was evaluated by using quantitative Real-Time PCR. Meanwhile, the protein level of HSP90 expression at the three stages was detected according to Western blot. The results showed that sperm parameters evaluated in fresh semen was the highest in the three groups. Sperm parameters in semen after equilibration were lower than those in fresh semen (P>0.05) and higher than those in post-thawed semen (P<0.05). Sperm parameters in frozen-thawed semen were the lowest among the three groups (P<0.05). This study indicated that HSP90 expression is proportional to sperm quality. HSP90 expression level in fresh semen was significantly higher than that in frozen-thawed semen (P<0.05). Although no significant differences in HSP90 expression were observed between fresh semen and semen after equilibration (P>0.05). Results in this study suggest that HSP90 level in bull spermatozoa was gradually declined following the process of freezing-thawing, and might be associated with sperm motility, plasma membrane integrity and acrosome integrity.

Interspecific variation in hypoxia tolerance, swimming performance and plasticity in cyprinids that prefer different habitats.

This study quantified and compared hypoxia tolerance and swim performance among cyprinid fish species from rapid-, slow- and intermediate-flow habitats (four species per habitat) in China. In addition, we explored the effects of short-term acclimation on swim performance, maximum metabolic rate (M(O2,max)) and gill remodelling to detect habitat-associated patterns of plastic response to hypoxia. Indices of hypoxia tolerance included oxygen threshold for loss of equilibrium (LOE50) and aquatic surface respiration (ASR50), and critical oxygen tension for routine metabolic rate (Pcrit). Critical swimming speed (Ucrit) and M(O2,max) were measured under normoxic and hypoxic conditions after 48 h acclimation to normoxia and hypoxia, and gill remodelling was estimated after 48 h of hypoxia exposure. Both traditional ANCOVA and phylogenetically independent contrast (PDANOVA) analyses showed that fish species from rapid-flow habitats exhibited lower LOE50 compared with fish from intermediate- and slow-flow habitats. Habitat-specific differences in Pcrit and Ucrit were detected using PDANOVA but not traditional ANCOVA analyses, with fish species from rapid-flow habitats exhibiting lower Pcrit but higher Ucrit values compared with fish from intermediate- and slow-flow habitats. Fish species from rapid-flow habitats were also characterized by less plasticity in swim performance and gill morphology in response to hypoxia acclimation compared with species from slow-flow habitats, but a greater drop in swim performance in response to acute hypoxia exposure. The study detected a habitat-specific difference in hypoxia tolerance, swimming performance and its plasticity among fish from habitats with different flow conditions, possibly because of the long-term adaptation to the habitat caused by selection stress. The PDANOVA analyses were more powerful than traditional statistical analyses according to the habitat effects in both hypoxia tolerance and swimming performance in this study.

Integrating environmental variation, predation pressure, phenotypic plasticity and locomotor performance.

The Wujiang River, a tributary of the Three Gorges Reservoir, has many dams along its length. These dams alter the river's natural habitat and produce various flow regimes and degrees of predator stress. To test whether the swimming performance and external body shape of pale chub (Zacco platypus) have changed as a result of alterations in the flow regime and predator conditions, we measured the steady (U(crit)) and unsteady (fast-start) swimming performances and morphological characteristics of fish collected from different sites along the Wujiang River. We also calculated the maximum respiratory capacity and cost of transport (COT). We demonstrated significant differences in swimming performance and morphological traits among the sampling sites. Steady swimming performance was positively correlated with water velocity and negatively correlated with the abundance of predators, whereas unsteady swimming performance was negatively correlated with water velocity. The body shape was significantly correlated with both swimming performance and ecological parameters. These findings suggested that selection pressure on swimming performance results in a higher U(crit) and a more streamlined body shape in fast-flow and (or) in habitats with low predator stress and subsequently results in a lower COT. These characteristics were accompanied by a poorer fast-start performance than that of the fish from the slow-flow and (or) high-predator habitats. The divergence in U(crit) may also be due in part to variation in respiratory capacity.