Effects Of Light On Metabolic Rate And Gene Expression In Triplophysa Rosa

Cave-dwelling fishes has many specialized features,such as small visual regions in the brain,highly degraded eyes and surface pigmentation,highly developed non-visual mechanical sensory organs,and repressed metabolic rate.All those specialized features are conductive to adapt to food-limited and dark cave environment and are of interests to understand the evolutionary fitness of animals in extreme environments with high-selective stress.Triplophysa rosa is a typical species of cave-dwelling fish and lives in dark cave waters with eyes degenerated into black eyespot or disappeared.This study took T.rosa and other closely related fishes as the research objects,and aimed: to determine the metabolic level of this typical cave fish and whether light would affect its metabolic level by measuring the body and organ?brain,heart and liver?metabolic rate of T.rosa treated by light;to test the effects of ligh on the gene expression of this fish by comparative transcriptome analysis of the brain and muscle tissues of T.rosa;to determine the link between interspecific differences of habitats,visual organ degradation,and metabolic levels by compare the individual and organ metbolic levels of three closely related fishes?Triplophysa bleekeri,Triplophysa longibarbatula and Triplphysa wulongensis sp.nov?tentative title??.The main results were as follows: 1.The relationship between the resting metabolic rate?RMR?and body weight?M?of the T.rosa was log RMR = 0.932 log M^-1.369,and the average mass-specific RMR?MS-RMR?was 38.3 mgO₂·h^-1·kg^-1,which was lower than those of most species of teleost fish under the same conditions.2.The light had no significant effects on RMR and organ metbolic rate?MO₂?of brain,heart,and liver of T.rosa,T.wulongensis sp.nov,and T.bleekeri.The diurnal metabolic rate showed no difference between those acclimated in darkness and those acclimated in regular photoperiods.Light had no significant effects on red blood cell count,red blood cell area,and hemoglobin content in the T.rosa.3.In the T.rosa,both heart mass and liver mass increased with increasing M,but brain mass did not correlate with M.No significant changes in the organ MO₂ of the brain and heart were observed with increasing of M,but MO₂ of liver increased.Organ mass of the brain,heart,and liver were averagedly responsible for 0.29%,0.08%,and 0.98% of the M and whole-organ MO₂ of the brain,heart,and liver were averagedly responsible for 8.62%,3.55%,and 8.61% of the RMR,respectively.In the T.wulongensis sp.nov,both heart mass and liver mass increased with increasing M,but brain mass did not correlate with M.Brain,heart,and liver MO₂ increased with increasing M.Organ mass of the brain,heart,and liver were averagedly responsible for 1.11%,0.18%,and 1.03% of the M and whole-organ MO₂ of the brain,heart,and liver were averagedly responsible for 5.64%,1.11%,and 1.31% of the RMR,respectively.In the T.bleekeri,brain,heart and liver mass showed no significantly change with increasing M.No significant changes in the organ MO₂ of the brain and heart were observed with increasing of M,but liver MO₂ increased.Organ mass of the brain,heart,and liver were averagedly responsible for 0.79%,0.13%,and 1.12% of the M and whole-organ MO₂ of the brain,heart,and liver were averagedly responsible for 1.57%,0.22%,and 0.75% of the RMR,respectively.4.The significantly enriched GO term and KEGG pathway in the T.rosa was associated with immunity and disease.After light treatment,the stress related genes hsp70,hsp90,hspa4,dnajb4,the motor related genes mylk4,sorbs1 and circadian rhythm related genes c-fos,c-jun,bhlhe40 were up-regulated.5.The RMR of T.rosa,T.wulongensis sp.nov,T.bleekeri and T.longibarbatula were 0.113,0.427,3.396,and 0.034 mgO₂·h^-1,respectively,when correcting M to the mean value of 2.596 g.The RMR of the T.wulongensis sp.nov was significantly higher than that of the T.rosa?F = 53.277,p < 0.001?,T.longibarbatula?F = 56.988,p < 0.001?,and T.bleekeri?F = 5.545,p = 0.023?by ANCOVA.The RMR of T.bleekeri was significantly higher than that of the T.rosa?F = 9.120,p = 0.004?and T.longibarbatula?F = 18.150,p < 0.001?.The RMR of T.rosa,T.wulongensis sp.nov,and T.longibarbatula scaled with M by exponent?b_R?of 0.932,0.625,1.108,respectively.The b_R of T.rosa and T.longibarbatula were higher and showed no significant difference with 1?p = 0.549;p = 1.108?,while the b_R of T.wulongensis sp.nov was lower and was significantly less than 1?p = 0.070?.There were no significant correlation between RMR and M of T.bleekeri.The conclusion of this study were as follows: 1.The metabolic level of T.rosa was lower than those of most fish species,which can be ascribed to its small brain and eyes,and then saved visual energy consumption.This is beneficial for this fish to live in the dark and food-limited cave environment.2.The individual and organ MO₂ of T.rosa showed no change after light treatment,suggesting that the metabolic consumption of T.rosa is not light sensitive.The RMR of T.rosa showed no difference between those acclimated in darkness and those acclimated in regular photoperiods,suggesting the metabolic rate of this species has no circadian rhythm.Light stimulation did not change red blood cell count,red blood cell area,and hemoglobin content of T.rosa,suggesting an unchanged blood oxygen transport capacity.3.After light treatment,the stress response genes including hsp70,hsp90,hspa4,dnajb4,and the motor function related genes including mylk4,sorbs,and circadian rhythm related genes including c-fos,c-jun,bhlhe40 of T.rosa were up-regulated,which indicates that light affects on expression of genes associated with those physiologcial processes.4.The heart mass and liver mass of T.rosa increased with increasing M,which is similar to the general pattern of organ size change in fish.However,brain mass did not correlate with M.The proportion of brain mass to M was lower,but the ratio of brain MO₂ to RMR was higher in T.rosa than in T.wulongensis sp.nov and T.bleekeri,and the whole brain MO₂ of the three species were higher than those of heart and liver,suggesting that brain is an expensive organ and maintaining a samll brain has obvious evolutionary advantages for the typically cave fish during ontogenetic process.5.The RMR of the two typical cave fish,T.rosa and T.longibarbatula,with degraded eyes were significantly lower than those of the two non-cave fish,T.wulongensis sp.nov and T.bleekeri,with normal eyes,which should be correlated with their habitat difference,as cave environment is food-limited and the lower metabolic level is conductive to enenrgy conservation.The degree of eye degeneration is clearly correlated with the metabolic level,because visual processes consume huge energy.Thus,the species with degraded eyes can reduce the vision related energy consumption,improving the evolutionary fitness in the cave.Besides,the relationship between RMR and M of the four species in this study is consistent with the prediction of the metabolic level boundary hypothesis that species with lower metabolic levels have higher b_R.