| In order to ensure productive success,animals must take the best reproductive strategy to maximize reproductive efficiency and fitness through trade-offs among life history traits,such as growth-reproduction trade-off,survival-reproduction trade-off,current reproduction-future reproduction trade-off,clutch size-egg size trade-off.However,reproductive strategy of amphibian was affected by many factors because of complex life history,thus amphibian has been regarded as an ideal study object in life history research.Recently,more and more attention has been paid to the effects of environmental pollution on variation of life history traits and survival in amphibian.Heavy metals,as common environmental pollutants which easily enriched but hardly degraded,could enrich in amphibian through digestive tract,respiratory tract and skin,leading to sperm quality decline,sex ratio change,gonad injury,growth and development retardation,and the like.However,effect of long-term heavy metal pollution on reproductive traits and reproductive strategy of amphibian under natural environment has not been reported.In the present study,Bufo raddei,a widespread anuran in northwest China,was chosen as the study object.Baiyin(BY)and Liujiaxia(LJX)were chosen as study sampling sites,BY is a polluted area by heavy metals mainly copper(Cu),zinc(Zn),lead(Pb)and cadmium(Cd)for a long period,while LJX is a relatively unpolluted area.The present study detected physiological and biochemical levels,reproductive characteristics and reproductive strategies of B.raddei from BY and LJX for four consecutive years between 2014 and 2017.Heavy metal concentrations,body condition,antioxidant level and fluctuating asymmetry level of B.raddei from BY and LJX were surveyed to explore the effect of environmental heavy metal pollution on corporeity and adaptation ability.Body size of sexual maturity,clutch size,egg size,age of sexual maturity and reproductive investment were analyzed to explore the effect of environmental heavy metal pollution on reproduction-related life history traits of B.raddei.Furthermore,to illuminate effect of environmental heavy metal pollution on reproductive strategy of B.raddei,trade-offs between survival and reproduction,as well as between clutch size and egg size were studied.The results were shown as follows:1.Enrichment of heavy metal in tissue of B.raddei.The results showed that,Cu concentrations in liver,Zn and Pb concentrations in blood,Cd concentrations in kidney of B.raddei from BY were significantly higher than those from LJX(P < 0.05).These results indicated that Cu,Zn,Pb and Cd significantly enriched in B.raddei under environmental heavy metal pollution.2.Effect of environmental heavy metal pollution on body condition and antioxidant level of B.raddei.The results showed that,body condition of B.raddei from BY was lower than that from LJX,glutathione peroxidase(GSH-Px)activity in kidney of B.raddei from BY was significantly lower than that from LJX(P < 0.05),while malonic dialdehyde(MDA)content in liver of B.raddei from BY was significantly higher than that from LJX(P < 0.05).These results indicated that body condition and antioxidant level of B.raddei decreased under environmental heavy metal pollution.3.Effect of environmental heavy metal pollution on fluctuating asymmetry level of B.raddei.The results showed that the levels of frequency of asymmetric manifestation of individuals(FAMI)and fluctuating asymmetry index of B.raddei from BY were significantly higher than those from LJX(P < 0.05).These results indicated that fluctuating asymmetry level of B.raddei increased under environmental heavy metal pollution.4.Effect of environmental heavy metal pollution on body size of sexual maturity,clutch size,egg size and age of sexual maturity B.raddei.The results showed that,body length and body weight of sexual maturity B.raddei at 3 years old from BY were significantly lower than those from LJX(P < 0.05).Age-specific clutch size of B.raddei from BY was significantly higher than that from LJX(P < 0.05),and agespecific mean egg mass of B.raddei from BY was lower than that from LJX.Age of sexual maturity in majority of B.raddei from BY and LJX was 2 and 3 years old,respectively.The individuals mainly involved in reproduction were 2 and 3 years old in BY,but 3 and 4 years old in LJX.These results indicated that body size of sexual maturity,egg size and age of sexual maturity decreased,while clutch size increased in B.raddei under environmental heavy metal pollution.5.Effect of environmental heavy metal pollution on reproductive investment of female B.raddei.The results showed that,reproductive investment of female B.raddei from BY tended to decrease with age,while reproductive investment of female B.raddei from LJX tended to increase with age.These results indicated that female B.raddei increased reproductive investment at the early age,while the breeding declines ahead of time under environmental heavy metal pollution.6.Effect of environmental heavy metal pollution on reproductive investment of male B.raddei.The results showed that,sperm total length of B.raddei from BY was significantly shorter than that from LJX(P < 0.05),sperm abnormality,sperm motility,call duration of advertisement call,forearm force,cross section of laryngeal area and breeding gland size in nuptial pad of B.raddei from BY were significantly higher than those from LJX(P < 0.05).These results indicated that male B.raddei increased reproductive investment under environmental heavy metal pollution.7.Effect of environmental heavy metal pollution on reproductive strategy of female B.raddei.The results showed that,there were differences in trade-offs between survival and reproduction,as well as between clutch size and egg size of female B.raddei from BY and LJX.Reproductive investment of female B.raddei from BY tended to decrease with age,whereas from LJX,it tended to increase with age.In addition,the average age of breeding female B.raddei from BY was younger than that from LJX,and age structure of breeding female B.raddei from BY showed a recessionary tendency.Meanwhile,female B.raddei from BY tended to produce bigger clutch size with smaller egg,while female B.raddei from LJX tended to produce smaller clutch size with larger egg.These results indicated that,for trade-off between survival and reproduction,female B.raddei tended to prioritize reproduction over survival,while for trade-off between offspring number and size,female B.raddei tended to prioritize offspring number over size,under environmental heavy metal pollution.8.Effect of environmental heavy metal pollution on reproductive strategy of male B.raddei.The results showed that,male B.raddei from BY increased investment in sperm motility,advertisement call,forearm force and secondary sex characteristics.Accordingly,male B.raddei from BY decreased their corporeity and survival,such as decrease of body condition,increase of fluctuating asymmetry level and decline of age structure in breeding season.These results indicated that male B.raddei tended to prioritize reproduction over survival for trade-off between survival and reproduction under environmental heavy metal pollution.In conclusion,under environmental heavy metal pollution,heavy metals significantly enriched in kidney and liver of B.raddei,meanwhile their body condition and antioxidant level decreased,fluctuating asymmetry level increased.In addition,life history traits of B.raddei obviously changed,in detail,body size of sexual maturity,egg size and age of sexual maturity decreased,while clutch size increased.Furthermore,reproductive strategy of B.raddei varied,B.raddei prioritized reproduction over survival for trade-off between survival and reproduction,while prioritized offspring number over size for trade-off between offspring number and size.The present results would provide scientific basis for further exploration in the mechanism of the amphibian bio-diversity variation caused by environmental pollution. |
PDF Full Text Request