Research On Rapid Evolution Of Waterfleas To Tire Wear Particle

The relationship between climate change and adaptive evolution has been a focus of evolutionary biology research.Environmental change brings great pressure to the survival of natural population,so that the population goes through natural selection,and rapid adaptive evolution can help the population cope with the environmental pressure brought by the rapidly changing environment.Recently,tire wear particle（TWP）,a new pollutant produced by vehicle tire friction,has attracted wide attention.Tire wear particle pose a great threat to aquatic organisms,the leacher formed by the tire wear particle soaked in water will seriously reduce the survival rate and reproductive rate of aquatic organisms.But whether organisms can evolve tolerance to such pollutants is not well studied.This study aims to explore whether and how zooplankton can cope with the increase of tire wear particle in water,including the following research contents:In order to investigate whether the phenomenon of"urban runoff mortality syndrome"similar to that of fish can be observed in zooplankton,this study was aimed to investigate whether Daphina pulex had an effect on the fitness at different times of highway runoff during a stormwater event.The results showed that the highway runoff in winter had no significant effect on the survival and reproduction of daphnia,and the intrinsic growth rate had little difference compared with the control treatment.In summer,the highway runoff reduced the survival rate of daphnia by about 30%and the reproduction rate by 90%in the first two periods,while the runoff of other periods had no difference compared with the control treatment,indicating that the early runoff had stronger toxicity than the late runoff:the intrinsic growth rate at the first runoff（0 h）was negative,and the intrinsic growth rate at 0.5 h was only about 40 percent of that in the control treatment.This could be due to seasonal differences in temperature or UV radiation.The increased concentration of tire wear particle is cause by the highway runoff formed by stormwater mainly.Therefore,zooplankton may be experiencing environmental changes with increased tire wear particle concentration in water,and further studies are needed to explore the way that zooplankton responds to tire wear particle toxicity.In order to demonstrate the evolutionary potential of zooplankton on tire wear particle,then explored whether zooplankton represented by cladoceran had intraspecial variation on tire wear particle.The size of a population and whether there is sufficient basis of genetic variation within a population are critical to the ability of a population to adapt to environmental changes and provide raw materials for the evolution of a population.In this study,Daphnia carinata and D.pulex were selected as the objects of study.The size of a population and whether there is sufficient basis of genetic variation within a population are critical to the ability of a population to adapt to environmental changes.Twenty clones of D.pulex were collected from 5 ponds in Chongming Island,Shanghai,and 24 clones of D.carinata were collected from Nanbin River,Shanghai.The degree of interpopulation variation and intrapopulation variation of the two species were investigated by the common garden experiment and found that there were significant differences in all the five life history traits of daphnia between treatments,except for net reproduction rate and size at maturity,the other life history traits were different among the populations,and the performance of clones of different geographical populations was significantly different:the intrinsic growth rate of high tolerance genotypes was about 0.2,while that of low tolerance genotypes was negative.The intrinsic growth rate of D.carinata clones was negative in most of the clones,but only about-0.1 was found in the highly tolerant genotypes and-0.9 in the lower tolerant genotypes.These results indicate that both cladocerans have the genetic basis to adapt to tire wear particle,which provides the possibility for adaptive evolution.With the basis of adaptive evolution,to explored whether zooplankton could rapidly evolve tolerance to tire wear particle through experimental evolution and artificial selection under the simulation of natural selection in the laboratory,and whether the removal of selection pressure could drive the loss of the tolerance in the biota.The results showed that under the concentration of 0.2 g L^-1 tire wear particle,daphnia quickly evolved tolerance after one month of selection.Extending the selection period to two months showed no further improvement in tolerance.However,after the removal of the selection pressure,the selected daphnia population did not quickly return to the state before selection,and still had resistance to tire wear particle.Extending the recovery time to two months,it was observed that the selection line had the same tolerance to tire wear particle as the control lines,but some morphological and life history traits did not return to the pre-selection state.These results suggested that daphnia was able to adapt quickly to the environment containing tire wear particle and evolve rapidly,but there is a limit to this evolution.The loss of tolerance in relaxation experiment suggested that evolution comes at a cost,and it took longer for populations to evolve in reverse.The mechanisms of evolution and reverse evolution require further demonstration of gene dynamics data from population genetics.The natural population in the wild is faced with a more complex and changeable environment.In order to further verify that the evolution of tire wear particle can also occur rapidly in the natural daphnia population,a mesocosm experiment was conducted.After 40-days selection,populations exposed to the mesocosm units containing tire wear particle showed significant evolutionary responses,in the form of higher intrinsic growth rate,average life span and net reproductive rate,compared to those exposed to normal natural conditions.Therefore,natural populations can also rapidly evolve tolerance to tire wear particle and develop local adaptations,which may result from strong selection pressures and restricted gene flow.In addition,the specific situation of evolutionary changes after the removal of selective pressure,the effects on biological communities and population dynamics are all worthy of study,which is of great significance for the risk assessment of tire wear particle in natural environment.In conclusion,this study found that the tire wear particle in highway runoff had significant ecotoxicological effects on daphnia,but the intraspecific variation of daphnia enabled them to adapt and evolve simultaneously in the laboratory and in the field.Considering the important position of daphnia in the food web,it is expected that the daphnia population will be able to cushion the impact of tire wear particle on the entire aquatic ecosystem in the future.This study provides a new insight into the evolution of daphnia tolerance to tire wear particle,and a new perspective for biodiversity conservation and ecological restoration in the context of the increase of tire wear particle.