Circular Run-and-reversal Motion Optimize Foraging Behavior In Benthic Diatoms

In nature,there exist various kinds of movement behaviors of living organisms,which play a fundamental role in their life cycles or survivals.Driven by natural selection,organisms have evolved unique movement behaviors to enhance their competitiveness,viability and adaptability in natural environments.Biological movements,such as human activities and species invasion,interact closely with the environment,and influence the function and structure of individuals,populations,communities and even ecosystems.Thus,the driving factors,movement modes and mechanisms of biological movements and their ecological function have drawn the great attention of scholars from multiple fields of ecology,biology,and physics.Benthic diatoms as well as its counterpart pelagic diatoms carry out a series of important ecological functions,such as the silicon and carbon cycling of aquatic ecosystems.Although a large number of experiments and theoretical work have focus on the movement behavior of benthic diatoms,most of them just clarify the basic question of "how to move”,in other words,they put emphasis on studying the driving mechanism or the molecular regulation mechanism of benthic diatoms.To elaborate the natural movement motivation and its function from the perspective of ecology and evolution are often ignored.In this thesis,Navicula(Navicula arenaria var.rostellata)is used as the research object to study the unique "circular run-andreverse" movement of benthic diatoms,as well as explore its evolutionary nature and ecological function by connecting the movement with its ecological benefits,which may shed light on the growth and reproduction of benthic diatoms and their cooperative and competitive mechanism among individuals and populations.To this end,in this thesis,"circular run-and-reverse" movement of Navicula was systematically experimented and theoretically analyzed.The basic behavior and macro statistical properties of Navicula movement were quantified by statistical physics methods.Through numerical simulation and control experiments,the ecological function was explored from the perspective of foraging,and the effectiveness of the search efficiency in complex environment was verified.The main conclusions are as follows,First,two typical ways of the motion behaviors are observed.One is the uniform circular run with the velocity ?17 ?m/s and the angular velocity ?0.0032 rad/s.Moreover,the frequency of clockwise and anticlockwise deflection is the same.The other is the directional reverse behavior with random occurrence.The number of reverse events per unit time follows a Poisson distribution,and the incidence of reverse events is 0.016 /s,that is,one reverse occurred in62.5 s on average.As the movement system of Navicula shows no memory effect,it can be modeled by an overdamped Langevin equation,and the Fokker-Planck equation is capable to be used to calculate the macro statistics such as mean square deviation displacement,angle correlation function and effective diffusion coefficient.At short time scale,the movement pattern of Navicula belongs to a kind of super-diffusion behavior,while becomes sub-diffusion or diffusion behavior with the increase of time scale.Second,the "circular run-and-reverse" movement pattern of Navicula was consistent with the prediction of optimal foraging theory.On one hand,the motion parameters(rotation noise and regression rate)of Navicula observed in the experiment are basically consistent with the parameters of optimal foraging efficiency in the simulation.On the other hand,Navicula cells can sense the concentration of local nutrients(silicon)and adjust their movement strategies accordingly.When the silicon concentration was low,Navicula increased the effective diffusion coefficient by increasing the velocity and decreasing the inversion rate.When the silicon concentration increased,Navicula slowed down the movement speed and increased the inversion rate,so that to stay in the position of rich nutrition.The findings above show that the movement of “circular run-and-reverse” follows the prediction of optimal foraging theory.Another conclusion driven from the research is that,although the trend of the search efficiency calculated by the simulation and the effective diffusion coefficient calculated by the theory are the same,they are not equivalent.The effective diffusion coefficient cannot fully reflect the search efficiency of the system,but are able to infer the search efficiency.Third,the porous media environment can significantly affect the parameter of the search efficiency in "circular run-and-reverse" movement,and the effect varies with the pore sizes.When the size of pore becomes smaller,the inflection point of the search efficiency curve begins to shift to the direction of high regression rate,and the overall search efficiency will decline.And when the size of pore becomes larger,the search efficiency in the low rotation noise region becomes lower,while the search efficiency in the high rotation noise region becomes higher and obvious peak appears.In addition,the influence of obstacle environment on the "circular run-and-reverse" movement is also significant.This effect is also directly related to the number of obstacles.With the increase of obstacles,the search efficiency curve of rotational diffusion coefficient will decrease significantly.Finally,in the complex environment,the optimal parameter interval of "circular run-and-reverse" movement is not greatly affected,and has a certain robustness.