Locomotion Of Cave-dwelling And Surface-living Ground Beetles

Cave biology(also known as “biospeleology”)has been an attractive subject since the Proteus anguinus was first ly discovered in Slovenia.After long-term adaptive evolution,subterranean animals are not only displaying conspicuous morphological characteristics(e.g.,compound eyes disappeared and appendages elongated),but also behavioral and physiological modifications(e.g.,lower metabolic rate).Dark,moist and temperature-constant cave environments are an ideal natural laboratory to study important aspects of evolutionary theory,with ongoing debates among followers of competing hypotheses related to the evolution of cave organisms.Even though morphological adaptations of cave-dwelling organisms have fascinated researchers since a long time,very few detailed documentations of the anatomy of cave beetles are available,let along the study of the locomotion.In this study we describe and compare external and internal legs and motion parameters of free-living and cave-dwelling trechinae carabid beetles(troglobite: Sinaphaenops wangorum Uéno et Ran,1998,troglophile: Trechiotes perroti Jeannel,1954,epigean: Agonum buchanani Hope,1831)using modern techniques,includ ing SEM,micro-CT,3D reco nstruct io n and hig h-speed camera video analysis.Main results of our research are followings:(1)Structures of legs: the length of the fore-,mid-and hindlegs and the ratio of the length of each leg proportion of S.wangorum are larger than that of T.perroti and A.buchanani;In the tarsus of the forelegs in male,there are disk-shape adhesion setae.The disk-shape adhesion setae of S.wangorum and T.perroti are distributed in the first and second tarsus,and the disk-shape adhesion setae of A.buchanani are distributed in the first to third tarsus.The setae of S.wangorum and T.perroti are distributed around the tarsus,while A.buchanani is only ventrally distributed on the tarsus.Compared with A.buchanani,pleurocoxal muscles,IIIdvm6 and IIIpcm4,are absent in S.wangorum and T.perroti.T.perroti and A.buchanani are with two muscles in femurs,while S.wangorum is present one.S.wangorum lack tarsus extensor and flexor in compare to T.perroti.(2)Locomotion behavior: the three species use typical tripod gait during crawling,and the main gait sequence is left foreleg(L1),right midleg(R2),left hindleg(L3),right foreleg(R1),left midleg(L2)and right hindleg(R3).The speed of S.wangorum is minimum(34.1824 mm/s),followed by T.perroti(59.9487 mm/s)and A.buchanani(73.6689 mm/s).S.wangorum mainly crawlies on non-linear trajectories,A.buchanani basically crawlies on linear trajectories,and T.perroti crawlies on two trajectories with similar probability.S.wangorum is longer than T.perroti and A.buchanani in both swing-and stance phase.The swing-and stance phase of S.wangorum,the swing-,stance phase and duty factor of T.perroti and A.buchanani decrease with the increase of the speed.There were significant differences in the swing-,stance phase,stride length,stride frequency and Tripod Coordination Strength(TCS)of the three species.Due to the cave environment,there are certain morphological differences between the surface-living and cave-dwelling ground beetles,such as the length of the legs,number of muscles,location of adhesion structures,etc.,which may further influence the locomotion behavior of them,thus showing significant differences in kinematics.However,the correlation differences between males and females are still uncertain.Therefore,in the future kinematics analysis work should include more species(especially the cave-dwelling ground beetles),and make gender distinction,so as to provide more powerful scientific evidence for the adaptive mechanism of cave organisms.