Biological Rhythms in Terrestrial Arthropods

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biological rhythms is very wide. The cycle s can range from some millis econds to some years. The rapid osci lla­ tions are especially characteristic of physiological rhythms which ensure the synchronization of all the internal process es in an organism. Such rhythms may be exemplifi ed by the rhythmic events in the enzym e-substrate system or by the pulsations of the heart muscle. Oscillations with daily or longer periods rank as a rule among ecolog ical rhythms which provid e for adapt a­ tion of plants and animals to fluctuations of enviro nmental factors. Internal oscillators are assumed to control such rhythms ; they are synch ronized by external timing elements (Zeitgeber = time-giv ers) which can be also termed as synch ronizers or entraining agents. Photope riod is especially im­ portant as this agent. The possession of int ernal oscillators enable s orga­ nisms to prepare in good ti me for the chang es of ecological conditions dur­ ing each day (daily rhyt hms), month (l unar rhythm s), or year (s eas onal rhyth ms). Adaptive implication and, cor res pondi ngly, mode of display ing the three type s of rhythms varies considerably. That's why, until recently, circadian and seasona l rhythms in arthropods have been investigated quite indepen­ dently. Daily rhythms were studied as biolo gical oscillations related to time measuring. As to inve stigations into seasonal cyclic phenomena , most atte n­ tion was paid to syst ems of neurosecr etory control of development and dia­ pause as well as to ecological aspects of the problem. The two points of view have been flected in reviews by Hark er (90) and de Wilde (207 ), published in previous volumes of Annual Review of Entomology. The material accumulated shows that some general princ iple s are th e basis of all the ecological rhythms. It dis plays especially clearly the synchro­ nization of the biological processes with rhythmic factors of the environ­ ment. The adaptations to lunar and seasonal periodicity evolve by way of 1 The follow in g abbrev iati ons are used in the text: PhPR (ph otop eriodic rea cti on); T of a free-running rhyth m); LL (constant ligh t); DD (constant darkness) ; LD (light-dark cycles which can be further specified as