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image of Crustaceana

Rhythms of locomotor activity in constant darkness, under a 24-hour skeleton photoperiod, and under 4-hour and 24-hour light-dark cycles were studied in the pill bug, Armadillidium vulgare (Isopoda). The animals showed clear daily rhythmicity under the 24-hour light-dark cycle but exhibited weak rhythmicity under the skeleton photoperiod and in constant darkness. Unmasking of free-running rhythms was not observed under the 4-hour light-dark cycle. The results indicate that pill bugs must possess an endogenous circadian pacemaker but that this pacemaker is either very weak or has a very weak connection with the mechanisms responsible for locomotor activity. The modulatory effect of light on the rhythm of locomotor activity is almost entirely due to negative masking.

Ritmos de atividade locomotora foram estudados no tatuzinho, Armadillidium vulgare, em condições de escuridão contínua, esqueleto de fotoperíodo de 24 horas, e ciclos de luz e escuridão de 4 horas e de 24 horas. Os animais exibiram ritmicidade robusta quando expostos ao ciclo de luz e escuridão de 24 horas mas ritmicidade muito fraca quando expostos ao esqueleto de fotoperíodo ou à escuridão contínua. Desmascaramento de ritmos em livre curso não foi observado sob a condição de ciclo de luz e escuridão de 4 horas. Os resultados indicam que o tatuzinho deve possuir um relógio circadiano endógeno mas que este relógio é muito fraco ou tem conexão muito fraca com os mecanismos responsáveis por atividade locomotora. O efeito modulatório da luz sobre of ritmo de atividade locomotora é quase inteiramente devido a mascaramento negativo.

Affiliations: 1: Circadian Rhythm Laboratory, University of South Carolina, P.O. Box 617, Allendale, SC 29810, U.S.A.


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