Abstract
The fan activity rhythm of Sabella spallanzanii (Gmelin, 1791) and its entrainment capability to light were studied. Animals were tested under constant darkness (DD) followed by two consecutive 24 h light-darkness regimes: a first 11 h light period (LD) and a second 9 h light period, with its phase inverted (DL). An infrared analogical video-camera took shots each 30 s. A number of pictures with open fan were counted every 15 min. In DD a weak free-running periodicity in the circadian range was found, thus reinforcing the matching of the 24 h period under study in both photoperiod regimes. A nocturnal activity was characterised with a consistent anticipation to lightOFF (i.e. entrainment). Moreover, this phase of entrainment differed between DL and LD. The presence of endogenous activity rhythm with a variable phase angle of entrainment is a distinctive feature of circadian pacemakers.
Highlights
The Mediterranean polychaete Sabella spallanzanii (Gmelin, 1791) is a large filter-feeder exhibiting a behavioural activity of fan opening and retraction, mainly related to feeding upon suspended particles and respiration (e.g. Riisgård and Ivarsson, 1990; Giangrande, 1991)
Animals were tested under constant darkness (DD) followed by two consecutive 24 h light-darkness regimes: a first 11 h light period (LD) and a second 9 h light period, with its phase inverted (DL)
A nocturnal activity was characterised with a consistent anticipation to lightOFF
Summary
The Mediterranean polychaete Sabella spallanzanii (Gmelin, 1791) is a large filter-feeder exhibiting a behavioural activity of fan opening and retraction, mainly related to feeding upon suspended particles and respiration (e.g. Riisgård and Ivarsson, 1990; Giangrande, 1991). Riisgård and Ivarsson, 1990; Giangrande, 1991). The interplay of endogenous activity rhythms and light-darkness cycles was postulated as a basis for the regulation of seasonal growth and reproduction (Olive, 1984). An important feature of the light-darkness cycle as a zeitgeber is the duration of its photophase whose variations produce different phase angles of entrainment (Aschoff, 1981). The entrainment of daily cycles in behaviour and physiology to different photoperiod lengths is of importance for polychaetes to regulate growth, reproduction and behaviour to seasons The occurrence of an endogenous fan activity rhythm and its entrainment capability were studied in S. spallanzanii kept under laboratory constant darkness and in different artificial photoperiod regimes
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