|Semilunar reproduction of Clunio marinus biological timing in the intertidal zone|
Neumann, D. (1976). Semilunar reproduction of Clunio marinus biological timing in the intertidal zone, in: Persoone, G. et al. (Ed.) Proceedings of the 10th European Symposium on Marine Biology, Ostend, Belgium, Sept. 17-23, 1975: 2. Population dynamics of marine organisms in relation with nutrient cycling in shallow waters. pp. 429-430
In: Persoone, G.; Jaspers, E. (Ed.) (1976). Proceedings of the 10th European Symposium on Marine Biology, Ostend, Belgium, Sept. 17-23, 1975: 2. Population dynamics of marine organisms in relation with nutrient cycling in shallow waters. IZWO/Universa Press: Wetteren. ISBN 90-6281-002-0. 712 pp., more
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|Document type: Conference paper|
The synchronisation of reproduction with favorable environmental conditions may increase both the rate of survival and the chance for mating. Examples for extremely accurate synchronisations are known from populations of several intertidal organisms reproducing every 15 or 30 days at the time of a distinct moon phase. Such lunar rhythms of reproduction are represented by the spawning of the famous palolo Eunice viridis Gray in the Pacific Ocean and the mediterranean 'Palolo' Platynereis dumerilii (Audouin et M. Edwards) grunion Leuresthes tenuis (Ayres) at the Californian beaches, the sexual reproduction of the brown algae Dictyota sp., and last not least by the semilunar reproduction of Clunio marinus (Hal.). In most of these cases there is evidence that the time of reproduction is adapted to a distinct tidal situation which recurs parallel to the lunar month every 15 or 30 days at the same time of day. The scientific film shown during the symposium is dealing with the semilunar reproduction of Clunio marinus. This marine insect may serve as a model of lunar rhythms and physiological timing mechanisms. The first part of the film shows some of the adaptations of this insect to marine environments 1) the synchronisation of reproduction with the low water of spring tides, 2) the extreme shortening of the adult life to a few hours only in order that emergence, mating and oviposition occur during the short time-space of exposure of the intertidal habitat, and 3) the change from flying to walking locomotion together with a peculiar sexual dimorphism. The second part of the film focuses on the principles of semilunar reproduction and some of the experiments by which insight into the physiological timing mechanisms and its controlling environmental factors is obtained. To analyse the timing problem it is necessary to notice, that on coasts with semidiurnal tides, the low-water time of spring tides always reoccurs at nearly the same time of day throughout the years, because the tidal cycle of 12.4 hr shifts 0.8 hr a day and 12 hr every 15 days, resulting in the same diurnal phase. The timing of Clunio is based on the combination of two physiological timing mechanisms, which control two different developmental events in each specimen, namely pupation and emergence. Because Clunio stays in the pupal stage for 3-5 days, the semilunar timing of reproduction corresponds with a 2 weeks periodicity of pupation control. In the laboratory this semilunar periodicity can be evoked by an artificial moonlight in the populations of southern Europe and by a combination of the 24 hr light-dark cycle with a tidal turbulence program in populations of northern regions. The effectiveness of moonlight in southern latitudes and of tidal turbulence in northern latitudes seems to be a successful geographic adaptation to different environmental conditions (Neumann, 1975). The emergence of the pharate imago (3-5 days after pupation) is controlled by a daily timing mechanism (circadian clock) which in turn is controlled by the 24 hr light-dark cycle. The phase-relationship between circadian clock and day-night cycle is a populations-specific and gene-controlled feature which is correlated with the local time of low water at spring tides (Neumann, 1967). The combination of semilunar timing of pupation and daily timing of emergence guarantees the temporal programming of reproduction with the optimal tidal situation in the lower mid-Iittoral zone. The film (Neumann, 1973) was made for lectures in order to discuss with the students, the adaptation of physiological characters to the environment as well as the principles of temporal programming of development. Producer and lender of the film (16 mm, 14 1/2 min, sound film, english version available) was the Institut fur den wissenschaftlichen Film in Gottingen, Federal Republic Germany. Further investigations have been focused on the adaptive differentiation of the physiological timing in various geographic populations between southern Europe and the Arctic (Neumann, 1975, 1976).