Jorg D. HARDEGE-1, Carsten T. MÜLLER-1, Matthew G. BENTLEY-2
and Manfred BECKMANN-3
1- University of Wales, PABlO, 50 Park Place, Cardiff CF1 3TL, U.K.,
2- Gatty Marine Laboratory, Univ. of St Andrews, KY 16 8LB, Scotland,
3- University of Oldenburg, 26110 Oldenburg, Germany
Most nereid polychaetes undergo a metamorphosis to ripe heteronereis stages and reproduce in the free water, performing a 'nuptial dance'. Epidemic swarming of most nereids is timed by environmental and endocrine control of maturation via spawning hormones, to occur simultaneously in a given population (1). The spawning behaviour, the 'nuptial dance', and also the final steps of the reproductive process, the release of gametes into the sea water, are controlled by sex pheromones (2). Located in the coelomic fluid of gravid specimens, one of the pheromones could be identified as the ketone 5-methyl-3-heptanone, responsible for the induction of the nuptial dance spawning t~ehaviour (3). Behavioural and electrophysiological assays (4) with a number of nereid species such as Platynereis dumerilii, Nereis succinea, N. virens and N. japonica confirm that heterospecific activity of coelomic fluid occurs. In both sexes, the nuptial dance as well as the release of gametes are elicited when individuals are exposed to coelomic fluid of another species (3).
The current investigation shows that such heterospecific activity occurs due to similar or identical chemical signal molecules extractable from the coeiomic fluid. HPLC analysis of extracted material followed by biological assays show that all investigated species contain of a 'cocktail of substances' of which they use perhaps only one or two species specific signals for the control of their reproduction, whilst the signals of other species may also be present and in some cases in very high concentrabtins. Figure 1 shows the HPLC analysis of an extract obtained from coelomic fluid of ripe Nereis japonica males containing the sex pheromones of three other species under investgation, Platynereis dumerilii, Nereis succinea and N. virens.
Although all active extracts contain a biologically active tri-peptide glutathione, described as a possible sex pheromone by Townsend (5), this substances is not the natural cue (Retention time is: 24.5 min). Chemical characterisation of the active substances are under way and present results suggest relatively diverse molecules including a tetrapeptide in Nereis succinea, as well as purine derivatives in Nereis virens and Platynereis dumerilii(6,7).
Whilst heterospecific activity of signals may be advantageous for some coral species reproducing simultaneously e.g. at the Great Barrier Reef (8), monotelic species, such as the nereids, could face severe disadvantages including waste of shedded gametes in response to false signals from other species. Heterospecific signals could also disturb other nereid species reproducing in the same area. Present data show that other factors prior to emission of the 'gamete release' inducing pheromones must exist to ensure species recognition and isolation. This is achieved by environmental factors such as lunar periodicity, temperature, different locations, diurnal rhythmicity and reproductive behaviour. Other sex pheromones, such as the volatile sex pheromone 5-methyl-3-heptanone, also play a significant role triggering the nuptial dance behaviour prior to the release of gametes in Platynereis dumerilii and Nereis succinea. In these species, the use of species specific concentrations of the same pheromone prevents direct contact during reproduction.
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