PAARUNGSSELEKTION BEI CHIRONOMUS 



1241 



SUMMARY 



In the course of an evening's swarming period of Chironomus plumosus we 

 observed that the numbers of maie and female spécimens in a swarm change 

 along with the ratio of sexes, and that the females vary in average, size. 



Examining the distribution of their respective présence in the swarm, we 

 established one period of maximum occurrence in maies, but two such periods 

 in females. The period of minimum female présence is between the two maxima 

 and coincides with the maximum occurrence of swarming maies. This we explain 

 through the fact that with their influx continuing, females having successfully 

 mated will leave the swarm, whereas maies stay on. 



The average size of females in the swarm is reduced to a minimum whenever 

 there exists a maximum ratio in favor of the maies. This phenomenon we demon- 

 strate, is due to sélective mating with size being the décisive factor: copulating 

 females are on the average somewhat larger than those swarming freely. 



The significance of the flight tone with respect to preferential mating is 

 discussed. 



LÏTERATUR 



Dokumenta Geigy. 1960. Wissenschaftliche Tabellen, 6. Auflage. J. R. Geigy AG, Basel. 

 Fisher, R. A. 1963! Statistical Methods for Research Workers. 13th Edition. Oliver and 



Boyd Ltd., Edinburgh. 

 Klôtzli, A. M., F. Rômer und S. Rosin. 1971. Jahreszeitliche Grôssenvarialion bei 



Chironomus plumosus L. Revue suisse Zool. 78: 587 — 603. 

 Rômer, F. 1970 a. Einfluss von Tempérai ur und Al ter auf die Flugtonhôhe beim Schwàrmen 



von Chironomus plumosus L. Revue suisse Zool. 77: 603 — 616. 



— 1970 b. Flugtône der Weibchen und Locktône fiir Mànnchen von Chironomus 



plumosus L. beim Schwàrmen. Revue suisse Zool. 77: 942 — 959. 



— und S. Rosin. 1969. Untersuchungen iiber die Bedeutung der Flugtône beim 



Schwàrmen von Chironomus plumosus L. Revue suisse Zool. 76: 734 — 740. 



— und S. Rosin. 1971. Einfluss von Licht und Temperatur auf die Schwârmzeit von 



Chironomus plumosus L. Revue suisse Zool. 78: 851-867. 



Rev. Suisse de Zool., T. 78, 1971. 



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