RESTING EGG-PRODUCTION AND OVIDUCAL CYCLING IN 2 SYMPATRIC SPECIES OFALPINE DIAPTOMIDS (COPEPODA, CALANOIDA) IN RELATION TO TEMPERATURE AND FOOD AVAILABILITY

Resting egg production and oviducal cycling were investigated for the calanoid copepods A rctodiaptomus alpinus and Acanthodiaptomus dentico rnis both in the laboratory and in a small karstic alpine lake by maki ng a census of the number of eggs produced and the proportion of femal es in each of four morphologically distinguished reproductive conditio ns each day in the laboratory or during a 2-3 week period in lake encl osures. In the laboratory, individuals were maintained on a mixed diet of natural phytoplankton at constant temperatures of 4, 10, 15 and 20 degrees C, respectively. Both species differed considerably in their temperature requirements for reproduction. Lifetime fecundity was high est at 10 degrees C in A.alpinus and at 20 degrees C in A.denticornis: with up to 327 eggs female(-1) spawned in the former and up to 582 eg gs female(-1) in the latter species. Unfavorable temperatures were fur ther reflected in an increase in egg mortality and the allocation of t ime spent in a post-reproductive phase, as well as in a decrease of lo ngevity. Increasing temperatures enhanced egg production rates due to decreasing clutch production periods, although clutch size was negativ ely correlated with temperature. Maximum rates reached 5.88 and 7.98 e ggs female(-1) day(-1) in the laboratory, and 0.73 and 0.55 eggs femal e(-1) day(-1) in enclosures in A.alpinus and A.denticornis, respective ly. Egg production rates and clutch size were clearly governed by nutr itional conditions in the lake, but were less affected by food supply in the laboratory. Here, rates of egg production were adapted to impro ving food supply by increasing the frequency of spawning events, rathe r than the number of eggs per clutch. No correlation was found between female body size and reproductive parameters in the laboratory. A ver y low proportion of total clutch production resulted in clutches compo sed of subitaneous eggs, i.e. 0.14% in A.denticornis and 1.20% in A.al pinus. Oviducal phase duration allocations indicate that there exists a temperature optimum for gamete maturation.