Photoperiodic Conditions, Food Patchiness and Fecundity

Many studies have shown that food quantity influences the fecundity of copepods. In most of these investigations fecundity has been determined at constant food levels. Few studies have determined fecundity under conditions of temporally varying food concentrations, though such conditions are more representative of the natural situation. This paper reports on the fecundity of Labidocera aestiva under different photoperiodic and food regimens. The food regimens differed in terms of the time of day during which food was available. Nauplii were reared to reproductive maturity at 12L–12D and 19°C. Mature adults were then exposed to the different experimental conditions. Food was available during either the dark phase, light phase, or both phases of a 12L–12D photoperiod, and during the first, second, or both 12-h phases of a 24D, and 24L regimen. Fecundity was determined at 12-h intervals for 2 to 5 days. At 12L–12D, egg production/female/day was two times greater in the treatment receiving food during the dark phase than in the treatment receiving food during the light phase. Based on fecundity there was no evidence that animals adjusted their feeding schedule to take advantage of food when it was available. The results indicate that availability of food with respect to time of day influences fecundity.