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FACTORS AFFECTING REPRODUCTION AND THE IMPORTANCE OF ADULT SIZE ON REPRODUCTIVE OUTPUT OF THE MIDGE, CHIRONOMUS TENTANS
Citation:
Sibley, P. K., G T. Ankley, AND D. A. Benoit. FACTORS AFFECTING REPRODUCTION AND THE IMPORTANCE OF ADULT SIZE ON REPRODUCTIVE OUTPUT OF THE MIDGE, CHIRONOMUS TENTANS. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. SETAC Press, Pensacola, FL, 20:1296-1303, (2000).
Description:
Incorporating reproductive endpoints into sediment toxicity tests has become an important consideration in ecological risk assessments. The capacity to assess reproduction was one of the primary objectives underlying the recent development of a life-cycle test with the midge, Chironomus tentans for assessing sediment toxicity. In the present study, we conducted two separate tests to evaluate the potential influence of several biological factors that could affect estimation and interpretation of reproductive output in this test. Specifically, we assessed the influence of adult size, mating frequency in males, and the age of both males and females at first mating on mating success (number of successful matings), fecundity (number of eggs/female), percent hatch, and number of offspring (number of hatched eggs). In one experiment, the effect of adult size on reproductive output was determined by mating midges reared in a low (small adults) or high (large adults) feeding regime (3.5 and 5.5 mg/beaker/day) which yielded one of four mating scenarios: 3.5 male x 3.5 female, 3.5 male x 5.5 female, 5.5 male x 3.5 female, and 5.5 male x 5.5 female. An increase in male weight at a constant female weight resulted in 8.3 and 16.4% increase in fecundity in low-and-high-fed females, respectively. An increase in female weight at a constant male weight resulted in a 49.5 and 60.7% increase in fecundity in low and high-fed males, respectively. Percent hatch was lowest in the low-food treatment, but was not affected at any of the other mating combinations. Mean number of offspring increased by 19.8 and 48.3% with male weight was increased and female weight held constant, and by 141.9% and 180.4% when female weight was increased and male weight held constant. The greater influence of female weight on reproductive output was also observed in a second experiment conducted at a single feeding rate; in this study, fecundity increased significantly with an increase in female weight but not male weight. The number of offspring was not significantly affected by adult weight. The age of males or females at first mating, and males mated up to seven consecutive days, had no affect on fecundity. However, the proportion of males successfully mating, percent hatch, and the number of offspring tended to decline after four matings. These results suggest that adult female size is the most important factor affecting reproductive output in C. tentans, and that optimal performance of the life-cycle test, with respect to all reproductive endpoints, might be achieved if males are not mated for more than four consecutive days.