Temperature Effects On Fecundity, Development And Survivalof The Benthopelagic Calanoid Copepod, Pseudocyclops Xiphophorus

摘要

The shallow-living, benthopelagic copepod species Pseudocyclops xiphophorus Wells (R Soc Edim-burg 67:1967), collected over a yearly cycle from the fouling material in the brackish water Lake Faro (North-eastern Sicily), showed marked seasonal fluctuations in population abundances, with maximum numbers recorded in autumn. Highest in situ egg production rates coincided with periods of low adult and juvenile densities and vice versa, except in autumn when peaks in egg production and adult population densities were coincident. In this period, mean daily egg production rates reached a maximum of 4-5 eggs per female, when surface water temperature was 17-18℃. Egg production rates declined drastically in winter and were completely arrested when surface temperatures dropped to 10-12℃. In March, daily egg production rates began to increase again with an increase in ambient temperatures, reaching a maximum at the end of August. In the laboratory, as in the field, mean daily egg production rates were positively correlated with temperature, with values ranging from 2.2 ± 0.3 (16℃) to 8.9 ± 2.6 (30℃) (mean ± S.D.) eggs per female per day. At 32℃, P. xiphophorus females survived but did not reproduce. At 34℃, all specimens died after a few days. In terms of total egg production for the entire female lifespan, maximum values occurred at 16℃ and minimum at 24℃. Temperature also dramatically affected female life span, which was shorter at higher temperatures. Development time of eggs decreased with increasing temperature, as also development time from egg to adulthood. Remating was necessary for the continued production of fertile eggs at 16℃ because female life span was longer. The unique egg-laying behaviour in this species may ensure higher survival rates of egg stages compared to free-spawning and egg-carrying calanoid species. After releasing the egg pair, the female swims over the eggs with a rotatory motion, secreting a substance which facilitates the adhesion of the eggs to the bottom; she then continues to swim over the eggs until they are attached. Although egg production rates in this species are low compared to other pelagic copepods, they are within the range of values reported for egg-carrying species. The greater fecundity at higher temperatures compared to other subtemperate species indicates that the species is well adapted to the higher temperatures of coastal lagoons and brackish water lakes where it contributes to the biofouling community.