LIFE-HISTORY, RESTING EGG FORMATION, AND HATCHING MAY EXPLAIN THE TEMPORAL-GEOGRAPHICAL DISTRIBUTION OF ARTEMIA STRAINS IN THE MEDITERRANEAN BASIN

Life history traits are presented for the sexual species (Artemia tunisiana) and for parthenogenetic diploid and tetraploid strains A. parthenogenetica reared at 15 degrees, 24 degrees and 29.5 degrees C. In laboratory cultures, we present evidence that the seasonal appearance of the sexual Artemia tunisiana (the dominant winter-spring population), and of two parthenogenetic populations of Artemia (the dominant spring-summer populations) in certain Spanish saltworks is controlled by temperature through its effect on reproductive and survival traits. Minimum and maximum reproductive output and survival for the sexual and parthenogenetic populations, respectively, occurred at a typical temperature (24 degrees C) of the late-spring season when the sexual population is replaced by parthenogenetic forms. Furthermore, the high production and hatchability of cysts from the sexual population at low temperatures (15 degrees C), and of the parthenogenetic populations at middle temperature (24 degrees C), indicate the role of dormancy as an adaptation regulating seasonal occurrence.