Demographic parameters of sexual and parthenogenetic Artemia: Temperature and strain effects

Demographic parameters are presented for the sexual species (Artemia tunisiana Bowen) and for parthenogenetic diploid and polyploid strains of A. parthenogenetica Barigozzi reared at 15 degrees 24 degrees and 30 degrees C. There is a significant reduction in e(o) (life expectancy) as temperature increases for all strains, with the sexual species' lifespan significantly smaller at 24 degrees and 30 degrees C than that of the parthenogenetic strain. Changes in age specific feundity rates (F-x) are also both temperature and strain-dependent. Across the range of temperatures studied, parthenogenetic diploid Artemia maintain similar population growth rates (r) while sexual and parthenogenetic tetroploid strains do not. At 15 degrees and 24 degrees C r values are significantly lower for the tetraploid strain because the majority of offspring are encysted. The tetraploid strain trades high population growth for the ability to withstand adverse environmental conditions via encystment of offspring. Although the sexual species at 15 degrees and 24 degrees C has T values (generation time) approximately one-half those of the parthenogenetic strains, at 30 degrees C the probability of survival (l(x)) until reproductive maturity is zero. Quantification of demographic parameters is critical for understanding spatial and temporal distributions, as well as recent competition experiments, of sexual and parthenogenetic Artemia.