Effects of temperature and algal density on life history characteristics and morphotype in offspring of two <i>Brachionus diversicornis</i> morphotypes

Abstract

Effects of temperature (15℃, 20℃, 25℃ and 30℃) and Scenedesmus obliquus density (0.75×10^6, 1.5×10^6, 3.0×10^6 and 6.0×10^6 cells/ml) on life history parameters including net reproductive rate, intrinsic rate of population increase, generation time, life expectancy at hatching and proportion of mictic offspring, and morphotype in offspring of two Brachionus diversicornis morphotypes were studied by means of individual culture. The results showed that at the four temperatures, the survivorship between the two B. diversicornis morphotypes was similar. The fecundities of the equal-spined rotifers at 15℃, 25℃ and 30℃ were significantly higher than those of the unequal-spined rotifer. Each of the life history parameters between the two B. diversicornis morphotypes was similar, except that the generation time of the equal-spined rotifers was longer than that of the unequal-spined rotifers at 30℃. The survivorship, the fecundity and each of all the life history parameters between the two B. diversicornis morphotypes were also similar at the four food densities. All the intrinsic rate of population increased, the generation time and the life expectancy at hatching of the two B. diversicornis morphotypes responded differently to increasing temperature, but food density only affected the net reproductive rate and the intrinsic rate of population increase of the equal-spined rotifers significantly. The net reproductive rate of the equal-spined rotifers at algal density of 6.0×10^6 cells/ml was lower than that at both 0.75×10^6 and 3.0×10^6 cells/ml, and the net reproductive rate at 1.5×10^6 cells/ml was similar with that at each of all the above-stated three food densities. The intrinsic rate of population increase of the equal-spined rotifers at 6.0×10^6 cells/ml was lower than that at 3.0×10^6 cells/ml, but both of them were similar with those at 0.75×10^6 and 1.5×10^6 cells/ml. At each of the four temperatures and food densities, the two B. diversicornis morphotypes produced both equal-and unequal-spined offspring. Only at 25℃, the proportion of equal-spined offspring produced by the equal-spined mothers was higher than that produced by the unequal-spined mothers. However, at each of all the four food densities, the proportion of equal-spined offspring produced by the two B. diversicornis morphotypes was similar. Temperature affected the proportion of equal-spined offspring produced by the equal-spined mothers significantly, but food density did not affect the proportion of equal-spined offspring produced by both the equal-and unequal-spined mothers. The proportions of equal-spined offspring produced by the equal-spined mothers at 15℃ and 25℃, and 20℃ and 30℃ were similar, respectively, but the former two were higher than the latter two.