| The taxonomical status of Keratella tropica and K. valga collected respectively from Lake Tingtang and Lake Jinghu in Wuhu city, China were analyzed using molecular marker technique, and their life history characteristics were studied at four temperatures and food densities. The main contents and results were presented as the following:1. COI genes of 29 K. tropica clones and 28 K. valga clones were sequenced and analyzed, and molecular phylogenetic trees including those COI gene sequences, and COI gene sequences of K. americanas, K. cochlearis, K. hiemalis and K. quadrata which were downloaded from Genbank were constructed by Maximum-Parsimony (MP), Neighbor-Joining (NJ) and Maximum-Likelihold (ML) with B. calyciflorus as an outgroup. The results showed that all the 62 clones belonged to 47 haplotypes. The sequence divergence is 24.9%-26.5% between K. tropica and K. valga, with an average of 25.7%, but the average sequence divergence is 0.75% and 1% among K. tropica haplotypes and K. valga haplotypes, respectively. All the three phylogenetic trees supported that the haplotypes of K. americanas and K. cochlearis belonged to a clade, and those of K. tropica and K. valga belonged to a single clade, respectively. In addition, rDNA ITS sequence of 27 K. tropica clones and 30 K. valga clones were analyzed, the sequence divergence is 6.6%-7.9% between K. tropica and K. valga, with an average of 7.25%, but the average sequence divergence is 0.35% and 0.55% among K. tropica haplotypes and K. valga haplotypes, respectively. The results stated above demonstrated that K. tropica and K. valga are different species.2. By means of individual culture and with 0.5×10~6 cells/ml of Scenedesmus obliquus as the food, development, survivor, reproduction and life table demography of K. tropica and K. valga both cultured at 15℃, 20℃, 25℃and 30℃were compared. The results showed that temperature affected significantly the durations of developmental periods, the average life-spans, the numbers of produced eggs, the intrinsic rates of population increase, life expectancies at hatching and generation times of the two rotifer species, and the net reproductive rate of K. valga. With the temperature increasing, the durations of pre-reproductive period, life expectancies at hatching and generation times of two rotifer species decreased significantly; the responses in the duration of post-reproductive period were similar, but the reverse was also true for the durations of reproductive period, average life-spans and the numbers of produced eggs. The intrinsic rate of population increase of K. tropica was the highest at 30℃, the lowest at 15℃, and similar at the other two temperatures. The intrinsic rate of population increase of K. valga was the highest at 25℃, the lowest at 30℃, and similar at the other two temperatures. The net reproductive rate of K. valga was the lowest at 30℃, and the highest at 15℃and 20℃. At each temperature, there also existed differences between K. tropica and K. valga in the durations of main developmental stages, the mean life-spans, the numbers of produced eggs, generation times, life expectancies at hatching, net reproductive rates, and intrinsic rates of population increase. The results indicated that K. tropica was adaptable to the higher temperature (30℃), while K. valga was adaptable to the lower temperature (25℃).3. By means of individual culture, development, survivorship, reproduction and life table demography of K. tropica and K. valga, both cultured at 20℃and with 0.5×10~6, 1.0×10~6, 2.0×10~6 and 4.0×10~6 cells/ml of S. obliquus as the food, were compared. The results showed that algal food density affected significantly the duration of pre-reproductive period, the number of produced eggs and the intrinsic rate of population increase of K. tropica as well as the duration of pre-reproductive period of K. valga. The intrinsic rate of population increase of K. tropica at 4.0×10~6 cells/ml was higher than that at 2.0×10~6 cells/ml. The differences in the durations of principal developmental stages, the number of produced eggs, the net reproductive rate, life expectancy at hatching and the generation time between the two rotifer species differed with food density. When the food density was 0.5×10~6 and 1.0×10~6 cells/ml, the net reproductive rate, the life expectancy at hatching and the generation time of K. tropica were higher or longer than those of K. valga. When the food density was 2.0×10~6 cells/ml, the net reproductive rates, life expectancies at hatching and the generation times of the two rotifer species were all similar. When the food density was 4.0×106 cells/ml, the net reproductive rate of K. tropica was higher than that of K. valga. At each food density, the intrinsic rates of population increase of the two rotifer species were similar. |
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