Experimental Study of Population Variations on the Morphology and Reproduction of Daphnia galeata from Three Chinese Lakes

Environmental heterogeneity affected the genetic differentiation and phenotypic plasticity of Daphnia spp. populations in different lakes. However, the effect mechanism of lake population on the morphology and reproduction of Daphnia spp. was still unclear. This paper studied the differences of the morphology and reproduction of D. galeata populations from three Chinese lakes (CH: Lake Chaohu, NH: Lake Nanhu, EH: Lake Erhai), which the area size, nutrient levels, phytoplankton biomass and dominant fish were obviously various in the three lakes. The results showed that lake population affected significantly the morphology (helmet length and tail spine length) and reproduction (no. offspring at first reproduction per female-1) of D. galeata. Both helmet lengths and tail spine lengths of three D. galeata populations increased quickly within the first five instars, and afterwards showed various patterns. Multiple comparisons indicated that helmet lengths of NH population were significantly higher than those in EH and CH populations (P<0.001) whereas tail spine lengths of NH population were significantly smaller than those in EH (P=0.001) and CH (P=0.003) populations. The ratio of relative helmet length of CH population was significantly shorter than those of EH population (P<0.001) and NH population (P<0.001), and the ratio of relative tail spine length at first pregnancy of EH population was significantly longer than those of CH population (P<0.001) and NH population (P<0.001). Moreover, there is four juvenile instars in EH population whereas there are three juvenile instars in CH and NH populations. With the increase of adult instars, the number of offspring produced by D. galeata in all three populations displayed a similar pattern, which increased quickly at first, and then gradually decreased. Average maximum number of offspring at first reproduction (6.3±1.4 ind. per female-1) appeared in CH population, followed by EH (5.2±1.7 ind. per female-1) and NH (4.9±1.4 ind.•per female-1) populations. The innate rate of increase of CH population was relatively higher than those of EH and NH populations, but no significant differences among three populations were observed. Our results suggested that environmental heterogeneity could affect the reproduction and morphological plasticity of Daphnia spp. in different lakes.