Effects Of Coal Ash Pollution On Population Genetic Structure And Morphological Characteristics Of Brachionus Calyciflorus

In this study, physicochemical conditions of water bodies of a coal-ash polluted lake (Lake Hui) and two unpolluted lakes (Lake Tingtang and Lake Fengming) were analyzed; rDNA ITS and mtDNA COI gene of Brachionus calyciflorus collected respectively from the three lakes and clonally cultured in laboratory were sequenced to investigate their population genetic structures. Besides, morphological parameters of the rotifers at different food concentrations (0.75×10~6, 1.5×10~6, 3.0×10~6 and 6.0×10~6 cells/mL) were also compared. The main results were listed as follows:1. The pH value and the contents of Al, As, B, Ca, Cr, K, Li, Mo, Se, Si and V in Lake Hui were all higher than those in Lake Tingtang and Lake Fengming, but the reverse was also true for the contents of DTN and chlorophyll-a. The concentrations of As, B, Mo, Sb, Se and V elements in Lake Hui were also higher than the limited values in Environmental Quality Standard for Surface Water.2. Analysis of rDNA ITS and mtDNA COI sequences supported that rotifers used in this study could be divided into two sibling species. Sibling speciesⅠandⅡcoexisted in both Lake Fengming and Lake Tingtang, but Sibling speciesⅡwas not observed in Lake Hui. Coal ash pollution decreased the genetic diversity of Brachionus calyciflorus complex and the number of sibling species in the complex, which may be attributed to the ecological characteristics of sibling speciesⅡ. As far as sibling speciesⅠexisting in all the three lakes was concernced, the analysis of rDNA ITS sequence showed that the haplotype diversity of sibling speciesⅠin Lake Hui was the lowest (h=0.9516), and the nucleotide diversity in Lake Hui (π=0.0066) was lower than that in Lake Tingtang (π=0.0073) but higher than that in Lake Fengming (π=0.0052). Similarly, the analysis of COI gene sequence confirmed that both haplotype diversity and nucleotide diversity in Lake Hui (h=0.9608;π=0.0292) were lower than those in Lake Tingtang (h=0.9722;π=0.0300) but higher than those in Lake Fengming (h=0.9581;π=0.0083). Coal ash pollution was deleterious for the genetic diversity of Brachionus calyciflorus population. The lower genetic diversity of rotifer population in Lake Fengming was probably attributed to the combined effects of the pollution from surrounding agricultural fields and higher predation pressure of Asplachna and Copepoda. AMOVA indicated that there was a remarkable genetic differentiation among populations from the three lakes. Nevertheless, calculations of Fst and Nm pointed out that the genetic differentiation among three populations mainly consisted of the dissimilarity between Lake Tingtang and Lake Fengming populations, rather than between coal-ash polluted and unpolluted lakes.3. The rotifers of sibling speciesⅠfrom the three lakes and those of sibling speciesⅡfrom Lake Tingtang were cultured at different concentrations of Scenedesmus obliquus to investigate their morphological differences. The results showed that the rotifer individuals of sibling speciesⅠfrom Lake Hui were the biggest at 3.0×10~6 cells/mL of food level, and those of sibling species I from Lake Tingtang were also the biggest size at 0.75×10~6 and 1.5×10~6 cells/mL of food levels. Body sizes of both sibling speciesⅡfrom Lake Tingtang and sibling speciesⅠfrom Lake Fengming did not differ with increasing food levels. The egg volume of the rotifers belonging to sibling speciesⅠand sibling speciesⅡfrom all the three lakes tended to be smaller with increasing food densities, which may be ascribed to the increasing clutch size and the decreasing energy investment into each egg at the higher food levels. Among the rotifers of sibling speciesⅠfrom all the three lakes, the posterior lateral spines of the rotifers from Lake Fengming were the longest at all the food densities, except that those of the rotifers from Lake Fengming and Lake Tingtang were similar at 6.0×10~6 cells/mL of food level. The reason for the longest posterior lateral spine may be the higher predator density in Lake Fengming. However, both anterior medial and lateral spine lengths did not agree with this pattern. The rotifers from Lake Hui were smaller than those of sibling speciesⅠfrom Lake Tingtang at both 1.5×10~6 and 6.0×10~6 cells/mL of food levels, but the reverse was also true for the egg volume produced at both 0.75×10~6 and 3.0×10~6 cells/mL of food levels. Smaller rotifers could reproduce faster, and bigger eggs could hatch larger offsprings which have stronger resistance, so that they could fit pollution. At all the four food densities, all the morphological parameters of the rotifers belonging to sibling specieⅡwere larger than those of all the rotifers belonging to sibling speciesⅠcollected from Lake Tingtang, except that posterior lateral spine length was similar between the two sibling species at 0.75×10~6 cells/mL of food level. The discriminant analysis also gave a clear result that the two sibling species could be distinguished just by the morphological characteristics, and the discriminant accuracy was both higher than 95% for each population. There was a significantly pattern of morphological differences between the two sibling species.