Studies On Life History And Population Genetic Structure Of Rotaria Rotatoria

The Bdelloidea rotifer is a kind of asexual freshwater invertebrates，and isalso the largest Metazoan phyla reproduced only in parthenogenesis, livingbenthic, epiphytic or sessile. Rotaria rotatoria is a common Bdelloidea specieseasily discovered. In this study, we studied the effects of temperature and foodconcentration on some main traits in its life history, compared the COIsequence of several strains of Rotaria rotatoria from4localities. Somevaluable information was obtained and it could be useful for the furtherresearch on this species and will expand the knowledge of the Bdelloid rotifers.The main results were presented as following:1. The duration of principal developmental stages and the populationgrowth parameters of females of Rotaria rotatoria from Wuhu were studiedunder the different food concentrations and different temperatures by individualculture method. The following parameters were calculated: the mean lifespan(Y), life expectancy at hatching (e0), net reproductive rate (R0), meangeneration time (T), intrinsic rate of natural increase (rm), and we comparedage-specific fecundity rates (mx) and age-specific survival rates (lx) in12different conditions. There were no females died in the first72hours in allconditions. No matter what the food densities were, when the temperature rose,age-specific survival curves tended to decrease earlier and steeper. The slowestand fastest decreasing speed of age-specific survival curves appeared in24℃,0.5×106cells/mL and32℃,1.0×106cells/mL. In24℃and28℃, theage-specific survival curves (Apart form the condition of2.0×106cells/mL,28℃). However, in32℃, the age-specific survival curves decreased slowerwhen the food concentration increased (Apart form the condition of0.5×106cells/mL,32℃).Age-specific fecundity curves performed with anearlier maximum when the temperature rose in every food density. The largest (mx=1.91in4.0×106cells/mL) and earliest (96h in every food densities)maximums were in32℃with the fastest decreasing speed, and the smallest(mx=0.48in0.5×106cells/mL) and latest (216h in1.0×106cells/mL and2.0×106cells/mL) maximums were in24℃. In24℃, the maximums had no significantdifferences in appearing time among different food densities. In28℃, theage-specific fecundity curves appeared time of the maximums delayed whenfood densities rose. In32℃the reproductive period shortened when the foodconcentration increased, and in other temperatures the differences were notsignificant.Results showed that there were highly significant effects of temperatureon all the parameters (P<0.05). Food concentration had significant effects onlyon e0and Y (P<0.05). The combined action of the two factors affectedobviously on e0, T, R0and Y (P<0.05). In24℃, e0, T and Y are the biggest, andrmis the smallest; In32℃, e0, T and Y are the smallest, rmis the biggest; In28℃,R0is the biggest and in24℃is the smallest. In24℃and28℃, e0and Ydecreased when the food concentration increased, but in32℃they increasedwhen the food concentration increased. T, R0and rmhad no significantdifference when the temperature rose.2. The total of82Rotaria rotatoria clones from6water bodies in4areaswere studied by researching their cytochrome oxidase I (COI) sequences,560bp of the gene were obtained after the PCR process leaded by the specificprimer. Two of the water bodies were removed from the population geneticstructure analysis because they contained only1clone.27haplotypes werefound and the average contents of A, C, T, G were measured as22.6%、9.8%、22.9%、44.7%after the composition analysis, with the obvious bigger ATcontents (67.3%) than CG contents (32.7%). Results of sequence analysisshowed that the genetic distance within groups is large in HX and WHD (0.085and0.095), and small in WHA and WX (0.020and0.048). The biggest geneticdistance between groups was in the HX and WHA pair, and the smallest was inthe HX and WX pair. The average of genetic distance between groups is0.104.The genetic differentiation index (Fst) between populations was smallest in HX and WHD (Fst=0.1056), and was biggest in WX and WHA(Fst=0.75433). TheFstof the four groups are0.45810、0.42552、0.44526and0.42736, average0.43757. The Fstwithin groups was bigger and the Fstamong groups were bothbig, The Fstwithin groups (56.2%) was bigger than that among groups (43.8%)(P<0.05).According to the ML tree, three lineages were generally divided. Lineage Icollected in Wuhu differentiated the earliest; Lineage III containing Wuhu andHexian groups differentiated the latest; Lineage II from Wuhu, Hexian andWuxi has a clutter branch. We suggested that lineage I was an old lineage,diffused to the other localities in the later period.