Studies On The Mechanism Of Resting Egg Asexual Reproduction And Intraspecific Chemical Pheromones Of Brachionus Calyciflorus

The vast majority of individuals reproduce via the familiar mechanism of sex: sexual reproduction and asexual reproduction.In theory,the species which transited to asexual reproduction can have substantial benefits and can quickly replace sexual reproduction.Compared with other reproduction methods,asexual reproduction has great competitive advantages.But in nature,sexual reproduction is stable,which creates a paradox.However,there are also genetic systems that resist an easy classification into “sexual” and “asexua”,like Periodic parthenogenesis.Periodic parthenogenesis takes advantage of this optimal mode of reproduction,which fully preserves the evolutionary advantages of recombination while minimizing the costs associated with male reproduction.Periodic parthenogenesis is an alternate reproductive mechanism of sexual and parthenogenesis,in which produce their offspring without fertilization.Patterns of parthenogenesis can generally be classified as apomixis and automixis.And this kind of reproduction mechanism has widely existed in protozoa such as rotifers.Rotifer is an important kind of water ecosystem.Brachionus calyciflorus is a typical cyclic parthenogenesis species,and is also a good starting model for understanding asexual and sexual reproduction.We used 64 different genotype clone population for ITS sequencing,and identified the B.calyciflorus used in this experiment as cryptic species C: B.calyciflorus sensu stricto through the blast of ITS gene and phylogenetic tree construction.The result of the loss of heterozygosity in 6microsatellite loci showed that the overall observation heterozygosity level is high.Combined with the growth of rotifers in the laboratory,four monoclonal populations of different genotypes were screened for experiments,and COI sequencing was further proved that these four monoclonal populations were the same cryptic species and could be used for further experiments.In the experimental condition without male present,the restingt eggs produced by the mother were collected and the DNA of the mother and their offspring was extracted to calculate the heterozygosity loss rate.By chi-square test of experimental heterozygosity loss rate and theoretical terminal fusion value,and excluding the reason of inbreeding and chromosome deletion,we found that B.calyciflorus can reproduce asexually and produce resting eggs without male and involved the terminal fusion of automictic production.Finally,we used Brachionus calyciflorus as the model individual,explained the ecological causes of resting eggs which produced by asexual reproduction.Chemical pheromones released by one genotypic population could only induce the same population to produce resting eggs by asexual reproduction,and the rate of resting eggs increased with the crowding chemical pheromone concentration.This study may provide necessary data for exploring the inducement and mechanism of asexual reproduction,and give an idea for the further understanding of asexual reproduction and sexual reproduction.