Rotifers reproduce asexually, how does variation occur without meiosis and fertilization?

In this case variation is caused by mutation and maintained by selection. 
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. Variation is the difference among the individual opf the same species, variation is mainly achieved through meiosis and fertilization, however rotifer reproduce asexually without fertilization or meiosis, therefore they rely on mutations and selection to maintain variation.