Molecular phylogeny and population genetic differentiation patterns inBrachionus calyciflorusPallas (Rotifera) complex from two lakes in China

Abstract

The spatio-temporal patterns of population genetic structures have been attracting increasing attention of late. Few of these efforts, however, have focused on the underlying mechanisms of the seasonal alterations of in rotifer clone groups. To gain insights into the seasonal variation patterns of genetic differentiation in rotifer populations, 158 clones of the Brachionus calyciflorus Pallas species complex, with seasonal sampling from Guangzhou and Wuhu in China, were sequenced and analyzed based on the nuclear internal transcribed spacer (ITS) region and the mitochondrial cytochrome c oxidase subunit I (COI) gene. DNA taxonomy provided estimates of evolving entities ranging from 3 to 21 by combining the mitochondrial and nuclear markers with the different ABGD, PTP, and GMYC models. The most conservative number of the three evolving entities was used for further phylogenetic and population structure analyses. The B. calyciflorus species complex was found to have extreme nucleotide diversity, revealing twice the diversity from the COI dataset than from ITS. The similar patterns of seasonal succession in B. calyciflorus were investigated in the two habitats of Guangzhou and Wuhu, and the clonal groups involved in seasonal succession were actually sibling or cryptic species within the B. calyciflorus complex. We assume that these cryptic species are specialized for their ecological niches, especially in terms of temperature preference. The spatio-temporal patterns of population genetic structure varied with cryptic species, e.g. cryptic species II (-COI/-ITS) had much greater genetic differentiation among sampling sites than among seasonal populations and cryptic species III (-COI/-ITS) displayed a reverse pattern.