The phylogenetic relationships of the genus Eimeria based on comparison of partial sequences of 18S rRNA

Abstract

Reverse transcription of ribosomal RNA (rRNA) was used to obtain partial sequences of the small subunit rRNA (ssrRNA) of three species of Eimeria: Eimeria maxima, Eimeria stiedae and Eimeria tenella. These sequences were aligned with the homologous ssrRNA sequence segments of a range of other organisms in the phylum Apicomplexa, along with representatives of the ciliates, fungi, flagellates, higher plants and higher eukaryotes. Two phylogenetic tree building methods were used to investigate the phylogenetic relationships among the Eimeria species, and between the Eimeria and the other organisms represented, using Vairimorpha necatrix as an outgroup. The results show that Eimeria is almost certainly monophyletic with the apicomplexans Sarcocystis, Toxoplasma and Cryptosporidium. The three species of Eimeria differ among each other at a maximum of 9 out of 600 nucleotides at the ssrRNA locus. Such intrageneric variation is high by vertebrate standards, but low by protist standards.