A combined 18S rDNA and rbcL phylogenetic analysis of Chloromonas and Chlamydomonas (Chlorophyceae, Volvocales) emphasizing snow and other cold-temperature habitats

Abstract

An extensive phylogenetic analysis of the biflagellate genera, Chlamydomonas Ehrenberg and Chloromonas Gobi emend. Wille, was undertaken using 18S rDNA and rbcL gene sequence analysis. Emphasis was placed on 21 cold-tolerant taxa of which 10 are from snow. These taxa occurred in four distinct clades each in the 18S rDNA and rbcL phylogenies, and when taken together suggest at least five distinct origins in cold habitats. Most of these taxa occur in a single clade (A), and all snow species occurred in this clade. In the rbcL and combined rbcL-18S rDNA analyses, the snow taxa fell into three groups. Two groups occurred in subclade 1: Chlamydomonas augustae Skuja CU, Chlamydomonas augustae UTEX, and Chlamydomonas sp.-A and Chloromonas clathrata Korshikov, Chloromonas rosae Ettl CU, and Chloromonas rosae v. psychrophila var. nov. The third snow group, subclade 2, included three species with unique cell divisions, Chloromonas brevispina (Fritsch) Hoham, Roemer et Mullet, Chloromonas pichinchae (Lagerheim) Wille, and Chloromonas sp.-D, and the basal Chloromonas nivalis (Chodat) Hoham et Mullet with normal cell divisions. This suggests that the snow habitat has been colonized at least twice and possibly three times in the history of these biflagellates. In the 18S rDNA tree, one cold-tolerant Chloromonas species fell outside clade A: Chloromonas subdivisa (Pascher et Jahoda) Gerloff et Ettl. In the rbcL tree, three cold-tolerant Chloromonas species fell outside clade A: Chloromonas subdivisa, Chloromonas sp.-ANT1, and Chloromonas sp.-ANT3. These results support previous findings that pyrenoids have been gained and lost several times within this complex.