The life history and ecology of the snow alga Chloromonas polyptera comb. nov. (Chlorophyta, Volvocales)

Abstract

Snow algae previously designated as Carteria nivale, Scotiella polyptera, S. polyptera var. polimantii, and S. polyptera var. magellanica were found to be developmental stages of the zygote of Chloromonas polyptera comb. nov. Five species of Scotiella from snow have now been identified as zygotes of different specis of Chloromonas. In this life cycle, biflagellate vegetative cells, zoospores, gametes, and sexual reproduction are reported for the first time. The different forms of the zygote have been reported previously in the literature from several parts of the world, but have been misinterpreted as several distinct taxa of snow algae. The stages in the life cycle of Chloromonas polyptera occur in old, rapidly melting snowbanks, usually less than 30 cm deep. In the same snowbanks, zygotes of C. polyptera germinate later than those reported for Chloromonas nivalis, Chloromonas brevispina, and Chloromonas pichinchae indicating the occurrence of algal succession. Higher light intensity and a more saturated snowbank appear necessary for germination of zygotes of C. polyptera when compared with other species of Chloromonas found in snow. Low levels of carbon dioxide in snow may be limiting for growth of C. polyptera and vegetative cells are sensitive to increasing temperature as observed through laboratory observation. Freezing does not appear to initiate meiosis in the zygotes of C. polyptera as reported for other Volvocalean algae found in snow.