A reinvestigation of collared flagellates in the genus Bicosta Leadbeater with special reference to correlations with climate

• Published in: Philosophical Transactions of the Royal Society of London. B, Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1980
• Subjects: Arctic; Galapagos; Alaska
• Online Access: http://dx.doi.org/10.1098/rstb.1980.0107; https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1980.0107

By combining light microscopy and electron microscopy, the range of geographically linked diversity in lorica size and construction has been recorded for each of the three species of Bicosta , on the basis of wild material processed directly from the sea, in many different parts of the world distributed from the high Arctic to the Equator and further south. Characteristic differences in responses to climatic pressures occur. The least sensitive species is B. minor , present throughout the temperature range ( - 1 to 22 °C), but with local differences of size depending on environmental factors other than temperature, the smallest cells having been recorded in south (but not north) Alaska and the largest at Portsmouth (England) and in the Galapagos Islands. The other two species are less tolerant of high temperatures and have not been found above 16 °C though they have crossed the Equator. Both are common in the Arctic, where the largest cells characteristically occur. The most elaborate responses were found in B. spinifera; these apparently resulted from two different factors, namely environmental selection among genetically predetermined biotypes differing in cell size, and environmentally induced local modifications, probably caused by the slowing down of critical developmental stages under the action of cold. The exaggerated spine length compared with cell length, characteristic of many large arctic specimens, is interpreted in this way, the critical stages involved being late in the replication cycle since both in B. minor and B. spinifera the costal strips formed first are the short ones. Other biologically significant observations include new information on the structure of the membrane subtending the protoplast and on its mode of attachment to the lorica, which is different in each of the species. Revised taxonomic descriptions summarizing selected parts of the new findings are given at the end of the paper.