Different life histories of Enteromorpha prolifera (Ulvales, Chlorophyta) from four rivers on Shikoku Island, Japan

Populations of Enteromorpha prolifera collected from four rivers on Shikoku Island in Japan had three different types of life history. One type was the typical sexual life history of Enteromorpha, which is isomorphic, with biflagellate anisogametes and quadriflagellate meiospores. The other two types were asexual life histories involving biflagellate or quadriflagellate zoids. Both biflagellate and quadriflagellate asexual zoids were intermediate in size between gametes and meiospores in the sexual life history, and both were negatively phototactic. Microspectrophotometric studies demonstrated similar amounts of DNA in the nuclei of vegetative cells in thalli generated asexually from biflagellate or quadriflagellate zoids, and in vegetative cells of sporophytes (2C) in the sexual life history. Furthermore, both types of asexual zoids had the same DNA value (2C), demonstrating that the asexual zoids are produced without meiosis. The three strains with different life histories were determined to be conspecific, on the basis of morphological similarities and low sequence divergence of the nuclear ribosomal DNA internal transcribed spacer (ITS1, ITS2 and 5.8S). However, there was no correlation between ITS sequence and life history. One river contained only E. prolifera reproducing via a sexual life history. In the other three rivers, where a mixture of life histories was found, individuals with different life histories were indistinguishable on the basis of morphology and ITS sequence.