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Life history studies on Urospora and Codiolum from southern British Columbia Hanic, Louis Anthony

Abstract

Life history studies, emphasizing cultural and cytological approaches, were conducted on Urospora and Codiolum from a number of localities in the Strait of Georgia and Juan de Fuca Strait. Urospora wormskioldii (Mertens) Rosenvinge (n = 12) is a dioecious species having a heteromorphic life cycle with a filamentous, dwarf and Codiolum stage. The Codiolum stage is produced by syngamy of aniso-gametes or by parthenogenetic development of female and probably male gametes. All three stages produce asexual quadriflagellate zoospores which develop into filament or dwarf plants. The range in variability of morphological features of the vegetative filament is very great and encompasses all species recorded from the Pacific Coast of North America. Crosses involving plants from six widely separate localities snowed no incompatability at the mating level. Sexuality occurred spontaneously at 10°C in cultures of both sexes through several serial subcultures in the female but only in the first culture in the male. Temperature changes, filament size and nutrition appear to be factors involved in the sexual response. Several vegetative clones, including a two-year-old isolate from Cape Cod, were sexually induced by a method involving a long thermo-period. However, the same method failed on other clones. Growth of Codiolum in culture was poor and it is suggested that daily exposure may be a requirement for normal growth. The fertility of zygotic and parthenogenetic Codiolum was low in cultures grown under constant temperature conditions. Attempts to induce fertility by cold treatments met with success in some isolates but not in others. Urospora vancouveriana (Tilden) Setchell and Gardner (n =9) is an asexual species, producing filamentous and dwarf stages via quadriflagellate zoospores at low temperatures and a Codiolum stage via Mflagellate zoospores at high temperatures. Cultural filaments are indistinguishable from U. wormskioldii. Urospora speciosa (Carm.) Leblond ex Hamel (n = ?) is recorded for the first time in North America and was discovered to be uninucleate. It contains filamentous and dwarf stages which reproduce via quadriflagellate zoospores. Other features of its life history are unknown. Codiolum gregarium A. Braun and C. pusillum (Lyngbye) Kjellman, in the areas studied, are considered to be merely form variants belonging to the life history of Urospora wormskioldii. The living nucleus and its staining characteristics are described. Nuclear divisions were followed but meiosis was not demonstrated. Fertility in both types was induced by cold and inhibited by short daily thermoperiods. Codiolum petrocelidis Kuckuck, found as an endophyte in Petro-celis franciscana Setchell and Gardner is a unicellular, uninucleate plant producing ovate quadriflagellate zoospores which give rise to branching filaments. C. petrocelidis, as found in the areas studied, is inferred to belong to the life history of Spongomorpha coalita (Ruprecht) Collins. The Codiolum cell is capable of reversing its direction of growth and this reversal is suggested to be governed by light intensity. It is also proposed that the mode of stipe growth rules out a multicellular condition. Operculation was discovered in S. coalita. Cytochemical studies were done on the walls of Urospora, Spon-goraorpha and their Codiolum stages. The inner walls of Urospora and Spongomorpha are composed of cellulose and pectic materials, while those of the Codiolum types are entirely pectic. The pectic component appears different from that of higher plants. Urospora, Spongomorpha and their Codiolum stages have an outer sheath of unknown composition which is singly refractive, gives a negative test for cellulose, chitin, pectin and fat. Three types of sheaths are represented, of which those of the two Codiolum types are the same. Several taxonomic implications result from these studies. To be meaningful, identification of Urospora species should he based on more than just purely vegetative features. To be of taxonomic value wall studies should include all stages where algae with heteromorphic life histories are concerned. Because of its operculate condition, Spongomorpha coalita should be transferred to the genus Acrosiphonia. This transfer would provide further evidence for the occurrence of a heteromorphic life history in Acrosiphonia. It would also re-establish Wille's basis for recognition of the two genera on nuclear condition. Acceptance of a unicellular condition for Codiolum petrocelidis, and a heteromorphic life history for Acrosiphonia would re-establish the basis for Jonsson's new family, the Acrosiphoniaciae and at the same time remove the main barriers to the inclusion of the Acrosiphonia-Spongomorpha complex in the Ulotrichales (sensu Kornmann).

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