REPRODUCTION AND SYSTEMATICS OF THE MARINE ALGA DERBESIA (CHLOROPHYCEAE) IN NEW ENGLAND1,2

Abstract

SUMMARYThe morphology, gross cytology, reproduction, and habitat ecology are described for Derbesia marina based on observations of New England field populations and laboratory cultures of this plant. These data, and additional observations on cultures of several other species of Derbesia from elsewhere and on type and other important collections, have been used to evaluate the systematic relationship of New England Derbesia with other species of this genus. The single Derbesia species in New England is referred to D. marina. The systematic criteria previously used to distinguish species within Derbesia are reviewed and interpreted within the context of the present investigation. In systematic studies, we stress the importance of the use of sporangial and chloroplast morphology, the presence or absence of pyrenoids, and reproductive history.Two types of life history are reported for D. marina in New England: (1) A form of D. marina collected at 20 m reproduces directly with stephanokontous zoospores growing into sporophytic plants of Derbesia morphologically identical to their parent thalli. (2) On the other hand, at least some New England, populations of D. marina have retained the genetic potential for producing a sexual generation (Halicystis ovalis), even though the latter is unknown for the coast of northeastern North America.3 Gametophytes (H. ovalis) were produced directly from enlargement and subsequent differentiation of uncleaved lateral sporangia in 2 cultured populations of New England D. marina. A single female and numerous male vesicles formed in this manner produced gametes, but neither fertilization nor parthenogenesis occurred; thus the entire life history was not completed in culture.The occurrence of the directly reproducing deep water form of D. marina is presented as evidence for speciation of a sporophyte (Derbesia) independent of its alternate gametophyte (Halicystis). An hypothesis is advanced to explain the source and means for expression of genetic variability necessary for speciation in a population of nonsexually reproducing Derbesia.