Dr. Len Dyck

iridaea@mail.botany.ubc.ca

PhD. Candidate

Explaining the persistence of stable biphasic isomorphic life histories is at the forefront of current efforts in life history theory. Recent models demonstrate that even small ecological differences between apparently isomorphic phases can maintain such cycles, allowing diploids to become dominant in certain portions of the available spatial and/or temporal environmental variation, and haploids in others. In Vancouver, Harbour, Canada, the isomorphic alga Mazzaella splendens has alternated between gametophyte dominance in summer and tetrasporophyte dominance in winter. Examination of these seasonal changes in density suggested that higher qrowth rates might be coupled with lower survivorship in haploids, while slower growth and greater survivorship co-occurred in diploids. This was interpreted as a possible divergence in ecological strategies between the two phases; the haploid being r-selected relative to a more K-selected diploid. Preliminary analysis of blade production and survivorship in M. splendens at Second Beach, Barkley Sound, Canada, however, indicates that growth and survivorship need not be coupled. Probability of loss fluctuates randomly for both phases, conferring no particular advantage on either, but new blade production contributes significantly to gametophyte dominance at this site. Continuing work will examine simultaneous changes in density, phase ratio, survivorship, growth and morphology over a three year period.