UC Santa Barbara

Many algal species have life cycles that involve an obligate alternation of generations between nearly identical, free-living haploid and diploid individuals. The percentages of haploids to diploids, and the spatial and temporal scales of variation of these percentages, must be examined before hypotheses about the relative importance of haploid and diploid demographic processes on population dynamics can be evaluated. In this paper, we investigated the spatial and temporal dynamics of the percentage of haploid and diploid stages in 4 congeners of the marine alga Mazzaella (M capensis, M flaccida, M laminarioides, and M splendens) across large portions of their geographical ranges. For the 3 species that were sampled over multiple years (M. flaccida, M. laminarioides, M splendens), the percentage of haploids varied significantly among sites. However, 2 of them (M flaccida, M. splendens) did not exhibit significant temporal (interannual) variation in the percentage of haploids. In addition, more fine-scale temporal studies on M flaccida populations revealed that there were also no significant intra-annual fluctuations in the percentage of haploids, although there was significant population turnover on this timescale. This spatial variability but temporal stability of haploid-diploid ratios (for M flaccida and M splendens) can be used to generate, and subsequently test, hypotheses on the regulation of haploid-diploid ratios and the relative importance of haploid and diploid demographic processes on population dynamics.