Spatial and temporal variation of haploids and diploids in populations of four congeners of the marine alga Mazzaella

Abstract

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.

Seasonal and spatial patterns of population density in the marine macroalga Mazzaella splendens (Gigartinales, Rhodophyta)

“…In wave‐sheltered areas there is a seasonal alternation between summer gametophyte and winter tetrasporophyte dominance (Adams 1979, as I. cordata ; De Wreede & Green 1990, as I. splendens ; Dyck & De Wreede 1995). Other studies of life history phase dominance in M. splendens , where observations were made only in spring and summer, have found consistent gametophyte dominance during this season (May 1986, as I. cordata ; Thornber & Gaines 2003).…”

Responses of the haploid-to-diploid ratio of isomorphic biphasic life cycles to time instability

“…Even in a generally stable environment, any sporadic instability in the population structure flows through the life cycle, in fast pulses and/or slowly diffusing, generating H:D time variability. Thus, a cyclic time variation of the H:D in a particular population, as observed by Thornber and Gaines [28], cannot be automatically taken as evidence of seasonality. Likewise, a change in the H:D over a period of 12 years [25] should not be immediately taken as evidence that the population is evolving to a new situation.…”

“…Such were the cases of Gracilaria verrucosa [4], Chondrus crispus [24], Chondracanthus chamissoi [10], Gelidium sesquipedale [20], Mazzaella cornucopiae [22], Sarcothalia crispata [15], Pterocladiella capillacea [27], Mazzaella splendens [5], Gelidium pusillum [17], Gracilaria gracilis [13] and Grateloupia turuturu [1], showing that the H:D time variability is worldwide. The H:D of Mazzaella flaccida observed at Piedras Blancas and Vandenberg (Pacific Coast of North America) with a fine temporal resolution [28] exhibited oscillations mismatching the seasonal cycle. At Piedras Blancas, they were slightly shorter, whereas at Vandenberg they were much longer.…”

Temporal Variation in Isomorphic Phase and Sex Ratios of a Natural Population of Ulva Pertusa (Chlorophyta)1

“…Many isomorphic red seaweeds exhibit persistence of one dominant phase or stable phase ratios for one or several years. For example, gametophyte dominance in Mazzaella species did not vary significantly within or between years (Thornber and Gaines 2003), and phase ratios in Gracilaria populations were relatively stable from year to year (Engel et al. 2001).…”