Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)
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In order to better understand the alternation of generations that characterizes haploid–diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.
KeywordsLife cycle evolution Gametophyte Sporophyte Ecological differences Asexual reproduction Light Salinity
This research was funded by Fondo Nacional de Desarrollo Científico y Tecnológico, Gobierno de Chile (FONDECYT #1090360) awarded to M-L. Guillemin. This study also constitutes a contribution from the Associated International Laboratory between France and Chile “Dispersal and Adaptation in Marine Species” (LIA DIAMS). We thank V. Flores, F. Rubio and N. Lavado for their help during the field sampling and the laboratory experiments and D. Roze and M. Valero for their helpful comments. We are also grateful to two anonymous reviewers for improving the early version of the manuscript.
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