JAPANESE JOURNAL OF ECOLOGY
Online ISSN : 2424-127X
Print ISSN : 0021-5007
ISSN-L : 0021-5007
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Feature Ecology and evolution of diverse reproductive systems in algae
  • Evolution and mathematics of the haploid-diploid life cycle in macroalgae
    Kazuhiro Bessho
    2023 Volume 73 Issue 2 Pages 33-47
    Published: 2023
    Released on J-STAGE: November 04, 2023
    DOIhttps://doi.org/10.18960/seitai.73.2_33
    JOURNAL OPEN ACCESS
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  • Toward an understanding of life cycle diversification in green seaweeds
    Yusuke Horinouchi
    2023 Volume 73 Issue 2 Pages 49-56
    Published: 2023
    Released on J-STAGE: November 04, 2023
    DOIhttps://doi.org/10.18960/seitai.73.2_49
    JOURNAL OPEN ACCESS
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    Many plants, including seaweeds, exhibit both a diploid (2n) body (sporophyte) and a haploid (1n) body (gametophyte). These two multicellular phases undergo alternation of generations, a life cycle that entails sexual reproduction in all terrestrial plants and most algal species. The Ulvophyceae are a class of marine green algae (seaweeds) that are primary producers in coastal ecosystems worldwide. The class contains six orders that exhibit sexual reproduction through life cycles that vary among species. Although relationships between life cycle and environment or ecological niche have long been suspected, the mechanisms driving the diversification of ulvophycean life cycles remain poorly understood. Additionally, some ulvophycean life cycles are difficult to distinguish according to conventional definitions. Therefore, in this review, I examine past findings on the diversity and ecological characteristics of ulvophycean life cycles, and propose avenues for future research that will lead to a better evolutionary and ecological understanding of green algal life cycle diversification.
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  • Reproductive strategy of florideophycean red algae with an isomorphic life cycle
    Mitsunobu Kamiya
    2023 Volume 73 Issue 2 Pages 57-
    Published: 2023
    Released on J-STAGE: November 04, 2023
    DOIhttps://doi.org/10.18960/seitai.73.2_57
    JOURNAL OPEN ACCESS
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    In florideophycean red algae with an isomorphic life cycle, the haploid gametophyte and diploid sporophyte exhibit similar gross morphology, distribution, and phenology, and the significance of this life cycle is not fully understood. Previous work has demonstrated that the phase ratio differs between wave-exposed and protected sites and that water content, strength of the thallus, and growth rates of germlings differ between the two phases. These characteristics suggest that such differences may be advantageous for adaptation to various coastal environments. In addition, independent sporophytes, which we refer to as “recycling successive sporophytes”, have been reported in various isomorphic red algae. Molecular phylogenetic analyses suggest multiple occurrences of independent sporophytes as distinct populations of Caloglossa leprieurii; in fact, independent sporophytes have been found in various red algal species with isomorphic life cycles. Furthermore, dominance of independent sporophytes has occasionally been observed within marginal habitats, as independent sporophytes can reproduce under wider temperature ranges than normal gametophytes/sporophytes, implying that independent sporophytes may help expand the species' distribution. Isomorphic life cycles, which involve ecophysiologically different phases and do not necessarily require sexual reproduction, may be effective for increasing fitness in various intertidal environments.
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  • Adaptive significance of asexual pathways in the life cycles of brown algae
    Masakazu Hoshino
    2023 Volume 73 Issue 2 Pages 67-
    Published: 2023
    Released on J-STAGE: November 04, 2023
    DOIhttps://doi.org/10.18960/seitai.73.2_67
    JOURNAL OPEN ACCESS
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    In addition to sexual reproduction pathways (zygote formation and meiosis), asexual pathways such as parthenogenesis and vegetative reproduction have been reported in the life cycles of many brown algae. However, most of these asexual pathways have been described based on observations made under laboratory culture conditions, and their significance in field populations remains unclear. In this paper, I describe the life cycles of several species of brown algae and outline how asexual pathways may impact the species' reproduction, distribution range, maintenance of sexual reproduction, and alternation of generations.
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