Daniel Liesner1,2, Rémy Luthringer1, Lineekela Kandjengo3, John J. Bolton4, Mark D. Rothman4,5, Gareth A. Pearson6, Philippe Potin7, Myriam Valero7, Fabian B. Haas1, Susana M. Coelho1
1Max Planck Institute for Biology Tübingen, Germany - 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany - 3University of Namibia, Namibia - 4University of Cape Town, South Africa - 5Department of Forestry, Fisheries and the Environment, South Africa - 6Universidade do Algarve, Portugal - 7CNRS, UMR 8227, Laboratory of Integrative Biology of Marine Models, Sorbonne Université, Station Biologique de Roscoff, France - 8CNRS, IRL 3614, Evolutionary Biology and Ecology of Algae, Sorbonne Université, Station Biologique de Roscoff, France
The life cycles of most brown algae alternate between generations of haploid gametophytes and diploid sporophytes, with various alternative pathways. In the marine forest-forming kelps (Laminariales), sex occurs in the haploid gametophyte stage, where distinct female and male individuals produce eggs and sperm, respectively. The developmental transition towards the sporophyte identity is controlled genetically upon syngamy. However, unfertilized gametes may also develop parthenogenetically into clonal partheno-sporophytes. We investigated the mechanisms involved in transitions between life cycle stage identity and between sexual and asexual reproductive modes in the Southern African kelp Laminaria pallida. To this end, we compared developmentally resolved transcriptomes along a time course of male and female asexual and sexual reproduction of L. pallida gametophyte isolates. We identified gene regulatory networks involved in determining life cycle stage identity in both reproductive modes. While we show that asexual reproduction via parthenogenesis is a trait maintained widely in gametophytes collected from wild populations, population genetic analyses indicate that asexual reproduction is not a prevalent trait in natural populations. Additional developmental and morphometric analyses revealed a fitness disadvantage of asexually derived sporophytes. Furthermore, we demonstrate that the prevalence of asexual reproduction is diminished in presence of individuals of the opposite sex, suggesting the existence of a mate sensing mechanism. This indicates that asexual reproduction via parthenogenetic development may function as an alternative reproductive strategy. Together, our results provide a comprehensive view of the genetic pathways and potential ultimate mechanisms driving reproductive modes in a kelp. We suggest that asexual reproduction is maintained at low cost in natural populations of L. pallida which may allow reproductive assurance under suboptimal conditions.
Biography
Daniel Liesner is a postdoctoral researcher interested in trait variability within brown algae. After obtaining his doctorate on thermal trait variation in kelp at Alfred Wegener Institute for Polar and Marine Research in Bremerhaven (DE), he continued as a postdoc researching sexual transitions in kelp at Max Planck Institute for Biology Tübingen (DE). Daniel recently joined GEOMAR Helmholtz Centre for Ocean Research Kiel (DE), where he is investigating heat adaptation of Baltic Fucus beds.