National Committee on Marine Sciences (NCMS)

We evaluated the life cycle of Leathesia marina through molecular analyses, culture studies, morphological observations, and ploidy measurements. Macroscopic sporophytes were collected from two localities in Atlantic Patagonia and were cultured under long-day (LD) and short-day (SD) conditions. Molecular identification of the microscopic and macroscopic phases was performed through the cox3 and rbcL genes and the phylogeny was assessed on the basis of single gene and concatenated datasets. Nuclear ploidy of each phase was estimated from the DNA contents of individual nuclei through epifluorescence microscopy and flow cytometry. Molecular results confirmed the identity of the Argentinian specimens as L. marina and revealed their conspecificity with L. marina from New Zealand, Germany, and Japan. The sporophytic macrothalli (2n) released mitospores from plurilocular sporangia, which developed into globular microthalli (2n), morphologically similar to the sporophytes but not in size, constituting a generation of small diploid thalli, with a mean fluorescent nuclei cross-sectional area of 3.21 ± 0.7 μm2. The unilocular sporangia released meiospores that developed two morphologically different types of microthalli: erect branched microthalli (n) with a nuclear area of 1.48 ± 0.07 µm2 that reproduces asexually, and prostrate branched microthalli (n) with a nuclear area of 1.24 ± 0.10 µm2 that reproduces sexually. The prostrate microthalli released gametes in LD conditions, which merged and produced macroscopic thalli with a nuclear cross-sectional area of 3.45 ± 0.09 µm2. Flow cytometry confirmed that the erect and prostrate microthalli were haploid and that the globular microthalli and macrothalli were diploid.

Known locally as “dugong” (Dugong dugon), this sea cow is a large, charismatic and gentle creature of the sea that is rarely seen nowadays in coastal and marine areas where they used to thrive. Shy as it is, very little is known about this very elusive marine mammal—its population and distribution, how and where it breeds or congregates, or where and how it raise its young. Fortunately, as a species, dugong is surviving the numerous human-induced threats, unlike its cousin, the Steller’s sea cow that lived off the coast of western North America, which became extinct in the 18th century mainly due to hunting.

National Committee on Marine Sciences (NCMS)

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