Lepidodinium

No Etymology is available for Lepidodinium. While not explicitly stated, viride likely refers to the green colour of the organism as it is derived from the Latin word meaning green and is commonly used to name green organisms, for example Asplenium viride, a green fern. The etymology for chlorophorum is also not stated but it seems likely to be derived from the uniqueness of the chloroplast in its acquisition and presence of chlorophyll a and b. Its type species is Lepidodinium viride. == History of knowledge ==

Lepidodinium viride was first described in 1987 before being identified as a new genus and named in 1990. The first specimen was obtained from a sample collected from the surface seawaters off the coast of Northern Japan. This genetic sequencing also revealed the relatively high level of similarity between Lepidodinium and Gymnodinium species, leading to the solidification of Lepidodinium as a sister genus to Gymnodinium. The fact that Lepidodinium is a genus where all species share a plastid in common led to the suggestion that endosymbiont acquisition in dinoflagellates is less frequent than first thought and can be used to usefully classify genera. Today, Lepidodinium chlorophorum and Lepidodinium virdiae are recognised as belonging to the same genus, Lepidodinium, which is a sister genera to Gymnodinium == Habitat and ecology ==

The presence of chlorophyll b allows L. chlorophorum to cause green seawater discolouration through large sea blooms worldwide that has significant ecological and economic impacts. The blooms are associated with high concentrations of ammonia and phosphates, along with transparent exopolymers particles, which results in localised hypoxia in the area. Significant vertical migration has been observed in L. chlorophorum in association with these blooms. This suggests that feeding on prey is an important mechanism for maintaining a normal N : P internally. Their selectivity during feeding is enhanced by increasing temperature, feeding on more high N prey in warmer conditions. This has important ecological implications in association with climate change as ocean temperatures rise. == Description ==

Morphology Lepidodinium are green, oval, dorsoventrally compressed and 20-30 μm in diameter. The plastid is most closely related to free-living members of the green algal genus Pedinomonas. Two previously undescribed dinoflagellates ("MGD" and "TGD") contain a closely related plastid that from tertiary endosymbiosis. Although MGD and TGD are known to have nucleomorphs, the observation of a green algal nucleus in Lepidodinium proper remains controversial. One slight issue in understanding the sequence of evolution is that although the phylogenetic tree built from Lepidodinium-MGD-TGD's plastid is monophyletic, the tree built from their host-nucleus DNA is not, implying that they might have acquired very similar algae independently. == Life cycles ==

The life cycle of Lepidodinium has not been fully documented. The formation of benthic cysts have been observed in culture but cysts have never been found in sediment in the field. However, Lepidodinium eDNA has been found in a non-bloom period in winter, suggesting a temporary pelagic stage in the life cycles of Lepidodinium. This would allow Lepidodinium to survive in the water column until the appropriate conditions for blooming are generated. == Genetics ==

Endosymbiotic gene transfer and horizontal gene transfer has occurred to a large extent in the genome of Lepidodinium. It contains codes for proteins with a range of origins creating a mosaic, hybrid proteome. Like other dinoflagellates, Lepidodinium has likely undergone multiple plastid replacement events, with proteins being obtained from these different plastids each time. These plastid replacement events in Lepidodinium include the loss of the secondary, chlorophyll c and peridinin containing plastid from red-algae thought to be the ancestral state that has been maintained in many other dinoflagellates. The Lepidodinium genome still contains plastid-targeting genes originated from this peridinin plastid that now function to target the new green algae plastid. L. chlorophorum possesses the GAPDH which is a plastid-targeted gene originated from a haptophyte, an alga taken up by other dinoflagellates but not currently present in Lepidodinium. Other origins of genes in L. chlorophorum include green algae, heterokonts, streptophytes, and peridinin-containing dinoflagellates. Some genes associated with lineages that have taken up green algae are present in the Lepidodinium genome and not in any other dinoflagellates. It has been suggested that at least three different plastids have led to the development of the Lepidodinium genome, along with horizontal gene transfer from prey. It's been suggested that mixotrophic organisms, such as Lepidodinium, are more susceptible to horizontal gene transfer. Although not examined in L. viride, L. chlorophorum appears to have a unique N-terminal pre-sequence (thought to be associated with plastid targeting) within the dinoflagellates. == Plastid acquisition ==

The genetic sequencing of the secondary plastids of Lepidodinium species reveal its origin to be Pedinomonas minor or a species closely related to Pedinomonas, a green algae. Another dinoflagellate species, Pedinomonas noctilucae, is known to take up a Pedinophyte endosymbiont in certain conditions but there is a very low level of integration, compared to the fully integrated plastid in Lepidodinium. This represents one of at least three independent secondary endosymbiosis events involving a green algae in the eukaryotes, the others being in the Euglenophytes and Chlorarachinophytes. The endosymbiont has lost a large number of genes, including those involved in essential functions, showing a high level of integration as an organelle. == Practical importance ==

The blooms of L. chlorophorum have significant economic and ecological impacts due to the hypoxic conditions the bloom generates. and the advisement against swimming during the blooms. The ecological consequences of these blooms stem from the hypoxic conditions that are generated from biomass recycling, in combination with the increased concentrations of DIP and NH4 inside the blooms, also associated with high levels of nutrient recycling. The oxygen concentration in L. chlorophorum blooms is frequently brought below the threshold that most benthic invertebrates can survive, representing just one of the ecological effects of these blooms. For bivalves, the typically observed response to hypoxia is reduced feeding and oxygen consumption, thought to negatively affect their growth and survival. It is thought that these blooms are becoming more common with climate change as waters become warmer and the elemental composition of seawater alters. Although the exact mechanism is not known, the presence of L. chlorophorum is correlated with negative effects on oyster (Crassostrea gigas) growth, causing economic harm for oyster farmers. It has been suggested that this is due to L. chlorophorum impairing the filtration ability of C. gigas by producing acid glycoconjugates and transparent exopolymer particles. It also appears that C. gigas has a poor ability to assimilate L. chlorophorum. Both of these mechanisms could explain the observed reduced growth. The problem this causes for farmers is exacerbated by the longevity of L. chlorophorum blooms. Marine mixotrophic protists such as Lepidodinium play an important role in oceans in terms of nutrient cycling as well as in the food chain. The carbon rich Transparent Exopolymer Particles (TEP) known to be produced by L. chlorophorum are important in the sedimentation of organic matter which enables bacteria abundance. Although many other organisms contribute to this process, L. chlorophorum is particularly important as it produces more TEP than many other organisms, with an average of 380g xanthan equiv [mg chl a] −1 d−1 being produced by L. chlorophorum. TEP production in L. chlorophorum also represents a much higher proportion of its carbon intake, with an average of 70% of carbon fixed by photosynthesis and excreted as TEP. During blooms of L. chlorophorum, the TEP concentration can become very high which promotes bacterial activity to the point where anoxic conditions and high levels of organic carbon degradation are created, leading to the ecological impacts. == Species ==

Source: • Lepidodinium chlorophorum • Lepidodinium viride == Scientific classification ==

Source: Chromista (Kingdom), Harosa (Subkingdom), Alveolata (Infrakingdom), Myzozoa (Phylum), Dinozoa (Subphylum), Dinoflagellata (Infraphylum), Dinophyceae (Class), Gymnodiniales (Order), Gymnodiniaceae (Family), Lepidodinium (Genus) ==References==