alexandrium (dinoflagellate) alexandrium (dinoflagellate) alexandrium is a genus of dinoflagellates. it contains some of the dinoflagellate species most harmful to humans, because it produces toxic harmful algal blooms (hab) that cause paralytic shellfish poisoning (psp) in humans. there are about 30 species of alexandrium that form a clade, defined primarily on morphological characters in their thecal plates. alexandrium scientific classification domain: eukaryota clade: diaphoretickes clade: sar clade: alveolata phylum: myzozoa superclass: dinoflagellata class: dinophyceae order: gonyaulacales family: ostreopsidaceae genus: alexandriumhalim, 1960 species alexandrium acatenella alexandrium affine alexandrium andersonii alexandrium australiense alexandrium balechii alexandrium camurascutulum alexandrium catenella alexandrium cohorticula alexandrium compressum alexandrium concavum alexandrium depressum alexandrium diversaporum alexandrium foedum alexandrium fraterculus alexandrium gaarderae alexandrium globosum alexandrium hiranoi alexandrium insuetum alexandrium kutnerae alexandrium leei alexandrium margalefii alexandrium mediterraneum alexandrium minutum alexandrium monilatum alexandrium ostenfeldii alexandrium pacificum alexandrium pohangense alexandrium pseudogonyaulax alexandrium satoanum alexandrium tamarense alexandrium tamyavanichii alexandrium tamutum alexandrium taylorii alexandrium tropicale introduction the group was not well-defined in the past and thus, due to interest of its toxic behaviour, people have revised the group through formal tabulation and usage of molecular markers such as the toxic gene, stx4a, to better understand not just the relationship between each species; but more importantly, to tell something about the spread and barriers to the bloom. even if, much is known about the life cycles related to the blooms, much is still unknown as to how each life stage is triggered and transitions to the next stage. predation and parasitism have proven to be great barriers for population growth. learning about the pathways of toxin synthesis can allow us to determine how species of alexandrium have adapted and co-evolved to persist. etymology in the 1960s, an egyptian researcher by the name of youssef halim discovered a red tide along the coast of the alexandria harbour in egypt. it was the first described red tide in egypt and later on, halim identified and named the culprit as alexandrium as homage to where it was found and he identified alexandrium minutum as the genus's type species. history of knowledge species currently included in alexandrium have been known for a long time, but initially they were classified in different genera, notably, gonyaulax. nonetheless, the first attempt at revising the genus, gonyaulax, was made by kofoid in 1911. kofoid was a very influential biologist during his time. his greatest work was the development of the universal "kofoid system" that classified dinoflagellates based on plate morphology very detailed drawings and well-defined structures. unfortunately, however kofoid divided gonyaulax into 4 subgenera based on shape, and included several species that should not have been classified under the name gonyaulax. lebour (1925) described a new species called gonyaulax tamarensis. whedon and kofoid in 1936 used the same tabulation as lebour and described two new species, gonyaulax acatenella and gonyaulax catenella. the latter was studied in much more detail due to the fact that it caused paralytic shellfish poisoning (psp) in humans, getting it from bivalve mollusks. as more and more species were described, they either put them into the "tamarensis group" or the "catenella group". by no means was it simple to put species into either group and this caused great confusion. the "tamarensis group" was divided into two subgroups and were separated by whether or not one of its thecal plates had contact with the ventral pore or not. goniodoma and gonyaulax were very similar. in 1954, gaarder stated that her goniodoma species described had very similar characteristics to the "tamarensis group" in gonyaulax. she is believed to be the first to clarify the differences in the two groups based on the plate tabulation. in 1960, halim created the new genus alexandrium with alexandrium minutum as the only species described in it and he put it into the "tamarensis group". the "tamarensis group" had become a taxonomical chaos by this time, in part because many scientists had differences in opinion about the species and genus taxonomy included in this group. many species from the same location had been given several names. the group included for example the genus: gonyaulax, goniodoma, pyrodinium, alexandrium, gessnerium, protogonyaulax, and glenodinium. in 1971, the group was revised by steidinger, who suggested that the "tamarensis group" should be separated from gonyaulax. she also recognized alexandrium as being part of the group. meanwhile, in the same year, balech suggested that the gonyaulax group should be separated into alexandrium or gessnerium. what gave people interest in studying alexandrium was because it produces paralytic shellfish toxins (pst). the theory of becoming toxic was that originally, bacteria in the ocean would compete with each other producing toxic by-products. alexandrium being bacterivorous would ingest these bacteria and gain the ability to produce these pst's. later studies have shown that indeed if you remove the symbiotic bacteria of specific alexandrium species, the dinoflagellate produces less toxin. if you put new bacteria into the alexandrium species, there is no change in toxin production. nonetheless, this theory needs more evidence to be supported. molecular phylogeny before molecular data, the main way to distinguish between alexandrium species was to identify whether or not it made chains or if the 1' thecal plate touched the ventral pore or not. (5) however, this was not very effective in distinguishing between different species, especially, as more and more species were described. hence, taxonomists have organized different species into different species complexes based on gene markers, of which the two most well-established and deadliest ones are the alexandrium tamarense species complex and the alexandrium minutum species complex. originally, the alexandrium tamarense species complex included alexandrium tamarense, alexandrium fundyense, and alexandrium catenella. the phylogeny was created using primarily large subunit and small subunit ribosomal rna. by constructing using rdna, researchers found that the phylogeny forms 5 different geographical clades in the alexandrium tamarense species complex. these are the north american, western european, temperate asian, tasmanian, tropical asian clades, and a mediterranean clade. the new revised alexandrium tamarense species complex is grouped into five clades that are named groups i-v. there are currently 5 species included in this complex: alexandrium fundyense (group i); alexandrium mediterraneum (group ii); alexandrium tamarense (group iii); alexandrium pacificum (group iv); alexandrium australiense (group v). there are three morphospecies that can be distinguished primarily based on morphology: a. catenella, a. fundyense, and a. tamarense. they have differences in their size (length to width ratio), the presence or absence of the ventral pore attached to the 1' or even the 4' thecal plate, and the differences in other thecal plates. a. catenella can form chains, while a. fundyense and a. tamarense cannot. a. catenalla has a lower length to width ratio than the other two. (5) a. tamarense has a ventral pore, but the other two do not. it has been found that many cells have intermediate morphologies between the morphologies described in a. tamarense and a.fundyense. as well, the ventral pore was sometimes present and sometimes absent in a. fundyense. although a. catenella is found in the same location as a. fundyense, it is suggested to not include it in the alexandrium tamarense species complex. morphological characteristics have been less distinctive than scientist have originally thought. however, using rdna has provided more confidence on differentiating them phylogenetically. using its/5.8s genetic distances within and between species, one can differentiate between differences in genomic mismatch between the two species. the genetic distance between the same species was much lower than between different species confirming the distinct species-specific clades. its2 compensatory base changes (cbc) are used as genetic markers that is used for studying the diversity of eukaryotic species. cbc in the secondary structure of helix iii are present in groups i, ii, and v, but absent in groups iii and iv. groups i and iii cannot produce viable cysts. scientists screened for presence or absence of the sxta4 domain of the sxta gene to determine the toxicity of each group. groups i and iv produce saxitoxin, while groups ii and iii do not. group v can sometimes produce or not produce saxitoxin. there are several other species that are not included in this group. alexandrium minutum species complex includes a. lusitanicum, a. angustitabulatum, a. minutum, a. andersonii, a. tamutum, and a. insuetum. the main difference between this group and the tamarense species complex, is that the a. minutum group species are much smaller and the development of toxicity is much variable, even between different strains. again, previously this group was defined based on morphology. but the morphology of this group is much more variable, especially in the different strains. a. insuetum was the only species that did not have the 1' plate connected to the ventral pore. both a. angustitabulatum and a. lusitanicum were very similar in morphology to a. minutum. a. andersonii was the most different from the group and was slightly larger than the average size of the group. a. tamutum is also similar to a. minutum but has a wider 6' plate. upon new morphological analysis, it was shown that there was no difference between the width of the s.a. plate and the 1' plate which was thought to have been the same in the past. when constructing the phylogeny, a. minutum is separated into two main clades. the larger clade included strains found in europe and the south pacific. the smaller clade included strains found in new zealand and taiwan. (6) a. angustitabulatum and a. lusitanicum did not differentiate into separate clades and were included in the a. minutum species complex. thus researchers have suggested that these two names be no longer separate and be included under the species a. minutum. a. insuetum formed a separate clade and the three strains were separated further; the two japanese strains were separated from the french strain. as well, a. tamatum also formed a well-supported clade with its 5 strains; the taiwanese strain was separated but basal to the italian strains. a. andersonii and a. ostenfeldii were found to be the outgroup and formed the root of the tree. the a. catenella group includes a. catenella and a. compressum. their morphological feature is that they form chains with anterior-posterior compressed cells and do not have a ventral pore. the fraterculus group includes a. affine, a. cohorticula, a. fraterculus, a. tamiyavanischii and a. tropicale. the defining feature is that they form chains and have a ventral pore. the kutnera group includes a. kutnera, and a. leei. the defining features is that it has a ventral pore. the ostenfeldii species complex includes a. ostenfeldii, and a. peruvianum, which are now considered synonyms. the defining feature is that they have a narrow 1' plate and a large ventral pore. some strains of these species can also produce a different toxin called spirolides. the pseudogonyaulax group includes a. pseudogonyaulax, a. hiranoi, a. taylorii, a.satoanum, and a.monilatum. the common feature of this group is that they do not form chains and produce goniodomins. the rest of the species have not been for the most part well-documented taxonomically and thus, there is limited molecular analysis on their phylogeny. hence, the phylogeny of the other species need to be revised. a publication in an obscure journal has suggested that alexandrium should be split in different genera, but a wide consensus has agreed not to follow this suggestion. habitat and ecology alexandrium as a whole is wide spread across the globe and has been identified in different parts of the northern and southern hemisphere. the genus can be found in oligotrophic, mesotrophic, and eutrophic coastlines. during the winter months of temperate regions, the cysts remain dormant because of the cold temperatures. they also have an internal biological clock that tells them when to germinate and thus, is the reason most of the blooms are season driven. cysts of a. tamarense can tolerate temperatures of -0.6 to 26.8 °c and this enables them to be well-distributed in marine seabeds. they cannot tolerate being anoxic. there may be large numbers of cyst populations, but only 20% of them can germinate and develop into a bloom, because oxygen is present mostly a few millimeters inside the sediment. cysts have been observed to have prominent roles in genetic diversity of subpopulations and in gene flow between subpopulations. with a few exceptions, the toxic and non-toxic forms do not overlap in range because these two forms are distinct biological species that