Phylogeny and biogeography of the toxic dinoflagellate Alexandrium
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https://hdl.handle.net/1912/2455DOI
10.1575/1912/2455Abstract
The incidence and known distribution of paralytic shellfish poisoning (PSP) have
both increased dramatically in recent decades. A concurrent rise in bloom frequency and
geographic range of PSP toxin-producing Alexandrium dinoflagellates explains the
increase in PSP, but the reasons for changes in Alexandrium occurrence are unknown.
This thesis explores the phylogeny, taxonomy, and biogeography of Alexandrium in light
of this recent expansion.
Alexandrium phylogeny was reconstructed through rDNA sequence analysis and
compared to traditional morphological taxonomy. Alexandrium split into two groups,
termed the α and ß clades. Interspecific relationships did not correlate with the
morphological traits traditionally used to identify and group species, although other traits
appeared phylogenetic ally conserved. The ability to produce toxins has been acquired
and/or lost multiple times during Alexandrium evolution.
Because most PSP events are caused by either the tamarensis or minutum complexes, the
phylogeny, species definitions, and biogeography of each complex was examined. The
morphospecies of the tamarensis complex, A. catenella, A. tamarense, and A. fundyense,
did not represent valid species by the phylogenetic, biologic or morphological species
concepts. Instead, five cryptic species were identified through phylogeny and mating
incompatibility. A. universa and A. toxipotens contain all toxic strains, while A.
mediterra, A. tamarensis and A. tasmanense contain only non-toxic isolates. Within the
minutum group, A. lusitanicum and A. angustitabulatum were also not distinct species
based on morphology and phylogeny while A. insuetum and A. tamutum were clearly
distinct. Three new minutum group species were identified on the basis of morphology,
phylogeny and prior research. Unlike the pattern found for the tamarensis complex, toxic
and non-toxic A. minutum strains cannot be segregated based upon LSU sequences. The
reconstructed biogeography of the tamarensis and minutum complexes indicate that both
natural dispersal and human-assisted transportation of Alexandrium have caused the
geographic spread. Human-assisted transport of toxic A. catenella-type cells from Asia
to the Thau Lagoon, France, was demonstrated in chapter iv.
This thesis demonstrates the importance of human action in the recent PSP increase,
better defines species boundaries and provides an invaluable genetic database for tracking
future Alexandrium spread and distinguishing between harmful and non-toxic
Alexandrium blooms.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003
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Suggested Citation
Thesis: Lilly, Emily L., "Phylogeny and biogeography of the toxic dinoflagellate Alexandrium", 2003-09, DOI:10.1575/1912/2455, https://hdl.handle.net/1912/2455Related items
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