Filogeografia do dinoflagelado tóxico Ostreopsis cf. ovata (Dinophyceae).

Abstract

Harmful algae blooms (HABs) are natural phenomena and include toxin producing species that can severely affect animals, including humans. However, toxic species do not cause harmful events in all places where they are, and can cause events of the same intensity in different locations. Thus, the multifaceted nature of HABs response to various environmental factors and their changes over time are difficult to understand. The increase in the occurrence of HABs in several temperate and tropical coastal regions leads to a series of environmental problems, such as the poisoning of marine animals, humans and the compromise of economic activities such as aquaculture and fishing. The main triggering organisms of the HABs in ma-rine systems are the dinoflagellates. In the blooms of the benthic dinoflagellate Ostreopsis cf. ovata, there may be mass mortality of marine organisms from intoxication with ovatoxin. The present work proposes to study the patterns of a spatial distribution of the genetic diversity of O. cf. ovata, contributing to a better understanding of the contemporary geographic distribu-tion of the species and, consequently, of this blooms. Phylogeographic analyses based on se-quences of three loci ITS, LSU-D1D3 and LSU-D8D10, available at Genbank, allowed the identification of 251 strains distributed in 126 sampling points. The strains analyzed came the three oceans from seven biogeographic ecoregions located in the tropical zone, and in part of the temperate zone: Temperate South America, Temperate North Atlantic, Tropical Atlantic, Central Indo Pacific, Western Indo Pacific, Temperate North Pacific and Tropical Eastern Pacific. Most strains came from three ecoregions, 34.6% from the Indo-Pacific, 32.2% from the Temperate North Atlantic and 23.1% from the Tropical Atlantic. There was a predomi-nance of occurrence of strains in surface ecoregions with warmer waters from 23 to 36ºC and salinity PSS predominantly above 34 in most areas. The phylogenetic reconstructions per-formed for the three loci analyzed produced trees with topologies and subclades (A, B, C, D and E) of O. cf. ovata usually described in the literature. The haplotype networks of O. cf. ovata returned 25 haplotypes of ITS loci, 33 haplotypes from LSU-D1D3 and 14 haplotypes from LSU-D8D10. At first, lineages A and E would perhaps be cosmopolitan, B would be more restricted to the Atlantic Ocean. Three lineages would be unique: C to the Indo-Pacific, D to the Pacific Ocean, and F to the Atlantic Ocean. Therefore, O. cf. ovata presents a phylo-geographic structure with divergent lineages and evidence of allopatric distribution and the presence of recent genetic exchanges between populations located in different biogeographic regions. These patterns are possibly explained by characteristics of the species such as the pre-dominance of asexual reproduction and encystment, and by different factors that facilitate dispersion, such as the carrying of cysts by ballast water from ships and carrying cysts through natural and artificial substrates.