Although the consequences of global warming in aquatic ecosystems are only beginning to be revealed, a key to forecasting the impact on aquatic communities is an understanding of individual species' vulnerability to increased temperature. Despite their microscopic size, phytoplankton support about half of the global primary production, drive essential biogeochemical cycles and represent the basis of the aquatic food web. At present, it is known that phytoplankton are important targets and, consequently, harbingers of climate change in aquatic systems. Therefore, investigating the capacity of phytoplankton to adapt to the predicted warming has become a relevant issue. However, considering the polyphyletic complexity of the phytoplankton community, different responses to increased temperature are expected. We experimentally tested the effects of warming on 12 species of phytoplankton isolated from a variety of environments by using a mechanistic approach able to assess evolutionary adaptation (the so-called ratchet technique). We found different degrees of tolerance to temperature rises and an interspecific capacity for genetic adaptation. The thermal resistance level reached by each species is discussed in relation to their respective original habitats. Our study additionally provides evidence on the most resistant phytoplankton groups in a future warming scenario.
The nucleotide sequence analysis of the PCR products corresponding to the variable large-subunit rRNA domains D1, D2, D9, and D10 from ten representative dinoflagellate species is reported. Species were selected among the main laboratory-grown dinoflagellate groups: Prorocentrales, Gymnodiniales, and Peridiniales which comprise a variety of morphological and ecological characteristics. The sequence alignments comprising up to 1,000 nucleotides from all ten species were employed to analyze the phylogenetic relationships among these dinoflagellates. Maximum parsimony and neighbor-joining trees were inferred from the data generated and subsequently tested by bootstrapping. Both the D1/D2 and the D9/D10 regions led to coherent trees in which the main class of dinoflagellates. Dinophyceae, is divided in three groups: prorocentroid, gymnodinioid, and peridinioid. An interesting outcome from the molecular phylogeny obtained was the uncertain emergence of Prorocentrum lima. The molecular results reported agreed with morphological classifications within Peridiniales but not with those of Prorocentrales and Gymnodiniales. Additionally, the sequence comparison analysis provided strong evidence to suggest that Alexandrium minutum and Alexandrium lusitanicum were synonymous species given the identical sequence they shared. Moreover, clone Gg1V, which was determined Gymnodinium catenatum based on morphological criteria, would correspond to a new species of the genus Gymnodinium as its sequence clearly differed from that obtained in G. catenatum. The sequence of the amplified fragments was demonstrated to be a valuable tool for phylogenetic and taxonomical analysis among these highly diversified species.
Infective Cryptosporidium parvum oocysts were detected in mussels (Mytilus galloprovincialis) and cockles (Cerastoderma edule) from a shellfish-producing region (Gallaecia, northwest Spain, bounded by the Atlantic Ocean) that accounts for the majority of European shellfish production. Shellfish were collected from bay sites with different degrees of organic pollution. Shellfish harboring C. parvum oocysts were recovered only from areas located near the mouths of rivers with a high density of grazing ruminants on their banks. An approximation of the parasite load of shellfish collected in positive sites indicated that each shellfish transported more than 10 3 oocysts. Recovered oocysts were infectious for neonatal mice, and PCR-restriction fragment length polymorphism analysis demonstrated a profile similar to that described for genotype C or 2 of the parasite. These results demonstrate that mussels and cockles could act as a reservoir of C. parvum infection for humans. Moreover, estuarine shellfish could be used as an indicator of river water contamination.Cryptosporidium parvum is a cause of diarrheal disease in humans and farm animals and is a major cause of diarrhea in children and neonatal ruminants (9). Moreover, in immunocompromised subjects, this disease can be life threatening. Transmission of C. parvum occurs mainly by ingestion of oocysts either by fecal-oral contact or through contaminated food or drinking water. Localized epidemics of food-borne cryptosporidiosis have been associated with uncooked sausage, offal, raw milk, apple cider, or foodstuffs, but waterborne transmission seems to play a more prominent role and is implicated in most outbreaks of human cryptosporidiosis (16). The presence of Cryptosporidium oocysts in drinking water supplies has been well documented since 1984, and waterborne epidemics of cryptosporidiosis have been reported frequently in the United States, United Kingdom, and Japan, among other countries (25). The potential for water contamination by cryptosporidial oocysts is high in areas where dumping of raw sewage is a common practice (25). In addition, the presence of waterborne C. parvum oocysts of animal origin needs to be considered, since a single neonatal ruminant can shed up to 10 10 oocysts during the course of infection (21).The presence of oocysts in river waters may also be a source of contamination of the marine environment. Rivers polluted by anthropogenic and livestock fecal discharges could play a major role in contamination by oocysts of shellfish in estuaries and coastal environments. Experimental data show that C. parvum oocysts can survive in seawater up to 30 ppt for as long as 1 month (11,24). Oocysts also have been detected in seawater in Hawaii near a sewage discharge site (18). Moreover, oocysts with a size, shape, and appearance consistent with those of C. parvum have been detected in mussels (Mytilus edulis) from western Ireland (6) and in bent mussels (Ischadium recurvum) from Chesapeake Bay in the United States (14). Laboratory data show that the...
Summary Investigating the differential capacity of the response of phytoplankton to human‐induced environmental forcing has become a key issue to understanding further the future repercussions on the functioning of aquatic ecosystems. The initial tolerance to the widely dispersed herbicide simazine was measured in diverse phytoplankton species. An experimental ratchet system maintaining large populations of dividing cells (which ensures the occurrence of rare spontaneous mutations that confer adaptation) and a strong selection pressure (which ensures the preservation of such mutations within the population) was later applied to estimate the capability of different groups of phytoplankton to adapt to simazine. Initially, simazine doses between 0.05 and 0.15 ppm were able to inhibit 100% growth in all the species tested. However, a significant increase in simazine resistance was achieved in all derived populations during the ratchet experiment. The differential capacity for simazine adaptation was observed among the different species. The capacity of different species to adapt to simazine can be explained in relation to taxonomic group, ploidy, growth rate and habitat preference. Haploid populations of continental Chlorophyta showed the greatest capacity to adapt to simazine. By contrast, populations of Haptophyta of open ocean regions were the group least capable of adapting to the herbicide.
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