| Abstract | The Alexandrium tamarense species complex is a group of economically and ecologically important marine dinoflagellates. The complex is comprised of three morphospecies A. tamarense, A. fundyense and A. catenella grouped according to ribosomal DNA or ‘ribotype’. There are five ribotype type groups (I-V) each consisting entirely of toxic or non-toxic isolates. Toxic isolates are associated with harmful algal blooms (HAB’s) due to their ability to produce powerful neurotoxins, which are responsible for outbreaks of paralytic shellfish poisoning in areas of shellfish production.
Sexual reproduction in A. tamarense has important implications for the initiation and termination of HAB’s associated with these species. Resistant, long-lived hypnozygotes are formed during blooms through gamete fusion and deposited in sediments. These hypnozygotes provide the source of inoculum of motile vegetative A. tamarense cells in temperate zones during subsequent spring/summer blooms. This study provides further insight into the mating interactions between toxic Group I and non-toxic Group III isolates primarily from UK coastal waters.
Study of the effect of temperature on the mating interactions of A. tamarense Group I and Group III in culture showed that temperature had a significant effect on both groups. Co-cultures of compatible Group III isolates showed a significant decrease (p<0.05) in hypnozygote yield at 15°C, compared to 20°C. In contrast the mating compatibility of co-cultures of Group I isolates showed significant increase (p<0.05) at 15°C, compared to 20°C. Similar to other studies, compatible Group I and Group III isolates formed non-viable hybrid hypnozygotes in co-culture. Comparison of the average vigour of inbred Group I crosses and outbred Group I/III crosses suggest that Group I isolates are more likely to out-breed with a compatible Group III isolate. A finding that may have significance in areas where the two groups co-occur.
Preliminary data suggesting the presence of both Group I and Group III ribotypes in some isolates has been generated from a nested single cell PCR/qPCR protocol using group specific primers. These data were compared to a dual probe whole cell fluorescent in situ hybridisation (whole cell FISH) assay of isolates. Whole cell FISH
showed no dual expression of ribosomal RNA. This suggests that some A. tamarense Group I and Group III isolates may have rDNA pseudogenes corresponding to different ribotypes. If correct this could have implications for the overestimation of A. tamarense group diversity in natural populations when using rDNA sequences for
identification. |
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