Genotyping an Emiliania huxleyi (prymnesiophyceae) bloom event in the North Sea reveals evidence of asexual reproduction

[摘要] Due to the unprecedented rate at which our climate is changing, the ultimateconsequence for many species is likely to be either extinction or migrationto an alternate habitat. Certain species might, however, evolve at a ratethat could make them resilient to the effects of a rapidly changingenvironment. This scenario is most likely to apply to species that have largepopulation sizes and rapid generation times, such that the genetic variationrequired for adaptive evolution can be readily supplied. Emilianiahuxleyi (Lohm.) Hay and Mohler (Prymnesiophyceae) is likely to be such aspecies, as it is the most conspicuous extant calcareous phytoplankton speciesin our oceans with growth rates of 1 day⁻¹. Here we report on avalidated set of microsatellites, in conjunction with the coccolithophoremorphology motif genetic marker, to genotype 93 clonal isolates collectedfrom across the world. Of these, 52 came from a single bloom event in theNorth Sea collected on the D366 United Kingdom Ocean Acidification cruise inJune–July 2011. There were 26 multilocus genotypes (MLGs) encountered onlyonce in the North Sea bloom and 8 MLGs encountered twice or up to six times.Each of these repeated MLGs exhibited P_sex values of less than0.05, indicating each repeated MLG was the product of asexual reproduction andnot separate meiotic events. In addition, we show that the two mostpolymorphic microsatellite loci, EHMS37 and P01E05, are reporting on regionslikely undergoing rapid genetic drift during asexual reproduction. Despitethe small sample size, there were many more repeated genotypes thanpreviously reported for other bloom-forming phytoplankton species, includinga previously genotyped E. huxleyi bloom event. This studychallenges the current assumption that sexual reproduction predominatesduring bloom events. Whilst genetic diversity is high amongst extantpopulations of E. huxleyi, the root cause for this diversity andultimate fate of these populations still requires further examination.Nonetheless, we show that certain CMM genotypes are found everywhere, whileothers appear to have a regional bias.

[学科分类] 地球化学与岩石