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Dinoflagellates are haploid eukaryotic microalgae in which rapid proliferation causes dense blooms, with harmful health and economic effects to humans. The proliferation mode is mainly asexual, as the sexual cycle is believed to be rare and restricted to stressful environmental conditions. However, sexuality is key to explaining the recurrence of many dinoflagellate blooms because in many species the fate of the planktonic zygotes (planozygotes) is the formation of resistant cysts in the seabed (encystment). Nevertheless, recent research has shown that individually isolated planozygotes in the lab can enter other routes besides encystment, a behavior of which the relevance has not been explored at the population level. In this study, using imaging flow cytometry, cell sorting, and Fluorescence In Situ Hybridization (FISH), we followed DNA content and nuclear changes in a population of the toxic dinoflagellate Alexandrium minutum that was induced to encystment. Our results first show that planozygotes behave like a population with an “encystment-independent” division cycle, which is light-controlled and follows the same Light:Dark (L:D) pattern as the cycle governing the haploid mitosis. Resting cyst formation was the fate of just a small fraction of the planozygotes formed and was restricted to a period of strongly limited nutrient conditions. The diploid-haploid turnover between L:D cycles was consistent with two-step meiosis. However, the diel and morphological division pattern of the planozygote division also suggests mitosis, which would imply that this species is not haplontic, as previously considered, but biphasic, because individuals could undergo mitotic divisions in both the sexual (diploid) and the asexual (haploid) phases. We also report incomplete genome duplication processes. Our work calls for a reconsideration of the dogma of rare sex in dinoflagellates. SI

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Growth performance and feeding activities of brown trout selected for growth (S) and control lines (C) maintained without a selection pressure were compared. Groups of 500 fish of each line with the same initial weight (4 g) were constituted and fed for 115 days ad libitum using self-feeders or automatic feeders (2 lines×2 feeding methods×3 replicates). After 35 days of food deprivation, all groups were re-fed by self-feeders for 46 days. The feeding demands of groups fed by self-feeders were recorded continuously. Growth, feed intake and uneaten feed were measured at regular intervals. In both lines, growth rates were higher in self-fed than in automatically fed fish (P 0.36), the better growth of S was caused by higher feed intake. Self-fed brown trout ate 16–20% of their daily intake at dawn and on average 5% per h thereafter. This feeding activity profile was more discernible for S, which ate more than C at dawn (P<0.01). At the end of the starving period the loss of weight was slightly higher for S than for C (P<0.06). It was compensated during the re-feeding period for both lines by hyperphagia and higher feed efficiency. The mean final BW was approximately 90% higher for S than for C. Both lines restored rapidly their own feeding profiles. How this selection process may determine the features of the correlated responses is discussed.

The research leading to the last developments of Diva has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 283607, SeaDataNet 2, and from project EMODNET (MARE/2008/03 - Lot 3 Chemistry - SI2.531432) from the Directorate-General for Maritime Affairs and Fisheries. Additional funding from the Local Government of the Balearic Islands (CAIB-51/2011 Grant) is also acknowledged. C. Troupin post-doctoral position is funded by MyOcean2 EU FP7 project Trabajo presentado en el 7th Coastal Altimetry Workshop, celebrado los días 7 y 8 de octubre de 2013 en Boulder, Co. (Estados Unidos) Peer Reviewed