Dynamique d'une population de Moina micrura (Crustacea, Cladocera) dans un bassin de lagunage à Marrakech (Maroc)

Au cours d'un suivi annuel du zooplancton d'un bassin de lagunage, une population de #Moina micrura$ s'est maintenue durant 1,5 mois (14 avril-2 juin). Des récoltes à intervalles de temps rapprochés (2 fois par semaine) ont permis de suivre la cinétique de la croissance de cette population. Celle-ci connait tout d'abord une période de croissance rapide et intensive : la fécondité élevée et la brièveté du développement juvénile ajoutées à un poids individuel élevé, aboutissent à un taux de croissance pondéral de la population assez exceptionnel. Une alimentation optimale en qualité et en quantité, des températures élevées (18 à 24°C) et l'absence de prédateurs expliqueraient ces fortes productions. Puis la population disparaît aussi soudainement qu'elle est apparue. Les causes de cette disparition sont analysées. La qualité de l'eau et une surdensité algale (effets toxiques de l'ammoniac ou de substances organiques ?) pourraient être les principales raisons de ce développement limité et l'absence de Daphniidés généralement commun dans ce type de milieu. (Résumé d'auteur

Modes, mechanisms and evidence of bet hedging in rotifer diapause traits

In this contribution, we review our knowledge on bet-hedging strategies associated with rotifer diapause. First, we describe the ecological scenario under which bet hedging is likely to have evolved in three diapause-related traits in monogonont rotifer populations: (1) the timing of sex (because diapausing eggs are produced via sexual reproduction), (2) the sexual reproduction ratio (i.e. the fraction of sexually reproducing females) and (3) the timing of diapausing egg hatching. Then, we describe how to discriminate among bet-hedging modes and discuss which modes and mechanisms better fit the variability observed in these traits in rotifers. Finally, we evaluate the strength of the empirical evidence for bet hedging in the scarce studies available, and we call for the need of research at different levels of biological complexity to fully understand bet hedging in rotifer diapause

Barcoding rotifer biodiversity in Mediterranean ponds using diapausing egg banks

The biodiversity of Mediterranean freshwater bodies is among the most threatened worldwide; therefore, its accurate estimation is an urgent issue. However, traditional methods are likely to underestimate freshwater zooplankton biodiversity due to its high species seasonality and cryptic diversity. We test the value of applying DNA barcoding to diapausing egg banks, in combination with the creation of a reference collection of DNA barcodes using adult individual samples, to characterize rotifer communities. We use monogonont rotifers from two lakes in Doñana National Park and one from Ruidera Natural Park in Spain as models to create a reference collection of DNA barcodes for taxonomically diagnosed adult individuals sampled from the water column, to compare with the sequences obtained from individual eggs from the diapausing egg banks. We apply two different approaches to carry out DNA taxonomy analyses, the generalized mixed Yule coalescent method (GMYC) and the Automatic Barcode Gap Discovery (ABGD), to the obtained sequences and to publicly available rotifer sequences. We obtained a total of 210 new rotifer COI sequences from all three locations (151 diapausing eggs and 59 adults). Both GMYC and ABGD generated the same 35 operational taxonomic units (OTUs), revealing four potential cryptic species. Most sequences obtained from diapausing eggs (85%) clustered with sequences obtained from morphologically diagnosed adults. Our approach, based on a single sediment sample, retrieved estimates of rotifer biodiversity higher than or similar to those of previous studies based on a number of seasonal samples. This study shows that DNA barcoding of diapausing egg banks is an effective aid to characterize rotifer diversity in Mediterranean freshwater bodies

Effect of female aging on the morphology and hatchability of resting eggs in the rotifer Brachionus plicatilis Müller

This study examined the morphology and hatchability of Brachionus plicatilis resting eggs as a function of the aging of maternal fertilized mictic females. One-hundred twenty fertilized B. plicatilis (Australian strain) were individually cultured and monitored daily until death. All cultures were maintained at 25°C, 11 ppt, and fed the micro-algae Tetraselmis tetrathele. Resting eggs produced by the females were investigated using two parameters: egg morphology, and hatching rate. Under these culture conditions, females normally produce 1-6 (mean ± SD = 2.7 ± 1.2) resting eggs during their lifetime. However, the number of resting eggs with abnormal morphology increased as a function of maternal age. Among resting eggs with normal morphology (n = 225), 82.2% were produced during the first and second spawning, and had hatching rates of more than 60%, while the hatching rates were below 30% in resting eggs with a spawning order of >2. Thus, the quality of B. plicatilis resting eggs was negatively correlated with maternal age