Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: Sami Souissi x
  • Search level: All x
Clear All

Abstract

In this study we examined the morphological anomalies of 2023 ovigerous females of the copepod Eurytemora affinis from laboratory and field samples. Field copepod collections were collected from 10 sites in Europe and North America. Laboratory cultured copepods were reared at 6 experimental conditions during several generations. The observation under the microscope of the ovigerous females’ bodies revealed the presence of a ‘Tumor Like Anomaly’ (TLA) on a few individuals, which were manifested on the urosome. The occurrence of TLA was only noticed on copepods from the field samples. This result shows that under controlled laboratory conditions, E. affinis do not manifest any abnormal morphology, even when temperature and salinity conditions are stressful, which also demonstrates the high plasticity of this copepod species and its capacity to live at a wide range of environmental parameters. In this study, we also confirmed that E. affinis is capable of producing eggs with a wide range of sizes, ranging from very small and abnormal eggs of 75.79 μm only, to very large eggs, reaching a maximal diameter of 128.71 μm. The observed large eggs are abnormal compared to the average size of the other eggs produced within the same clutch. Other abnormalities on eggs, such as deformed eggs or eggs infested by fungi, are only observed from field samples at a few sampling sites. In the Seine estuary, several abnormalities in eggs and adult females were observed during February 2010. The critical period for E. affinis’ development is sampling site-specific and needs to be accurately studied in the future to better explain the causes of the abnormalities described in this work, and their effects at population level.

In: Crustaceana

Résumé

Dans cette étude, nous avons examiné les anomalies morphologiques de 2023 femelles ovigères du copépode Eurytemora affinis provenant de collectes sur le terrain et en conditions de laboratoire. Nous avons échantillonné des copépodes sur le terrain au niveau de 10 sites en Europe et en Amérique du Nord. Les copépodes cultivés en laboratoire ont été élevés dans 6 conditions expérimentales pendant plusieurs générations. L’observation au microscope des corps de femelles ovigères a révélé la présence d’une «anomalie ressemblant à une tumeur» (TLA en anglais) sur quelques individus qui se manifestait sur l’urosome. L’occurrence de TLA n’a été observée que sur les copépodes prélevés sur le terrain. Ces résultats montrent que dans des conditions de laboratoire contrôlées, E. affinis ne présente aucune morphologie anormale, même lorsque les conditions de température et de salinité sont stressantes, ce qui démontre également la plasticité élevée de cette espèce de copépode et sa capacité de vivre dans un large spectre de paramètres environnementaux. Dans cette étude, nous avons également confirmé que E. affinis est capable de produire des œufs d’une grande variété de tailles, allant de très petits œufs anormaux de diamètre égal à 75,79 μm à de très gros œufs atteignant un diamètre maximal de 128,71 μm. Les gros œufs observés sont anormaux par rapport à la taille moyenne des autres œufs produits dans la même couvée. D’autres anomalies sur les œufs, comme les œufs déformés ou les œufs infestés par des champignons, ne sont observées qu’à quelques sites d’échantillonnage sur le terrain. Dans l’estuaire de la Seine, en février 2010, plusieurs anomalies ont été observées au niveau des œufs et chez les femelles adultes. La période critique pour le développement d’E. affinis est propre au site d’échantillonnage et doit être étudiée avec précision à l’avenir afin de mieux expliquer les causes des anomalies décrites dans ce travail et leurs effets au niveau de la population.

In: Studies on Eurytemora
In: Studies on Eurytemora
Proceedings of the Eurytemora Conference, St. Petersburg, 2019
This monograph is a summary of the conference on Eurytemora, gathering renowned researchers from all over the world to discuss new advances in Phylogeny, Biogeography, Taxonomy, and Ecology of this important group of estuarine crustaceans, held the 13-17 May 2019 in St. Petersburg, Russia. The present volume includes 17 selected papers, in which you will discover new aspects of the modern theory on the history and recent geographical distribution (biogeography) of an important group of estuarine crustaceans, revealing coincidences with a modern model of continental drift. The researchers suggest a new hypothesis on time and place of origin of continental calanoid copepods. The specialists show that studying external morphology in detail helps to increase identification and differentiation between closely related sibling species within the Eurytemora group. Several ecological questions on invasive and pseudocryptic copepod species are debated. Finally, the last chapter of this monography is devoted to taxa related to the Eurytemora group, Epischura, Temora, Temoropia, and Pseudodiaptomus.

First published as a Special Issue of Crustaceana 93(3-5): 241-547.

Many Asian aquaculture farms cultivate copepods as live-feed for aquaculture species, as copepod nutritional and behavioural qualities are usually higher than those of traditional live-feeds (i.e., Artemia and rotifers). The most convenient method to use zooplankton in aquaculture as live feed involves dormant eggs. In this study, to establish whether the copepod species of the tropical Taiwanese ponds exhibit quiescence of their eggs, several sediment samples were collected from the ponds and incubated at low temperature. After 3 months of cold incubation, several nauplii of Acartia bilobata Abraham, 1970 hatched from the sediment at high temperature over several days. Further investigations need to be conducted to understand the origin of the dormancy (i.e., induced originally in the field or in the laboratory). Nevertheless, it is the first reported case of dormant eggs in calanoid copepods in tropical regions. The present study will certainly find some interest in tropical aquaculture as our results showed that long-term storage of tropical calanoid copepod eggs is possible, even if collected directly from the sediment without sorting the eggs.

In: Crustaceana

Abstract

Eurytemora represents a challenging group of species due to their taxonomy, in particular the former group of cryptic species known as E. affinis sensu lato. In this paper, we analyse DNA sequences that are all available in GenBank, along with our own data on the genus Eurytemora. For this study, a set of mitochondrial and nuclear genes (CO1, nITS and 18SrRNA) was used. In total 543 sequences were analysed (437 CO1; 54 nITS; 52 18SrRNA). However, this work is mainly meta-analytical, and only 67 sequences from unstudied earlier populations or species were obtained specifically for this work to analyse the genetic differentiation of the morphologically described species. We found that relatively young species of the E. affinis complex are different from each other in the CO1 and nITS genes, but not in the conservative 18SrRNA nuclear gene. Nucleotide differences among affinis-group species in the CO1 gene are 9.4-11.8%; in the nITS genes, 1.1-5.0%. At the same time, all other studied Eurytemora species have significant differences from each other in the CO1 and nITS genes, as well as in 18SrRNA. The level of differences among the species is 13.2-19.2% for the CO1 gene, 18.0-27.6.2% for nITS genes, and 0.4-1.8% for the 18SrRNA gene.

In: Crustaceana