Evangelia Michaloudi

The zooplankton of Lake Mikri Prespa

A study from June 1990 to October 1992 revealed thatthe pelagic zooplankton community of Lake Mikri Prespaconsists of 45 invertebrate species (28 Rotifera, 11Cladocera, 6 Copepoda and 1 mollusc). It includes A. steindachneri, an endemic calanoid of the WesternBalkans. Half of the species are first records for thelake.The total abundance and biomass ranged from 61 to 905 indl−1 and 58 to 646 µg l−1,respectively. Seasonal fluctuations agreed with thePEG-model. Copepods prevailed throughout the year. Thespecies composition and seasonal variability wereaffected by temperature-dependent food conditions,competition and predation. These factors induced aseasonal succession which involved a replacement oflarger species or individuals by smaller ones duringsummer. The cladoceran population, as a whole, wascharacterised by small size classes of the speciespresent, probably due to fish predation. Anexamination of the horizontal distribution showedthat, although seasonal variability was the same atall stations sampled, the central station showedhigher abundance. Inshore-offshore diel migrations ofjuvenile fish is considered to account for this unevendistribution. Shannon‘s diversity index ranged from0.98 to 2.95 and evenness from 0.3 to 0.9. Both wereinfluenced by temperature.

Integrative Taxonomy Recognizes Evolutionary Units Despite Widespread Mitonuclear Discordance: Evidence from a Rotifer Cryptic Species Complex

Mitonuclear discordance across taxa is increasingly recognized as posing a major challenge to species delimitation based on DNA sequence data. Integrative taxonomy has been proposed as a promising framework to help address this problem. However, we still lack compelling empirical evidence scrutinizing the efficacy of integrative taxonomy in relation to, for instance, complex introgression scenarios involving many species. Here, we report remarkably widespread mitonuclear discordance between about 15 mitochondrial and 4 nuclear Brachionus calyciflorus groups identified using different species delimitation approaches. Using coalescent-, Bayesian admixture-, and allele sharing-based methods with DNA sequence or microsatellite data, we provide strong evidence in support of hybridization as a driver of the observed discordance. We then describe our combined molecular, morphological, and ecological approaches to resolving phylogenetic conflict and inferring species boundaries. Species delimitations based on the ITS1 and 28S nuclear DNA markers proved a more reliable predictor of morphological variation than delimitations using the mitochondrial COI gene. A short-term competition experiment further revealed systematic differences in the competitive ability between two of the nuclear-delimited species under six different growth conditions, independent of COI delimitations; hybrids were also observed. In light of these findings, we discuss the failure of the COI marker to estimate morphological stasis and morphological plasticity in the B. calyciflorus complex. By using B. calyciflorus as a representative case, we demonstrate the potential of integrative taxonomy to guide species delimitation in the presence of mitonuclear phylogenetic conflicts.

Feeding and predation impact of chaetognaths in the north Aegean Sea (Strymonikos and Ierissos Gulfs)

The feeding of the most important chaetognath species (Sagitta eqflata, Sagitta minima, Sagitta setosa and Sagitta serratodentata) found in a grid of 35 stations in the north Aegean Sea (Strymonikos and Ierissos Gulfs) was investigated through gut content analysis during five sampling periods from June 1997 to May 1998. Sagitta enflata and S. minima were the most abundant species in summer autumn 1997 and in spring 1998, respectively. Copepods were the main food for all chaetognath species in spring 1998, while cladocerans in summer autumn 1997 dominated the diet, especially of S. enflata. In September 1997, the juvenile specimens of cladocerans were the most important prey of the immature Stage I specimens of S. enflata. which resulted from the major breeding period in late summer. The estimated impact of chaetognath predation on the copepod and cladoceran communities ranged between 0.02 2.76% and 0.01 1.29% of the copepod and cladoceran standing stock, respectively. Stage 1 specimens of S. enflata accounted for nearly 90% of the total copepod and cladoceran standing stock consumed per day by the total population of this species in September 1997.

Morphological and taxonomic demarcation of Brachionus asplanchnoidis Charin within the Brachionus plicatilis cryptic species complex (Rotifera, Monogononta)

Three well-defined groups, consisting of 15 species, have recently been ascribed to organisms historically identified as the Brachionus plicatilis species complex. One of these groups, the large clade, is composed of two named species (Brachionus plicatilis s.s. and Brachionus manjavacas) and two species identifiers (B. ‘Nevada’ and B. ‘Austria’). B. ‘Austria’ has been confirmed to be B. asplanchnoidis. As no type specimen exists for this species, and the original taxonomic description is lacking in detail, we give a detailed account of this species using material from Obere Halbjochlacke in Austria where B. ‘Austria’ was first identified genetically. Our analysis of B. asplanchnoidis populations was of global scope, an approach that revealed a great degree of morphological variability. However, combining aspects of both the dorsal and ventral surfaces clearly discriminated B. asplanchnoidis from the rest of the large-type members. This approach may prove useful in taxonomic studies of other cryptic species with relatively few morphological features. We also observed a geographic pattern of genetic divergence within B. asplanchnoidis. Average uncorrected COI divergences for a 554-bp fragment of the COI gene ranged from 3.9% within species to 17.5% between species of the large clade and indicate deep divisions within the cryptic species complex.

Reverse taxonomy applied to the Brachionus calyciflorus cryptic species complex: Morphometric analysis confirms species delimitations revealed by molecular phylogenetic analysis and allows the (re)description of four species

The discovery and exploration of cryptic species have been profoundly expedited thanks to developments in molecular biology and phylogenetics. In this study, we apply a reverse taxonomy approach to the Brachionus calyciflorus species complex, a commonly studied freshwater monogonont rotifer. By combining phylogenetic, morphometric and morphological analyses, we confirm the existence of four cryptic species that have been recently suggested by a molecular study. Based on these results and according to an exhaustive review of the taxonomic literature, we name each of these four species and provide their taxonomic description alongside a diagnostic key.

Period of public commentary begins on the revised proposal of species-group level names, and on the proposal of genus-group level names of the Candidate Part of List of Available Names (LAN) in the phylum Rotifera

Following ICZN (1999) Article 79 Chapter 17 http://www.nhm.ac.uk/hosted-sites/iczn/code/), we, with the full support of the international community of rotifer researchers as expressed during subsequent international Rotifera symposia, developed a Candidate Part of the List of Available Names for species and genera of Rotifera from the start of zoological nomenclature to the year 2000.