Complete mitochondrial genome of Lernaea cyprinacea (Copepoda: Cyclopoida)

New species of Dermoergasilus Ho & Do, 1982 (Copepoda: Cyclopoida: Ergasilidae) parasitizing endemic cichlid Paretroplus polyactis (Bleeker) in Madagascar

Dermoergasilus madagascarensis n. sp. is described from the gills of Paretroplus polyactis, an endemic cichlid fish in Madagascar, using a combined morphological (light microscopy and SEM) and molecular approach (partial 18S rDNA, 28S rDNA, and COI sequences). The new species is characterized mainly by possessing: (i) roughly pentagonal cephalosome; (ii) antennal endopodal segments covered with slightly inflated membrane; (iii) maxillule bearing 2 equally long outer setae and a minute inner seta; (iv) interpodal sternites of swimming legs ornamented with 3–4 rows of spinules; (v) genital segment and first abdominal somite both barrel-shaped; and (vi) a caudal ramus projecting into a digitiform process with inconspicuous terminal seta and bearing 3 terminal setae. The obtained DNA sequences of Malagasy species represent the first molecular data for species of Dermoergasilus. The 28S rDNA phylogeny showed the affiliation of D. madagascarensis n. sp. to Ergasilidae and its sister relationship with cosmopolitan Ergasilus sieboldi von Nordmann, 1832. The first checklist for all species of Dermoergasilus is provided.

Genetic characterisation of four Lamproglena spp. (Copepoda, Lernaeidae) from Africa and the first mitochondrial data

Females of species of Lamproglena von Nordmann, 1832 are parasitic on the gills of teleost fishes and the 38 nominal species are based on mainly morphological data. Only four of these species have been genetically characterised and no mitochondrial data are available for the genus. The present study aimed to provide representative ribosomal DNA (rDNA) data for two additional species of Lamproglena from Africa: Lamproglena clariae Fryer, 1956 and Lamproglena hoi Dippenaar, Luus-Powell et Roux, 2001, alongside mitochondrial DNA (mtDNA) for these and two other African species, Lamproglena hemprichii von Nordmann, 1832 and Lamproglena monodi Capart, 1944. The four species were collected from Clariidae, Cyprinidae, Alestidae and Cichlidae, respectively. Representative 18S rDNA and 28S rDNA data were obtained for L. clariae and L. hoi, while cox1 mtDNA was obtained for all four species. The respective haplotypes supported the distinctness of all species using all three gene regions investigated. Interestingly, species appeared to be grouped more by geographical origin than host family, with L. hoi more closely related to other African species than to Asian species also collected from cyprinid hosts. Even though the results presented here greatly add to the molecular data available for Lamproglena, there are still 32 (>80%) species for which no genetic data are available. The interpretation of the results presented here is thus preliminary and much more data are required before the phylogeny of this genus, and other members of the family, such as Lernaea Linnaeus, 1758, can be studied appropriately.

Immune responses of Cyprinus carpio induced by protein extracts of Lernaea cyprinacea Linnaeus, 1758

Lernaea cyprinacea Linnaeus, 1758 is an ectoparasite showing widespread infections in tropical aquaculture, and the present study aimed to determine the specific immune responses against this parasite. For the experiment, whole parasite extracts were injected intraperitoneally into Cyprinus carpio Linnaeus, 1758, and samples of epidermal mucus and blood were drawn at 0, 1, 7 and 14-days post-injection (DPI). The results revealed high levels of protein, protease and lysozyme activities in the experimental fish which were injected with L. cyprinacea protein extract. In the epidermal mucus, the total protein concentration of the control fish was 460 μg/mL, and the level raised significantly to 800 μg/mL in the experimental fish. The lysozyme activity increased from 741.5 u/mL to a peak level of 1448.5 u/mL at 7DPI. The protease activity was also found elated gradually from 2.91 u/μL to 4.49 u/μL at 1 to 14 DPI. In the serum samples, the protein concentration remained steady throughout the experiment period. However, all the experimental fish displayed statistically high levels of lysozyme and protease activity, from 890 u/mL to 1220 u/mL, and 6.10 u/μL to 11.88 u/μL, respectively. In the whole blood samples, the haemoglobin content and the red blood cells (RBC) count did not show any significant change in any of the experimental groups. But, the percentage of lymphocytes showed a marginal increase from 0.47 to 0.6 in the experimental groups. Overall, the immune responses induced by L. cyprinacea protein extracts depicts a pattern of specific responses, in which the local humoral responses dominate the systemic humoral/cellular response. The results further revealed the possibility of futuristic approaches to control freshwater ectoparasites.

Morphology is not a reliable taxonomic tool for the genus Lernaea: molecular data and experimental infection reveal that L. cyprinacea and L. cruciata are conspecific

Background

Species belonging to the genus Lernaea are cosmopolitan parasites that can infect many different freshwater fish hosts. Due to a high degree of morphological intraspecific variability and high levels of interspecific similarities, their classification is extremely difficult and controversial. Although the suitability of the shape of cephalic horns has been questioned decades ago by some experimental infection studies, this character still plays the central role in the identification of Lernaea spp.

Methods

We used the nominal species Lernaea cyprinacea and Lernaea cruciata to test the hypothesis that the shape of the anchor can exhibit host-induced morphological variability, and that the two taxa may be synonymous.

Results

We examined 517 wild or farmed specimens of five host fish species (four cyprinids and a mosquitofish), and found that all 16 parasite specimens collected from mosquitofish could be morphologically identified as L. cruciata, whereas the remaining 25 parasite specimens were all identified as L. cyprinacea. We experimentally infected goldfish and mosquitofish specimens with offspring (copepodids) of a single L. cyprinacea specimen: the adult parasites from goldfish were morphologically identified as L. cyprinacea, and those from mosquitofish as L. cruciata. We then used molecular data to corroborate that all these specimens are conspecific.

Conclusions

Our results suggest that L. cyprinacea and L. cruciata may be synonyms, misidentified as different species as a result of host-induced morphological variation. Given the current shortage of molecular data for the genus Lernaea, in order to resolve the taxonomy of this genus (determine the exact number of species), future studies should aim to sequence as much molecular data as possible, and conduct further experimental infections.

Mitochondrial genomes of the key zooplankton copepods Arctic Calanus glacialis and North Atlantic Calanus finmarchicus with the longest crustacean non-coding regions

We determined the nearly complete mitochondrial genomes of the Arctic Calanus glacialis and its North Atlantic sibling Calanus finmarchicus, which are key zooplankton components in marine ecosystems. The sequenced part of C. glacialis mitogenome is 27,342 bp long and consists of two contigs, while for C. finmarchicus it is 29,462 bp and six contigs, what makes them the longest reported copepod mitogenomes. The typical set of metazoan mitochondrial genes is present in these mitogenomes, although the non-coding regions (NCRs) are unusually long and complex. The mitogenomes of the closest species C. glacialis and C. finmarchicus, followed by the North Pacific C. sinicus, are structurally similar and differ from the much more typical of deep-water, Arctic C. hyperboreus. This evolutionary trend for the expansion of NCRs within the Calanus mitogenomes increases mitochondrial DNA density, what resulted in its similar density to the nuclear genome. Given large differences in the length and structure of C. glacialis and C. finmarchicus mitogenomes, we conclude that the species are genetically distinct and thus cannot hybridize. The molecular resources presented here: the mitogenomic and rDNA sequences, and the database of repetitive elements should facilitate the development of genetic markers suitable in pursuing evolutionary research in copepods.