10 research outputs found
Ct, number of cells and grazing rate of Rhodomonas balthica, Isochrysis galbana and Thalassiosira weissflogii in Acartia tonsa gut content after grazing experiment
Grazing experiment with Acartia tonsa
Marine copepods provide the major food-web link between primary producers and higher trophic levels, and their feeding ecology is of acute interest in light of global change impacts on food-web functioning. Recently, quantitative polymerase chain reaction (qPCR) protocols have been developed, which can complement classic diet quantification methods, such as stable isotope or fatty acid analyses tools. Here, we present first results of feeding experiments assessing sex- and stage-specific food intake by the ubiquitous calanoid copepod Acartia tonsa by 18S targeted qPCR and microscopic grazing assessment. In triplicated mixed-diet feeding treatments, three suitable A. tonsa diets, the cryptophyte Rhodomonas balthica, the haptophyte Isochrysis galbana, and the diatom Thalassiosira weissflogii, were offered in equal biomass proportions under constant conditions. Prey uptake substantially varied between different algal species, as did the extent of sex- and stage-specificity of prey uptake. Male adult copepods had higher R. balthica gut contents than females, and nauplii contained more of this prey source than copepodites or adult copepods in mixed treatments. A trend towards higher amounts of ingested T. weissflogii in adult females than in males and in nauplii than in other stages was detected. Genetic gut content quantifications indicated low feeding on I. galbana, and no consistent sex- or stage-specific differences of I. galbana content in A. tonsa. Our results highlight diet-specific feeding differences between Acartia life stages and sexes, which can have implications on food-web dynamics and specific nutrient transfer to higher trophic levels in copepod populations of varying age composition under changing environmental parameters, such as rising temperatures and increasing ocean acidification
Cell counts of Rhodomonas balthica, Isochrysis galbana and Thalassiosira weissflogii in Acartia tonsa gut content after grazing experiment
First genetic quantification of sex- and stage-specific feeding in the ubiquitous copepod Acartia tonsa
Marine copepods provide the major food-web link between primary producers and higher trophic levels, and their feeding ecology is of acute interest in light of global change impacts on food-web functioning. Recently, quantitative polymerase chain reaction (qPCR) protocols have been developed, which can complement classic diet quantification methods, such as stable isotope or fatty acid analyses tools. Here, we present first results of feeding experiments assessing sex- and stage-specific food intake by the ubiquitous calanoid copepod Acartia tonsa by 18S targeted qPCR and microscopic grazing assessment. In triplicated mixed-diet feeding treatments, three suitable A. tonsa diets, the cryptophyte Rhodomonas balthica, the haptophyte Isochrysis galbana, and the diatom Thalassiosira weissflogii, were offered in equal biomass proportions under constant conditions. Prey uptake substantially varied between different algal species, as did the extent of sex- and stage-specificity of prey uptake. Male adult copepods had higher R. balthica gut contents than females, and nauplii contained more of this prey source than copepodites or adult copepods in mixed treatments. A trend towards higher amounts of ingested T. weissflogii in adult females than in males and in nauplii than in other stages was detected. Genetic gut content quantifications indicated low feeding on I. galbana, and no consistent sex- or stage-specific differences of I. galbana content in A. tonsa. Our results highlight diet-specific feeding differences between Acartia life stages and sexes, which can have implications on food-web dynamics and specific nutrient transfer to higher trophic levels in copepod populations of varying age composition under changing environmental parameters, such as rising temperatures and increasing ocean acidification
Recommended from our members
Sex steroid dynamics and mRNA transcript profiles of growth- and development-related genes during embryogenesis following induced follicular maturation in European eel
Hormones and mRNA transcripts of maternal origin deposited in the egg may affect early embryonic development in oviparous species. These hormones include steroids, such as estradiol-17β (E2), testosterone (T), 11-ketotestosterone (11-kt), 17α,20ß-dihydroxy-4-pregnen-3-one (DHP), and cortisol, which also play an important role in fish reproduction. In European eel, Anguilla anguilla, which does not reproduce naturally in captivity, vitellogenesis in female broodstock is commonly induced by administration of salmon or carp pituitary extract (PE) as an exogenous source of gonadotropins, while follicular maturation is stimulated by a priming dose of PE followed by provision of DHP as a maturation inducing hormone. In this regard, the main purpose of the present study was to evaluate effects of induced follicular maturation on reproductive success in European eel, focusing on maternal transfer and dynamics of steroids and mRNA transcripts of growth- and development-related genes throughout embryogenesis. The results showed that maternal blood plasma concentrations of E2, T and DHP were reflected in the unfertilized eggs. Moreover, a negative relationship between concentrations of E2 and DHP in eggs and embryos and quality parameters measured as fertilization success, cleavage abnormalities, embryonic survival, and hatch success was found. Concomitant mRNA transcript abundance analysis including genes involved in stress response (hsp70, hsp90), somatotropic axis (gh, igf1, igf2a, igf2b), lipid (cpt1a, cpt1b, pigf5) and thyroid metabolism (dio1, dio2, dio3, thrαb, thrβa, thrβb) varied among unfertilized egg batches. For the majority of genes, mRNA abundance increased during the maternal-to-zygotic transition in connection to activation of the transcription of the embryos own genome. mRNA abundance of dio1, cpt1a and cpt1b throughout embryogenesis was related to embryonic developmental competence. Notably, mRNA abundance of dio3 was positively associated with E2 concentrations, while the mRNA abundance of thrαb was negatively related to T concentrations in the unfertilized eggs, which may suggest an interaction between the thyroid and steroid hormone systems. Altogether, maternal plasma concentrations of E2 and DHP were reflected in the eggs, with high concentrations of these steroids in the eggs being negatively associated with embryonic developmental competence. Additionally, high transcript levels of two of the investigated genes (dio1, cpt1b) were positively associated with embryonic developmental competence. This study reveals maternal transfer of steroids and mRNA transcripts to the eggs, which may be significant contributors to the variability in embryonic survival observed in European eel captive reproduction
Recommended from our members
Differential impacts of carp and salmon pituitary extracts on induced oogenesis, egg quality, molecular ontogeny and embryonic developmental competence in European eel
Low egg quality and embryonic survival are critical challenges in aquaculture, where assisted reproduction procedures and other factors may impact egg quality. This includes European eel (Anguilla anguilla), where pituitary extract from carp (CPE) or salmon (SPE) is applied to override a dopaminergic inhibition of the neuroendocrine system, preventing gonadotropin secretion and gonadal development. The present study used either CPE or SPE to induce vitellogenesis in female European eel and compared impacts on egg quality and offspring developmental competence with emphasis on the maternal-to-zygotic transition (MZT). Females treated with SPE produced significantly higher proportions of floating eggs with fewer cleavage abnormalities and higher embryonic survival. These findings related successful embryogenesis to higher abundance of mRNA transcripts of genes involved in cell adhesion, activation of MZT, and immune response (dcbld1, epcam, oct4, igm) throughout embryonic development. The abundance of mRNA transcripts of cldnd, foxr1, cea, ccna1, ccnb1, ccnb2, zar1, oct4, and npm2 was relatively stable during the first eight hours, followed by a drop during MZT and low levels thereafter, indicating transfer and subsequent clearance of maternal mRNA. mRNA abundance of zar1, epcam, and dicer1 was associated with cleavage abnormalities, while mRNA abundance of zar1, sox2, foxr1, cldnd, phb2, neurod4, and neurog1 (before MZT) was associated with subsequent embryonic survival. In a second pattern, low initial mRNA abundance with an increase during MZT and higher levels persisting thereafter indicating the activation of zygotic transcription. mRNA abundance of ccna1, npm2, oct4, neurod4, and neurog1 during later embryonic development was associated with hatch success. A deviating pattern was observed for dcbld1, which mRNA levels followed the maternal-effect gene pattern but only for embryos from SPE treated females. Together, the differences in offspring production and performance reported in this study show that PE composition impacts egg quality and embryogenesis and in particular, the transition from initial maternal transcripts to zygotic transcription