Morphology of lentic and lotic tadpoles from Madagascar

Background The morphology of anuran larvae is suggested to differ between species with tadpoles living in standing (lentic) and running (lotic) waters. To explore which character combinations within the general tadpole morphospace are associated with these habitats, we studied categorical and metric larval data of 123 (one third of which from lotic environments) Madagascan anurans. Results Using univariate and multivariate statistics, we found that certain combinations of fin height, body musculature and eye size prevail either in larvae from lentic or lotic environments. Conclusion Evidence for adaptation to lotic conditions in larvae of Madagascan anurans is presented. While lentic tadpoles typically show narrow to moderate oral discs, small to medium sized eyes, convex or moderately low fins and non-robust tail muscles, tadpoles from lotic environments typically show moderate to broad oral discs, medium to big sized eyes, low fins and a robust tail muscle.

One pair of motor neurons provokes early spontaneous motor behavior through periodic bursting in the chordate ascidian embryo

Swimming aquatic animals exhibit spontaneous motor behaviors before the maturation of swimming locomotion. In this study, we demonstrated that a single pair of motor neurons, A10.64/MN2, which exhibits periodic bursting, is essential for early spontaneous motor behaviors in the invertebrate chordate Ciona intestinalis type A (Ciona robusta). The Ca2+ oscillation was first observed only in a pair of cells at mid tailbud II (St.22) with an 80-sec interval, which shortened to 25 sec at late tailbud II (St.24). A dissociation experiment revealed that the Ca2+ oscillation occurred in a single cell independently. The start of the Ca2+ oscillation coincided with the Ca2+ elevation in ipsilateral tail muscle cells at late tailbud I (St.23). Cell lineage tracking revealed that a pair of cells exhibiting Ca2+ oscillation corresponded to A10.64/MN2 motor neurons. Simultaneous imaging of Ca2+ and membrane potential demonstrated that the Ca2+ oscillation coupled with a burst firing of membrane potential. Interestingly, the number and frequency of tail muscle contractions initially coincided with those of the burst, but gradually came to coincide with those of spikes in the burst as the embryos developed toward late tailbud II (St.24). Finally, single-cell photoablation of A10.64/MN2 abolished early spontaneous motor behaviors until late tailbud II (St.24), suggesting that the early spontaneous motor behavior of Ciona is directly regulated by only a single pair of A10.64/MN2 motor neurons. These findings revealed that the chordate early spontaneous motor behavior was generated by a minimum motor circuit, consisting of a pair of motor neurons exhibiting periodic bursting.Significance StatementThe ascidian provides insights into formation of chordate motor neural circuits that generate early spontaneous motor behavior. Whole-body Ca2+ imaging revealed that a pair of motor neurons exhibit spontaneous Ca2+ oscillation coinciding with Ca2+ elevation in tail muscle cells at a later stage. The cell lineage of the neuron exhibiting Ca2+ oscillation was identified as a motor neuron, A10.64/MN2. In this study, we emphasize that only one pair of motor neurons firstly exhibit rhythmic activity and directly triggers early spontaneous motor behavior. These findings markedly improve our understanding of the development of chordate motor neural circuits involved in early spontaneous motor behavior.

Microcystins in European Noble Crayfish Astacus astacus in Lake Steinsfjorden, a Planktothrix-Dominated Lake

Lake Steinsfjorden, an important Norwegian location for noble crayfish (Astacus astacus), is often affected by cyanobacterial blooms caused by microcystin (MC)-producing Planktothrix spp. The impact of MCs on noble crayfish as a food source and crayfish health is largely unknown. We investigated the quantities and correlations of MCs in noble crayfish and lake water during and after a cyanobacterial bloom peaking in June–July 2015. Noble crayfish and water samples were collected monthly from June to October 2015 and in October 2016. The content of MCs was analysed by ELISA from tail muscle, intestine, stomach and hepatopancreas. PCR analysis for Planktothrix gene markers was performed on crayfish stomach content. Water samples were analysed for phytoplankton composition, biomass and MCs. PCR-positive stomach contents indicated Planktothrix to be part of the noble crayfish diet. Concentrations of MCs were highest in the hepatopancreas, stomach and intestine, peaking in August–September. Tail muscle contained low concentrations of MCs. Similar levels of MCs were found in crayfish from 2016. Except in September 2015, a normal portion of boiled noble crayfish tails was below the tolerable daily intake (TDI) for MCs for humans. Removing the intestine more than halved the content of MCs and seems a reasonable precautionary measure for noble crayfish consumers.

Marked variations in gut microbiota and some innate immune responses of fresh water crayfish, marron (Cherax cainii, Austin 2002) fed dietary supplementation of Clostridium butyricum

This study aimed to investigate the effects of Clostridium butyricum as a dietary probiotic supplement in fishmeal based diet on growth, gut microbiota and immune performance of marron (Cherax cainii). Marron were randomly distributed into two different treatment groups, control and probiotic fed group. After 42 days of feeding trial, the results revealed a significant (P < 0.05) increase in growth due to increase in number of moults in marron fed probiotics. The probiotic diet also significantly enhanced the total haemocyte counts (THC), lysozyme activity in the haemolymph and protein content of the tail muscle in marron. Compared to control, the 16S rRNA sequences data demonstrated an enrichment of bacterial diversity in the probiotic fed marron where significant increase of Clostridium abundance was observed. The abundance for crayfish pathogen Vibrio and Aeromonas were found to be significantly reduced post feeding with probiotic diet. Predicted metabolic pathway revealed an increased activity for the metabolism and absorption of carbohydrate, degradation of amino acid, fatty acid and toxic compounds, and biosynthesis of secondary metabolites. C. butyricum supplementation also significantly modulated the expression level of immune-responsive genes of marron post challenged with Vibrio mimicus. The overall results suggest that C. butyricum could be used as dietary probiotic supplement in marron aquaculture.