Effects of reduced salinities on metamorphosis of a freshwater-tolerant sesarmid crab, Armases roberti: Is upstream migration in the megalopa stage constrained by increasing osmotic stress?

Numerous species of estuarine and freshwater-tolerant crabs show an export strategy, i.e. an early larval downstream transport towards coastal marine waters, later zoeal development at higher salinities, and a return of the last larval stage, the megalopa, into estuaries or rivers. The speed and extent of the upstream migration of the megalopa through strong salinity gradients may be constrained by increasing hypo-osmotic stress. In an experimental laboratory study with Armases roberti, a freshwater-inhabiting sesarmid crab from the Caribbean region, we studied in the megalopa stage (after zoeal rearing at 25) the tolerance of reduced salinities. In the first experiment, the larvae were exposed directly to various constant salinities (125). For the second experiment, they were transferred stepwise to strongly diluted media (within 6 days from 25 to ≤3), simulating differential scenarios of upstream migration into brackish or freshwater habitats. When postmoult megalopae were exposed directly to salinities ≤3, they all died within 24 h. A slightly higher salt concentration (5), however, allowed for considerable survival (46%) through metamorphosis to the first juvenile crab stage. In treatments with continuous exposure to 1015, as well as in a control group (25), survival to metamorphosis was significantly higher (8396%), and the average duration of development was shorter compared to 5 (1213 vs. 16 days). In the second experiment, with stepwise salinity reductions, gradual acclimation to decreasing osmotic pressures permitted a successful development to metamorphosis at ≤3 and even in freshwater (b0.2). This strong physiological adaptability enables the megalopa of A. roberti to cross during its upstream migration, within a short time (6 days), strong osmotic gradients, so that metamorphosis is possible also in freshwater habitats where the conspecific adult crabs live. The speed of migration appears to be limited by physiological constraints related to changes in the capability for osmoregulation occurring during the course of the moulting cycle

New Targeted Approaches for Epigenetic Age Predictions

AbstractAging causes epigenetic modifications, which are utilized as a biomarker for the aging process. While genome-wide DNA methylation profiles enable robust age-predictors by integration of many age-associated CG dinucleotides (CpGs), there are various alternative approaches for targeted measurements at specific CpGs that better support standardized and cost-effective high-throughput analysis. In this study, we utilized 4,650 Illumina BeadChip datasets of blood to select the best suited CpG sites for targeted analysis. DNA methylation analysis at these sites with either pyrosequencing or droplet digital PCR (ddPCR) revealed a high correlation with chronological age. In comparison, bisulfite barcoded amplicon sequencing (BBA-seq) gave slightly lower precision at individual CpGs. However, BBA-seq data revealed that the correlation of methylation levels with age at neighboring CpG sites follows a bell-shaped curve, often accompanied by a CTCF binding site at the peak. We demonstrate that within individual BBA-seq reads the DNA methylation at neighboring CpGs is not coherently modified but reveals a stochastic pattern. Based on this, we have developed an alternative model for epigenetic age predictions based on the binary sequel of methylated and non-methylated sites in individual reads, which reflects heterogeneity in epigenetic aging within a sample. Thus, the stochastic evolution of age-associated DNA methylation patterns, which seems to resemble epigenetic drift, enables epigenetic clocks for individual DNA strands.</jats:p