The core story: intertwined maternal and progeny signatures enclosed in the otolith - Data collection

Analytical imaging to retrieve biological information from otoliths from the data generated via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We produced hyperfine elemental maps of a 25 μm diameter length area centred on the core, referred to as the pre-hatch zone, as it corresponds to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co) and nickel (Ni), as well as sulphur (S) to count growth increments. Whatever the species, the sagitta forms a week before hatching, a Ca pit consistently marked the core and the amphidromous species exhibited Mn enrichment at the core. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signal in the pre-hatch zone was compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. While Co and Ni seem to mark individual growth processes with no relation to environmental conditions, it is worth looking into Cr as a marker of early-life environment. Finally, while we caution against the use of Sr:Ca ratio for life history interpretations at the core because of the Ca pit, the Sr signal analysis uncovered possible variations in the parental behaviour, potentially playing a role in determining whether the newly hatched juveniles migrate to sea, or not. Our results demonstrate that the microchemistry of otolith that forms during early development is a melting of maternal signal during egg yolk elaboration, of the environmental signal during egg incubation and of individual physiology during early growth.