The core story: intertwined maternal and progeny signatures enclosed in the otolith.

synchrotron-XRF spectrometry acquisition hyperspectral dataset (.h5) and R script Analytical imaging via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We undertook a hyperfine elemental scanning of a 25 μm diameter length area centred on the core, namely the pre-hatch zone, corresponding to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co) and nickel (Ni) and sulphur (S), the latter to count growth increments. Whatever the species, a Ca pit consistently marked the core; the amphidromous species exhibited Mn enrichment at the core and the sagitta forms a week before hatching. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signal in the pre-hatch zone were compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. We found that Co and Ni otolith signals had no relation to environmental conditions, but 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 that potentially trigger newly hatched juvenile migration to sea or residency. Our results demonstrate that the microchemistry of otolith forming 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.

本数据集包含同步辐射X射线荧光光谱法（synchrotron-XRF spectrometry）采集的高光谱数据集（格式为.h5）及配套R脚本（R script）。本研究采用同步辐射成像分析技术，对4种具有溯洄性（amphidromous）或淡水定居型生活史的淡水海龙属物种的矢状耳石（sagittal otoliths）开展研究。我们以耳石核心——即胚胎发生期（embryogenesis）形成的矢状体的孵化前区域——为中心，对直径25μm的长度区域开展超高精度元素扫描。本次分析涵盖的元素包括钙（Ca）、锶（Sr）、锰（Mn）、铬（Cr）、钴（Co）、镍（Ni）与硫（S），其中硫元素用于计数耳石生长纹（growth increments）。无论所属物种为何，耳石核心均存在标志性的钙坑（Ca pit）；溯洄性物种的耳石核心可见锰元素富集，且矢状体在孵化前一周形成。上述结果揭示了保守的耳石形成机制。我们将孵化前区域的锶与重金属信号，与耳石边缘（包含成年淡水环境（adFW）特征的区域）的对应信号进行对比。研究发现，钴与镍的耳石信号与环境条件无显著关联，而铬元素有望作为早期生活环境的标志物开展进一步研究。最后，鉴于核心区域存在钙坑，我们提醒研究者不可直接使用锶钙比进行核心区的生活史（life history）解读，但通过锶信号分析可揭示亲本行为（parental behaviour）的潜在差异，该差异可能是诱导新孵化幼体洄游入海或淡水定居的诱因。本研究结果表明，早期发育阶段形成的耳石微化学组成，综合了卵黄形成期（egg yolk elaboration）的母体信号、卵孵化期（egg incubation）的环境信号以及早期生长阶段的个体生理特征。