Ontogenetic changes in the salinity tolerance and ionoregulatory plasticity in mummichog (Fundulus heteroclitus)

Abstract

Mummichogs (Fundulus heteroclitus) exhibit a remarkable euryhaline capacity in adulthood, attributed to their highly plastic ionoregulatory mechanisms. Although adult mummichogs are highly tolerant of varying salinities, early developmental stages exhibit reduced tolerance, and the mechanisms underlying this ontogenetic difference remain unclear. My thesis aimed to understand the relationship between salinity tolerance and ionoregulatory plasticity during early development. I identified specific developmental stages at which salinity tolerance changes, with freshwater tolerance appearing after hatch and hypersaline tolerance developing later. I also determined that reduced freshwater tolerance in embryos coincided with limited ionoregulatory plasticity, reflected by reduced transcriptional responses to salinity challenges. These differences are also evident in a reduced capacity of embryos to maintain ion content across different salinities compared to larvae. Overall, I linked the reduced salinity tolerance during early development to a lower degree of ionoregulatory capacity, a novel finding in this area of research.