Microchemical Analyses of Otoliths Reveal Habitat Differentiation Between a Sympatric Species Pair in the Coastal Waters of China

While secondary contact between distant lineages or sister species is a common evolutionary outcome, the factors that promote their coexistence are often unknown, especially for marine species. Focusing on two sister fish species from the East China Sea, Bostrychus donghaiensis and B. sinensis , it was assessed whether they differ in microhabitat use and life history using otoliths. Morphological data were used to test for phenotypic differences in otolith morphology between the focal species and employed laser ablation inductively coupled plasma mass spectrometry to measure microchemical changes throughout their life history. The study revealed that otolith shapes not only differ between the two species, but also between B. sinensis individuals from within and outside the contact zone. This was further supported by the microchemical analysis, indicating that both B. donghaiensis and B. sinensis from outside the contact zone primarily inhabit high salinity environments throughout their entire life history without migration. In contrast, B. sinensis from the contact zone migrates to estuaries of lower salinity during the breeding season. Overall, these findings highlight the importance of habitat changes in limiting niche competition, contributing to the understanding of life history processes of species during secondary contact.