The highly-connected marine habitats have nurtured extremely rich biodiversity. Therefore, marine organisms challenge the classical theories of local adaptation and speciation, dubbed as the "marine speciation paradox".

Recently, researchers led by Prof. LIN Qiang from the South China Sea Institute of Oceanology (SCSIO) of the Chinese Academy of Sciences revealed how ecological specialization arises in widely distributed marine species with integrated analysis of morphological, genetic and ecological data.

Their findings were published in Diversity and Distributions on May 4.

The researchers investigated the cranial morphology, genetic structure and ecological niche of S. schlegeli along Chinese seashores to reveal their phylogeographical patterns.

Ecological niche characterization with hypervolumes indicated that the three clades (Yellow Sea clade, East China Sea clade, and South China Sea clade) diverged in their realized niches across their distribution range, and the genetic results also showed three distinct clusters that represent three geographical lineages.

Habitat suitability projections for this species showed a clear geographical separation between south and north populations during the Last Glacial Maximum, which may lead to the genetic split between ECS-YS (East China Sea and Yellow Sea) and SCS (South China Sea) lineages.

In addition, identification of genes under natural selection is important to determine the genetic basis of local adaptation affecting fitness traits development and population divergence, and many key genes are involved in growth (pax7), cold adaptation (csde1) and eye development (eys, rx3).

This study will help to better understand the differentiation of marine fish populations, and also provide new insight into the studies of distribution, dispersal, and speciation of marine species.