Barnacles are special crustaceans usually enclosed by calcareous plates, and attach themselves firmly to marine substrates such as rocks, boats, and other animals.
They are a unique group that has evolved in parallel identical somatotypes (sessile, stalked and asymmetric) in both normal and chemosynthetic environments.
Recently, a research team led by Prof. LI Xinzheng from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) performed a comprehensive mitogenomic analysis to explore the evolutionary history of barnacle, and to characterize the genetic adaptive features of barnacles which live in the harsh marine chemosynthetic habitat.
The study was published in Frontiers in Marine Science on Sept. 15.
The phylogenetic inferences and topology test demonstrated the common origination of pollicipedids, calanticids and balanomorphs. However, phylogenetic, morphological and fossil evidences indicate an alternative origin for verrucomorphs, namely they might originate from archaeolepadomorphs at the upper Triassic (225 million years ago).
Two distinct barnacle lineages inhabiting chemosynthetic habitat were recovered based on the mitochondrial genome data, indicating that barnacles have colonized deep-sea chemosynthetic habitat at least twice in history.
Selective pressure analyses show that both two lineages had undergone relatively high selective pressures when their ancestors colonized the chemosynthetic biotope. But the specific selective sites of these two lineages were various. This phenomenon reveals that genomic response to environmental change not only depends on external factors but also relates to themselves.
The researchers found that the divergence times of chemosynthetic lineages occurred just posterior to the Cretaceous-Paleogene mass extinction and Cenomanian/Turonian oceanic anoxic event. These events had greatly reduced the diversity of marine organisms, so a lot of ecological niches would have been created following these events.
"Combined with our results, we speculate that ecological niche vacancy, sitotaxis, and gene specificity in adaptive stress responses contribute to the origin and diversification of barnacles in chemosynthetic ecosystems," said GAN Zhibin, first author of the study.
"Our study outlines a credible evolutionary history for barnacle lineages, especially for the chemosynthetic lineages, and provides new insights into the phylogeny of barnacle. It is furthermore confirmed that the evolution of animal is promoted by multiple factors," said Prof. LI.
