Unraveling the Evolutionary Patterns of Genus Frontonia: An Integrative Approach with Morphological and Molecular Data

Abstract

Simple Summary: Ciliates, particularly the genus Frontonia, have been studied to understand their evolutionary history, but challenges remain. This study investigated the evolutionary patterns of Frontonia using genetic and morphological data. Molecular analysis of the SSU rRNA gene revealed four major phylogenetic groups within Frontonia, suggesting its paraphyly. The common ancestor existed approximately 420 million years ago, with distinct groups emerging during the Mesozoic era. Diversification analysis showed higher extinction rates than speciation rates within the genus. Morphological traits, including habitat adaptations, were examined through ancestral state reconstructions, revealing a complex evolutionary history. Habitat transitions were not directly linked to morphological traits such as contractile vacuoles, emphasizing the role of genetic diversity and environmental adaptation. These findings provide valuable insights into the interplay between evolution, extinction, and morphology in ciliates, advancing our understanding of biodiversity and evolutionary biology. Ciliates of the genus Frontonia have been extensively studied to resolve their phylogenetic and evolutionary history, but challenges remain. This study used molecular analyses of SSU rRNA genes, phylogenetic tree reconstruction, molecular dating, and diversification analysis, together with ancestral state reconstruction of morphological traits and habitat preferences. Data included newly sequenced Korean species, GenBank records and published morphological information. Phylogenetic trees revealed paraphyly within Frontonia, identifying four groups that emerged in the Mesozoic era: Group I (similar to 172 mya), Group II (similar to 83 mya), Group III (similar to 115 mya), and Group IV (similar to 190 mya), with a common ancestor dating to similar to 420 mya in the Palaeozoic era. Diversification analysis revealed higher extinction rates (0.826 and 0.613 species/year) than speciation rates (0.011 and 0.016 species/year). Morphological evolution showed habitat adaptation and plasticity, with habitat transitions unrelated to contractile vacuolar traits. The SSU rRNA gene polymorphism likely contributed to the paraphyletic state of Frontonia. These results highlight the complex evolutionary patterns of the genus, shaped by genetic diversity, morphology, and environmental constraints