Morphological variation in the porcelaneous benthic foraminifer Quinqueloculina seminula (Linnaeus, 1758): Genotypes or Morphotypes? A detailed morphotaxonomic, molecular and ecological investigation

Abstract

Quinqueloculina seminula (Linnaeus, 1758) is a common porcelaneous benthic foraminifer and plays a crucial role in biomonitoring assessment and palaeoenvironmental reconstruction. However, high morphological variability within the species and the long list of synonymy has resulted in confused taxonomy that to date remains unresolved. Moreover, the lack of clearly defined morpho-taxonomic criteria led to a great confusion concerning the discrimination of Quinqueloculine and Triloculine tests. This study provides the first ribosomal DNA sequences of Q. seminula complemented with the detailed morphological and ecological investigation, based on material collected from an intertidal region along the Rajapuri creek, Maharashtra coast, north-eastern Arabian Sea. By analysing the characteristic morphological features, i.e., number of chambers, and length: width ratio, the specimens were sorted into different morpho-groups viz. juvenile (resembling Triloculina) and the typical adult forms. The genetic analysis utilising partial small subunit ribosomal DNA (18S rDNA) showed that all morphotypes of Q. seminula from the studied site branches within a single clade significantly differ from the sequences of Q. seminulum, suggesting a putative novel adaptation to different ecological conditions. Our results are in contrast with the assumption that all ecophenotypes of Q. seminula represent a genetically continuous species with a unique habitat and widespread biogeographic distribution. Our environmental investigation further indicates that the species favours intertidal hypersaline conditions, and seasonal distribution pattern shows a positive correlation with the salinity and temperature.