10:15 AM - 10:30 AM
[BCG07-06] Morphological identification of cryptic species in a planktic foraminifer
Keywords:Pulleniatina obliquiloculata, cryptic species, morphometrics, genetic type, planktic foraminifers
Planktic foraminifers have been traditionally classified based on morphology of test. These morphological species are widely used as indicators for the past and present marine environments due to their specific geographical distribution associating with ecological characteristics. However, these classification methods have led to argument that morphological plasticity was involved in species traits. Molecular phylogenetic studies have revealed that a morphospecies is a complex of multiple biological species (genetic types), each of which exhibits distinct geographic distribution and ecological differences. These new knowledges genetic types have been incorrectly sorted as previous ecophenotypes, though most genetic types have not been morphologically identified. This study addressed morphometric analyses to distinguish morphological traits of biological species from ecophenotypic variations by using the three known genetic types of Pulleniatina obliquiloculata.
Living specimens of P. obliquiloculata were collected from two areas: the central Pacific and the Tosa Bay. We employed the GITC* method, which can preserve calcium carbonate tests after DNA extraction, to analyze both genetic type and morphological characteristics on a same specimen. Each of DNA samples was applied to Restriction Fragment Length Polymorphism (RFLP) and molecular phylogenetic analyses after amplification of the partial small subunit ribosomal DNA (SSU rDNA). The test was measured at the aperture side using a digital microscope and the 3D tomography of the test was reconstructed using the convolution back projection methos based on the measurement of the micro-focus X-ray computed tomography. The two out of three genetic types were found in each area: Types I and IIa were found in the central Pacific and Types I and IIb in the Tosa Bay, based on the RFLP and molecular phylogenetic analyses. The eight morphological parameters, reconstructed using the 2D and 3D morphometric measurements, were selected to determine morphological differences among the three genetic types. However, four parameters showed significant differences between two populations of Type I in the central Pacific and the Tosa Bay probably due to phenotypic plasticity. On the other hand, the other four parameters: test shape, aspect ratio of the aperture, aperture size and test thickness, showed significant differences among the three genetic types regardless of sampling locations. The morphology of Type IIb test is characteristics of elliptical shape with a large aperture. The test thickness of IIa is the largest followed by Type I and IIb. Thus, these four parameters allow for the classification of P. obliquiloculata genetic types based on test morphology. Morphometric approaches enable us to statistically evaluate morphological traits of biological species and is applicable to fossil specimens, which lack DNA information. This method could be contributed on future studies to understand the evolution of planktic foraminifers as well as to establish a precise environmental indicator at biological species level.
Living specimens of P. obliquiloculata were collected from two areas: the central Pacific and the Tosa Bay. We employed the GITC* method, which can preserve calcium carbonate tests after DNA extraction, to analyze both genetic type and morphological characteristics on a same specimen. Each of DNA samples was applied to Restriction Fragment Length Polymorphism (RFLP) and molecular phylogenetic analyses after amplification of the partial small subunit ribosomal DNA (SSU rDNA). The test was measured at the aperture side using a digital microscope and the 3D tomography of the test was reconstructed using the convolution back projection methos based on the measurement of the micro-focus X-ray computed tomography. The two out of three genetic types were found in each area: Types I and IIa were found in the central Pacific and Types I and IIb in the Tosa Bay, based on the RFLP and molecular phylogenetic analyses. The eight morphological parameters, reconstructed using the 2D and 3D morphometric measurements, were selected to determine morphological differences among the three genetic types. However, four parameters showed significant differences between two populations of Type I in the central Pacific and the Tosa Bay probably due to phenotypic plasticity. On the other hand, the other four parameters: test shape, aspect ratio of the aperture, aperture size and test thickness, showed significant differences among the three genetic types regardless of sampling locations. The morphology of Type IIb test is characteristics of elliptical shape with a large aperture. The test thickness of IIa is the largest followed by Type I and IIb. Thus, these four parameters allow for the classification of P. obliquiloculata genetic types based on test morphology. Morphometric approaches enable us to statistically evaluate morphological traits of biological species and is applicable to fossil specimens, which lack DNA information. This method could be contributed on future studies to understand the evolution of planktic foraminifers as well as to establish a precise environmental indicator at biological species level.