5:15 PM - 6:45 PM
[BPT02-P10] Morphometric analyses of the test identify cryptic species in a planktic foraminifer
Keywords:planktic foraminifers, morphometrics, genetic type, cryptic species, test size
Planktic foraminiferal species are traditionally classified based on test morphology. Their ecological traits, assigned at each morphospecies, are used as environmental indicators to reconstruct the paleo-environmental changes. On the other hand, molecular phylogeographic studies have discovered high number of biological species (=genetic types) in morphospecies over the world oceans. Many genetic types show the specific pattern in geographic distribution implying that they have ecological differences from one another. The ecological traits of genetic types could be novel environmental indicators in high resolution. However, genetic identification is not applicable to fossil specimens because they lack DNA information. We now need to reassess morphological characters of foraminiferal tests at biological species level. Three genetic types (Types I, IIa, and IIb) of a planktonic foraminifer, Pulleniatina obliquiloculata, diverged according with the development of the tropical oceans in the Pliocene-Pleistocene and showed specific geographic distribution (Ujiié and Ishitani, 2016). Thus, these genetic types could be key indicators for understanding the evolutionary process with the development of the tropical ocean environment. In this study, we challenged to establish morphometric methods for tests of genetic types.
Two populations of P. obliquiloculata collected from the central Pacific (102 specimens) and the Tosa Bay (100 specimens) were used to examine quantitative differences of test morphology between genetic types as well as between locations. We obtained both DNA and test samples from a same specimen and identified its genetic type using RFLP and molecular phylogenetic analysis. Two genetic types were found in each population: Types I and IIa in the central Pacific (Ujiié et al., 2012) and Types I and IIb in the Tosa Bay, respectively. We performed morphological measurement of nine items on the aperture side of the tests. In each population, the test size was significantly different between genetic types: Type IIa was bigger than Type I in the central Pacific and Type I was bigger than Type IIb in the Tosa Bay. Although the test size is useful to identify genetic types in a same location, the test size of Type I also showed significant differences between two populations indicating that test size is not applicable to compare samples among multiple locations. Two relative ratios: the aperture oblateness and the ratio of the last chamber height to the total length, could cancel differences in absolute values such as the test size. By using these two parameters, no significant differences were confirmed in Type I between two locations. Moreover, these parameters of Type IIb significantly differed from those of the other genetic types. Our morphometric analyses showed the test size is useful parameter to distinguish genetic types within a same population (location), and the relative ratios of morphological items are applicable to detect differences among genetic types regardless of locations. The size differences of Type I between locations may indicate ecophenotypic variation, necessitating a deeper exploration of ecology.
References
Ujiié, Y., Asami, T., de Garidel-Thoron, T., Liu, H., Ishitani, Y., de Vargas, C. 2012. Longitudinal differentiation among pelagic populations in a planktic foraminifer. Ecology and Evolution. 2: 1725–1737. pmid:22957176
Ujiié Y, Ishitani Y. 2016. Evolution of a planktonic foraminifer during environmental changes in the tropical oceans. PLoS ONE 11(2): e0148847. doi:10.1371/journal.pone.0148847
Two populations of P. obliquiloculata collected from the central Pacific (102 specimens) and the Tosa Bay (100 specimens) were used to examine quantitative differences of test morphology between genetic types as well as between locations. We obtained both DNA and test samples from a same specimen and identified its genetic type using RFLP and molecular phylogenetic analysis. Two genetic types were found in each population: Types I and IIa in the central Pacific (Ujiié et al., 2012) and Types I and IIb in the Tosa Bay, respectively. We performed morphological measurement of nine items on the aperture side of the tests. In each population, the test size was significantly different between genetic types: Type IIa was bigger than Type I in the central Pacific and Type I was bigger than Type IIb in the Tosa Bay. Although the test size is useful to identify genetic types in a same location, the test size of Type I also showed significant differences between two populations indicating that test size is not applicable to compare samples among multiple locations. Two relative ratios: the aperture oblateness and the ratio of the last chamber height to the total length, could cancel differences in absolute values such as the test size. By using these two parameters, no significant differences were confirmed in Type I between two locations. Moreover, these parameters of Type IIb significantly differed from those of the other genetic types. Our morphometric analyses showed the test size is useful parameter to distinguish genetic types within a same population (location), and the relative ratios of morphological items are applicable to detect differences among genetic types regardless of locations. The size differences of Type I between locations may indicate ecophenotypic variation, necessitating a deeper exploration of ecology.
References
Ujiié, Y., Asami, T., de Garidel-Thoron, T., Liu, H., Ishitani, Y., de Vargas, C. 2012. Longitudinal differentiation among pelagic populations in a planktic foraminifer. Ecology and Evolution. 2: 1725–1737. pmid:22957176
Ujiié Y, Ishitani Y. 2016. Evolution of a planktonic foraminifer during environmental changes in the tropical oceans. PLoS ONE 11(2): e0148847. doi:10.1371/journal.pone.0148847