Biodiversity in diatom endosymbionts and their nummulitid foraminiferan hosts: a molecular approach

Foraminifera are one of the most diverse groups among protists and mainly occur in marine habitats. All modern larger Foraminifera are housing endosymbiotic algae and are restricted to the euphotic zones of tropical and subtropical reefs and other carbonate depositional environments. The majority of extant families of larger Foraminifera are hosts for endosymbiotic diatoms, among them also Nummulitidae, which are the largest calcareous foraminiferans. Nummulitidae are generally associated with reef environments and extend their depth distribution down to the base of the photic zone. They reach their highest diversity and abundance in the western Pacific. The morphology and distribution of Nummulitidae is well investigated and preliminary work has been carried out on their molecular characterization. Investigations of morphological and ultrastructural features provide limited information about the diversity of their diatom symbionts, but nothing is known about the genetic diversity of their endosymbionts. The purpose of this project is to explore the molecular diversity of nummulitid foraminiferans and their diatom endosymbionts. The species diversity of nummulitids and diatoms will be examined by sequencing SSU rDNA genes and the internal transcribed spacers (ITS) region for both groups. Additionally, molecular diversity of endosymbiotic diatoms will be probed in 3 other families of larger Foraminifera (Calcarinidae, Amphisteginidae and Alveolinidae), which are mostly restricted to the upper 50 m of the photic zone. To explore the occurence of symbiotic diatoms outside their hosts, total DNA will be extracted and examined from environmental samples collected in the vicinity of living larger Foraminifera. Furthermore, FISH probes will be used to identify endosymbiotic diatoms in situ. The project will allow to assess phylogenetic relationships in Nummulitidae and diatom endosymbiotic algae, to identify the key species of diatom symbionts and to determine the specific habitats of both, host and symbiont. The results are likely to provide the establishment of a more robust taxonomic division of Nummulitidae, with implications in ecological, biogeographic and paleoenvironmental studies. Like reef building endosymbiotc corals, larger Foraminifera react very sensitive to ecosystem disturbances introduced by human activities and a better understanding of host-symbiont relationships will provide useful insights for monitoring environmental changes.