Algal Endosymbiosis: an Engine for the Diversification of larger Foraminifera

Foraminifera comprise a major group of protists that are abundant in marine environments. Larger foraminifera live in shallow tropical and semitropical seas and play an important role in carbonate production. They are also common fossils in Mesozoic and Cenozoic neritic sediments and are used in micropaleontology for stratigraphical and environmental analyses, to establish biozonations. Adaptation for symbiosis seems to have been a key driving force in the evolution of larger foraminifera. Larger foraminifera are not a taxonomic unit, they occur in several extant suborders and share several characters in common, namely their large size (up to several cm), complex internal test structures and their associations with algae. Of all marine invertebrates known to house algal endosymbionts, larger foraminiferans house the greatest diversity. Members of the suborder Miliolina comprise the families Alveolinidae and Peneroplidae, which are hosts to diatom and rhodophycean algae respectively, and the family Soritidae which is subdivided into Archaiasinae, harbouring chlorophycean endosymbionts and Soritinae, which are hosts to dinoflagellates with the exception of parasorites that harbours chlorophyceans. The suborder Rotaliina also contains several families of algal bearing larger foraminiferans, the Nummulitidae, Calcarinidae and Amphisteginidae, which are all hosts to diatom endosymbionts. The aim of the project is to infer the molecular phylogeny and diversity of larger foraminiferans in detail by using by using ribosomal gene sequences. The results of this project will enhance our knowledge about the origin and diversity of recent larger foraminifera and lead to a better understanding about their patterns of rapid evolution and extinction in the past. Larger foraminifera are an important component of reef communities and are threatened by global climate changes. Reef decline on a global scale is of growing concern because of the loss of marine biodiversity and the potentially devastating economic impacts accompagnying the phenomen. The use of molecular methods will deliver information about a potential coevolution in larger foraminifera and their endosymbionts, it will be possible to identify their main symbiont types and to elucidate geographical patterns of host-symbiont distribution. The information can be used for reef-resource management and to watch reef health, using larger foraminiferans as bioindicators.