Looking for cophylogenetic patterns in a mutualistic symbiosis between Soritinae (Foraminifera, Miliolida) and the genus Symbiodinium (Dinophyta, Suessiales)

In aquatic habitats, Symbiodinium endosymbionts has been recorded in many differents hosts: in invertebrates such as anemones, corals, mollusks or in some eukaryotic microorganisms like ciliates and foraminifera. Nine Symbiodinium clades are currently defined and display distinct biogeographic patterns. According to several molecular studies, only some Symbiodinium clades are found in association with the Soritinae, but this biological system is currently very poorly known, as are the determinants of host specificity (i.e. ecological and/or phylogenetic) in this symbiotic association. The main objective of this work is to estimate the level of cospeciation between Soritinae and their Symbiodinium. Phylogenies were built from the 18S rDNA for the Soritinae and the ITS2 region for Symbiodinium. There is a large number of Soritinae and Symbiodinium strains in databases, with uncertain taxonomic status, so we used species delimitation techniques to define potential species. Molecular dating methods using fossil calibration points were used to assess if emergence and diversification is concomitant in hosts and their symbionts. The cospeciation level was tested using two types of cophylogenetic analyzes on our datasets: the first assesses global congruence between the two phylogenies, and the second infers evolutionary scenarios. Hosts and symbionts phylogenies are globally congruent, but no clear cophylogenetic scenario could be produced. However, localized congruences were inferred within a complex cophylogenetic history.