Divergence times in demosponges (Porifera): first insights from new mitogenomes and the inclusion of fossils in a birth-death clock model

Abstract

BackgroundApproximately 80% of all described extant sponge species belong to the class Demospongiae. Yet, despite their diversity and importance, accurate divergence times are still unknown for most demosponge clades. The estimation of demosponge divergence time is key to answering fundamental questions on the origin of Demospongiae, their diversification and historical biogeography. Molecular sequence data alone is not informative on an absolute time scale, and therefore needs to be “calibrated” with additional data such as fossils. Here, we calibrate the molecular data with the fossilized birth-death model, which compared to strict node dating, allows for the inclusion of young and old fossils in the analysis of divergence time. We use desma-bearing sponges, a diverse group of demosponges that form rigid skeletons and have a rich and continuous fossil record dating back to the Cambrian (~500 Ma), to date the demosponge radiation and constrain the timing of key evolutionary events, like the transition from marine to freshwater habitats. To infer a dated phylogeny of Demospongiae we assembled the mitochondrial genomes of six desma-bearing demosponges from reduced-representation genomic libraries. The total dataset included 33 complete demosponge mitochondrial genomes and 30 fossils.ResultsOur study supports a Neoproterozoic origin of Demospongiae. Novel age estimates for the split of freshwater and marine sponges dating back to the Carboniferous and the previously assumed recent (~18 Ma) diversification of freshwater sponges is supported. Moreover, we provide detailed age estimates for a possible diversification of Tetractinellidae (~315 Ma), the Astrophorina (~240 Ma), the Spirophorina (~120 Ma) and the family Corallistidae (~188 Ma) all of which are considered as key groups for dating the Demospongiae due to their extraordinary rich and continuous fossil history.ConclusionThis study provides novel insights into the evolution of Demospongiae. Observed discrepancies of our dated phylogeny with their putative first fossil appearance dates are discussed for selected sponge groups. For instance, a Carboniferous origin of the order Tetractinellida seems to be too late, compared to their first appearance in the fossil record in the Middle Cambrian. This would imply that Paleozoic spicule forms are not homologous to post-Paleozoic forms.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1230-1) contains supplementary material, which is available to authorized users.

Evidence of signaling and adhesion roles for β-catenin in the sponge Ephydatia muelleri

“…However, to study the deepest periods of animal ancestry it will be critical to incorporate data from non-bilaterian animals such as sponges and ctenophores (Dunn et al 2015) . Non-bilaterians are more phylogenetically divergent from each other, and from other animals, than are the research models listed above (Dohrmann and Wörheide 2017;Schuster et al 2017) , but detailed mechanistic knowledge about their cell and developmental biology is limited. However, progress in this area has accelerated due to advances in comparative genomics, with the initially surprising result that starkly different organisms share highly conserved developmental regulatory genes (McGinnis et al 1984;Kusserow et al 2005;Technau et al 2005;Nichols et al 2006) .…”

Tracing animal genomic evolution with the chromosomal-level assembly of the freshwater sponge Ephydatia muelleri

“…Despite the diversity of sponges in the most species-rich class, the Demospongiae, only one group, the Spongillida, made the transition to freshwater some 250-300 million years ago (Mya) (Fig. 1A), later diversifying into the extant range of modern taxa worldwide around [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] .…”

Genetic analysis confirms the freshwater origin of the endemic Caspian sponges (Demospongiae, Spongillida, Metschnikowiidae)

“…The first two features are also attributable to sponges of another ancient lake, the Baikal. Being relatively young (Schuster et al 2018b), its endemic sponges (family Lubomirskiidae) exhibit a large number of transitional morphological forms between species and possess overlapping morphotraits (Itskovich et al 2015(Itskovich et al , 2017. Thus, the morphological variety of studied M. tuberculata seems not to be surprising.…”