Meeting Abstract
Hox and ParaHox genes are highly conserved animal-specific transcription factors that pattern the primary body axis during embryogenesis. Until recently, it was thought that sponges, a lineage that branched off early in animal evolution, lacked Hox and ParaHox genes, which would indicate that these genes originated relatively recently in evolution. However, a 2014 study identified ParaHox genes (Cdx) in two calcareous sponge species, putting this long-held doctrine into question. A closer look at these findings led us to the hypothesis that the results of this study are heavily dependent on the distance-based phylogenetic methods employed, which are sensitive to long-branch attraction artifacts, as well as the limited taxon sampling employed. To test this hypothesis, we reanalyzed the original datasets with multiple methods and also analyzed a new dataset that included a more diverse set of taxa. All but one of our maximum-likelihood (ML) and Bayesian analyses suggest that the two reported calcareous sponge genes are not ParaHox genes, but rather belong to the NKL subclass homeoboxes. Similarly, neighbor-joining analyses of our more diverse dataset yielded the same conclusion. Based on these results, we assert that the previous evidence suggesting the presence of Hox/ParaHox genes in sponges is reliant on distance-based methodology and the taxon sampling employed in the original study. Our new results suggest that Hox and ParaHox genes arose after sponges diverged from the rest of animals.
