Matters of the heart
Tunicates, such as sea squirts, are the closest relatives to vertebrates. Most of these marine organisms become sessile — unable to move themselves – when their free-swimming larvae turn into sedentary adults. Appendicularian tunicates, however, do not undergo this transformation and swim freely throughout their lives. The origin of sessility within tunicates and how this relates to appendicularians is the source of much debate. In this week’s issue, Cristian Cañestro and his colleagues offer a fresh perspective on the evolution of tunicates. The researchers focused on heart development in appendicularians and found that their cardiopharyngeal gene regulatory network has been ‘deconstructed’ by massive gene losses. This deconstruction, the team suggests, has contributed to the loss of features that characterized a sessile lifestyle present in the ancestral tunicate. This deconstruction can be connected to evolutionary adaptations that helped appendicularians transition from a sessile to a free-living lifestyle upon the innovation of the ‘house’, a jelly filtration device that characterizes this group of organisms, as shown on the cover.
https://www.nature.com/nature/volumes/599/issues/7885
