Improved phylogenetic resolution within Siphonophora (Cnidaria) with implications for trait evolution

Catriona Munro,Stefan Siebert,Felipe Zapata,Mark Howison,Alejandro Damian-Serrano,Samuel H Church,Freya E Goetz,Philip R Pugh,Steven H.D Haddock,Casey W Dunn

doi:10.1016/j.ympev.2018.06.030

Abstract

Siphonophores are a diverse group of hydrozoans (Cnidaria) that are found at most depths of the ocean - from the surface, like the familiar Portuguese man of war, to the deep sea. They play important roles in ocean ecosystems, and are among the most abundant gelatinous predators. A previous phylogenetic study based on two ribosomal RNA genes provided insight into the internal relationships between major siphonophore groups. There was, however, little support for many deep relationships within the clade Codonophora. Here, we present a new siphonophore phylogeny based on new transcriptome data from 29 siphonophore species analyzed in combination with 14 publicly available genomic and transcriptomic datasets. We use this new phylogeny to reconstruct several traits that are central to siphonophore biology, including sexual system (monoecy vs. dioecy), gain and loss of zooid types, life history traits, and habitat. The phylogenetic relationships in this study are largely consistent with the previous phylogeny, but we find strong support for new clades within Codonophora that were previously unresolved. These results have important implications for trait evolution within Siphonophora, including favoring the hypothesis that monoecy arose at least twice.

Highlights

Siphonophores (Figs. 1 and 2) are among the most abundant gelatinous predators in the open ocean, and have a large impact on ocean ecosystems (Choy et al, 2017; Pagès et al, 2001; Pugh, 1984; Pugh et al, 1997; Purcell, 1981; Williams and Conway, 1981)
The most familiar species is the Portuguese man of war Physalia physalis, which floats at the surface and can wash up conspicuously onto beaches (Totton, 1960)
Using 1,423 genes, we find strong support for many relationships found in the earlier phylogeny (Dunn et al, 2005), and provide new resolution for key relationships that were unresolved in that previous study

Summary

Introduction

Siphonophores (Figs. 1 and 2) are among the most abundant gelatinous predators in the open ocean, and have a large impact on ocean ecosystems (Choy et al, 2017; Pagès et al, 2001; Pugh, 1984; Pugh et al, 1997; Purcell, 1981; Williams and Conway, 1981). Siphonophores, which belong to Hydrozoa (Cnidaria), are found at most depths in the ocean, with the deepest recorded species found around 4,300 m (Lindsay, 2005). The most familiar species is the Portuguese man of war Physalia physalis, which floats at the surface and can wash up conspicuously onto beaches (Totton, 1960). Most species are planktonic, living in the water column, where some grow to be more than 30 m in length (Mackie et al, 1987). There is a small clade of benthic siphonophores, Rhodaliidae, that are tethered to the bottom for part of their lives (Pugh, 1983). There are currently 187 valid described siphonophore species (Schuchert, 2018)

Methods

Results

Conclusion