Molecular phylogeny of Sinophysis: Evaluating the possible early evolutionary history of dinophysoid dinoflagellates

Dinophysoids are a group of thecate dinoflagellates with a very distinctive thecal plate arrangement involving a sagittal suture: the so-called dinophysoid tabulation pattern. Although the number and layout of the thecal plates is highly conserved, the morphological diversity within the group is outstandingly high for dinoflagellates. Previous hypotheses about character evolution within dinophysoids based on comparative morphology alone are currently being evaluated by molecular phylogenetic studies. Sinophysis is especially significant within the context of these hypotheses because several features within this genus approximate the inferred ancestral states for dinophysoids as a whole, such as a (benthic) sand-dwelling lifestyle, a relatively streamlined theca and a heterotrophic mode of nutrition. We generated and analysed small subunit (SSU) rDNA sequences for five different species of Sinophysis, including the type species (S. ebriola, S. stenosoma, S. grandis, S. verruculosa and S. microcephala). We also generated SSU rDNA sequences from the planktonic dinophysoid Oxyphysis (O. oxytoxoides). Temperate and tropical species as well as the complete spectrum of thecal ornamentation within Sinophysis was addressed in our study. The sequences from the Sinophysis species formed a robust monophyletic group that was the sister to a robust clade consisting of all other dinophysoid genera, including Oxyphysis, in some analyses. Although the sister relationship received weak statistical support, this tree topology was consistent with inferences based on comparative morphology. Dinophysoids are a morphologically diverse group of dinoflagellates with a highly distinctive thecal plate pattern involving a sagittal suture (e.g. Kofoid & Skogsberg 1928; Taylor 1976; Fensome et al. 1993). Character evolution within dinophysoids has been hypothesized based on morphology alone (e.g. Tai & Skogsberg 1934; Abé 1967a, b, c; Taylor 1980; Hoppenrath et al. 2007) and is only now being evaluated by molecular phylogenetic studies of ribosomal gene sequences (Handy et al. 2009; Hastrup Jensen & Daugbjerg 2009; Gómez et al. 2011, 2012). Comparisons of extant morpho-species suggest that the ancestral dinophysoids were benthic and consisted of relatively streamlined cells that subsequently evolved more elaborate extensions of the theca in association with planktonic lifestyles (e.g. expansions of the cingular and sulcal lists in Histioneis and Ornithocercus). Different habitats, modes of nutrition and levels of toxicity are known in dinophysoids, but these features are not understood within a molecular phylogenetic context. Of the 12 genera and about 280 species of dinophysoids recognized today, only one genus is benthic: Sinophysis Nie and Wang (e.g. Hoppenrath 2000; Selina & Hoppenrath 2004; Chomérat et al. 2009). Sinophysis consists of seven species: S. microcephala (the type) and S. canaliculata are found in tropical habitats and S. ebriola, S. grandis, S. stenosoma, S. minima and S. verruculosa are found in temperate habitats (Herdman 1924; Nie & Wang 1944; Balech 1956; Quod et al. 1999; Hoppenrath 2000; Selina & Hoppenrath 2004; Chomérat et al. 2009). Selina & Hoppenrath (2004) and Chomérat et al. (2009) have previously addressed the distinctive morphological features within this genus. We were interested in using a broad sampling of molecular phylogenetic data to test whether the relatively streamlined theca, heterotrophic mode of nutrition and a benthic life style From: Lewis, J. M., Marret, F. & Bradley, L. (eds) 2013. Biological and Geological Perspectives of Dinoflagellates. The Micropalaeontological Society, Special Publications. Geological Society, London, 199–206. # The Micropalaeontological Society 2013. Publishing disclaimer: http://www.geolsoc.org.uk/pub_ethics 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112