Phylogeography of the genus Ulva (Ulvophyceae, Chlorophyta), with special reference to the Japanese freshwater and brackish taxa

Abstract

The nuclear-encoded ITS and associated 5.8S rDNA regions were sequenced for 72 specimens of Ulva collected from 44 rivers across Japan, including U. prolifera Müller from the Shimanto River, Kochi Prefecture, as well as 26 samples originally identified as U. linza L. from 20 coastal marine areas. Sequence data revealed that the samples fall into six distinct clades: the U. flexuosa Wulfen clade (2 samples), the Ulva linza-procera-prolifera (LPP) complex clade (75 samples), Ulva sp. 1 clade (3 samples), Ulva sp. 2 clade (7 samples), Ulva sp. 3 clade (4 samples) and Ulva sp. 4 clade (7 samples). The LPP complex contained a mixture of 26 samples collected from seashores and 49 samples obtained from rivers, including U. prolifera from the Shimanto River, and GenBank data for U. linza and U. procera Ahlner. The samples of the LPP complex differed by only 0-7 substitutions (0-1.149%). Subsequent phylogeographic analyses of the LPP complex based on the 5S rDNA spacer region revealed the presence of two further groupings: a group including 22 strictly marine littoral U. linza samples and a U. prolifera group composed of a mixture of 4 marine samples and all 49 river samples. The monophyly of all river samples indicates that adaptation to low salinity might have occurred only once in the evolutionary history of the LPP complex.

Phylogeny and Molecular Evolution of the Green Algae

“…The group is predominantly marine, but several transitions to freshwater or terrestrial habitats have occurred independently (Shimada et al, 2008;Ichihara et al, 2009;Suutari et al, 2010). The orders Ulvales and Ulotrichales have traditionally been distinguished based on life history features: the Ulvales have a life cycle involving isomorphic alternations of multicellular stages, while in the Ulotrichales the diploid, spore-producing stage is a small, thick-walled unicell that is attached to the substrate by a stalk (Codiolum stage) (O'Kelly et al, 2004b).…”

<i>Ulva partita</i> sp. nov., a Novel <i>Enteromorpha</i>-Like <i>Ulva</i> Species from Japanese Coastal Areas

“…Ulva partita has identical nrITS2 sequences to Ulva sp. collected at Rumoi, Hokkaido, Japan (AB275872; Shimada et al 2008) and Mikata-goko, Fukui pref., Japan (AB830498; Ogawa et al 2013). The relatedness of U. clathratioides was supported based on nrITS2 analysis, but the two species were clearly distinguished based on morphological features.…”

“…The nrITS2 sequence was also identical to Ulva sp. collected at Rumoi, Hokkaido (AB275872; Shimada et al 2008) and Mikata-goko, Fukui pref. (AB830498; Ogawa et al 2013).…”

“…The green algal genus Ulva, including species previously placed in the genus Enteromorpha (Hayden et al 2003), is known for its wide distribution in marine, brackish water, and freshwater environments globally (van den Hoek et al 1995, Maggs et al 2007, Shimada et al 2008, Ichihara et al 2009, Mareš et al 2011. A total of 107 species are taxonomically accepted (Guiry and Guiry 2015), of which 29 are currently recognized in Japan (Masakiyo and Shimada 2014).…”

“…Therefore, many studies have used DNA-based species identification and molecular phylogenetic analysis to resolve the relationships among Ulva species (Loughnane et al 2008, Shimada et al 2008, Kraft et al 2010, O Kelly et al 2010, Horimoto et al 2011, Mareš et al 2011, Wolf et al 2012, Kirkendale et al 2013. These studies also revealed many unidentified or undescribed Ulva species globally (Hayden and Waaland 2004, Shimada et al 2008, Kraft et al 2010, O Kelly et al 2010, Wolf et al 2012, Masakiyo and Shimada 2014.…”