Phylogenetics of Trachylina (Cnidaria: Hydrozoa) with new insights ...

1680 allen g. collins et al.Fig. 8. Phylogenetic hypothesis based on combined 16S, SSU, and LSU data (dataset 5). Phylogram of ML topology, with bootstrap indices under bothML and MP at each node. ‘ , ’ indicates a bootstrap index of less than 61; a single 100 or , was placed at nodes if indices under both criteria were 100or less than 61, respectively. For ML analyses, the assumed model of nucleotide evolution was GTR þ I þ G. Scale bar is equivalent to 0.1 substitutionsper site.Craspedacusta; the trachymedusan genera Geryonia and Lirope(Geryoniidae); the trachymedusan genera Haliscera, Halicreasand Botrynema (Halicreatidae); the trachymedusan generaRhopalonema and Pantachogon; the trachymedusan generaAmphogona, Aglaura and Aglantha; and, the narcomedusangenera Aegina, Solmundella and Solmissus.Figure 6 shows the strict consensus of 21 MP trees found insearches using the SSU dataset. With three exceptions, all ofthe relationships strongly supported by the mitochondrial16S analyses (Figure 5) receive method independent supportfrom the SSU data. The first exception is that there is nosupport for the splitting of Trachylina into two main clades.The second exception is that the ML bootstrap support forthe node linking Haliscera, Halicreas and Botrynema(Halicreatidae) is only 54. The third exception is that theclade linking Aegina citrea, Solmundella and Solmissus alsoincludes Tetraplatia volitans, which had an uncertain positionbased on the 16S data. Additional clades receiving support, asmeasured by both MP and ML bootstraps are: the limnomedusantaxa Aglauropsis (marine) and Maeotias (brackish)with the freshwater Craspedacusta and Limnocnida; the limnomedusangenus Olindias with Geryoniidae; and, the twotrachmedusan clades (Rhaopalonema þ Pantachogon andAmphogona þ Aglaura þ Aglantha).The strict consensus of 12 MP trees based on the LSUdata supports many of the relationships also indicated bythe 16S and SSU analyses (Figure 7). One of the two maintrachyline clades (non-geryoniid trachymedusans, narcomedusansand the actinulidan Halammohydra sp.) suggestedby 16S is also supported by LSU data. Two additional cladesthat receive high bootstrap support from LSU data underboth MP and ML criteria are: all sampled representatives ofRhopalonematidae plus Halammohydra sp.; and, all sampledrepresentatives of Narcomedusae.Finally, Figure 8 shows the ML topology using the combineddataset. Given the great amount of correspondencebetween the different single-marker analyses, it is not surprisingthat this combined analysis contains nearly all ofthe associations enumerated above. In total comparingacross all the single-marker analyses, there is only oneinstance of relationships receiving strong contradictorysupport. The SSU, LSU and combined data support an allianceof Aegina citrea, Solmundella, Solmissus andTetraplatia volitans, whereas the 16S analyses suggestedthat the first three taxa form a well-supported clade exclusiveof Tetraplatia.D I S C U S S I O NScope of LimnomedusaeLimnomedusae has a somewhat complicated taxonomic historythat reflects uncertainty about the phylogenetic affinities of thegroups that constitute it, as well as confusion arising from thehistorical use of separate taxonomic systems by experts onhydromedusae and hydroids. The taxon was created in thelate 1930s (Kramp, 1938; Browne & Kramp, 1939) for species