DICTYOTALES, PHAEOPHYCEAE) BASED on Rbcl and 26S RIBOSOMAL DNA SEQUENCE ANALYSES1
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J. Phycol. 42, 1271–1288 (2006) r 2006 by the Phycological Society of America DOI: 10.1111/j.1529-8817.2006.00279.x A REVISED CLASSIFICATION OF THE DICTYOTEAE (DICTYOTALES, PHAEOPHYCEAE) BASED ON rbcL AND 26S RIBOSOMAL DNA SEQUENCE ANALYSES1 Olivier De Clerck2, Frederik Leliaert, Heroen Verbruggen Research Group Phycology and Centre for Molecular Phylogenetics and Evolution, Biology Department, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Christopher E. Lane Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada Joel Campos De Paula Departamento de Biologia Vegetal, Instituto de Biologia, Universidade do Estado do Rio de Janeiro, Rua Sa˜o Francisco Xavier, 524, Rio de Janeiro, CEP 20550-013, Brazil Dioli Ann Payo, and Eric Coppejans Research Group Phycology and Centre for Molecular Phylogenetics and Evolution, Biology Department, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Dictyota is a genus of tropical to warm temperate Key index words: Canistrocarpus; Dictyota; Dictyo- brown algae characterized by parenchymatous, flat- tales; molecular phylogeny; rbcL; Rugulopteryx; sys- tened thalli that grow from a single, transversely tematics; 26S rDNA oriented apical cell. Dictyota is currently distin- guished from allied genera of the tribe Dictyoteae Abbreviations: BI, Bayesian inference; ML, max- (Dilophus, Glossophora, Glossophorella, and Pachy- imum likelihood; MP, maximum parsimony; MPT, dictyon) by the structure of the cortical and medul- most parsimonious tree; PBS, partitioned Bremer lary layers, as well as the relative abundance of support surface proliferations. Even though the traditional classification of the Dictyoteae has repeatedly been criticized in the past, the absence of sound molec- The Dictyotales represents one of the few brown ular data has so far discouraged any new taxonomic algal orders whose members can form a conspicuous proposals apart from a merger of Dilophus with Dic- or even dominant component of tropical and temper- tyota, which has been accepted by only part of the ate marine algal floras. The success of these mac- phycological community. Phylogenetic analysis of roalgae has often been linked to their ability to deter rbcL gene, partial 26S rDNA sequence, and com- grazers in environments subject to severe grazing pres- bined data sets, including four of five generitypes, sure, which makes them an important competitor of demonstrates that the traditional classification does corals and other sessile benthic organisms for both not accurately reflect the evolutionary history of the space and light in many marine coastal ecosystems. group. None of the genera are resolved as a mono- From a systematic point of view, the order Dictyotales phyletic clade. Hence, a merger of Glossophora, is welldefined, all members being characterized by ap- Glossophorella, and Pachydictyon in Dictyota is pro- ical growth, flattened parenchymatous thalli, and hairs posed. Two new genera, Canistrocarpus (incorporat- aggregated in small tufts on the thallus surface. The ing D. cervicornis, D. crispata, and D. magneana) and life cycle is diplohaplontic and isomorphic. Sexual re- Rugulopteryx (accommodating D. radicans, Dil. suh- production is always oogamous, and the male gametes rii, and Dil. marginata), are proposed. Both genera are generally uniflagellate, except in some Zonaria are supported by molecular indications and a com- species, which are characterized by biflagellate bination of reproductive and vegetative characters. spermatozoids (van den Hoek et al. 1995, Phillips The position of Dil. fastigiatus as a clade sister to 1997). The diploid sporophyte typically produces uni- Dictyota s.l. and the absence of Dil. gunnianus, the locular sporangia with four nonflagellate meiospores generitype of Dilophus, from the analyses, prevent- (tetraspores), but a few genera produce eight aplano- ed us from making a more definite statement on the spores per sporangium (e.g. Lobophora and Zonaria) status of the latter genus. or flagellate spores (e.g. Exallosorus, Phillips 1997), features that are considered primitive. The order Dictyotales consists of the large family 1Received 27 July 2005. Accepted 3 July 2006. Dictyotaceae, in which some 20 genera are currently 2Author for correspondence: e-mail: [email protected]. recognized, plus two little-known monospecific genera, 1271 1272 OLIVIER DE CLERCK ET AL. TABLE 1. Genera of the Dictyoteae with indication of the respective generitypes, defining characters, and number of species. Currently recognized Genus Type species Defining characters species Dictyota D. dichotoma (Hudson) Lamouroux Medullary layers 1, cortical layers 1 ~ 46 Dilophus Dil. gunnianus J. Agardh Medullary layers 41, cortical layers 1 16 Glossophora G. kunthii (C. Agardh) J. Agardh Surface proliferations, medullary and 3 cortical layers 1 to variable Glossophorella G. dhofarensis Nizamuddin and Campbell Surface proliferations, medullary 1( À 2) and cortical layers 41 near the base Pachydictyon P. furcellatum J. Agardh [ 5 P. polycladum Medullary layers 1, cortical layers 414 (Ku¨tzing) Womersley] Dictyotopsis and Scoresbyella, that are each provisionally layers were placed in Pachydictyon. Glossophora, a genus assigned to a separate family, the Dictyotopsidaceae comprising only three species restricted to Australia, (Allender 1980) and Scoresbyellaceae (Womersley New Zealand, the Pacific coast of South America, and 1987), respectively. The family Dictyotaceae is subdiv- the Galapagos Archipelago, was chiefly characterized ided into the two tribes Dictyoteae and Zonarieae on by the presence of multiple surface proliferations that the basis of the number of meristematic cells at the even occasionally may bear reproductive structures. frond apices. In contrast the Zonarieae have a row or a Glossophora is only to a lesser extent defined on the small group of such cells, members of the Dictyoteae number of cortical and medullary layers, which are are characterized by a single, transversely oriented, reported to be variable even within the respective spe- lenticular apical cell. Recent molecular phylogenies cies (Womersley 1987). Surface proliferations also have largely confirmed this traditional tribal classifica- characterize several Dictyota and Dilophus species, but tion (Lee and Bae 2002, Hoshina et al. 2004, Kraft they are always less abundant than in Glossophora and et al. 2004). There is much less consensus, however, never serve as sporophylls. Recently a fifth genus, about genus delineations within the tribe Dictyoteae. J. Glossophorella, was added to the Dictyoteae. It is charact- Agardh (1882, 1894) originally recognized four genera erized by multiple cortical layers, duplication of med- (Dictyota, Dilophus, Glossophora, and Pachydictyon) that ullary cells near the margins, and the presence of sur- were distinguished by the relative number of cortical face proliferations (Nizamuddin and Campbell 1995). and medullary layers and by the presence or absence The distinction among these four or five genera has of surface proliferations (Table 1, Fig. 1). In Agardh’s been the subject of considerable debate, as some spe- system, Dictyota comprised species with a unilayered cies are particularly hard to assign to one or another cortex and medulla, whereas those with a multilayered genus (Setchell and Gardner 1925, Taylor 1945, Daw- medulla, in at least some part of the thallus, were as- son 1950). Ho¨rnig et al. (1992a, b) demonstrated signed to Dilophus. Species with a unilayered medulla experimentally that the number of medullary layers but a cortex that is at least locally composed of several can be altered in many species depending on the Dictyoteae Tribe Dictyota rface + su ns ratio olife Glossophora pr Glossophorella + surface proliferations Genera Dilophus FIG. 1. Schematic representation of the traditional defining characters of Pachydictyon genera in the tribe Dictyoteae. MOLECULAR SYSTEMATICS OF THE DICTYOTEAE 1273 culture conditions. They concluded that Dilophus did classification recognizing all five genera of the not warrant recognition at the generic level and hence Dictyoteae. proposed a merger of Dilophus with Dictyota. Although several authors have accepted the merger, others con- MATERIALS AND METHODS tinue to recognize Dilophus as a separate genus (Phillips 1992, Huisman 2000). Moreover, recently published Taxon sampling and laboratory protocols. Broad taxon sam- pling was carried out to ensure as complete a representation molecular phylogenies (Lee and Bae 2002, Hoshina as possible of the Dictyoteae (Table 2). This sampling in- et al. 2004, Kraft et al. 2004) indicate that the separ- cluded generitypes of all but one genus, as well as several ation of Dilophus and Dictyota is justified, but taxon species that are questionably placed in their present genera sampling in these studies was on the low side for draw- based on morphological inconsistencies. Sequences of the ing sound taxonomic conclusions. The status of Pachy- Dictyoteae were supplemented by a wide selection of taxa dictyon, Glossophora, and Glossophorella has received spanning the entire phylogenetic spectrum of the Zonarieae. The latter were defined as out-group. The sole representa- much less attention. The morphological data pre- tive of the family Scoresbyellaceae, S. profunda, was also in- sented on Dictyota naevosa (Suhr) Montagne and cluded. D. radicans Harvey by De Clerck and Coppejans Following Chase and Hillis (1991), DNA was extracted from (2003) show that generic boundaries between