Taxonomia, distribuição geográfica e filogenia do gênero Codium Stackhouse (Bryopsidales-Chlorophyta) no litoral brasileiro

Abstract

Codium Stackhouse is a genus exclusively marine which is represented by 125 taxa and it is distributed in the seas of almost the whole world, except for the polar regions. The highest infrageneric diversity is found in the temperate and subtropical zone seas. In Brazil, there are few informations about the genus, and the majority of the studies deals with floristic surveys from many localities, with just few publications. The aim of this work is to present the survey of this genus with emphasis to its taxonomy and the distribution of its representatives. The morphological studies were based in material collected from many Brazilian states (PB, PE, BA, ES, RJ, SP, SC and RS), in the intertidal region, during the low tides, with the help of spatulas and when necessary through diving in the reef ponds. The specimens were preserved with formalin (4%). For a better comprehension of the phenotypical variations and aiming to contemplate a number of samples as high as possible in the Brazilian states, the material of Codium was studied in the following indexed national herbaria: JPB, PEUFR, ALCB, HUEFS, RB, R, HB, RFA, SP, SPF and FLOR. They were also analyzed the exsiccates of the specimens collected by the Almirante Saldanha, Canopus and Recife Commission oceanographic expeditions. Besides, wereanalyzed as exsiccates of Codium from Brazil deposited in the Herbarium of the University of California, Berkeley (UC). All the exsiccates were carefully analyzed and confirmed and/or corrected as for the identifications. The identification of the taxa was based in morphological characters (habit, ramification pattern and the dimensions of the stalks), anatomical (diameter of the medular filaments, morphology and dimensions of the utricula and disposition of the hairs or scars) and reproductive (morphology, dimentions and insertions of the gametangia). In the Brazilian coast, it was registered the occurrence of seven infrageneric taxa, distributed in the following sections: Adhaerentia (C. Intertextum), Spongiosa (C. spongiosum), Tomentosa (C. isthmocladum, C. repens and Codium sp.) and Elongata (C. decorticatum and C. taylorii). From this work, C. tomentosum is considered as a doubtful species to the Brazilian littoral and C. profundum as “nome nudum” and because of this, cited as Codium sp. As for the great morphological plasticity the species C. decorticatum, C. isthmocladum and C. taylorii were those which showed the greatest difficulties in the taxonomical identification. Three species of straight habit as C. isthmocladum, C.decorticatum and C. taylorii and prostrate habit C. intertextum were those which presented the highest distribution in the Brazilian coast. Through the present study,some species had their geographical distribution increased to the Brazilian coast, as C. decorticatum (Ceará, Paraíba and Alagoas); C. intertextum (Alagoas), C. isthmocladum (Alagoas, Sergipe and Paraná) and C. taylorii (Ceará, Paraíba, Alagoas and Paraná). Besides the taxonomy based in morphological and reproductive characters the DNA sequencing was performed aiming the comprehension of the polymorphism found in some species. In the moment, the DNA sequencing is the most powerful technique to detecting the polymorphism in the genotype and it has been very used in comparing the different taxonomical levels. Sequences of the first exon of the large subunity RUBISCO (rbcL) has been used in the molecular delimitation and phylogeny of the species. To the present study, samplings were obtained from Codium in many localities of Brazil (PB, PE, BA, RJ, SP and SC), besides Fernando de Noronha Islands. The extraction process, amplification, sequencing and analysis of data were performed in the University of São Paulo (USP) in the laboratory of Marine Algae Edson J. de Paula (LAM). In this study, the sequences for the exon 1 of the gene rbcL were obtained from 24samplings of six species found in the Brazilian coast: C. decorticatum, C. intertextum, C. isthmocladum, C. spongiosum, C. taylorii and C. repens. The exon 1 of the rbcL showed 788 pairs of the base for all samplings. From the 24 sequenced samplings, ten unique sequences were obtained, which were phylogenetically analyzed with other sequences from GenBank, using different methods of inferences. The resulting trees were similar and they showed three principal monophyletic groupings. The grouping A, composed by non-ramificated prostrated habit species and in the majority with grouped and small utricules; the grouping B, consisting in the great majority, species with erect habit, cylindrical stalk, with individual utricules with intermidiary sizes. The Brazilian species group with similar from other geographical localities and they are between the main monophyletic groupings. These results indicate that the colonization of the South American Atlantic occurred many times possibly of species which came from Indo-Pacific.