11 research outputs found
Molecular systematics of the marine Dothideomycetes
Phylogenetic analyses of four nuclear genes, namely the large and small
subunits of the nuclear ribosomal RNA, transcription elongation factor 1-alpha
and the second largest RNA polymerase II subunit, established that the
ecological group of marine bitunicate ascomycetes has representatives in the
orders Capnodiales, Hysteriales, Jahnulales,
Mytilinidiales, Patellariales and Pleosporales.
Most of the fungi sequenced were intertidal mangrove taxa and belong to
members of 12 families in the Pleosporales: Aigialaceae,
Didymellaceae, Leptosphaeriaceae, Lenthitheciaceae,
Lophiostomataceae, Massarinaceae, Montagnulaceae,
Morosphaeriaceae, Phaeosphaeriaceae, Pleosporaceae,
Testudinaceae and Trematosphaeriaceae. Two new families are
described: Aigialaceae and Morosphaeriaceae, and three new
genera proposed: Halomassarina, Morosphaeria and
Rimora. Few marine species are reported from the
Dothideomycetidae (e.g. Mycosphaerellaceae,
Capnodiales), a group poorly studied at the molecular level. New
marine lineages include the Testudinaceae and Manglicola
guatemalensis in the Jahnulales. Significantly, most marine
Dothideomycetes are intertidal tropical species with only a few from
temperate regions on salt marsh plants (Spartina species and
Juncus roemerianus), and rarely totally submerged (e.g. Halotthia
posidoniae and Pontoporeia biturbinata on the seagrasses
Posidonia oceanica and Cymodocea nodosum). Specific
attention is given to the adaptation of the Dothideomycetes to the
marine milieu, new lineages of marine fungi and their host specificity
Analysis of the mitochondrial 12S rRNA gene supports a two-clade hypothesis of the evolutionary history of scleractinian corals
Scleractinian corals have long been assumed to be a monophyletic group characterized by the possession of an aragonite skeleton. Analyses of skeletal morphology and molecular data have shown conflicting patterns of suborder and family relationships of scleractinian corals, because molecular data suggest that the scleractinian skeleton could have evolved as many as four times.\ud
Here we describe patterns of molecular evolution in a segment of the mitochondrial (mt) 12S ribosomal RNA gene from 28 species of scleractinian corals and use this gene to infer the evolutionary history of scleractinians. We show that the sequences obtained fall into two distinct clades, defined by PCR product length. Base composition among taxa did not differ significantly when the two clades were considered separately or as a single group. Overall, transition substitutions accumulated more quickly relative to transversion substitutions within both clades. Spatial patterns of substitutions along the 12S rRNA gene and likelihood ratio tests of divergence rates both indicate that the 12S rRNA gene of each clade evolved under different constraints. Phylogenetic analyses using mt 12S rRNA gene data do not support the current view of scleractinian phylogeny based upon skeletal morphology and fossil records. Rather, the two-clade hypothesis derived from the mt 16S ribosomal gene is supported
Genetic diversity and population structure of an insular tree, Santalum austrocaledonicum in New Caledonian archipelago
We present a study of the genetic diversity and structure of a tropical tree in an insular system. Santalum austrocaledonicum is endemic to the archipelago of New Caledonia and is exploited for oil extraction from heartwood. A total of 431 individuals over 17 populations were analysed for eight polymorphic microsatellite loci. The number of alleles per locus ranged from 3 to 33 and the observed heterozygosity per population ranged from 0.01 in Maré to 0.74 in Ile des Pins. The genetic diversity was lowest in the most recent islands, the Loyautés, and highest in the oldest island, Grande Terre, as well as the nearby small Ile des Pins. Significant departures from panmixia were observed for some loci-population combinations (per population FIS = 0-0.03 on Grande-Terre and Ile des Pins, and 0-0.67 on Loyautés). A strong genetic differentiation among all islands was observed (FsT = 0.22), and the amount of differentiation increased with geographic distance in Iles Loyauté and in Grande Terre. At both population and island levels, island age and isolation seem to be the main factors influencing the amount of genetic diversity. In particular, populations from recent islands had large average FIS that could not be entirely explained by null alleles or a Wahlund effect. This result suggests that, at least in some populations, selfing occurred extensively. Conclusively, our results indicate a strong influence of insularity on the genetic diversity and structure of Santalum austrocaledonicum. (Résumé d'auteur