The 5S rDNA family evolves through concerted and birth-and-death evolution in fish genomes: an example from freshwater stingrays

Background: Ribosomal 5S genes are well known for the critical role they play in ribosome folding and functionality. These genes are thought to evolve in a concerted fashion, with high rates of homogenization of gene copies. However, the majority of previous analyses regarding the evolutionary process of rDNA repeats were conducted in invertebrates and plants. Studies have also been conducted on vertebrates, but these analyses were usually restricted to the 18S, 5.8S and 28S rRNA genes. The recent identification of divergent 5S rRNA gene paralogs in the genomes of elasmobranches and teleost fishes indicate that the eukaryotic 5S rRNA gene family has a more complex genomic organization than previously thought. The availability of new sequence data from lower vertebrates such as teleosts and elasmobranches enables an enhanced evolutionary characterization of 5S rDNA among vertebrates.Results: We identified two variant classes of 5S rDNA sequences in the genomes of Potamotrygonidae stingrays, similar to the genomes of other vertebrates. One class of 5S rRNA genes was shared only by elasmobranches. A broad comparative survey among 100 vertebrate species suggests that the 5S rRNA gene variants in fishes originated from rounds of genome duplication. These variants were then maintained or eliminated by birth-and-death mechanisms, under intense purifying selection. Clustered multiple copies of 5S rDNA variants could have arisen due to unequal crossing over mechanisms. Simultaneously, the distinct genome clusters were independently homogenized, resulting in the maintenance of clusters of highly similar repeats through concerted evolution.Conclusions: We believe that 5S rDNA molecular evolution in fish genomes is driven by a mixed mechanism that integrates birth-and-death and concerted evolution

Dépérissement et diversité des insectes forestiers - une étude de cas dans les sapinières pyrénéennes

National audienceEn raison de changements climatiques profonds, on constate une augmentation de fréquence et d'intensité des sécheresses dans certaines parties du globe (dont l'Europe) avec des conséquences déjà visibles sur les forêts. Dans ce contexte, le projet Climtree porte sur les Impacts écologiques et socio-économiques du dépérissement des arbres induit par les changements climatiques dans les forêts de montagne. Grâce à l'étude de 56 placettes dans 2 régions des Pyrénées, nous analysons ici la réponse de la diversité des assemblages entomologiques (i) à l'intensité du dépérissement local de la sapinière, (ii) au niveau de dépérissement des sapinières dans le paysage ? et (iii) aux coupes de récupération mises en oeuvre dans les peuplements dépérissants. Les premiers résultats montrent que le niveau de dépérissement local affecte la structure des sapinières, la composition générale des communautés d'insectes, l'abondance moyenne des xylo- et saproxylophages de résineux mais pas le nombre moyen d'espèces de coléoptères saproxyliques. Le niveau régional de dépérissement montre un effet significatif sur l'abondance des xylophages potentiels ravageurs de faiblesse, sur la richesse des xylo- et saproxylo-phages de résineux, l'abondance et la richesse moyenne des espèces rares et l'abondance moyenne des espèces cavicoles et fongicoles. La coupe de récupération ne provoque pas d'érosion générale de la diversité des assemblages de coléoptères saproxyliques et provoque de faibles changements de composition des communautés d'insectes

Les dendromicrohabitats et la biodiversité associée sont-ils affecéts par le dépérissement forestier ? Une étude de cas dans les sapinières pyrénéennes

International audienceForest diebacks are likely to increase in response to climate change, with increased frequency and intensity of droughts. In line with climate change scenarios, ecoclimatic modelling predicts a decrease in the range of silver fir, a drought-sensitive species, in its southern limit in the French Pyrenees. Diebacks are expected to induce a pulse of resources potentially favorable to certain forest species, e.g. tree-related microhabitats (TreM) for saproxylic species. The impact of forest dieback on biodiversity has nonetheless been poorly studied. As part of the international Climtree project, we set up a balanced sampling design of 56 plots crossing the intensity of local silver fir dieback and the salvage logging of weakened or dead trees. Detailed stand structure metrics and insect communities sampled by Malaise traps (insect MOTUs) or flight-interception traps (saproxylic beetles) have been measured. The structure of fir stands was affected by the level of decline, and to a lesser extent by salvage logging. We indeed observed a slight increase in CWD and in some TreM-bearing trees (crown deadwood, annual polypores , trunk rot holes) with dieback intensity, and a slight decrease in some TreM-bearing trees (crown deadwood, annual polypores) in salvaged compared with unharvested plots. However, these stand changes did not strongly affect local insect assemblages. Guilds of TreM-associated insects did not increase in abundance or richness with dieback-induced increase in resources. In conclusion, forest changes through dieback result in habitat and resource changes with still hard-to-predict impacts at the stand scale on a major reservoir of biodiversity