Conserved although very different karyotypes in Gliridae and Sciuridae and their contribution to chromosomal signatures in Glires.

Rodents represent the largest order of living mammals. It comprises 5 sub-orders, among which Sciuromorpha (Sciuridae, Gliridae and Aplodontiidae) are assumed to occupy a basal position in rodent evolution. Banded karyotypes of some representatives of the Sciuridae family have been compared to each other, and comparisons with man were performed using chromosome paintings. Sciuridae karyotypes have conserved several eutherian ancestral syntenies. Like Sciuridae, Gliridae possess some chromosomes easily comparable with those of Primates. Comparisons of Gliridae and Sciuridae chromosomes with those of the presumed eutherian ancestor provide information about their chromosomal evolution and their position among Rodentia. Although both Sciuridae and Gliridae karyotypes are relatively conserved, they display many differences, indicating their early divergence. The reconstruction of their chromosomal evolution allowed us to propose the composition of their presumed ancestral karyotypes, with 2n = 48 and 2n = 38 for Gliridae and Sciuridae, respectively. Since rodent emergence, a single rearrangement is common to these 2 families. It formed a chromosome with fragments homologous to human chromosomes 4-8p-4-12-22, not detected in other rodents, and thus characteristic for the Sciuromorpha. This allowed us to reassess the chromosomal signatures of Rodentia. Finally, we show that the speed of chromosomal evolution in Gliridae is intermediate between that of Sciuridae (low) and Muridae (high).

Using next-generation sequencing for molecular reconstruction of past Arctic vegetation and climate.

Palaeoenvironments and former climates are typically inferred from pollen and macrofossil records. This approach is time-consuming and suffers from low taxonomic resolution and biased taxon sampling. Here, we test an alternative DNA-based approach utilizing the P6 loop in the chloroplast trnL (UAA) intron; a short (13-158 bp) and variable region with highly conserved flanking sequences. For taxonomic reference, a whole trnL intron sequence database was constructed from recently collected material of 842 species, representing all widespread and/or ecologically important taxa of the species-poor arctic flora. The P6 loop alone allowed identification of all families, most genera (>75%) and one-third of the species, thus providing much higher taxonomic resolution than pollen records. The suitability of the P6 loop for analysis of samples containing degraded ancient DNA from a mixture of species is demonstrated by high-throughput parallel pyrosequencing of permafrost-preserved DNA and reconstruction of two plant communities from the last glacial period. Our approach opens new possibilities for DNA-based assessment of ancient as well as modern biodiversity of many groups of organisms using environmental samples.

Links between early pollen development and aperture pattern in monocots.

Although the pollen grains produced in monocots are predominantly monosulcate (or monoporate), other aperture types are also found within this taxonomic group, such as the trichotomosulcate, inaperturate, zonaperturate, di-, or triaperturate types. The aperture pattern is determined during the young-tetrad stage of pollen development and it is known that some features of microsporogenesis can constrain the aperture type. For example, trichotomosulcate pollen is always associated with simultaneous cytokinesis, a condition considered as derived in the monocots. Our observations of the microsporogenesis pathway in a range of monocot species show that this pathway is surprisingly variable. Our results, however preliminary, reveal that variation in microsporogenesis concerns not only cytokinesis but also callose deposition among the microspores and shape of the tetrads. The role played by these features in aperture pattern determination is discussed.