There are two mechanisms of achiasmate segregation in Drosophila females,one of which requires heterochromatic homology

There are numerous examples of the regular segregation of achiasmate chromosomes at meiosis I in Drosophila melanogaster females. Classically, the choice of achiasmate segregational partners has been thought to be independent of homology, but rather made on the basis of availability or similarities in size and shape. To the contrary, we show here that heterochromatic homology plays a primary role in ensuring the proper segregation of achiasmate homologs. We observe that the heterochromatin of chromosome 4 functions as, or contains, a meiotic pairing site. We show that free duplications carrying the 4th chromosome pericentric heterochromatin induce high frequencies of 4th chromosome nondisjunction regardless of their size. Moreover, a duplication from which some of the 4th chromosome heterochromatin has been removed is unable to induce 4th chromosome nondisjunction. Similarly, in the absence of either euchromatic homology or a size similarity, duplications bearing the X chromosome heterochromatin also disrupt the segregation of two achiasmate X chromosome centromeres. Although heterochromatic regions are sufficient to conjoin nonexchange homologues, we confirm that the segregation of heterologous chromosomes is determined by size, shape, and availability. The meiotic mutation Axs differentiates between these two processes of achiasmate centromere coorientation by disrupting only the homology-dependent mechanism. Thus there are two different mechanisms by which achiasmate segregational partners are chosen. We propose that the absence of diplotene-diakinesis during female meiosis allows heterochromatic pairings to persist until prometaphase and thus to co-orient homologous centromeres. We also propose that heterologous disjunctions result from a separate and homology-independent process that likely occurs during prometaphase. The latter process, which may not require the physical association of segregational partners, is similar to those observed in many insects, in Saccharomyces cerevisiae and in C. elegans males. We also suggest that the physical basis of this process may reflect known properties of the Drosophila meiotic spindle. © 1993 Wiley-Liss, Inc.     

Elevated Mutagenicity in Meiosis and Its Mechanism

Diploid germ cells produce haploid gametes through meiosis, a unique type of cell division. Independent reassortment of parental chromosomes and their recombination leads to ample genetic variability among the gametes. Importantly, new mutations also occur during meiosis, at frequencies much higher than during the mitotic cell cycles. These meiotic mutations are associated with genetic recombination and depend on double‐strand breaks (DSBs) that initiate crossing over. Indeed, sequence variation among related strains is greater around recombination hotspots than elsewhere in the genome, presumably resulting from recombination‐associated mutations. Significantly, enhanced mutagenicity in meiosis may lead to faster divergence during evolution, as germ‐line mutations are the ones that are transmitted to the progeny and thus have an evolutionary impact. The molecular basis for mutagenicity in meiosis may be related to the repair of meiotic DSBs by polymerases, or to the exposure of single‐strand DNA to mutagenic agents during its repair.     

Phylogeny of woodcreepers of the genus Lepidocolaptes (Aves,Furnariidae), a widespread Neotropical taxon

Arbeláez‐Cortés, E., Navarro‐Sigüenza, A. G. & García‐Moreno J. (2012). Phylogeny of woodcreepers of the genus Lepidocolaptes (Aves, Furnariidae), a widespread Neotropical taxon. —Zoologica Scripta, 41, 363–373. Phylogeny of woodcreepers of the genus Lepidocolaptes (Aves, Furnariidae), a widespread Neotropical taxon. The phylogeny of the genus Lepidocolaptes was reconstructed based on three mitochondrial DNA regions and one nuclear DNA intron, using Bayesian analysis. A general pattern of diversification among the lowland species followed by the diversification of highland species, and a close relationship among montane species with the two Atlantic Forest endemics, seem to depict the history of this genus. Results also showed that the two Mesoamerican species are sister‐taxa with high support. Finally, our data also suggest the existence of previously unknown intraspecific genetic structure within some taxa, especially among populations of Lepidocolaptes souleyetii.     

Knowledge of Colombian biodiversity: published and indexed

Documenting patterns of published studies on the biodiversity of megadiverse countries can offer valuable insights on global biodiversity knowledge. Here, I present results from a bibliometric analysis of 5,264 indexed publications on biodiversity in Colombia published during the period 1990–2011 and gathered by searching the Web of Knowledge database. I classified studies into six overlapping subjects: taxa lists, new taxa, new records, conservation, genetic diversity, and other. Publications were also classified by geographic location and the taxonomic group studied. I found variation in the number of studies per year, which presented a long-term trend of increasing volume. The 31 continental departments of Colombia and both the Atlantic and the Pacific oceans were represented in the studies, which included 98 taxonomic classes from 47 phyla. However, there were strong biases in taxonomic, geographic, and subject coverage. For instance, 75 % of studies focused on animals; and the Atlantic Ocean showed the highest number of studies, followed by Antioquia and Valle del Cauca departments. Genetic diversity and conservation were the least-studied subjects. I also found that Colombian researchers and Colombian institutions have played an important role in documenting the country’s outstanding biodiversity. However, Colombian biologists still prefer to publish in domestic or Latin American journals, which are mainly regional and have low international visibility. The patterns I present here can have important implications for optimizing and guiding research on Colombian biodiversity, and the paper concludes with some recommendations.