Modelling intraspecific resting egg shape variation in a freshwater fairy shrimp Tanymastix stagnalis (L., 1758) (Crustacea, Branchiopoda)

The shape of the resting eggs of a large branchiopod crustacean, the Anostraca Tanymastix stagnalis , is represented very accurately by analytical expressions. The occurrence of atypical shape of some T. stagnalis eggs may be viewed as a simple change of the analytical expression describing the usual egg shape. Their unusual shape may be explained by a higher embryo volume within an envelope of a given size. Biological implications are briefly discussed and hypothesized in an evolutionary point of view.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 55–60.     

Natural antisense (rTSalpha) RNA induces site-specific cleavage of thymidylate synthase mRNA

The 3' untranslated region (UTR) of rTSalpha RNA is complementary (i.e., antisense) to human thymidylate synthase (TS) RNA. When HEp2 cells (human epidermoid carcinoma) progressed from late-log to plateau phase growth, ribonuclease protection assay (RPA) revealed an inverse correlation between the levels of rTSalpha RNA and TS mRNA, suggesting a possible effect of rTSalpha RNA on TS mRNA levels. HEp2 cells expressing a Tet-On transactivator were transiently co-transfected with pHook-1 and a construct containing rTSalpha (protein and antisense RNA), rTSalphaDelta3' (rTSalpha protein only), rTSalpha-3' (antisense RNA-luciferase) or luciferase. Transfected cells were selected and evaluated for the effects of induced transgene expression on TS mRNA. Induced expression of transfected rTSalpha or rTSalpha-3', but not rTSalphaDelta3' or luciferase, resulted in decreased TS mRNA levels as measured by RPA. These results demonstrated that the antisense region of rTSalpha RNA is necessary and sufficient for this down-regulation of TS mRNA. RPA for TS mRNA also showed the enhanced appearance of two partial-length protected fragments in rTSalpha or rTSalpha-3' transfected cells. RPA stringency evaluations and primer extension assays indicated that TS mRNA is cleaved in vivo in a site-specific manner. These data demonstrate that rTS gene expression likely plays a role in down-regulating TS through a natural RNA-based antisense mechanism.     

Diversity of mitochondrial large subunit rDNA haplotypes of Glomus intraradices in two agricultural field experiments and two semi‐natural grasslands

Glomus intraradices, an arbuscular mycorrhizal fungus (AMF), is frequently found in a surprisingly wide range of ecosystems all over the world. It is used as model organism for AMF and its genome is being sequenced. Despite the ecological importance of AMF, little has been known about their population structure, because no adequate molecular markers have been available. In the present study we analyse for the first time the intraspecific genetic structure of an AMF directly from colonized roots in the field. A recently developed PCR‐RFLP approach for the mitochondrial rRNA large subunit gene (mtLSU) of these obligate symbionts was used and complemented by sequencing and primers specific for a particularly frequent mtLSU haplotype. We analysed root samples from two agricultural field experiments in Switzerland and two semi‐natural grasslands in France and Switzerland. RFLP type composition of G. intraradices (phylogroup GLOM A‐1) differed strongly between agricultural and semi‐natural sites and the G. intraradices populations of the two agricultural sites were significantly differentiated. RFLP type richness was higher in the agricultural sites compared with the grasslands. Detailed sequence analyses which resolved multiple sequence haplotypes within some RFLP types even revealed that there was no overlap of haplotypes among any of the study sites except between the two grasslands. Our results demonstrate a surprisingly high differentiation among semi‐natural and agricultural field sites for G. intraradices. These findings will have major implications on our views of processes of adaptation and specialization in these plant/fungus associations.     

Multiple messenger RNAs for dihydrofolate reductase

The species of RNA containing homologous sequences to a cDNA prepared against murine dihydrofolate reductase have been identified and partially characterized in a methotrexate-resistant subclone of the murine lymphoma L5178Y. Twelve discreet species have been identified by Northern blot analysis in the cytoplasm and four are associated with the nucleus. A majority of the cytoplasmic species are shown to be polyadenylated and range in size from approximately 0.8 to greater than 23.7 kb. Of the cytoplasmic species, four (i.e., 1.6, 1.3, 1.1, 0.8 kb) are found in the parental line as well as the MTX-resistant line. The 0.8-kb species is shown to be lacking a large portion of a 3′ noncoding region present on some of the higher-molecular-weight species. The 0.8- and 1.3-kb mRNAs containing dihydrofolate reductase coding sequences have been purified away from the other species and shown to translate to dihydrofolate reductase in an in vitro protein synthesis system. It is concluded that within the dihydrofolate reductase gene-amplified cell line L5178Y C₃ there are multiple messenger RNAs coding for dihydrofolate reductase and that this multiple translatable mRNA phenomenon is not the result of gene amplification.     

Extinction vulnerability of tropical montane endemism from warming and upslope displacement: a preliminary appraisal for the highest massif in Madagascar

One of the predicted biological responses to climate warming is the upslope displacement of species distributions. In the tropics, because montane assemblages frequently include local endemics that are distributed close to summits, these species may be especially vulnerable to experiencing complete habitat loss from warming. However, there is currently a dearth of information available for tropical regions. Here, we present a preliminary appraisal of this extinction threat using the herpetological assemblage of the Tsaratanana Massif in northern Madagascar (the island's highest massif), which is rich with montane endemism. We present meteorological evidence (individual and combined regional weather station data and reanalysis forecast data) for recent warming in Madagascar, and show that this trend is consistent with recent climate model simulations. Using standard moist adiabatic lapse rates, these observed meteorological warming trends in northern Madagascar predict upslope species displacement of 17–74 m per decade between 1993 and 2003. Over this same period, we also report preliminary data supporting a trend for upslope distribution movements, based on two surveys we completed at Tsaratanana. For 30 species, representing five families of reptiles and amphibians, we found overall mean shifts in elevational midpoint of 19–51 m upslope (mean lower elevation limit 29–114 m; mean upper elevation limit ?8 to 53 m). We also found upslope trends in mean and median elevational observations in seven and six of nine species analysed. Phenological differences between these surveys do not appear to be substantial, but these upslope shifts are consistent with the predictions based on meteorological warming. An elevational range displacement analysis projects complete habitat loss for three species below the 2 °C ‘dangerous’ warming threshold. One of these species is not contracting its distribution, but the other two were not resampled in 2003. A preliminary review of the other massifs in Madagascar indicates potential similar vulnerability to habitat loss and upslope extinction. Consequently, we urgently recommend additional elevational surveys for these and other tropical montane assemblages, which should also include, when possible, the monitoring of local meteorological conditions and habitat change.