Which came first: insecticides or resistance?

Mutations that confer resistance to insecticides are well documented. However, so far, we have been unable to determine whether these mutations arose before or after the introduction of insecticides. Recently, a landmark study showed that resistance to Malathion can be detected in pinned specimens of Australian sheep blowflies that were collected before the introduction of the insecticide. This finding has numerous implications for our understanding of the prevalence of resistance to new compounds. It also indicates that pre-existing resistance alleles might not carry the fitness cost that is associated with new mutations.     

Which came first, the lung or the breath?

Lungs are the characteristic air-filled organs (AO) of the Polypteriformes, lungfish and tetrapods, whereas the swimbladder is ancestral in all other bony fish. Lungs are paired ventral derivatives of the pharynx posterior to the gills. Their respiratory blood supply is the sixth branchial artery and the venous outflow enters the heart separately from systemic and portal blood at the sinus venosus (Polypteriformes) or the atrium (lungfish), or is delivered to a separate left atrium (tetrapods). The swimbladder, on the other hand, is unpaired, and arises dorsally from the posterior pharynx. It is employed in breathing in Ginglymodi (gars), Halecomorphi (bowfin) and in basal teleosts. In most cases, its respiratory blood supply is homologous to that of the lung, but the vein drains to the cardinal veins. Separate intercardiac channels for oxygenated and deoxygenated blood are lacking. The question of the homology of lungs and swimbladders and of breathing mechanisms remains open. On the whole, air ventilatory mechanisms in the actinopterygian lineage are similar among different groups, including Polypteriformes, but are distinct from those of lungfish and tetrapods. However, there is extreme variation within this apparent dichotomy. Furthermore, the possible separate origin of air breathing in actinopterygian and 'sarcopterygian' lines is in conflict with the postulated much more ancient origin of vertebrate air-breathing organs. New studies on the isolated brainstem preparation of the gar (Lepisosteus osseus) show a pattern of efferent activity associated with a glottal opening that is remarkably similar to that seen in the in-vitro brainstem preparation of frogs and tadpoles. Given the complete lack of evidence for AO in chondrichthyans, and the isolated position of placoderms for which buoyancy organs of uncertain homology have been demonstrated, it is likely that homologous pharyngeal AO arose in the ancestors of early bony fish, and was pre-dated by behavioral mechanisms for surface (water) breathing. The primitive AO may have been the posterior gill pouches or even the modified gills themselves, served by the sixth branchial artery. Further development of the dorsal part may have led to the respiratory swimbladder, whereas the paired ventral parts evolved into lungs.     

Which came first,the virus or the cell?

The nature of viruses and the fundamental difference between their reproduction mechanism and cell division are discussed. The ways for storage and expression of genetic information in viruses are considerably more diverse than in cells. It is widely accepted nowadays that the “RNA world” appeared earlier than the “DNA world.” Hypotheses of the origin of viruses are discussed in conjunction with these theories (a hypothesis that cells with a RNA-genome appeared first, and were followed by viruses, and a hypothesis according to which RNA-containing viruses appeared first). It is suggested in both cases that the DNA-genomes first appeared in viruses, and that viruses played a definitive role in the origin of archaeans, eubacteria, and eukaryotes.     

Czech alien flora and the historical pattern of its formation: what came first to Central Europe?

Temporal patterns of immigration to the country were analysed using 668 alien species in the flora of the Czech Republic for which the dates of the first record were available (64.8% of the total number of 1031 so-called neophytes, i.e. aliens introduced after the year 1500). After a period of initial slow increase lasting to the 1840s, the accumulation of neophytes over time could be best fitted by a linear model that explained 97% of the variance. The intensity of floristic research, which varied between periods, did not significantly affect the overall increase in the number of aliens. The effect of species traits on the year of introduction was evaluated, with continent of origin, introduction type (deliberate or accidental), life history, Grime's life strategy, onset of flowering, mode of dispersal and propagule size as explanatory variables. Species of European origin and CSR strategists arrived earlier than those with other origins and strategies. Deliberately introduced species appeared earlier than accidental arrivals, and those cultivated for utilitary reasons on average arrived earlier than ornamentals. Species capable of early flowering were remarkably more prevalent among early newcomers. A separate analysis of accidentally introduced American species also identified life history as a significant predictor of immigration time, with annuals being introduced earlier than biennials and perennials. The data contribute to an understanding of a crucial stage of the invasion process that has received little attention in the literature. The model "early alien" to Central Europe is a European species with a CSR strategy deliberately brought for cultivation as a utilitary plant. Once it escaped from cultivation, its establishment in the wild was favoured by its ability to flower early and, therefore, complete the life cycle.     

Is the number of antennal plate organs (sensilla placodea) greater in hygienic than in non-hygienic Africanized honey bees?

Hygienic behavior is a desirable trait in honey bees (Apis mellifera L.), as hygienic bees quickly remove diseased brood, interrupting the infectious cycle. Hygienic lines of honey bees appear to be more sensitive to the odors of dead and diseased honey bee brood, and Africanized honey bees are generally more hygienic than are European honey bees. We compared the number of sensilla placodea, antennal sensory structures involved in the perception of odor, in 10 bees from each of six hygienic and four non-hygienic colonies of Africanized honey bees. The sensilla placodea of three of the terminal segments (flagellomeres) of the right antenna of each bee were counted with a scanning electron microscope. There were no significant differences in the mean numbers of sensilla placodea between the hygienic and non-hygienic bees, though the variance was higher in the hygienic group. Flagellomere 4 had significantly more sensilla placodea than flagellomeres 6 and 8. However, there was no significant difference between the other two flagellomeres. As hygienic bees are capable of identifying dead, injured, or infested brood inside a capped brood cell, sensilla placodea probably have an important role in enabling worker bees to sense sick brood. However, we did not find greater numbers of this sensory structure in the antennae of hygienic, compared to non-hygienic Africanized honey bees.     

Are the most numerous sensilla of terrestrial isopods hygroreceptors? Ultrastructure of the dorsal tricorn sensilla of Porcellio scaber

The ultrastructure of the tricorn sensilla of the woodlouse Porcellio scaber was investigated in cryofixed and freeze-substituted, or chemically fixed specimens. The tricorn sensilla have a foramenized triangular-shaped outer hair and bear a poreless rod-like inner hair. The conical base of the inner hair is connected to the base of the outer hair by a complex cuticular structure. Each sensillum contains three sensory cells. The tip of one of the three dendrites contains a tubular body and is clamped between two bulges of the dendritic sheath. The two other dendrites protrude to the tip of the inner hair, flush against the cuticular wall. The microtubules in the ciliary segments are arranged in nine double tubuli that have neither osmiophilic cores nor arms. The ciliary rootlets are small. The inner segment of the largest dendrite wraps around the two smaller dendrites and one of seven enveloping cells in a mesaxon-like manner. Although this ultrastructure deviates considerably from most crustacean mechanosensitive sensilla, it nevertheless suggests a mechanosensitive function, at least for one of the sensory cells. In many aspects, the tricorn sensilla resemble the thermohygrosensilla of insects. However, our results suggest that the structural criteria for thermo-hygro-sensitivity used in insects cannot simply be applied to crustaceans.     

Centrin- and α-actinin-like immunoreactivity in the ciliary rootlets of insect sensilla

Summary Long ciliary rootlets are a characteristic feature of the dendritic inner segments of the sensory cells in insect sensilla. These rootlets are composed of highly ordered filaments and are regularly cross-striated. Collagenase digestion and immunohistochemistry reveal that the rootlets are probably not composed of collagen fibers. However, double-labeling experiments with phalloidin and anti--actinins show that antibodies to -actinin react with the ciliary rootlets of the sensilla, but do not stain the scolopale, which is composed of actin filaments as visualized by phalloidin. Antibodies to centrin, a contractile protein isolated from flagellar rootlets of green algae, also stain the ciliary rootlets. Within the ciliary rootlets of insect sensilla, -actinin may be associated with filaments other than actin filaments. The immunohistochemical localization of a centrin-like protein suggests that contractions probably occur within the rootlets. The centrin-like protein may play a role during the mechanical transduction or adaptation of the sensilla.     

Extinction and diversification in the Devonian Brachiopoda of New York state: No correlation with sea level?

Sea level highstand is generally considered to promote high species diversities among marine organisms through habitat expansion and global climatic amelioration, and marine regression to trigger elevated extinction rates among marine benthic organisms by habitat reduction (the species‐area effect), and among both marine and terrestrial organisms by global climatic deterioration. The Devonian is unusual in that the Late Devonian mass extinction occurs during an interval of global sea level highstand. To further explore this anomaly, the potential relationship between relative sea level and evolutionary biology is analyzed here for the Brachiopoda of the Devonian Period. Successive linear modeling reveals a total lack of correlation between relative sea level and either origination rates, extinction rates, or standing diversity among the Devonian brachiopods.     

Did the Quaternary climatic fluctuations really influence the tempo and mode of diversification in European rodents?

The objective of this study was to establish whether the Quaternary climatic fluctuations influenced the tempo and mode of diversification in European rodents. Our case study is the subgenus Microtus (Terricola) distributed from western Europe to the Caucasus. Mitochondrial cytochrome b gene sequences from several representatives of all the species were used to generate maximum‐likelihood and Bayesian phylogenetic trees, to estimate divergence times, to identify biogeographic ancestral areas and to study the rate of diversification. Results showed that phylogenetic tree topologies were similar to previous published studies but with a better resolution at some nodes. The origin of Microtus (Terricola) is dated back to approximately 4.05 Myr in the Early Pliocene, and molecular dating for most Terricola species corresponds to several glacial periods of the Pleistocene. Results of the biogeographic ancestral area reconstruction suggest that Microtus (Terricola) diversified from the Caucasus/Turkey/Iran area through western Europe. Several periods of diversity variation were highlighted as follows: two period of diversity increase, between 3 and 2 Myr, and after 1 Myr; two periods of diversity decrease, before 3 Myr, and between 2 and 1 Myr. The diversification rate of Microtus (Terricola) was 0.353 ± 0.004 event/Myr, a rate similar to that of the Muridae family. To conclude, although the Pleistocene glacial conditions had an impact on the speciation events, the Quaternary does not appear however as a period with an exceptional rate of diversification for European rodents.