Chromosomal localization of actin genes in the malaria mosquito Anopheles darlingi

Physical and genetic maps have been used for chromosomal localization of genes in vectors of infectious diseases. The availability of polytene chromosomes in malaria mosquitoes provides a unique opportunity to precisely map genes of interest. We report the physical mapping of two actin genes on polytene chromosomes of the major malaria vector in the Amazon, Anopheles darlingi (Diptera: Culicidae). Clones with actin gene sequences were obtained from a cDNA library constructed from RNA isolated from adult females and males of An. darlingi. Each of the two clones was mapped to a unique site on chromosomal arm 2L in subdivisions 21A (clone pl05‐A04) and 23B (clone pl17‐G06). The obtained results, together with previous mapping data, provide a suitable basis for comparative genomics and for establishing chromosomal homologies among major malaria vectors.     

Host shifts and signal divergence: mating signals covary with host use in a complex of specialized plant‐feeding insects

A combination of divergent natural and sexual selection is a powerful cause of speciation. This conjunction of evolutionary forces may often occur when divergence is initiated by ecological differences between populations because local adaptation to new resources can lead to changes in sexual selection. The hypothesis that differences in resource use contribute to the evolution of reproductive isolation by altering the nature of sexual selection predicts that: (1) differences in sexual traits, such as signals and preferences, are an important source of reproductive isolation between species using different resources; (2) there are identifiable sources of selection on sexual traits that differ between species using different resources; and (3) signals vary between populations using different resources to a larger extent than between populations using the same resource at different localities. Testing these predictions requires a group of closely‐related species or populations that specialize on different resources and for which the traits involved in mate choice are known. The Enchenopa binotata species complex of treehoppers (Hemiptera: Membracidae) are host plant specialists in which speciation is associated with shifts to novel host plants. Mating in this complex is preceded by an exchange of vibrational signals transmitted through host plant stems, and the signal traits important for mate choice have been identified. In the E. binotata complex, previous work has supported the first two predictions: (1) signal differences between species are important in mate recognition and (2) host shifts can alter both the trait values favoured by sexual selection and the evolutionary response to that selection. In the present study, we tested the last prediction by conducting a large‐scale study of mating signal variation within and between the 11 species in the complex. We find that differences in host use are strongly associated with differences in signal traits important for mate recognition. This result supports the hypothesis that hosts shifts have led to speciation in this group in part through their influence on divergence in mate communication systems. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 60–72.     

IBERIAN AZURE-WINGED MAGPIE CYANOPICA (CYANA) COOKI NESTLINGS BEGGING CALLS: CALL CHARACTERIZATION AND HUNGER SIGNALLING

ABSTRACT

Nestling begging behaviour has long been seen as a signal by which nestlings solicit care from parents and most of the existing evidence provides some support for it being an honest signal. Begging is a multicomponent signal in which both sound and vision components are usually important. Although it is known that begging encodes information about nestling hunger the present knowledge about the specific behavioural features that convey the information is still scarce. The aim of this study was to describe begging calls of Iberian Azure-winged Magpie Cyanopica (cyana) cooki nestlings and examine how information on nestling hunger might be encoded in the begging calls. Nestlings were experimentally submitted to different periods of food deprivation and the call variation within individuals was studied. The young were individually tested and stimulated to beg by simulating parental visits. When subject to increasing food deprivation periods, nestlings increased the response level to simulated parental visits. The study also found that for the studied size differences, nestlings did not differ in their response level. Results confirmed that information on nestlings' hunger might be encoded in parameters of the calling behaviour. When the food deprivation periods increased, nestlings tended to start begging earlier, begged more often, extended their calling bout and increased the call duration, changing both at the level of the call and vocal begging bout. Overall the results support the view of begging as an honest signal, namely that begging should reflect nestling hunger and that only some call features might encode information about hunger.     

Functional differences between woodland savannas and seasonally dry forests from south‐eastern Brazil: Evidence from 15N natural abundance studies

Nitrogen availability and N‐cycling dynamics across ecosystems play a critical role in plant functioning and species distribution. Measurements of ¹⁵N natural abundance provides a way to assess ecosystem N dynamics, and the range of nitrogen stable isotope values (δ¹⁵N) for plants in an ecosystem can indicate divergent strategies for N uptake. We tested the hypotheses that the N‐rich seasonally dry forest would have higher soil and leaf δ¹⁵N and a smaller range of leaf δ¹⁵N values compared to the N‐poor cerradão (savanna woodland). We measured N concentration and δ¹⁵N in two soil depths and leaves of 27 woody species in cerradão and 26 in seasonally dry forest. As expected, total soil N concentration decreased while soil δ¹⁵N value increased with soil depth. Regardless of soil depth, seasonally dry forest soils had higher δ¹⁵N and total N concentration compared to cerradão soils. Foliar δ¹⁵N values varied from ?6.4‰ to 5.9‰ in cerradão and from ?2.3‰ to 8.4‰ in seasonally dry forest plants. Phylogenetically independent contrasts analysis and comparisons of δ¹⁵N mean values of the most abundant species and species co‐occurring in both sites confirmed the hypothesis of higher δ¹⁵N for seasonally dry forest in comparison to cerradão. These results corroborate the expectation of higher soil and leaf δ¹⁵N values in sites with higher soil N availability. However, except for the most abundant species, no across‐site leaf–soil (δ¹⁵N leaf –δ¹⁵N soil) differences (Δδ¹⁵N) were found suggesting that differences in leaf δ¹⁵N between cerradão and seasonally dry forest are driven by differences in soil δ¹⁵N. Variation of leaf δ¹⁵N was large in both sites and only slightly higher in cerradão, suggesting high diversity of N use strategies for both cerradão and seasonally dry forest communities.     

Molecular phylogeny of the western Atlantic species of the genus Portunus (Crustacea, Brachyura, Portunidae)

The genus Portunus encompasses a comparatively large number of species distributed worldwide in temperate to tropical waters. Although much has been reported about the biology of selected species, taxonomic identification of several species is problematic on the basis of strictly adult morphology. Relationships among species of the genus are also poorly understood, and systematic review of the group is long overdue. Prior to the present study, there had been no comprehensive attempt to resolve taxonomic questions or determine evolutionary relationships within this genus on the basis of molecular genetics. Phylogenetic relationships among 14 putative species of Portunus from the Gulf of Mexico and other waters of the western Atlantic were examined using 16S sequences of the rRNA gene. The resultant molecularly based phylogeny disagrees in several respects with current morphologically based classification of Portunus from this geographical region. Of the 14 species generally recognized, only 12 appear to be valid. We recommend that P. vossi be hereafter regarded as a junior synonym of P. spinimanus and that P. bahamensis be regarded as a junior synonym of P. depressifrons . Our analysis suggests that western Atlantic members of the genus can be subdivided into at least three well-defined clades. Pending further molecular analyses with a large subset of species, it appears that the genus is not monophyletic and that it warrants further taxonomic revision.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 211–220.     

Gene Cloning and Biochemical Characterization of an Alcohol Dehydrogenase from Euglena gracilis1

ABSTRACT. Euglena gracilis is a freshwater free‐living organism able to grow with ethanol as carbon source; to facilitate this metabolism several alcohol dehydrogenase (ADH) activities have been detected. We report the gene cloning, over‐expression, and biochemical characterization of a medium‐chain NAD⁺‐dependent ADH from E. gracilis (EgADH). The enzyme's amino acid sequence displayed the highest percentages of similarity and identity with ADHs of bacteria and fungi. In the predicted three‐dimensional model, all the residues involved in Zn²⁺, cofactor, and substrate binding were conserved. A conventional signal peptide for import into mitochondria could not be clearly identified. The protein of 37 kDa was over‐expressed, purified to homogeneity, and kinetically characterized. The enzyme's optimal pH was 7.0 for ethanol oxidation displaying a V_m of 11.7±3.6 U/mg protein and a K_m of 3.2±0.7 mM for this substrate. Isopropanol and isopentanol were also utilized, although with less efficiency. It showed specificity for NAD⁺ with a K_m value of 0.39±0.1 mM and Mg²⁺ or Zn²⁺ were essential for activity. The recombinant EgADH reported here may help to elucidate the roles that different ADHs have on the metabolism of short‐ and long‐chain alcohols in this microorganism.     

Interaction between wind-induced seiches and convective cooling governs algal distribution in a canyon-shaped reservoir

1. Wind is considered the dominant factor controlling phytoplankton distribution in lentic environments. In canyon‐shaped reservoirs, wind tends to blow along the main axis generating internal seiches and advective water movements that jointly with biological features of algae can produce a heterogeneous phytoplankton distribution. Turbulence generated by wind stress and convection will also affect the vertical distribution of algae, depending on their sinking properties. 2. We investigated the vertical and horizontal distribution of phytoplankton during the stratification period in Sau Reservoir (NE Spain). Sites along the main reservoir axis were sampled every 4 h for 3 days, and profiles of chlorophyll‐a and temperature were made using a fluorescent FluoroProbe, which can discriminate among the main algal groups. Convective and wind shear velocity scales, and energy dissipation were calculated from meteorological data, and simulation experiments were performed to describe non‐measured processes, like vertical advection and sinking velocity of phytoplankton. 3. Wind direction changed from day to night, producing a diel thermocline oscillation and an internal seiche. Energy dissipation was moderate during the night, and mainly attributed to convective cooling. During the day the energy dissipation was entirely attributed to wind shear, but values indicated low turbulence intensity. 4. The epilimnetic algal community was mainly composed of diatoms and chlorophytes. Chlorophytes showed a homogeneous distribution on the horizontal and vertical planes. Diatom horizontal pattern was also homogeneous, because the horizontal advective velocities generated by wind forcing were not high enough to develop phytoplankton gradients along the reservoir. 5. Diatom vertical distribution was heterogeneous in space and time. Different processes dominated in different regions of the reservoir, due to the interaction between seiching and the daily cycle of convective‐mediated turbulence. As the meteorological forcing followed a clear daily pattern, we found very different diatom sedimentation dynamics between day and night. Remarkably, these dynamics were asynchronous in the extremes of the seiche, implying that under the same meteorological forcing a diatom population can show contrasting sedimentation dynamics at small spatial scales (approximately 10³ m). This finding should be taken into account when interpreting paleolimnological records from different locations in a lake. 6. Vertical distribution of non‐motile algae is a complex process including turbulence, vertical and horizontal advection, variations in the depth of the mixing layer and the intrinsic sinking properties of the organisms. Thus, simplistic interpretations considering only one of these factors should be regarded with caution. The results of this work also suggest that diatoms can persist in stratified water because of a synergistic effect between seiching and convective turbulence.     

Maintenance of Integrity,Viability, and Adhesion of Entamoeba histolytica Trophozoites in Different Incubation Media12

We have determined the integrity, viability and adhesion of Entamoeba histolytica HK9 and HM1 trophozoites during their incubation in two basal culture media (TP and TYI) and three saline media (“maintenance medium” MM-1 and two others buffered with HEPES). In basal culture media, more than 70% of the trophozoites maintained their integrity and adhesion to human red blood cells (RBC) for up to 4 h, and the proportion of those excluding Trypan blue decreased slowly after 2 h. In saline media, the number of ameba-RBC complexes reached a maximum after 20–30 min and then decreased rapidly (and fastest in MM-1), less than 10% of the amebae were intact after 3–4 h, and dye exclusion fell abruptly from the start of incubation. The number of ameba-RBC complexes formed and the rate of adhesion were highest in basal TP medium. Normal nonvacuolated refringent (NVR) trophozoites deteriorated progressively in all media—although much faster in the saline ones—to vacuolated refringent (VR), nonrefringent, and disrupted. Trypan blue was excluded by all NVR and a fraction of the VR trophozoites. Horse serum helped to maintain ameba integrity and viability, but inhibited adhesion in a concentration-dependent manner. We conclude that E. histolytica trophozoite integrity and adhesion are adequately preserved and should be characterized only in basal culture media, that refringence without vacuolization is a more stringent characteristic of ameba quality than Trypan blue exclusion, and that some serum component inhibits ameba adhesion.