Protein polymorphism inEligmodontia typus. Genetic divergence with other phyllotine cricetids

By means of gel electrophoresis of tissue extracts we have studied protein polymorphism inEligmodontia typus. The analysis was performed on specimens from five population samples collected at different sites in Patagonia (Argentina). Mean heterozygosity (\-h) and proportion of polymorphic loci (P) were determined on the basis of 19 loci. Considering all individuals as one sample, \-h gave a value of 0.16 and P was 70%. Although these values are much higher than those reported for most rodent species, they are very similar to those obtained by us for four species of the genusCalomys and forGraomys griseoflavus. There is a striking genetic identity (I_N=0.99) among populations from regions with different environmental conditions, indicating that the species possesses a common genic pool. Genetic distance with other species of the Phyllotini was estimated. D_N was lower betweenE. typus andCalomys (mean D_N=0.88) than betweenE. typus andGraomys griseoflavus (D_N=1.01). The high morphological similarity between these last two species, especially regarding those characters related to desert life adaptation, could be assigned, at least in part, to convergent evolution.     

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.      

Enzyme polymorphism in a population of Calomys musculinus (Rodentia,Cricetidae)

NAD-linked lactate, malate, glycerophosphate, alcohol and nonspecific dehydrogenases, aspartate aminotransferases, and soluble esterases from extracts of tissues of individuals from a wild population of Calomys musculinus (Rodentia, Cricetidae) have been analyzed by means of starch gel electrophoresis and specific staining. Allelic frequencies and heterozygosity have been determined. Mendelian inheritance of some of the variants detected was confirmed by breeding experiments. Ten out of fifteen (66.6%) of the genetic loci investigated presented polymorphism. Mean heterozygosity per locus was very high (H=0.2014, se 0.046).This work has been supported, in part, by grants from the Secretaria de Ciencia y Tecnología de la Nación (National Program for Endemic Diseases) and from the Fundación Emilio Ocampo. C. N. G. is a Fellow and A. B. a Career Investigator of the Consejo Nacional de Investigaciones Científicas y Técnicas of Argentina.     

Improving the clinical assessment of consciousness with advances in electrophysiological and neuroimaging techniques

In clinical neurology, a comprehensive understanding of consciousness has been regarded as an abstract concept - best left to philosophers. However, times are changing and the need to clinically assess consciousness is increasingly becoming a real-world, practical challenge. Current methods for evaluating altered levels of consciousness are highly reliant on either behavioural measures or anatomical imaging. While these methods have some utility, estimates of misdiagnosis are worrisome (as high as 43%) - clearly this is a major clinical problem. The solution must involve objective, physiologically based measures that do not rely on behaviour. This paper reviews recent advances in physiologically based measures that enable better evaluation of consciousness states (coma, vegetative state, minimally conscious state, and locked in syndrome). Based on the evidence to-date, electroencephalographic and neuroimaging based assessments of consciousness provide valuable information for evaluation of residual function, formation of differential diagnoses, and estimation of prognosis.     

Genetic structure of populations of Calomys laucha (muridae, sigmodontinae) from central Argentina

The genetic structure of populations of the Sigmodontinae rodent Calomys laucha was studied by means of allozyme electrophoresis. This highly opportunistic species is found preferably in periodically perturbed habitats of crop fields in central Argentina, where it can attain very high densities. A total of 17 enzymatic proteins assayed gave information on 25 loci; only four were monomorphic in the seven populations studied. Levels of genetic variability (H_o from 0.144 to 0.171; P_95% from 44% to 56%) were higher than mean values reported for mammals and rodents. These high levels of heterozygosity could be maintained by large populations that do not experience great fluctuations in size, or by a social structure consistent in many small breeding groups that are formed and dissappear every breeding season. Genetic differentiation at a macrogeographical scale (θ=0.018) was low but statistically significant, and showed no correlation with geographic distance between pairs of populations. The pattern of population differentiation found is compatible with a relatively recent range expansion.     

Oligoryzomys flavescens (Rodentia, Muridae): gene flow among populations from central-eastern Argentina

In species acting as hosts of infectious agents, the extent of gene flow between populations is of particular interest because the expansion of different infectious diseases is usually related to the dispersal of the host. We have estimated levels of gene flow among populations of the sigmodontine rodent Oligoryzomys flavescens, in which high titers of antibodies have been detected for a Hantavirus in Argentina that produces a severe pulmonary syndrome. Enzyme polymorphism was studied by means of starch gel electrophoresis in 10 populations from the area where human cases of Hantavirus have occurred. Genetic differentiation between populations was calculated from F_ST values with the equation Nm = [(1/F_ST−1]/4. To assess the relative importance of current gene flow and historical associations between populations, the relationship of population pairwise log Nm and log geographic distance was examined. Low F_ST (mean = 0.038) and high Nm (15.27) values suggest high levels of gene flow among populations. The lack of an isolation by distance pattern would indicate that this species has recently colonized the area. The northernmost population, located on the margin of a great river, shows very high levels of gene flow with the downstream populations despite the large geographic distances. Passive transport of animals down the river by floating plants would promote unidirectional gene flow. This fact and the highest mean heterozygosity of that northernmost population suggest it is a center of dispersal within the species' range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Morphological, genetic, and chromosomal variation at a small spatial scale within a mosaic hybrid zone of the grasshopper Dichroplus pratensis Bruner (Acrididae)

Hybrid zones are regions where genetically different populations meet and mate, resulting in offspring of mixed characteristics. In organisms with limited dispersal, such as melanopline grasshoppers, hybrid zones can occur at small spatial scales (i.e., <500 m). We assessed levels of morphological, chromosomal, and molecular variability in adult males of the grasshopper Dichroplus pratensis Bruner (N = 137 males, 188 females) collected at 12 sites within a mosaic hybrid zone in a heterogeneous environment in Sierra de la Ventana, Argentina. In this hybrid zone, 2 Robertsonian chromosomal races, polymorphic for different centric fusions, meet (the "Northern race" at low altitudes and the "Southern race" at higher altitudes), forming hybrids that show monobrachial homologies during meiosis. High morphometric variation in 6 traits was revealed among grasshoppers of both sexes, with male body size positively and significantly correlated with increasing altitude. Frequency of Robertsonian fusions characteristic of the Southern race increased significantly with altitude. Moreover, fusion frequencies covaried between samples. Considerable genetic variation was revealed by random amplification of polymorphic DNA markers, with heterozygosity ranging from 0.3477 to 0.3745. Insects from low-altitude and high-altitude populations showed significant genetic differentiation, as indicated by F(ST) values. The proposed model for D. pratensis, involving the generation and maintenance by chromosomal fusions, of gene complexes adaptive in different environments, could explain the observed clinal patterns within the contact zone.     

The molecular phylogenetics of the genus Oligoryzomys (Rodentia: Cricetidae) clarifies rodent host–hantavirus associations

Several species of the genus Oligoryzomys are natural hosts of different hantavirus genotypes affecting humans. The systematics of the genus is confusing, which complicates the identification of the rodent host and hence the potential endemic areas of hantavirus pulmonary syndrome. In this study, we analyse molecular data to infer phylogenetic relationships among Central and South American specimens of Oligoryzomys, and compare our results with previously published data on karyotypic, geographic distribution and host–virus associations to solve contradictory taxonomic reports. We identified 25 clades, each one corresponding to a different putative species. The phylogenetic trees show that Oligoryzomys longicaudatus is strongly related to the Oligoryzomys flavescens complex, which comprises four clades; Oligoryzomys nigripes is related to Oligoryzomys stramineus, Oligoryzomys vegetus is related to Oligoryzomys fulvescens from Central America, and Oligoryzomys brendae is the sister species of Oligoryzomys aff. destructor. We identified the following rodent host–hantavirus genotype relationships: O. longicaudatus–Andes; O. flavescens ‘West'–Bermejo; O. flavescens ‘East'–Lechiguanas; O. nigripes–Juquitiba; Oligoryzomys microtis–Rio Mamore and Rio Mamore‐3; Oligoryzomys chacoensis–Oran; Oligoryzomys costaricencis–Choclo; Oligoryzomys delicatus–Maporal; Oligoryzomys utiaritensis–Castelo dos Sonhos; Oligoryzomys sp. RT2012–Rio Mamore‐4; Oligoryzomys sp. (and not Oligoryzomys fornesi)–Anajatuba. This work, besides contributing to the development of prevention programmes for hantavirus epidemiology in Latin America, represents a comprehensive update of the systematics of the genus Oligoryzomys. © 2014 The Linnean Society of London     

Phylogenetic relationships among species of the genus Oligoryzomys (Rodentia,Cricetidae) from Central and South America

González‐Ittig, R. E., Salazar‐Bravo, J., Barquez, R. M. & Gardenal, C. N. (2010). Phylogenetic relationships among species of the genus Oligoryzomys (Rodentia, Cricetidae) from Central and South America. —Zoologica Scripta, 39, 511–526. The genus Oligoryzomys includes several species very similar in external morphology, which has resulted in a confusing specific taxonomy. Accurate species identification is particularly important because several species of Oligoryzomys act as natural hosts of hantaviruses affecting humans. Here, we assign specific status to individuals from a wide geographical area of Argentina and Chile using sequences of the mtDNA control region. We also compare cytochrome b sequences of 14 species recognized from Central and South America to infer the phylogenetic relationships within the genus. In addition, the results were analysed using available data on chromosome numbers, and the host–parasite relationships reported for the genus Hantavirus. We confirm the geographical distribution of Oligoryzomys longicaudatus (Argentina, Chile), Oligoryzomys nigripes (Argentina, Paraguay, Brazil), Oligoryzomys chacoensis (Argentina, Bolivia, Paraguay), Oligoryzomys fornesi (Argentina, Paraguay), Oligoryzomys destructor (Argentina, Bolivia) and Oligoryzomys microtis (Bolivia, Brazil). Oligoryzomys longicaudatus is strongly related to the Oligoryzomys flavescens complex, which comprises four clades; O. nigripes is closely related to Oligoryzomys stramineus, and Oligoryzomys vegetus, to Oligoryzomys fulvescens from Central America. Oligoryzomys chacoensis, O. destructor, O. fornesi, O. longicaudatus, O. microtis, O. nigripes, O. stramineus, Oligoryzomys moojeni, Oligoryzomys rupestris, O. fulvescens and O. vegetus are confirmed as valid species, whereas O. flavescens, Oligoryzomys magellanicus, Oligoryzomys griseolus, Oligoryzomys victus, Oligoryzomys andinus and Oligoryzomys arenalis need exhaustive revision. The sister species to all the remaining entities of the genus was O. microtis, suggesting an Amazonian origin for the genus.     

Recent range expansion and low levels of contemporary gene flow in Calomys musculinus: its relationship with the emergence and spread of Argentine haemorrhagic fever

The geographic distribution of haplotype diversity in the rodent Calomys musculinus, sampled from 16 wild populations of Argentina, was analysed on two geographical scales. The species is the natural reservoir of the Junin virus, the etiological agent of the Argentine haemorrhagic fever (AHF). In all, 24 composite haplotypes were recognised in the mtDNA D-loop region. Haplotypes 1 and 2, internal in the network, were the most frequent and were present in almost all populations. The absence of large genetic gaps between widely distributed haplotypes, the existence of exclusive haplotypes in more than 50% of the sampled populations and the absence of isolation by distance at a macrogeographical scale are in support of the hypothesis of a recent range expansion of the populations of the Humid Pampa, with low to moderate current gene flow. The dispersal of this opportunistic species would have been favoured by the explosive increments in density after agriculture was introduced. When only nearby populations within the endemic area of AHF were considered, a pattern of isolation by distance was detected. At present, genetic drift appears to be the main force acting to randomly differentiate C. musculinus populations, which would also lead to random differentiation of Junin virus strains and a reduction in the virulence of the pathogen in 'historic' AHF areas. The knowledge of migration patterns of the reservoir populations facilitates reliable prediction of the potential spread of the human disease.