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E Nevo

Publications and source records attributed to E Nevo.

At least 19 recordsLinked to original sources
PubMed1992

Differential olfactory perception of enantiomeric compounds by blind subterranean mole rats (Spalax ehrenbergi).

The behavior of mole rats (Spalax ehrenbergi) near pairs of enantiomeric compounds was examined in 901 two-choice experimental tests. Positioning of the nest and food store and the preferred location of the tested animal were used to assess attraction or aversion to the tested odorants. The results indicated that mole rats respond differentially to odors of stereoisomers (enantiomers of carvone, citronellol, and fechone). They responded to one enantiomer of each tested pair but were indifferent to or did not smell the other. Both sexes were attracted to the odor of R-(-)-carvone and repelled by the odor of (+)-citronellol. Females were attracted to the odor of (-)-fenchone while males had no preference. By contrast, all animals were indifferent to or did not smell the odor of S-(+)-carvone, (-)-citronellol, and (+)-fenchone. Further research to distinguish between these alternatives (indifference vs hyposmia/anosmia) is suggested.

Acyclic Monoterpenes↗
PubMed1992

Selection for class II Mhc heterozygosity by parasites in subterranean mole rats.

Mhc organization and polymorphism have previously been studied in the four chromosomal species of the Spalax ehrenbergi superspecies in Israel, serologically, and at the DNA, RFLP and sequence levels of class I and class II genes. Here we demonstrate that the observed heterozygosity of Mhc class II genes P alpha 1 with 11 alleles, and Q beta, with at least 14 alleles, is positively and significantly correlated with infectivities of ectoparasites (gamasid mites) and endoparasites (helminths). Mhc heterozygosity is highest in the most infected area, which is in the most humid-warm region of the superspecies range, or where two zoogeographic regions overlap. We conclude that the evolutionary forces responsible for the Mhc class II two-gene polymorphisms include selection for increased heterozygosity as a defense strategy against ecto- and endoparasite infections.

Animals↗
PubMed1992

Sexual pheromones in lipids and other fractions from urine of the male mole rat, Spalax ehrenbergi.

Spalax ehrenbergi mole rats are blind, solitary, territorial, aggressive, subterranean rodents with a yearly breeding season that peaks in December and January. We confirm here an earlier report that estrous females are attracted to substances present in the urine of homospecific as compared to heterospecific adult males. We have also found that nonestrous female mole rats show avoidance behavior to the same homospecific urine. Our objective was to ascertain the nature of the pheromone(s) and gain insight as to its possible role in reproductive isolation and speciation. An active principle, detected in either two- or three-choice behavior tests, was found to be extractable from urine by methylene chloride (CH2Cl2) and mainly found in the neutral lipid fraction. Total lipids were chromatographed by thin layer chromatography on silica gel G60 plates. Most of the activity was found in a zone bounded by Rfs 0.2 and 0.7. Cholesterol, other sterols, and ethyl esters of fatty acids chromatographed in this zone as determined by standards and staining. Ethyl esters of fatty acids were also detected in this fraction by GC/MS analysis. Although a large amount of activity was found in lipids, it only accounted for about 1% of that found in urine. Some activity may have been destroyed or lost during the extraction procedure and some may remain in a lipid insoluble form. Preliminary tests of lipid extracts of various portions of the male urogenital tract revealed pheromonal activity present, particularly in tissues associated with testes, epididymis, prostate, and bladder.

Animals↗
PubMed1992

Electrophysiological mapping of body representation in the cortex of the blind mole rat.

The cortex of the blind mole rat (Spalax ehrenbergi) was explored for somatosensory responses with special reference to an extension into the occipital cortex which serves vision in sighted mammals. Head and body representation was similar as in other rodents or mammals. However, the somatosensory area extended far into the occipital cortex. No responses to auditory or visual stimulation were found caudal to the somatosensory area. However, auditory responses were recorded in an area lateral to and slightly caudal to the head representation. It is concluded that in this naturally blind animal the area normally occupied by the visual cortex serves somatosensory function.

Animals↗
PubMed1991

Seismic communication in a blind subterranean mammal: a major somatosensory mechanism in adaptive evolution underground.

Seismic communication, through low-frequency and patterned substrate-borne vibrations that are generated by head thumping, and which travel long distances underground, is important in the nonvisual communication of subterranean mole rats of the Spalax ehrenbergi superspecies (2n = 52, 54, 58, and 60) in Israel. This importance pertains both intraspecifically in adaptation and interspecifically in speciation. Neurophysiologic, behavioral, and anatomic findings in this study suggest that the mechanism of long-distance seismic communication is basically somatosensory and is independent of the auditory mechanism. Seismic communication thus appears to be a channel of communication important in the evolution of subterranean mammals that display major adaptation to life underground.

Acoustic Stimulation↗
PubMed1991

Hypoxic survival differs between two mole rat species (Spalax ehrenbergi) of humid and arid habitats.

1. Two chromosomal species, 2n = 52 and 2n = 60 of the mole rat superspecies (Spalax ehrenbergi), occupy humid (2n = 52) and arid (2n = 60) habitats in Israel. 2. Gas conductivity of the soil of the 2n = 52 mole rat is lower than that of the 2n = 60 mole rat, and the 2n = 52 mole rat is better adapted to hypoxia. 3. The hypothesis that the 2n = 52 mole rat can survive to a lower pO2 than the 2n = 60 mole rat was tested. 4. Terminal pO2 (Torr) of four females 2n = 52 was lower, 18.0 +/- 2.9 (SD), than the terminal pO2 of five females 2n = 60, 28.2 +/- 5.1 (SD). 5. The hypoxic survival of the 2n = 52 mole rat as compared to that of the 2n = 60 mole rat correlates with other physiological traits: breathing and heart frequencies, blood hemoglobin and tissue gas tensions.

Acclimatization↗
PubMed1990

Genetic polymorphism of urine deoxyribonuclease I isomerases of subterranean mole rats, Spalax ehrenbergi superspecies, in Israel: ecogeographical patterns and correlates.

Genetic polymorphism of urine deoxyribonuclease I (DNase I) of mole rats was analyzed by isoelectric focusing in a thin-layer polyacrylamide gel (IEF-PAGE). One hundred and three subterranean mole rats, comprising 13 populations belonging to the four chromosomal species (2n = 52, 54, 58, 60) of the actively speciating Spalax ehrenbergi superspecies in Israel, were tested. The following results were indicated. (i) Spalax DNase I consisted of 6-12 major isozymes. (ii) Four phenotypes (numbers in parentheses) were 1 (92), 1-2 (5), 1-3 (4), and 2 (1). The decreasing order of genetic diversity, He, in the four species was 0.37, 0.13, 0.10, and 0.0 for 2n = 58, 52, 54, and 60, respectively. (iii) Spearman rank correlations and multiple regression analyses indicated associations of allele frequencies and genetic diversity with climatic and vegetation factors. We concluded that (a) climatic selection, either directly or indirectly through plant (i.e., food resources) diversity, plays an important role in DNase genetic differentiation and (b) no gene flow and introgression occur between the recent derivative of speciation (2n = 60) and its ancestor (2n = 58), suggesting the operation of reproductive isolation between both species despite natural hybridization.

Animals↗
PubMed1990

Aldolase DNA polymorphism in subterranean mole-rats: genetic differentiation and environmental correlates.

We analysed the genetic diversity and environmental correlates of the aldolase A and B genes by means of restriction endonucleases (DNA RFLP analysis), in the four chromosomal species (2n = 52, 54, 58 and 60) of the actively speciating subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel. The results indicated that: (i) both aldolase genes are highly polymorphic; (ii) fragment frequencies and fragment profiles display geographical patterns and significant ecological correlates; (iii) discriminant analysis largely succeeded in separating the four chromosomal species on the basis of variation of aldolase RFLPs.

Animals↗
PubMed1990

Synaptonemal complex analysis of mole rats (Spalax ehrenbergi): unusual polymorphisms of chromosome 1.

Two unusual structural polymorphisms in the largest chromosomal pair of the Israeli mole rat, Spalax ehrenbergi, were analyzed from surface-spread and silver-stained preparations of synaptonemal complexes. A C-band negative polymorphism for the length of the 1p arm was visible as axial length differences during late zygonema and early pachynema. This region underwent synaptic adjustment resulting in a fully paired, mid-pachytene synaptonemal complex with equalized axial lengths. The somatically variable and nonargentophilic secondary constriction in the 1q arm was evident as a distinct silver-stained thickening along the synaptonemal complex. Presence of this structure on the synaptonemal complex varied both among individuals and among cells within individuals. The intraindividual variation of this region is hypothesized to represent differential biochemical activity with its cellular visualization being regulated in a manner similar to that of nucleolus organizer regions.

Animals↗
PubMed1990

The Spalacidae: evolutionary history, speciation and population biology.

The evolutionary history of Spalacidae is reviewed taxonomically, paleontologically and neontologically. We focused selectively on taxonomy, biogeography, paleontology and evolutionary origins, chromosomal evolution, population biology and the species concept in Spalacidae. We concluded that the taxonomy of Spalacidae needs a modern revision based on chromosome and molecular-genetic data, beside that of morphology, physiology and behavior. The subterranean Spalacidae originated probably from a muroid-cricetoid stock in Asia Minor or vicinity, in Upper Oligocene times and adaptively radiated underground in the Balkans, steppic Russia and Middle East, extending into North Africa. The major important evolutionary feature in peripatric or allopatric speciation and adaptive radiation was karyotypic evolution, primarily through Robertsonian changes. More than 30 karyotypes (2n = 38-62; NF = 72-124) earlier represented by 8 classical species, occur primarily allopatrically or parapatrically, with only marginal sympatry, across the Eastern Mediterranean range of the family. Most karyotypes represent biospecies adapted at multiple organizational levels to their different ecologies. A short overview is presented on population biology and life history parameters of the Spalacidae which result in K-selected, "equilibrium species". Speciation in action and adaptive radiation embracing molecular and organismal adptations to the subterranean unique ecotope and to four different climatic regimes, have been multidisciplinarily studied in the Israeli Spalax ehrenbergi superspecies.

Animals↗
PubMed1990

Molecular evolutionary genetics of isozymes: pattern, theory, and application.

Isozyme studies at the population genetics-ecology interface conducted at the Institute of Evolution, University of Haifa, during 15 years, 1974-1989, are reviewed in terms of the evidence, theoretical, and practical implications. These studies involve numerous individuals, populations, species, and higher taxa in nature of plants, animals, and humans tested for variation at 15 to 50 primary isozyme loci. The isozyme studies have been conducted mainly in individuals sampled in natural populations at the local, regional, and global levels. Two of the species studied were wild cereals, the progenitors of wheat and barley in the Near East Fertile Crescent. These studies have been complemented by laboratory controlled a priori experimentation of inorganic and organic pollution biology. The human genetics laboratory compared isozyme structure of Jewish and non-Jewish populations. Our results indicate that: (i) isozyme diversity in nature in abundant, at least partly adaptive, and is oriented and maintained primarily by ecological factors. (ii) Natural selection in action is highlighted by stresses involving among others thermal, chemical, and climatic factors. (iii) Speciation can occur with little change in isozyme diversity. (iv) Jews from diverse countries, and in spite of 2,000 years of Diaspora, retain in the frequencies of some isozymes their Near Eastern origins. (v) Wild cereals harbor rich genetic resources exploitable in breeding either directly as adaptive structures, or indirectly as genetic markers for genotypic production of elite agronomic traits. (vi) Isozymes have been utilized as genetic monitors of marine pollution thereby contributing to environmental quality and conservation. (vii) Isozymes can substantially contribute to conservation biology. (viii) Isozymes have been successfully utilized in constructing molecular phylogenies and in revealing new sibling species. (ix) Future theoretical and practical directions of isozyme studies at the protein and DNA levels are outlined.

Animals↗
PubMed1990

The eye of the blind mole rat, Spalax ehrenbergi. Rudiment with hidden function?

The rudimentary eyes of the mole rat (Spalax ehrenbergi) are located under the skin and do not respond to light stimuli. However, removal of the eyes disturbs photoperiod perception in these animals. To help clarify the possibly remaining function of the eyes in this species, the authors studied their development and ultrastructure. In the early embryos the presumptive eye regions--the epithelium, lens vesicle, and optic cup--appear initially normal. As development progresses, the iris-ciliary body complex originates prematurely from the margin of the optic cup and shows a very rapid and massive growth. This pigment-laden tissue mass remains attached to the corneal stroma, obliterates the anterior chamber, and prevents the formation of the corneal endothelium and Descemet's membrane. In the developing lens the elongation of the lens fibers leads to the formation of a rudimentary lens nucleus that becomes disorganized and vacuolated and eventually also becomes vascularized. The optic fissure fails to close, the eyes remain colobomatous, and the optic disc appears atrophic. In contrast, retinal histogenesis progresses relatively normally, resulting in structurally reduced but well-differentiated photoreceptor, neuronal, and ganglion cell layers in the adult eye. Immunohistochemically, the presence of opsin could be demonstrated in the photoreceptor cells. The latter features may indicate that these rudimentary eyes are still functioning in the complex neuroendocrine pathways mediating photoperiodicity.

Animals↗
PubMed1990

Genetic diversity and its ecological correlates in nature: comparisons between subterranean, fossorial, and aboveground small mammals.

We have reanalyzed the levels of observed heterozygosity based on old and new material of small mammals in attempt to retest the environmental theory of genetic diversity or the niche-width variation hypothesis. This study involves old and new material of 184 small mammalian species both insectivores and rodents; 111 living aboveground and 73 species living partly (fossorial, N = 28) or totally (subterranean, N = 45) underground. The results indicated that (i) in general, insectivores harbor significantly lower levels of heterozygosity than rodents, and (ii) both overall, and in insectivores and rodents separately, the narrow-niche fossorial and subterranean species displayed significantly lower levels of observed heterozygosity than small mammalian species living aboveground. This is true in almost all parametric and nonparametric analyses. Subterranean and fossorial small mammals are more homozygous in protein diversity, primarily isozymes, compared with aboveground species. This pattern corroborates the environmental theory or niche-width variation hypothesis of genetic diversity.

Animals↗
PubMed1990

Ribonuclease in different chromosomal species of the mole rat, superspecies Spalax ehrenbergi: concentration in the pancreas and primary structure.

Ribonucleases are found in considerable quantities in the pancreas of a number of mammalian taxa and a few reptiles. The ribonuclease content varies greatly in different species. Large quantities are found in ruminants and species that have a ruminant-like digestion and in a number of species with coecal digestion. This is a response to the necessity of digesting large amounts of RNA derived from the microflora of the stomach of ruminants or species with ruminant-like digestion or of the coecum of species with coecal digestion. The amino acid sequence of pancreatic ribonuclease from the chromosomal species 2n = 60 of the mole rat, superspecies Spalax Ehrenbergi was determined. From the comparison of the sequence with those of other mammalian species we found that Spalax diverged from the myomorph rodent branch before the divergence of the Muridae (mouse, rat) from the Cricetidae (hamster, muskrat). Spalax ribonuclease shares several amino acid residues with other myomorph rodent species. These are not or only rarely observed outside this rodent suborder. Although the ribonuclease content varies greatly in different mammalian species, the variation in content between individuals within a species is small. Spalax is an exception to this with ribonuclease contents varying over more than an order of magnitude in different individuals. Ribonucleases isolated from the chromosomal species 2n = 52, 2n = 58 and 2n = 60 have identical elution positions on reversed-phase HPLC. The enzyme from the 2n = 54 species, however, elutes at a slightly earlier elution position. No amino acid sequence differences have been found hitherto between the ribonucleases of the four chromosomal species of Spalax ehrenbergi occurring in Israel. However, due to lack of material we were unable to determine more than about 20% of the sequence of the enzyme from the 2n = 54 species, which is the oldest offshoot.

Amino Acid Sequence↗
PubMed1989

Middle ear and cochlear receptors in the subterranean mole-rat, Spalax ehrenbergi.

The eardrum and the auditory ossicles of the middle ear, and the population of cochlear receptors in subterranean mole-rats of Spalax ehrenbergi complex were qualitatively and quantitatively analyzed. The area of the eardrum was 10.2 (S.D. = 0.9) mm2, that of the stapedial footplate 0.6 (S.D. = 0.07) mm2, the malleus: incus lever ratio was 1.25:1. The malleus is simply built, not attached to the tympanic ring. The incus is large; its long process is almost parallel to the manubrium of the malleus. The short process of the incus is provided with a peculiar bony cap, a structure thus far undescribed in mammalian auditory ossicles. Firmness of mutual connection of the ossicles may vary among different forms of Spalax. The size and form of the stapes are characterized by a large variability as well. The length of the basilar membrane was 12.6 (S.D. = 0.7) mm. The mean density of inner hair cells amounted to 93.3 that of outer hair cells to 386.4 cells per mm of the basilar membrane length. In general, the density increased from the base towards the apex. On average there were 415 outer, 100 inner hair cells in the organ of Corti; the ratio being constant along the basal 65% of the length and decreasing in the apical part of the organ of Corti. The radial width of the triad of outer hair cells increased and remained constant along the apical half of the Corti organ. Based on available findings of comparative and functional morphology, most of the studied features may be considered correlates of low-frequency tuning of the hearing organ in mole-rats.

Animals↗
PubMed1989

Relationships of the chromosomal species in the Eurasian mole rats of the Spalax ehrenbergi group as determined by DNA-DNA hybridization, and an estimate of the spalacid-murid divergence time.

DNA-DNA hybridization was used to measure the average genomic divergence among the four chromosomal species of the Eurasian mole rats belonging to the Spalax ehrenbergi complex (Rodentia: Spalacidae). The percent nucleotide substitutions in the single-copy nuclear DNA among the species ranged from 0 to 5%, suggesting that speciation has occurred with minor genomic changes in these animals. The youngest chromosomal species appear to differ by 0.2-0.6% base pair mismatch, which is only between one and three base differences in a 500-bp fragment. The interspecific values of percent nucleotide differences permit the recognition of two well-separated speciation events in the S. ehrenbergi complex, the older (of Lower Pleistocene age) having isolated the chromosomal species 2n = 54 before the divergence of the three other species. DNA-DNA hybridization was also used to compare the Spalacinae (Eurasian mole rats), Murinae (Old World rats and mice), and Arvicolinae (voles and lemmings). These data enabled us to estimate the time of divergence of the spalacids at ca. 19 million years ago. The dates of divergence among the other rodent lineages, as predicted by DNA hybridization results, agree well with paleontological data. These dates of divergence are obtained by the relation between geological time and single-copy nuclear DNA change, a relation that was calibrated by Catzeflis et al. (1987) through the use of fossil Arvicolinae and Murinae data.

Animals↗