Selection for class IIMhc heterozygosity by parasites in subterranean mole rats

Mhc organization and polymorphism have previously been studied²⁶ in the four chromosomal species of theSpalax 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 ofMhc class II genesP₁ with 11 alleles, andQ, with at least 14 alleles, is positively and significantly correlated with infectivities of ectoparasites (gamasid mites)¹⁷ and endoparasites (helminths)¹⁸.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 theMhc class II two-gene polymorphisms include selection for increased heterozygosity as a defense strategy against ecto- and endoparasite infections.     

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.     

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.     

Hematocrit and hemoglobin concentration in four chromosomal species and some isolated populations of actively speciating subterranean mole rats in Israel

Summary Hematocrit (HCT) and hemoglobin (Hb) concentration were measured in four chromosomal species and some peripherally semi-isolated and isolated populations of the mole rat superspeciesSpalax ehrenbergi in Israel. HCT was 52.0, 51.4, 50.9, and 47.8%, and Hb was 16.0, 16.6, 16.3, and 14.7 g/100 ml for 2n=52, 58, 54, and 60, respectively. The species 2n=60, which lives in arid habitats, had lower HCT and Hb than the other three species. HCT decreased as aridity increased between the species and within the species 2n=60. Changes in HCT probably reflect clinal changes in both soil permeability to gases and ambient temperature.     

Hematocrit and hemoglobin concentration in four chromosomal species and some isolated populations of actively speciating subterranean mole rats in Israel

Hematocrit (HCT) and hemoglobin (Hb) concentration were measured in four chromosomal species and some peripherally semi-isolated and isolated populations of the mole rat superspecies Spalax ehrenbergi in Israel. HCT was 52.0, 51.4, 50.9, and 47.8%, and Hb was 16.0, 16.6, 16.3, and 14.7 g/100 ml for 2n = 52, 58, 54, and 60, respectively. The species 2n = 60, which lives in arid habitats, had lower HCT and Hb than the other three species. HCT decreased as aridity increased between the species and within the species 2n = 60. Changes in HCT probably reflect clinal changes in both soil permeability to gases and ambient temperature.     

Olfactory discrimination as an isolating mechanism in speciating mole rats.

Olfactory discrimination was tested in two chromosome forms of the speciating fossorial rodent, Spalax ehrenbergi, in Israel. Females of the chromosome forms 2n = 52 and 2n = 58 were tested for male odour discrimination, the source of odour being either case litter or urine. Estrous females of both forms preferred homochromosomal odurs, whereas diestrous females showed no discrimination. These results suggest that olfactory discrimination may serve as a reproductive isolating mechanism in the speciation of mole rats.     

Adaptive respiratory variation in 4 chromosomal species of mole rats

Summary Oxygen and carbon dioxide pressures were measured in subcutaneous gas pockets of 4 chromosomal species of theSpalax ehrenbergi complex. Oxygen pressures of 11.8, 13.6, 16.9, and 17.2 torr and CO₂ pressures of 84.2, 82.9, 80.1, and 64.1 torr were measured for the chromosomal species 2n=52, 54, 58, and 60, respectively. The differences between the 4 chromosomal species in their subcutaneous gas tension appear to reflect adaptive respiratory variation associated with geographic variation in climate. It underlies an important respiratory physiological correlate of ecological speciation in the extremely hypoxic and hypercapnic subterranean environment.     

Adaptive respiratory variation in 4 chromosomal species of mole rats

Oxygen and carbon dioxide pressures were measured in subcutaneous gas pockets of 4 chromosomal species of the Spalax ehrenbergi complex. Oxygen pressures of 11.8, 13.6, 16.9, and 17.2 torr and CO2 pressures of 84.2, 82.9, 80.1, and 64.1 torr were measured for the chromosomal species 2n = 52, 54, 58, and 60, respectively. The differences between the 4 chromosomal species in their subcutaneous gas tension appear to reflect adaptive respiratory variation associated with geographic variation in climate. It underlies an important respiratory physiological correlate of ecological speciation in the extremely hypoxic and hypercapnic subterranean environment.     

Penicillamine induced changes in growing rats. II. liver parenchymal cell

Zusammenfassung d-Penicillamin als Kupferchelator bewirkt im Langzeitversuch eine isolierte Veränderung der stereologischen Parameter der Mitochondrien und der «microbodies». Zusammenhänge mit der Aktivitätshemmung kupferhaltiger Oxydasen in den beiden Zellorganellen werden vermutet.     

Adaptive heart and breathing frequencies in 4 ecologically differentiating chromosomal species of mole rats in Israel

Summary Breathing (f_R) and heart (f_H) frequencies decreases as aridity increases in 4 chromosomal species of theSpalax ehrenbergi that inhabits humid to arid habitats in Israel in the order 2n=52, 58, 54, 60. Breathing frequencies were 50.0, 46.9, 45.9, and 43.4% of the expected values, and f_H were 37.6, 32.7, 27.8, and 25.8% for 2n=52, 58, 54, and 60, respectively. The decrease of f_R and f_H has a genetic basis and correlates with the metabolism of the mole rat.     

Developmental homeostasis and heterozygosity for blood group loci in a human population

Summary Relationship between the variability of 5 independent morphological characters and the heterozygosity level at 4 blood group loci were determined in Israel. An increase in the heterozygosity level led to a reduction of the range and coefficient of variation of the morphological traits and also led to an increase of modal phenotype frequencies in the group.We are very grateful to Professor B. Arensburg of our department at the Tel Aviv University for his kind permission to use anthropometric data collected by him.     

Genetic polymorphisms and intrauterine development. Evidence of decreased heterozygosity in light-for-dates human newborn babies.

In 2 independent samples of low-birth-weight infants the proportion of females and homozygotes for a series of polymorphic systems was higher in light-for-dates than in preterm babies. The observation seems to give support to the hypothesis that homozygosity for 'normal' polymorphisms may decrease in general intrauterine growth rate. Since it is known that survival rate is strongly related to birth weight, a correlation between growth retardation and homozygosity may have a major role in the maintenance of such polimorphisms.     

Sertoli cells of adult rats in vitro. II. Effect of different steroid precursors on estradiol 17 beta-synthesis.

The estradiol 17 beta-synthesis by delta 4 pathway has been studied in homogenous cultures of Sertoli cells isolated from adult rat testes. The data reported clearly demonstrate that progesterone, androstenedione, testosterone and estrone induce an increase of the estradiol 17 beta-production.     

Genetic polymorphisms and intrauterine development. Evidence of decreased heterozygosity in light-for-dates human newborn babies

Summary In 2 independent samples of low-birth-weight infants the proportion of females and homozygotes for a series of polymorphic systems was higher in light-for-dates than in preterm babies. The observation seems to give support to the hypothesis that homozygosity for normal polymorphisms may decrease in general intrauterine growth rate. Since it is known that survival rate is strongly related to birth weight, a correlation between growth retardation and homozygosity may have a major role in the maintenance of such polimorphisms.We thank Prof. L. Ginzburg for helpful comments.     

Adaptive optimal sound for vocal communication in tunnels of a subterranean mammal (Spalax ehrenbergi)

The adaptive value of sound signal characteristics for transmission in the underground tunnel ecotope was tested using tunnels of the solitary territorial subterranean mole rats. We analyzed the propagation of synthetic calls with various frequencies through natural tunnels along different distances. Here we present evidence that sound propagation proved efficient only across short distances (a few meters). The least attenuation of sounds occurred at low frequencies. The 440 Hz sound was transmitted better than the lower (220 Hz) or higher (880, 1760, 3520 Hz) tested frequencies. These characteristics matched perfectly with the mole rat features of vocalization and hearing, thus reflecting the operation of natural selection for adaptive vocal communication in the underground tunnel ecotope.