Sexual selection and natural selection in body size differentiation of subterranean mole rats

We exlored indirectly, the operation of sexual selection in subterranean mole rats of the Spalax ebrenbergi superspecies in Israel comprising four chromosomal species, 2n = 52, 54, 58 and 60. We reanalzed two previously available data sets of 1. body size differentiation (Nevo et al. 1986a) and 2. the intensity of “Total Aggression” in mole rats (Nevo et al. 1986b). We correlated the mean size difference between the two sexes, in each of the 12 populations of the chromosomal species, with the mean level of agression, and with climatic factors, both displaying significant correlations. The results indicated that for 2n = 52, 54, 58 and 60, the population averae difference in body weight between the sexes decreases southward as follows: 37.7g (30.8 % of females body weight), 39.3g(29.0%) 26.3g(22.8%) and 20.3g (19.3%), respectively. We interpret the higher body size diherential ketween the sexes in the north as due to sexual selection.     

Penial differentiation in speciation of subterranean mole rats Spalax ehrenbergi in Israel

Geographic and ontogenetic variation was examined in the glans penes and bacula of 92 specimens representing four biological species with the karyotypes 2n=52, 54, 58 and 60 of the Spalax ehrenbergi superspecies in 13 populations from Israel and one disjunct population from northern Egypt. Five measured and three calculated penial characters were analysed and employed in multivariate statistics. Comparison was made between penial morphological characters and craniometric biochemical and chromosomal data. The baculum is strongly species-specific and its length bears no significant relationships with head and body length. The results of these analyses suggest that different bacular morphologies may provide a basis for species-specific prezygotic isolating mechanisms, thus, together with other factors, contributing to reproductive isolation and speciation.     

Brain organization and evolution in subterranean mole rats

Relative brain component sizes have been analyzed in subterranean mole rats of the Spalax ehren-bergi superspecies in Israel. Our results indicate that brain size and brain component sizes may have evolved in association with specific stresses underground involving the distinct development of vocalzation, olfaction and tactile sensory communication systems all compensating for the loss of vision.     

Aggression patterns in adaptation and speciation of subterranean mole rats

The patterns and correlates of aggressionwithin andbetween actively speciating subterranean mole rats of theSpalax ehrenbergi superspecies in Israel were tested in an attempt to approach an evolutionary theory of aggression related to both adaptation and speciation. Laboratory experiments were conducted on 314 adult mole rats (188 males and 126 females) caught in nature, representing 12 populations and comprising four chromosomal species (2n = 52, 54, 58, 60). The present analysis concentrates on “total aggression” comprising four aggressive variables: attacks, bitings, head-ons and sniffing with open mouth, out of 23 recorded variables. The results indicate that (a) aggression is distributed as a multipeak, discontinuous phenotypic parameter, displaying polymorphism within all 12 populations and 4 species tested; (b) the level of aggression was higher in males than in females, in the breeding than in the nonbreeding season, and displayed clinal geographic variation in both sexes across the superspecies range, where “militancy” increased northwards; (c) aggression was significantly correlated with ecological, physiological, genetical and ethological factors. These results support an evolutionary theory of aggression related to the intertwined processes of adaptation and speciation.     

Brain size diversity in adaptation and speciation of subterranean mole rats

We have tested brain size diversity and encephalization in the actively speciating subterranean mole rats of the Spalax ehrenbergi superspecies in Israel. Our sample involved 171 individuals comprising 12 populations and 4 chromosomal species (2n = 52, 54, 58 and 60) distributed parapatrically from the northern Mediterranean region southward (2n = 52, 54→+58→60) into increasingly more arid and unpredictable climatic regimes, approaching the Negev Desert. Our results indicate that relative brain size and encephalization are highest in 2n = 60 as compared with 2n = 52, 54 and 58. We hypothesize that this pattern is adaptive and molded by natural selection. Brain evolution and higher encephalization in the S. ehrenbergi complex appears to be associated with increasing ecological stresses of aridity and climatic unpredictability.     

Chromosomal polymorphisms in subterranean mole rats: origins and evolutionary significance

Two distinct chromosomal polymorphisms, among others, characterize the short (p) and long (qh) arms of chromosome number 1 of the Spalax ehrenbergi complex in Israel. We have studied the geographic distributions of these two polymorphisms in 60 animals belonging to four chromosomal species (2 n = 52, 54, 58 and 60). These comprised 15 populations: 12 from continuously distributed populations, two from semi-isolates, and one isolate in the northern Negev Desert.
Our results indicate that: (i) the two polymorphisms are widespread not only within populations and species but most strikingly between different bone marrow cells within an individual; this may reflect a diversity generating mechanism; (ii) the two polymorphisms of p and qh, primarily of p, are correlated with climatic factors of water availability and temperature, as well as geographical distances; these correlations are significantly above those expected by chance, (iii) The semi-isolates and the isolate display high levels of polymorphism in both p and qh, but particularly in qh, despite the small size population effects.
We suggest that at least the polymorphism in p is involved in the adaptive radiation of mole rats into diverse climatic regimes. Furthermore, we speculate that the forces generating chromosomal polymorphisms relevant to speciation (i.e. Robertsonian mutations), coupled with the evolutionary forces operating in small peripherally isolated populations, may be appropriate for the origin of new chromosomal species through peripatric speciation.     

Ribosomal DNA non-transcribed spacer polymorphism in subterranean mole rats: genetic differentiation,environmental correlates and phylogenetic relationships

Summary An analysis is presented of genetic differentiation in the non-transcribed spacers of ribosomal DNA (NTS rDNA). Diversity, environmental correlates and the phylogenetic relationships are examined within and between species of the actively speciating subterranean mole rat, superspeciesSpalax ehrenbergi (2n=52, 54, 58, 60) in Israel. This analysis is based on a previous study of the geographic distribution of restriction fragment length polymorphisms of NTS rDNA. Here we present results indicating that NTS rDNA diversity exists mostly (66%) within populations, while 20% is between populations within species, and 14% between species. Multivariate discriminant analysis succeeded in separating 10 of the 13 populations (77%) into their correct chromosomal species, on the basis of the combination of three NTS rDNA repetypes. The phylogenetic relationships suggest that the complex involves two pairs of closely related species (2n=52–54 and 2n=58–60). NTS rDNA diversity, as well as the decrease southward in frequency of repetype C, are correlated with climatic factors of humidity and temperature. These data are discussed in terms of the evolutionary forces of migration and selection which may cause NTS rDNA differentiation. Climatic selection appears to be the major differentiating factor of NTS rDNA.     

Adaptive energy metabolism in four chromosomal species of subterranean mole rats

Summary Gross energy intake and apparent dry matter digestibility of animals fed carrots ad lib in the laboratory, were measured in the four chromosomal species of the Spalax ehrenbergi superspecies in Israel. Gross energy intake of 132.8 and 155.9 kJ/day was measured for the 2n=52 and 2n=58 chromosomal mesic species, while in the 2n=54 and 2n=60 chromosomal xeric species it measured only 80.3 and 75.0 kJ/day, respectively. Dry matter digestibility ranged between 92.3 and 95.6% in thefour chromosomal species. The differences in gross energy intake between the mesic and xeric species, appeared to reflect adaptive energy metabolism variation associated with geographic variation in climate, habitat productivity, and food availability.     

Allozyme variations in Anatolian populations and cytotypes of the blind mole rats (Nannospalax)

Enzymatic proteins encoded by 28 putative loci in 326 samples of 12 mol rat cytotypes collected from 97 localities in Anatolia were investigated by standard horizontal starch-gel electrophoresis. A total of 61 alleles were determined for 28 isozyme loci and 23 of the 28 were polymorphic. Eight of the 23 polymorphic loci were agreeable to the Hardy–Weinberg equilibrium. It was determined that deviations from the Hardy–Weinberg equilibrium in the examined populations were due to a heterozygote deficiency. It was revealed by allozyme analyses that mole rat populations in Anatolia have formed 4 cytotypes groups, represented by 4 species (Nannospalax xanthodon, Nannospalax ehrenbergi, N. cilicicus, and N. nehringi). Cytotypes in western Anatolia (2n = 36, 2n = 38, 2n = 40, 2n = 52) showed private alleles in different enzyme systems; therefore, these cytotypes were genetically different, both from each other and other cytotypes. Although cytotypes in central Anatolia (2n = 52S, 2n = 56, 2n = 58, and 2n = 60) contained a different diploid chromosome number, they showed identical patterns in terms of their allele content in the 28 enzymatic loci.     

Adaptive variation in structure and function of kidneys of speciating subterranean mole rats

Summary We report on kidney structure and function in subterranean mammals of four chromosomal species (2n=52, 54, 58 and 60) belonging to the Spalax ehrenbergi superspecies, in relation to their speciation and adaptive radiation from mesic (2n=52) to xeric (2n=60) environments in Israel. Structural variables measured involved: (1) Relative Medullary Thickness, (RMT); (2) Relative Kidney Weight. (RKW); and (3) Percentage of Kidney out of Body Weight (PKW). Functional variables involved: (i) Urine Solid Concentration, (USC); and (ii) Urine Osmotic Concentration (UOC). The results for chromosomal species 2n=52, 54, 58 and 60 indicated nonsignificant increase southward for RMT, but displayed significant increase along the same transect for RKW, PKW, and USC. The UOC was significantly lower in mesic 2n=52 as compared to the other three species when experimental animals were fed in the laboratory on regular carrot food. However, protein stress food (soybean) and salt stress of 0.45 mol NaCl, caused significant, three and a half fold increase of UOC in 2n=52, 54 and 58; but four and a half fold increase in 2n=60, significantly higher than in the other three species. We conclude that both structurally and functionally, the kidneys differentiated adaptively during the Pleistocene evolution of S. ehrenbergi in Israel, in accordance with aridity stress and halophyte food resources towards the desert. Nevertheless, Spalax generally shows clear upper limits in kidney structural and functional capacities, preventing it from colonizing the true desert, south of the 100 mm isohyete.     

MtDNA polymorphisms: evolutionary significance in adaptation and speciation of subterranean mole rats

Patterns of mtDNA diversity in subterranean mole rats of the Spalax ehrenbergi superspecies (2n = 52, 54, 58 and 60) were previously studied in the main ranges of the four chromosomal species, and specifically in the 2n = 60 species and its peripheral steppe semi-isolates and desert isolates. In the present study we correlated mtDNA diversity indices, nucleon diversity, h , and nucleotide divergence, π, with physical (climatic), biotic (parasites) and biological (genetical, morphological, physiological and behavioural) factors, showing that mtDNA diversity is structured ecogeographically and biologically. The following significant correlations of mtDNA diversity were indicated with: (i) climatic heterogeneity and unpredictability; (ii) levels of ecto- and endoparasites; and (iii) biological diversities, primarily with physiological diversity associated with the energy budget. Small steppe semi-isolates and desert isolates harbour high levels of mtDNA haplotype diversity, some novel, which may be a prerequisite for future speciation events. We conclude that the ecogeographical and biological correlates, as well as the maintenance of mtDNA polymorphisms in small isolated populations, strongly suggest that mtDNA diversity is not neutral. Diversifying natural selection appears to be an important differentiating factor of mtDNA diversity in the twin evolutionary processes of adaptive radiation and active speciation. We suggest critical experiments to substantiate our conclusions and highlight the contribution of mtDNA diversity to fitness, i.e. to the biological function of mtDNA diversity in the evolutionary process.     

On the systematics and distribution of the molluscan genus Siphonaria in South Africa

Summary A revision of the systematics of the genus Siphonaria found around the South African coast from Port Nolloth on the West coast to Inhaca Island on the East coast is given. Of the twelve species described by Hubendick (1946) as occuring on the South African coast only five are valid. The remainder are reduced to synonyms. Two new species and one new variety are described.The horizontall distribution along the coastline of the valid species is described. Three species are recorded from the cold waters of the West coast while six species are recorded from the East coast. S. deflexa and S. oculus have a western distribution limit in False Bay. While S. dayi sp. nov. is only known from Inhaca Island. S. anneae and S. carbo occur in the subtropical waters near Durban. S. capensis and S. aspera are ubiquitous. S. compressa sp. nov. occurs only on the West coast in the sheltered waters of Langebaan lagoon, Saldanha Bay.Department of Zoology, University of Cape Town     

Variations in ribosomal DNA and mitochondrial DNA among chromosomal species of subterranean mole rats

Restriction site variations in nuclear ribosomal DNA (rDNA) spacers and mitochondrial DNA (mtDNA) were examined in several populations of mole rats with variable numbers of chromosomes, which represented the two superspecies Spalax leucodon (2n = 38, 54, or 62) and Spalax ehrenbergi (2n = 52, 54, 58, or 60). Sequence divergence of rDNA spacers between the members of the superspecies was approximately 8%, while the variation within each superspecies was 4% on average. The intrasuperspecies differentiation of rDNA spacers was generally associated with changes in the diploid number of chromosomes. However, substantial divergence (approximately 1.5%) was also detected among populations with the same diploid number of chromosomes. The sequence divergence of mtDNA among haplotypes of S. ehrenbergi was 10% or higher and among haplotypes of S. leucodon it was approximately 12%. By contrast, the range of sequence divergence between superspecies was 7.4%-12%. The large divergence of mtDNAs within each superspecies of mole rats may be explained by the preservation of ancient mtDNA polymorphisms.      

Karyotype and genetic evolution in speciation of subterranean mole rats of the genus Spalax in Turkey

Karyotype (2fl) and allozymc diversity at 37 gene loci were determined in 69 subterranean mole rats in Turkey belonging to the two superspecies: the ancestor Spalax leucodon ( n = 55; 20 populations) and the descendant S. ehrenbergi ( n = 14; lour populations). We identified remarkable variation of diploid chromosome numbers in the S. leucodon superspecies: 2 n = 38. 40. 50, 54, 60 and 62; and in the S. ehrenbergi superspecies: 2 n = 52, 56 and 58. Genetic diversity indices were low on average in both S. leucodon and S. ehrenbergi superspecies: Allele diversity, A = 1.081 and 1.074; polymorphism, P-5%= 0.077 and 0.068; heterozygosity, H = 0.038 and 0.027; and gene diversity, H, = 0.038 and 0.034, respectively. H ranged from 0 in mesic or semimesic regions to 0.088 in arid Anatolia. We consider the populations with different diploid chromosome numbers, 2 n , as good biological species. Karyotypic diversity may mark extensive ecological speciation. Nei's genetic distances, D (average 0.174, range 0.002 0.422) and ecogeographical criteria suggest that almost each population may represent a different biological species, but critical future testing is necessary to support this claim. Karyotypes and allozymes are nonrandomly distributed across Turkey, displaying remarkable correlations with climatic and biolir factors. Both In and H are significantly correlated with aridity stress (2 n /rainfall, r , =–0.74; P < 0.001), and in our region also with climatic unpredictability. These results support the niche-width genetic variation hypothesis in space and time. Climatic selection in Turkey appears to be a major architect of karyotype and genetic (allozymc) diversity and divergence in mole rat evolution, in both speciation and adaptation.     

Speciation and adaptive radiation of subterranean mole rats, Spalax ehrenbergi superspecies, in Jordan

The major initial mechanism of speciation in subterranean blind mole rats, Spalacidae, is chromosomal, primarily through Robertsonian rearrangements. Here we highlight another scenario of chromosomal rearrangement leading to ecological speciation and adaptive radiation apparently initiated by pericentric inversions and genie divergence to different ecologies in mole rats in Jordan. We analysed karyotype, allozyme, size and ecological diversity across the range of mole rats in Jordan from mesic Irbid in the north to xeric Wadi Musa (Petra region) in the south, a transect of 250 km. We examined mole rats for chromosome ( N =71), size ( N =76), and allozyme ( N =67) diversities, encoded by 32 loci, in 12 populations of the Spalax ehrenbetgi superspecies in Jordan. By a combination of chromosome morphology, genetic distance, body size and ecogeography, we identified four new putative biological species. All species (except two animals in Madaba) share 2 n = 60 but vary in chromosome morphology, caused by pericentric inversions and/or centromeric shifts. The 'north Moav' species is karyotypically polymorphic for 2 n (2 n = 60; including locally also two animals with 2 n = 62). The distribution of the four species is associated with ecogeographical different domains and climatic diversity. Genetic diversity indices were low, but like chromosome arms (NFa) were positively correlated with aridity stress. Discriminant analysis correctly classified 91% of the individuals into the four species utilizing combinatorially chromosome, allozyme and size diversities. It is hypothesized that mole rat evolution underground is intimately associated with climatic diversity stress above ground.     

Adaptive differentiation of body size in speciating mole rats

Summary We report the body weight of 1,653 subterranean mole rats comprising 12 populations and 4 chromosomal species (2n=52, 54, 58 and 60) of the Spalax ehrenbergi superspecies in Israel. The sample was collected from 1970 to 1985 and includes all captured animals with a minimal age of 10 months. The results indicated the following. (a) Body weight of males was significantly higher than that of females. (b) There is a southward latitudinal gradient in body size. Northern animals living in cooler and more productive mesic environments are larger than southern animals living in warmer and less productive xeric environments. (c) The interspecific differences for each sex are statistically significant. (d) Body size is negatively correlated with temperature variables, and positively correlated with plant cover (reflecting productivity or food resources) and rainy days. (e) The best predictors of body size, explaining up to 87% of the variation in size included various combinations of temperature variables and plant cover.We conclude that in both adaptation and speciation natural selection is a major agent of differentiation of body size in accordance with multiple factors, primarily temperature and food resources operating on the energetics balance.     

植物遗传多样性和系统学研究中的等位酶分析*

本文对“等位酶”的概念、等位酶分析方法在植物遗传多样性和系统学研究中应用的范围（包括种上和种下）进行了介绍和讨论,并对其优点和缺点进行了评论。认为等位酶分析是研究生物遗传多样性的重要方法,并为系统学和进化研究进入分子水平开辟了广阔而实用的前景,但使用分子资料并不意味着可以抛弃形态、细胞等其他方面的资料,它们的关系是互相补充,而决不是互相代替。     

植物遗传多样性和系统学研究中的等位酶分析*

本文对“等位酶”概念、等位酶分析方法在植物遗传多样性和系统学研究中应用的范围（包括种上和种下）进行了介绍和讨论,并对其优点和缺点进行了评论。认为等位酶分析是研究生物遗传多样性的重要方法,并为系统学和进化研究进入分子水平开辟了广阔而实用的前景,但使用分子资料并不意味着可以抛弃形态、细胞等其他方面的资料,它们的关系是互相补充,而决不是互相代替。     

Odour–genes covariance within a natural population of subterranean Spalax galili blind mole rats

Previous research, using habituation techniques with multiple rodent species as subjects, has demonstrated (from kin to across species) the greater perceptual similarity in the qualities of individual odours of more closely genetically related individuals ('odour–genes covariance', abbreviated 'OGC'). This predictable relationship between individual genotypes and individual odours has only been assessed in rodents in which the genetic similarities and dissimilarities are known either through laboratory breeding or by selecting odour donors from different populations or species. To study OGC within a natural population of rodents, we genotyped Spalax galili blind mole rats using ten microsatellite markers, and conducted pairwise genetic distance comparisons to estimate genetic similarity and to calculate the relatedness coefficient between pairs of individuals. We then used habituation-generalization techniques to assess whether perceived odour similarities covaried with the genetic similarities we had identified. Indeed, animals treated odours from genetically closer donors as more similar than odours from less genetically similar donors. The results suggest an accurate and subtle ability to resolve genetically determined odour distinctions among familially unrelated animals within a population. Graded differential responses to conspecific odours based on degrees of similarity between other individuals' odours and one's own have been demonstrated in kinship and species discriminations and preferences. The evidence presented here provides the basis for hypothesizing a similar process that could promote optimal outbreeding and inclusive fitness within populations of conspecifics. The evolutionary implications of these findings are discussed.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 483–490.