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.     

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.     

DNA sequence variation in the mitochondrial control region of subterranean mole rats,Spalax ehrenbergi superspecies,in Israel

The complete mitochondrial control region was sequenced for 60 individuals representing different populations for each of the four species of the subterranean mole rat Spalax ehrenbergi superspecies in Israel: Spalax galili (2n = 52), S. golani (2n = 54), S. carmeli (2n = 58), and S. judaei (2n = 60). The control region of all species and populations is very similar both in length (979 to 983 bp) and in base composition. As in agreement with previous surveys on mitochondrial control regions on mammals, the mole rat control region can be divided into a central domain and two flanking domains, ETAS (extended termination associated sequences) and CSB (conserved sequence blocks). Along with the common conserved blocks found in these domains (ETAS1, ETAS2, CSB1, CSB2, and CSB3), we have also detected in all individuals an ETAS1-like and a CSB1-like element, both in the ETAS domain. The most conserved region was the central domain, followed by the CSB and ETAS domains, showing important differences in the four species analyzed. Phylogenetic analysis supported the existence of two clades. One clade contained individuals belonging to Spalax galili (2n = 52) and S. golani (2n = 54), separated in two different branches depending on the species. The other clade contained individuals belonging to S. carmeli (2n = 58) and S. judaei (2n = 60) mixed together, suggesting a more recent event of speciation. Within species we have observed a southward trend of increasing variability. These results have been explained as a consequence of the adaptation of the species to ecological factors such as aridity and temperature stresses.     

Total body water and adaptive water turnover rate in four chromosomal species of subterranean mole rats of the Spalax ehrenbergi superspecies in Israel

Total body water (TBW) and water turnover rate (WTR) were measured in 24 subterranean mole rats comprising four populations, each belonging to a different chromosomal species of the Spalax ehrenbergi superspecies in Israel. The four species range in different climates: humid-cool (2n = 52); semiarid-cool (2n = 54); humid-warm (2n = 58) and arid-warm (2n = 60). TBW, as a percentage of body weight, measured by tritiated water (HTO), was 72.4%±4–7 in 2n = 52, significantly ( P < 005) higher than the similar estimates 61.7%± 7.2, and 59.4%± 5–3, for 2n = 60 and 58, respectively. A comparison of HTO space, as a percentage of TBW, closely approximated TBW, ranging from 97% to 108%. WTR was high, 218.1 and 230.9 ml/kg^0-75/day in the mesic populations of 2n = 58 and 52, respectively. By contrast, WTR estimates were significantly lower , ( P < 0.001), 150.2 and 148.9 ml/kg^0-75/day in the xeric populations of 2n = 54 and 60, respectively. The biological half-life time, T_1/2, was similar and faster, 32.7 and 27.9 hours in the mesic populations of 2n = 52 and 58, as compared with slower, 47.9 and 40.8 hours in the xeric populations of 2n = 54 and 60, respectively. Urine osmolarity in the most xeric northern Negev steppic population of 2n = 60 (737 ± 45 mmol/kg) was significantly ( P < 0.001) higher than in the other species.
We conclude that adaptive radiation in the Spalax ehrenbergi superspecies involves speciation in semiarid (2n = 54) and arid (2n = 60) climates by physiological adaptations of kidney water conservation, along with multiple morphological, physiological and behavioural syndromes of climatic adaptations to increasing aridity (Nevo, 1986).     

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.     

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.     

Extensive chromosomal polymorphism revealed by ribosomal DNA and satellite DNA loci in 13 Citrus species

Little is known about the chromosomal variability and polymorphism existing in mitotic chromosomes of Citrus, mainly due to lack of reliable chromosomal markers and small chromosome size. To test the hypothesis of chromosomal polymorphism and provide the foundation of the genome organization in the Citrus cultivars, we have developed molecular cytogenetic markers for 13 Citrus species collected from Jeju island, Korea. In this study, we demonstrated that the chromosomal locations of cytogenetic markers are quite variable and extremely polymorphic, in contrast to the previous studies. The data obtained in this study will be of utmost importance in cytological systematics and karyotyping of the Citrus species.     

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.     

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.     

Comparative study on DNA sequences of ribosomal DNA and cytochrome c oxidase subunit 1 of mitochondrial DNA among five species of gnathostomes

The nucleotide sequences of partial 18S, complete internal transcribed spacer region 1 (ITS1), complete 5.8S, complete ITS2 and partial 28S of ribosomal DNA (rDNA) and cytochrome c oxidase subunit 1 of mitochondrial DNA (MCOI) from five species of gnathostomes (G. spinigerum, G. doloresi, G. nipponicum, G. hispidum and G. binucleatum with the former four species being distributed in Japan and Asia) that cause human gnathostomiasis were compared by direct polymerase chain reaction cycle-sequencing. The nucleotide sequences of each region of the18S (613 bp), 5.8S (158 bp) and 28S (598 bp) rDNA from the five species were almost identical. The ITS1 region was different in length for the five species. The nucleotide sequences of each region of ITS2 and partial MCO1 regions were different among the five species. Therefore, these two regions can be used as genetic markers for identification of worms.     

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.     

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.     

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.     

Phylogenetic relationships in European Ceriporiopsis species inferred from nuclear and mitochondrial ribosomal DNA sequences

The aim of this work was to clarify taxonomy and examine evolutionary relationships within European Ceriporiopsis species using a combined analysis of the large subunit (nLSU) nuclear rRNA and small subunit (mtSSU) mitochondrial rRNA gene sequences. Data from the ITS region were applied to enhance the view of the phylogenetic relationships among different species. The studied samples grouped into four complex clades, suggesting that the genus Ceriporiopsis is polyphyletic. The generic type Ceriporiopsis gilvescens formed a separate group together with Ceriporiopsis guidella and Phlebia spp. in the phlebioid clade. In this clade, the closely related species Ceriporiopsis resinascens and Ceriporiopsis pseudogilvescens grouped together with Ceriporiopsis aneirina. C. resinascens and C. pseudogilvescens have identical LSU and SSU sequences but differ in ITS. Ceriporiopsis pannocincta also fell in the phlebioid clade, but showed closer proximity to Gloeoporus dichrous than to C. gilvescens or C. aneirina–C. pseudogilvescens–C. resinascens group. Another clade was composed of a Ceriporiopsis balaenae–Ceriporiopsis consobrina group and was found to be closely related to Antrodiella and Frantisekia, with the overall clade highly reminiscent of the residual polyporoid clade. The monotypic genus Pouzaroporia, erected in the past for Ceriporiopsis subrufa due to its remarkable morphological differences, also fell within the residual polyporoid clade. Ceriporiopsis subvermispora held an isolated position from the other species of the genus. Therefore, the previously proposed name Gelatoporia subvermispora has been adopted for this species. Physisporinus rivulosus appeared unrelated to two other European Physisporinus species. Moreover, Ceriporiopsis (=Skeletocutis) jelicii grouped in a separate clade, distinct from Ceriporiopsis species. Finally, the ITS data demonstrated the proximity of some Ceriporiopsis species (Ceriporiopsis portcrosensis and Ceriporiopsis subsphaerospora) to Skeletocutis amorpha.     

The chromosomal location of ribosomal DNA in the mouse

In situ hybridization of I¹²⁵-labelled ribosomal RNA to mouse chromosomes was used to determine the location of the rDNA loci. The results demonstrate the presence of rDNA sites on chromosomes 15, 18 and 19.     

Oxygen and carbon dioxide fluctuations in burrows of subterranean blind mole rats indicate tolerance to hypoxic-hypercapnic stresses

The composition of oxygen (O2), carbon dioxide (CO2), and soil humidity in the underground burrows from three species of the Israeli subterranean mole rat Spalax ehrenbergi superspecies were studied in their natural habitat. Two geographically close populations of each species from contrasting soil types were probed. Maximal CO2 levels (6.1%) and minimal O2 levels (7.2%) were recorded in northern Israel in the breeding mounds of S. carmeli in a flooded, poor drained field of heavy clay soil with very high volumetric water content. The patterns of gas fluctuations during the measurement period among the different Spalax species studied were similar. The more significant differentiation in gas levels was not among species, but between neighboring populations inhabiting heavy soils or light soils: O2 was lower and CO2 was higher in the heavy soils (clay and basaltic) compared to the relatively light soils (terra rossa and rendzina). The extreme values of gas concentration, which occurred during the rainy season, seemed to fluctuate with partial flooding of the tunnels, animal digging activity, and over-crowded breeding mounds inhabited by a nursing female and her offspring. The gas composition and soil water content in neighboring sites with different soil types indicated large differences in the levels of hypoxic-hypercapnic stress in different populations of the same species. A growing number of genes associated with hypoxic stress have been shown to exhibit structural and functional differences between the subterranean Spalax and the above-ground rat (Rattus norvegicus), probably reflecting the molecular adaptations that Spalax went through during 40 million years of evolution to survive efficiently in the severe fluctuations in gas composition in the underground habitat.     

Differential gene flow of mitochondrial and nuclear DNA markers among chromosomal races of Australian morabine grasshoppers (Vandiemenella, viatica species group)

Recent theoretical developments have led to a renewed interest in the potential role of chromosomal rearrangements in speciation. Australian morabine grasshoppers (genus Vandiemenella, viatica species group) provide an excellent study system to test this potential role of chromosomal rearrangements because they show extensive chromosomal variation and formed the basis of a classic chromosomal speciation model. There are three chromosomal races, viatica19, viatica17, and P24(XY), on Kangaroo Island, South Australia, forming five parapatric populations with four putative contact zones among them. We investigate the extent to which chromosomal variation among these populations may be associated with barriers to gene flow. Population genetic and phylogeographical analyses using 15 variable allozyme loci and the elongation factor-1alpha (EF-1alpha) gene indicate that the three races represent genetically distinct taxa. In contrast, analyses of the mitochondrial cytochrome c oxidase subunit I (COI) gene show the presence of three distinctive and geographically localized groups that do not correspond with the distribution of the chromosomal races. These discordant population genetic patterns are likely to result from introgressive hybridization between the chromosomal races and range expansions/contractions. Overall, these results suggest that reduction of nuclear gene flow may be associated with chromosomal variation, or underlying genetic variation linked with chromosomal variation, whereas mitochondrial gene flow appears to be independent of this variation in these morabine grasshoppers. The identification of an intact contact zone between P24(XY) and viatica17 offers considerable potential for further investigation of molecular mechanisms that maintain distinct nuclear genomes among the chromosomal races.     

The wheat ribosomal DNA spacer region: Its structure and variation in populations and among species

Summary The wheat rDNA clone pTA250 was examined in detail to provide a restriction enzyme map and the nucleotide sequence of two of the eleven, 130 bp repeating units found within the spacer region. The 130 bp units showed some sequence heterogeneity. The sequence difference between the two 130 bp units analysed (130.6 and 130.8) was at 7 positions and could be detected as a 4 °C shift in Tm when heterologous and homologous hybrids were compared. This corresponded to a 1.2% change in nucleotide sequence per Tm of 1 °C. The sensitivity of the Tm analysis using cloned sequences facilitated the analysis of small sequence variations in the spacer region of different Triticum aestivum cultivars and natural populations of T. turgidum ssp. dicoccoides (referred to as T. dicoccoides). In addition spacer length variation was assayed by restriction enzyme digestion and hybridization with spacer sequence probes.Extensive polymorphism was observed for the spacer region in various cultivars of T. aestivum, although within each cultivar the rDNA clusters were homogeneous and could be assigned to particular chromosomes. Within natural populations of T. dicoccoides polymorphism was also observed but, once again, within any one individual the rDNA clusters appeared to be homogeneous. The polymorphism, at the sequence level (assayed by Tm analysis), was not so great as to prevent the use of spacer sequence variation as a probe for evolutionary relationships. The length variation as assayed by restriction enzyme digestion did not appear to be as useful in this regard, since its range of variation was extensive even within populations of a species.