Convergent reduction of V1R genes in subterranean rodents.

BACKGROUND: Vomeronasal type 1 receptor genes (V1Rs) are expected to detect intraspecific pheromones. It is believed that rodents rely heavily on pheromonal communication mediated by V1Rs, but pheromonal signals are thought to be confined in subterranean rodents that live in underground burrows. Thus, subterranean rodents may show a contrasting mode of V1R evolution compared with their superterranean relatives. RESULTS: We examined the V1R evolution in subterranean rodents by analyzing currently available genomes of 24 rodents, including 19 superterranean and 5 subterranean species from three independent lineages. We identified a lower number of putatively functional V1R genes in each subterranean rodent (a range of 22-40) compared with superterranean species (a range of 63-221). After correcting phylogenetic inertia, the positive correlation remains significant between the small V1R repertoire size and the subterranean lifestyle. To test whether V1Rs have been relaxed from functional constraints in subterranean rodents, we sequenced 22 intact V1Rs in 29 individuals of one subterranean rodent (Spalax galili) from two soil populations, which have been proposed to undergo incipient speciation. We found 12 of the 22 V1Rs to show significant genetic differentiations between the two natural populations, indicative of diversifying selection. CONCLUSION: Our study demonstrates convergent reduction of V1Rs in subterranean rodents from three independent lineages. Meanwhile, it is noteworthy that most V1Rs in the two Spalax populations are under diversifying selection rather than relaxed selection, suggesting that functional constraints on these genes may have retained in some subterranean species.

Adaptive methylation regulation of p53 pathway in sympatric speciation of blind mole rats, Spalax.

Epigenetic modifications play significant roles in adaptive evolution. The tumor suppressor p53, well known for controlling cell fate and maintaining genomic stability, is much less known as a master gene in environmental adaptation involving methylation modifications. The blind subterranean mole rat Spalax eherenbergi superspecies in Israel consists of four species that speciated peripatrically. Remarkably, the northern Galilee species Spalax galili (2n = 52) underwent adaptive ecological sympatric speciation, caused by the sharply divergent chalk and basalt ecologies. This was demonstrated by mitochondrial and nuclear genomic evidence. Here we show that the expression patterns of the p53 regulatory pathway diversified between the abutting sympatric populations of S. galili in sharply divergent chalk-basalt ecologies. We identified higher methylation on several sites of the p53 promoter in the population living in chalk soil (chalk population). Site mutagenesis showed that methylation on these sites linked to the transcriptional repression of p53 involving Cut-Like Homeobox 1 (Cux1), paired box 4 (Pax 4), Pax 6, and activator protein 1 (AP-1). Diverse expression levels of p53 between the incipiently sympatrically speciating chalk-basalt abutting populations of S. galili selectively affected cell-cycle arrest but not apoptosis. We hypothesize that methylation modification of p53 has adaptively shifted in supervising its target genes during sympatric speciation of S. galili to cope with the contrasting environmental stresses of the abutting divergent chalk-basalt ecologies.

Stress, adaptation, and speciation in the evolution of the blind mole rat, Spalax, in Israel.

Environmental stress played a major role in the evolution of the blind mole rat superspecies Spalax ehrenbergi, affecting its adaptive evolution and ecological speciation underground. Spalax is safeguarded all of its life underground from aboveground climatic fluctuations and predators. However, it encounters multiple stresses in its underground burrows including darkness, energetics, hypoxia, hypercapnia, food scarcity, and pathogenicity. Consequently, it evolved adaptive genomic, proteomic, and phenomic complexes to cope with those stresses. Here I describe some of these adaptive complexes, and their theoretical and applied perspectives. Spalax mosaic molecular and organismal evolution involves reductions or regressions coupled with expansions or progressions caused by evolutionary tinkering and natural genetic engineering. Speciation of Spalax in Israel occurred in the Pleistocene, during the last 2.00-2.35 Mya, generating four species associated intimately with four climatic regimes with increasing aridity stress southwards and eastwards representing an ecological speciational adaptive trend: (Spalax golani, 2n=54→S. galili, 2n=52→S. carmeli, 2n=58→S. judaei, 2n=60). Darwinian ecological speciation occurred gradually with relatively little genetic change by Robertsonian chromosomal and genic mutations. Spalax genome sequencing has just been completed. It involves multiple adaptive complexes to life underground and is an evolutionary model to a few hundred underground mammals. It involves great promise in the future for medicine, space flight, and deep-sea diving.

Macro-anatomical and karyological features of two blind mole rat subspecies (Rodentia: Spalacidae) from Turkey.

The morphometric and karyological analyses of 52 specimens belonging to the two subspecies of Nannospalax leucodon were examined from 14 localities in Turkey. Five karyotypic forms were recorded (2n = 60, the total numbers of chromosomal arms (NF) = 74, the numbers of autosomal arms (NFa) = 70; 2n = 60, NF = 76, NFa = 72; 2n = 60, NF = 82, NFa = 78; 2n = 56, NF = 72, NFa = 68; 2n = 38, NF = 74, NFa = 70). The morphological features of two subspecies were studied using both numerical taxonomy and traditional methods. Thirty skull measurements and four baculum measurements were subjected to discriminant function analysis to find morphometric criteria allowing subspecies identification. Two subspecies were clearly separated from each other by macroanatomical characterictics and numeric characteristics. The first upper molar has four alveoli cubicles in young specimens of Nannospalax leucodon anatolicus, while M(1) has 1 cubicle in Nannospalax leucodon cilicicus. In the western subspecies (N. l. anatolicus, 2n = 38), urethra openness is surrounded by three lobes. However, in the eastern subspecies (N. l. cilicicus, 2n = 60), there are two lateral lobes.

Discrimination of 2n = 60 Spalax leucodon cytotypes (Spalacidae, Rodentia) in Turkey by means of classical and molecular cytogenetic techniques.

Comparative studies among seven populations of 2n = 60 S. leucodon employing classic cytogenetics (G- bands, C-bands, AgNOR-staining), fluorochrome staining, and fluorescence in situ hybridization of telomeric and rDNA probes are reported here for the first time. The studied specimens were assigned to two cytotypes: 2n = 60W and 2n = 60R. The basic karyotype of both cytotypes consisted of eight pairs of subtelocentric and 21 pairs of acrocentric autosomes, subtelocentric X and acrocentric Y chromosomes. Both cytotypes had variable numbers of B-chromosomes (1-3) and variable numbers of autosomal arms (NFa = 74-76) caused by amplification (deletion) of heterochromatin short arms in the second pair. The short arms of subtelocentric chromosomes were comprised of heterochromatin in both cytotypes. Nucleolar organizer regions (NORs) and rDNA clusters were detected at telomeric sites of the short arms in pairs Nos. 3, 5, 6, 9, and 13 in cytotype W, and in the short arms of pair No. 6, 8, 12, 13, and 16 in cytotype R. Different locations of rDNA clusters allowed unambiguous discrimination between two S. leucodon cytotypes possessing the same 2n = 60 and similar NFa (74-76) variability. Our findings suggest a high level of chromosomal divergence, which means that it is possible to consider these cytotypes as a well-differentiated, chromosomal lineage within the leucodon group.