Mole Rat Spalax: Evolutionary Significance of Chromosome Variation

Wahrman, J.; Goitein, Ruth; Nevo, Eviatar

doi:10.1126/science.164.3875.82

Cited by 126 publications

(56 citation statements)

References 2 publications

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“…The karyotype of the Mauritious black rats, 2n=42, was apparently evolved from the karyotype of the Oce anian black rats, 2n=38, by centric fission of two pairs of small metacentric chromosome (Yoshida et al 1979). Similar type of species differentiation by centric fission has been re ported in some taxa such as the mole rats (Wahrman et al 1969), the prairie dogs (Nadler and Harris 1967), the root voles (Fredga and Bergstrom 1970), Japanese raccoon dogs (Yoshida and Wada 1984), and others. Todd (1970) suggested that this type of karyotype transforma tion was related to explosive speciation and adaptive radiation of the mammalia.…”

supporting

confidence: 63%

Variation and evolution in the karyotype of Lycoris, Amaryllidaceae. VII. Modes of karyotype alteration within species and probable trend of karyotype evolution in the genus.

Kurita

1988

cytologia

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supporting

confidence: 63%

Variation and evolution in the karyotype of Lycoris, Amaryllidaceae. VII. Modes of karyotype alteration within species and probable trend of karyotype evolution in the genus.

Kurita

1988

cytologia

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“…In many rodents, for example, a combination of asociality manifested in strong individual territoriality, limited adult vagility and juvenile dispersal distance, and patchy distributions can produce the small deme size necessary for rapid chromosomal fixation (29). While specific data on the types of social structuring within various rodent genera are generally not available, the strongly fossorial groups [e.g., pocket gophers (Thomomys, Geomys, and their relatives), mole rats (Spalax), and tucotucos (Ctenomys)] are considered to represent the epitome of this pattern (30,31). These genera are also among the most chromosomally diverse rodents known (32)(33)(34).…”

Section: Resultsmentioning

confidence: 99%

Rapid speciation and chromosomal evolution in mammals.

Bush¹,

Case²,

Wilson³

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

507

299

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To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and *drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes. Among evolutionary biologists there is a widespread acceptance of the hypothesis that small populations are essential for rapid speciation (1-7). According to this hypothesis, new species may arise from populations initially founded by a small number of individuals isolated on the periphery of the range of the parental species-the founder principle (3-5)-or in small demes maintained by social structuring and ecology (7,8). Widespread also is the idea that small populations are essential for chromosomal evolution, and some authors suggest that the two processes-speciation and chromosomal evolution-may be causally related (7)(8)(9)(10)(11)(12). It is now possible to test these ideas quantitatively because methods have been developed recently for estimating both rates of speciation (13,14) and rates of evolutionary change in gene arrangement (8,15). Unfortunately, few estimates of effective population size are available. Hence, it is not easy to make a direct examination of the relationship between population size and rates of evolution. It is possible, however, to examine quantitatively the relationship between rate of speciation and rate of chromosomal evolution. If both processes are dependent on the occurrence of small demes, the two rates should be correlated. Such a correlation was found in higher plants (14).The present article deals with vertebrates. Rates of chromosomal evolution vary greatly in these animals, being an order of magnitude higher in most mammals than in most other vertebrates (8,15). It was important, therefore, to estimate rates of speciation in a wide variety of vertebrates. The results of such estimates are reported below and compared with the results of an improved method for estimating rate of chromosomal evolution.

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“…Higher rates of karyotype evolution occur in placental mammals (9), small populations (11,43), and species-rich genera (13), with limited mobility (8), as in the Spalacidae (32). The canalization model of chromosomal evolution (10) implies that the karyotype represents an "adaptive strategy" (but see ref.…”

Section: Methodsmentioning

confidence: 99%

Chromosomal speciation and adaptive radiation of mole rats in Asia Minor correlated with increased ecological stress.

Nevo

Filippucci

Redi

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

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The evolutionary forces causing chromosomal speciation and adaptation are still enigmatic. Here we tested the Israeli evolutionary model of positive assciation of diloid chromosome number (2n) and genetic diversity with aridity stress in subterranean mde rats, on a 30-times-larger scale in Asia Minor. We analyzed both karyotype and allozyme diversity across Turkey, based on 37 allozymic loci in 20 localities of the Spalx kucodon and 4 localities of the Spaax ehrenbergi superspecies. We foumd extensive chromosomal speciation in S. leucodon (2n = 38, 40, 50, 54, 60, and 62) Speciation and adaptation, the major twin processes of evolution, are yet largely mysterious, notwithstanding the great past achievements and the present molecular biological revolution. The unresolved issues involve the relative importance of the relevant evolutionary forces, origin, genetics, mechanisms, modes, dynamics, and abiotic/biotic environmental correlates (1-6). This is true for most catalogued species, which are only a small fraction of the unknown number of living species (7). Likewise, the significance of karyotypic evolution has been extensively debated (6,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Highlighting these extremely complex problems calls for multidisciplinary studies involving molecular, genetic, chromosomal, organismal, and ecological insights (e.g., ref. 1). Here we explore two major unresolved problems of evolutionary biology in mole rats: (i) What is the role of diploid chromosome number (2 n) values and allozymes in evolution, primarily in speciation and adaptation? and (ii) Is the evolutionary process in Spalax oriented primarily by stochastic, nonselective, and neutral factors, or, by contrast, is it driven by selective factors? In short, is the origin of species and adaptation chaotic or ordered (20), reflecting adaptive environmental patterns?The evolutionary model of subterranean mole rats of the Spalax ehrenbergi superspecies in Israel (1) supports the environmental theory of genic and chromosomal diversity in both speciation and adaptation. The four chromosomal species (2n = 52, 54, 58, and 60), previously considered one species, represent four biological sibling species at progressive stages of speciation (1) We show that in Turkish Spalax, speciation and adapta-

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Mole Rat Spalax: Evolutionary Significance of Chromosome Variation

Cited by 126 publications

References 2 publications

Variation and evolution in the karyotype of Lycoris, Amaryllidaceae. VII. Modes of karyotype alteration within species and probable trend of karyotype evolution in the genus.

Variation and evolution in the karyotype of Lycoris, Amaryllidaceae. VII. Modes of karyotype alteration within species and probable trend of karyotype evolution in the genus.

Rapid speciation and chromosomal evolution in mammals.

Chromosomal speciation and adaptive radiation of mole rats in Asia Minor correlated with increased ecological stress.

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