Speciation: Chromosomal Mechanisms


Chromosomal speciation is one of the major modes of the origin of new species through the splitting of preexisting species. New species may originate by gene speciation, and also by the establishment of post‐mating reproductive isolation through structural chromosome rearrangements. The latter may induce low‐hybrid fitness, generated by macromutations, and even by micromutations, that is, molecular changes causing meiotic disturbances (e.g. GC incompatibilities), although the latter awaits empirical support. Criticism against the traditional model of chromosomal speciation led to renewed theoretical models arguing that chromosomal rearrangements can generate reproductive isolation between species by suppressing recombination within rearranged regions. Reduced recombination permits the accumulation of alleles contributing to reproductive isolation and adaptive divergence and radiation. Likewise, coding and noncoding genomes, and novel chromosomal breakpoint regions can generate novel combinations of genes and regulatory elements that contribute to both adaptive radiation and ecological speciation. Chromosomal speciation is certainly an important speciation mode across life, although we cannot yet quantify it in relation to other modes. The spalacid example of blind subterranean mole rats in the East Mediterranean is presented as a widely studied case of chromosomal ecological speciation. The proportion of chromosomal speciation in nature, particularly in animals, remains a future challenge.

Key Concepts:

  • Speciation – the evolutionary process leading to the multiplication of species and generating biodiversity.

  • Chromosomal speciation – the theory asserting that chromosomal rearrangements cause reproductive isolation between populations and lead to speciation.

  • Peripatric speciation – the origin of a new species by budding from a parental species established beyond the periphery of the parental species range.

  • Sympatric speciation – speciation without geographic (spatial) isolation; the origin of a new species within a deme.

  • Polyploidy – the condition in which the number of chromosomes is an integral greater than two of the haploid numbers.

  • Biological species concept (BSC) – defines species as groups of interbreeding natural populations that are reproductively (genetically) isolated from other such groups.

  • Allopatric speciation – the evolution of a population into a separate species involving a period of geographic isolation.

  • The evolutionary divergence of a single phyletic line into different niches or adaptive zones.

Keywords: speciation; species concept; chromosomal rearrangements; post‐mating reproductive isolation; Spalax ehrenbergi; mole rats

Figure 1.

Geographic distribution in Israel of the four chromosomal species belonging to the S. ehrenbergi superspecies that are separated by narrow hybrid zones (2n=52, 54, 58 and 60 now called S. galili, S. golani, S. carmeli and S. judaei, respectively; see Nevo et al., ).

Figure 2.

Comparison between the four most common karyotypes of Spalax discussed in this article and now named as four biological species (Nevo et al., ). Metacentrics of groups B ‘Robertsonian chromosomes’ and C ‘inversion chromosomes’ in boxes. Acrocentrics were arbitrarily assigned to groups B and C. Reproduced with permission from Wahrman et al..

Figure 3.

Geographic distribution and karyotypes of sampling localities (*) of subterranean mole rats in Turkey. Karyotypes are represented by their circled diploid number (2n); when two localities have the same karyotype and are geographically and genetically distant, they are designated with East (E), Central (C) or West (W), 54W, 54E, 52W, 52E, 50W, 50E, 60W and 60E, which are considered here as good biological species (From Nevo et al., ).

Figure 4.

Karyotypic evolution of all karyotypes of S. leucodon superspecies (2n=38, 40, 50, 54, 60 and 62) and S. ehrenbergi superspecies (2n=52, 54, 56, 58 and 60); the two karyotypes 2n=54 and 60 are from Israel (Nevo, ). The ecological trend across which speciation presumably proceeded in both Israel and Turkey is from mesic to xeric environments, in accordance with increased aridity stress and climatic unpredictability. Rb, Robertsonian from Nevo et al., where detailed elaboration of the karyotype evolution as a function of aridity stress is presented (From Nevo et al., ).



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Nevo, Eviatar(Dec 2012) Speciation: Chromosomal Mechanisms. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001757.pub3]