Chromosomes and microevolutionary processes

Abstract

The role of chromosomal rearrangement in microevolutionary processes is discussed, considering numerous aspects of the complex mechanisms of chromosomal speciation. The different degrees of chromosome-derived subfertility, a consequence of the different kinds of structural heterozygosities in the inter-racial hybrids, are discussed with reference to the effectiveness of the postmating reproductive barrier. A «non meiotic» view of the reproductive fitness of the Robertsonian heterozygotes and homozygotes is proposed. It is based on the possibility that Robertsonian fusion, and chromosomal structural rearrangement in general, may alter the internal topography of interphasic nucleus. Consequent upon any such change would be an alteration in the collocation of the gene clusters in the nuclear domains programmed for their regular function. It is claimed that these considerations explain the selective advantage that the new homokaryotype must have over the nonrearranged type for the new chromosomal variant to be fixed and maintained within a panmyctic population. Also discussed are the role of the demographic factors involved in chromosomal speciation and the molecular mechanisms responsible for the chromosomal rearrangement. An alloperipatric model of chromosomal speciation seems not to conflict with the «geographical» speciation principle of Mayr, and to be fully justified in terms of biological theory.

Robertsonian polymorphism in the common shrew (Sorex araneus L.) and selective advantage of heterozygotes indicated by their higher maximum metabolic rates

“…Another more plausible explanation is the so-called fusion effect of Capanna and Redi (1994), which is consistent with modern research on the interphase nucleus structure. The chromosomes tend to occupy exclusive territories in the interphase nuclei and there is a correlation between nuclear architecture and gene expression.…”

Developmental Instability in Wild Chromosomal Hybrids of the House Mouse

“…In the case of balanced rearrangements, structural reorganization of chromosomes may induce changes that could play an important role in modifying and/or disrupting some of the coadapted gene systems. These modifications may involve losses in DNA content such as those observed in telomeric sites and satellite DNA for Rb fusions in house mice (Garagna et al 1995;Nanda et al 1995), or changes in recombination patterns and rates (Dutrillaux 1986;Davisson and Akeson 1993;Eyrewalker 1993;Qumsiyeh 1994;Nevo et al 1995), and in the position of chromosomes within the interphasic nucleus with potential consequences on gene expression (Capanna and Redi 1994;Qumsiyeh 1995). In this study, the two chromosomal races showed no differences in the levels of FA of tooth characters, which suggests that genomic coadaption has not been disrupted by the new chromosomal organization of the genome.…”

“…Thus, the lower level of DS in Tunisian hybrids suggests that a breakdown of genomic coadaption has occurred and, consequently, that the genome of the Tunisian Rb race has sufficiently diverged from the all-acrocentric one to reach the incompatibility threshold. However, such incompatibilities were not predicted from the low level of allozyme divergence between these two races (Nei's genetic distance, D Nei = 0.07; Said and Britton-Davidian 1991), unless differentiation of genes specifically in- 4-7 9 Number of heterozygous fusions could lead to distorted cytodifferentiation pathways in early stages of germ cell development (Redi and Capanna 1988), thus affecting reproductive fitness in hybrids (Capanna and Redi 1994). Such features related to the multiplication and differentiation of cells may also concern development, suggesting that DS could be impaired in chromosomal hybrids between taxa showing only slight genic differentiation.…”

“…The reduced fitness of karyotypic heterozygotes results in the formation of a chromosomal barrier that reduces gene flow between parental taxa and further enhances genic differentiation which may lead to the establishment of additional genomic incompatibilities. However, another possible feature of chromosomal evolution is the consequences of changes in the structure of the karyotype on genome function (Capanna and Redi 1994). The nuclear organization of chromosomes is known to be spatially nonrandom and gene expression has been shown to be related to chromosomal position (HeslopHarisson and Bennet 1990;Milot et al 1996;Marshall et al 1997;Park and De Boni 1998).…”

“…The nuclear organization of chromosomes is known to be spatially nonrandom and gene expression has been shown to be related to chromosomal position (HeslopHarisson and Bennet 1990;Milot et al 1996;Marshall et al 1997;Park and De Boni 1998). Thus, structural rearrangements which modify the topology of interphasic chromosomes within the nucleus may lead to alterations of genome activity and contribute to reduce the fitness of the carriers (Capanna and Redi 1994;Qumsiyeh 1995). Disruption of coadaption related to a modified spatial organization of chromosomes may be expected to occur at either of two stages of chromosomal evolution: in recent karyotypically rearranged homozygotes before a new equilibrium is reached or, if the latter is achieved, in hybrids between chromosomally divergent taxa.…”