Chromosomal Rearrangements and Speciation in Animals

Geographical variation in postzygotic isolation and its genetic basis within and between twoMimulusspecies

“…After all, as Darwin clearly stated, natural selection should not favour postzygotic isolation, since the 'sterility of hybrids could not possibly be of any advantage to them' (Darwin 1859, p. 221). For example, chromosomal rearrangements may cause partial F 1 hybrid sterility, especially in plants (White 1969;Coyne & Orr 2004;Rieseberg & Willis 2007), because of the production of aneuploid gametes. But selection against heterokaryotypes must also have occurred during the initial spread of novel rearrangements within species, suggesting that selection may have been overwhelmed by random genetic drift and/or minimized by homozygosity owing to high rates of inbreeding (e.g.…”

Multivalents resulting from monobrachial homologies within a hybrid zone in Dichroplus pratensis (Acrididae): meiotic orientation and segregation

“…Chromosomal differences between taxa have long been recognized but the role of chromosomal rearrangements in evolution is controversial. Opinions range from an almost total rejection of any role for the chromosome to the more extreme positions that have been put forward by Matthey, 1966;White, 1968White, , 1969White, , 1970White, , 1973White, , 1975White, , 1978bWhite, , 1982Mayr, 1970Mayr, , 1982Bush, 1975;Bush et al, 1977;Bickham & Baker, 1979;Hewitt, 1979Hewitt, , 1985John, 1981John, , 1983Templeton, 1981;Kirig, 1982Kirig, , 1985Kirig, , 1987Patton & Sherwood, 1983;Reig, 1984;Camacho, 1985;Lande, 1985;Baker & Bickham, 1986;Sites & Moritz, 1987;Bidau, 1988Bidau, , 1990Nachman & Myers, 1989. Some biologists, however, have maintained a judicious and critical view by analysing available data in an impartial way (John, 1981;Patton & Sherwood, 1983;Sites & Moritz, 1987).…”

HYBRIDIZATION OF KARYOTYPICALLY DIFFERENTIATED POPULATIONS IN THE SCELOPORUS GRAMMICUS COMPLEX (IGUANIDAE)

“…Although it seems likely that species limits in the complex are coordinate with the karyotypic variants, it yet remains to be determined if chromosomal modifications themselves have functioned in any causal way in relation to species formation, either by the spread of chromosomal mutants through continuously distributed populations (White, 1969) or according to other models of "chromosomal speciation," including those involving the fixation of chromosomal variants in small, isolated populations (Mayr, 1969). In the case of PI and F6, geographic isolation of moderately large populations (especially likely as far as F6 is concerned), followed by secondary contact after chromosomal and genic differentiation had occurred, seems plausible.…”

“…Diploid (2n) chromosome numbers vary from 22 to 46 (Cole, 1970(Cole, , 1971Hall, 1973), a range exceeding that known for any other lizard genus. Because comparable variation has been detected in several groups of vertebrates, including other lizard genera (Gorman and Atkins, 1968;Matthey and van Brink, 1960) and rodents (review by Nadler, 1969), and in many invertebrates, evolutionists are becoming increasingly concerned with the role of karyotypic changes in animal speciation (White, 1969;Mayr, 1969Mayr, , 1970.…”

“…1A). Males with the S karyotype have only 19 microchromosomes due to the presence of an X 1X2 Y sex chromosome trivalent (White, 1954), which also occurs in the grammicus populations with differing karyotypes. Since very similar or identical karyotypes are found in the eight karyo- Among the approximately 60 species of the lizard genus Sceloporus, there is much karyotypic diversity, resulting primarily from the fixation of "Robertsonian rearrangements" (centric fusions and fissions; Hsu and Mead, 1969;Jackson, 1971).…”